Genetic basis and biotechnological manipulation of sexual dimorphism and sex determination in fish.

PubMed

Mei, Jie; Gui, Jian-Fang

2015-02-01

Aquaculture has made an enormous contribution to the world food production, especially to the sustainable supply of animal proteins. The utility of diverse reproduction strategies in fish, such as the exploiting use of unisexual gynogenesis, has created a typical case of fish genetic breeding. A number of fish species show substantial sexual dimorphism that is closely linked to multiple economic traits including growth rate and body size, and the efficient development of sex-linked genetic markers and sex control biotechnologies has provided significant approaches to increase the production and value for commercial purposes. Along with the rapid development of genomics and molecular genetic techniques, the genetic basis of sexual dimorphism has been gradually deciphered, and great progress has been made in the mechanisms of fish sex determination and identification of sex-determining genes. This review summarizes the progress to provide some directive and objective thinking for further research in this field.

Variation in the strength of male mate choice allows long-term coexistence of sperm-dependent asexuals and their sexual hosts.

PubMed

Mee, Jonathan A; Otto, Sarah P

2010-10-01

In several asexual taxa, reproduction requires mating with related sexual species to stimulate egg development, even though genetic material is not incorporated from the sexuals (gynogenesis). In cases in which gynogens do not invest in male function, they can potentially have a twofold competitive advantage over sexuals because the asexuals avoid the cost of producing males. If unmitigated, however, the competitive success of the asexuals would ultimately lead to their own demise, following the extinction of the sexual species that stimulate egg development. We have studied a model of mate choice among sexual individuals and asexual gynogens, where males of the sexual species preferentially mate with sexual females over gynogenetic females, to determine if such mating preferences can stably maintain both gynogenetic and sexual individuals within a community. Our model shows that stable coexistence of gynogens and their sexual hosts can occur when there is variation among males in the degree of preference for mating with sexual females and when pickier males pay a higher cost of preference. © 2010 The Author(s). Journal compilation © 2010 The Society for the Study of Evolution.

Coexistence of Y, W, and Z sex chromosomes in Xenopus tropicalis

PubMed Central

Roco, Álvaro S.; Olmstead, Allen W.; Degitz, Sigmund J.; Amano, Tosikazu; Zimmerman, Lyle B.; Bullejos, Mónica

2015-01-01

Homomorphic sex chromosomes and rapid turnover of sex-determining genes can complicate establishing the sex chromosome system operating in a given species. This difficulty exists in Xenopus tropicalis, an anuran quickly becoming a relevant model for genetic, genomic, biochemical, and ecotoxicological research. Despite the recent interest attracted by this species, little is known about its sex chromosome system. Direct evidence that females are the heterogametic sex, as in the related species Xenopus laevis, has yet to be presented. Furthermore, X. laevis’ sex-determining gene, DM-W, does not exist in X. tropicalis, and the sex chromosomes in the two species are not homologous. Here we identify X. tropicalis’ sex chromosome system by integrating data from (i) breeding sex-reversed individuals, (ii) gynogenesis, (iii) triploids, and (iv) crosses among several strains. Our results indicate that at least three different types of sex chromosomes exist: Y, W, and Z, observed in YZ, YW, and ZZ males and in ZW and WW females. Because some combinations of parental sex chromosomes produce unisex offspring and other distorted sex ratios, understanding the sex-determination systems in X. tropicalis is critical for developing this flexible animal model for genetics and ecotoxicology. PMID:26216983

The Chromosomal Constitution of Embryos Arising from Monopronuclear Oocytes in Programmes of Assisted Reproduction

PubMed Central

2014-01-01

The assessment of oocytes showing only one pronucleus during assisted reproduction is associated with uncertainty. A compilation of data on the genetic constitution of different developmental stages shows that affected oocytes are able to develop into haploid, diploid, and mosaic embryos with more or less complex chromosomal compositions. In the majority of cases (~80%), haploidy appears to be caused by gynogenesis, whereas parthenogenesis or androgenesis is less common. Most of the diploid embryos result from a fertilization event involving asynchronous formation of the two pronuclei or pronuclear fusion at a very early stage. Uniparental diploidy may sometimes occur if one pronucleus fails to develop and the other pronucleus already contains a diploid genome or alternatively a haploid genome undergoes endoreduplication. In general, the chance of obtaining a biparental diploid embryo appears higher after conventional in vitro fertilization than after intracytoplasmic sperm injection. If a transfer of embryos obtained from monopronuclear oocytes is envisaged, it should be tried to culture them up to the blastocyst since most haploid embryos are not able to reach this stage. Comprehensive counselling of patients on potential risks is advisable before transfer and a preimplantation genetic diagnosis could be offered if available. PMID:25763399

A single mutation results in diploid gamete formation and parthenogenesis in a Drosophila yemanuclein-alpha meiosis I defective mutant.

PubMed

Meyer, Régis E; Delaage, Michèle; Rosset, Roland; Capri, Michèle; Aït-Ahmed, Ounissa

2010-11-16

Sexual reproduction relies on two key events: formation of cells with a haploid genome (the gametes) and restoration of diploidy after fertilization. Therefore the underlying mechanisms must have been evolutionary linked and there is a need for evidence that could support such a model. We describe the identification and the characterization of yem1, the first yem-alpha mutant allele (V478E), which to some extent affects diploidy reduction and its restoration. Yem-alpha is a member of the Ubinuclein/HPC2 family of proteins that have recently been implicated in playing roles in chromatin remodeling in concert with HIRA histone chaperone. The yem1 mutant females exhibited disrupted chromosome behavior in the first meiotic division and produced very low numbers of viable progeny. Unexpectedly these progeny did not display paternal chromosome markers, suggesting that they developed from diploid gametes that underwent gynogenesis, a form of parthenogenesis that requires fertilization. We focus here on the analysis of the meiotic defects exhibited by yem1 oocytes that could account for the formation of diploid gametes. Our results suggest that yem1 affects chromosome segregation presumably by affecting kinetochores function in the first meiotic division. This work paves the way to further investigations on the evolution of the mechanisms that support sexual reproduction.

Hybridogenesis and a potential case of R2 non-LTR retrotransposon horizontal transmission in Bacillus stick insects (Insecta Phasmida).

PubMed

Scavariello, Claudia; Luchetti, Andrea; Martoni, Francesco; Bonandin, Livia; Mantovani, Barbara

2017-02-06

Horizontal transfer (HT) is an event in which the genetic material is transferred from one species to another, even if distantly related, and it has been demonstrated as a possible essential part of the lifecycle of transposable elements (TEs). However, previous studies on the non-LTR R2 retrotransposon, a metazoan-wide distributed element, indicated its vertical transmission since the Radiata-Bilateria split. Here we present the first possible instances of R2 HT in stick insects of the genus Bacillus (Phasmida). Six R2 elements were characterized in the strictly bisexual subspecies B. grandii grandii, B. grandii benazzii and B. grandii maretimi and in the obligatory parthenogenetic taxon B. atticus. These elements were compared with those previously retrieved in the facultative parthenogenetic species B. rossius. Phylogenetic inconsistencies between element and host taxa, and age versus divergence analyses agree and support at least two HT events. These HT events can be explained by taking into consideration the complex Bacillus reproductive biology, which includes also hybridogenesis, gynogenesis and androgenesis. Through these non-canonical reproductive modes, R2 elements may have been transferred between Bacillus genomes. Our data suggest, therefore, a possible role of hybridization for TEs survival and the consequent reshaping of involved genomes.

Amplified fragment length polymorphism analysis to assess crossover interference and homozygosity in gynogenetic diploid Pacific abalone (Haliotis discus hannai).

PubMed

Nie, H-T; Li, Q; Kong, L-F

2014-06-01

Recombination analysis in gynogenetic diploids is a powerful tool for assessing the degree of inbreeding, investigating crossover events and understanding chiasma interference during meiosis. To estimate the marker-centromere recombination rate, the inheritance pattern of 654 amplified fragment length polymorphism (AFLP) markers was examined in the 72-h veliger larvae of two meiogynogenetic diploid families in the Pacific abalone (Haliotis discus hannai). The second-division segregation frequency (y) of the AFLP loci ranged from 0.00 to 0.96, with 23.9% of loci showing y-values higher than 0.67, evidencing the existence of interference. The average recombination frequency across the 654 AFLP loci was 0.45, allowing estimation of the fixation index of 0.55, indicating that meiotic gynogenesis could provide an effective means of rapid inbreeding in the Pacific abalone. The AFLP loci have a small proportion (4.4%) of y-values greater than 0.90, suggesting that a relatively low or intermediate degree of chiasma interference occurred in the abalone chromosomes. The information obtained in this study will enhance our understanding of the abalone genome and will be useful for genetic studies in the species. © 2014 Stichting International Foundation for Animal Genetics.

A single mutation results in diploid gamete formation and parthenogenesis in a Drosophila yemanuclein-alpha meiosis I defective mutant

PubMed Central

2010-01-01

Background Sexual reproduction relies on two key events: formation of cells with a haploid genome (the gametes) and restoration of diploidy after fertilization. Therefore the underlying mechanisms must have been evolutionary linked and there is a need for evidence that could support such a model. Results We describe the identification and the characterization of yem1, the first yem-alpha mutant allele (V478E), which to some extent affects diploidy reduction and its restoration. Yem-alpha is a member of the Ubinuclein/HPC2 family of proteins that have recently been implicated in playing roles in chromatin remodeling in concert with HIRA histone chaperone. The yem1 mutant females exhibited disrupted chromosome behavior in the first meiotic division and produced very low numbers of viable progeny. Unexpectedly these progeny did not display paternal chromosome markers, suggesting that they developed from diploid gametes that underwent gynogenesis, a form of parthenogenesis that requires fertilization. Conclusions We focus here on the analysis of the meiotic defects exhibited by yem1 oocytes that could account for the formation of diploid gametes. Our results suggest that yem1 affects chromosome segregation presumably by affecting kinetochores function in the first meiotic division. This work paves the way to further investigations on the evolution of the mechanisms that support sexual reproduction. PMID:21080953

Distinguishing between incomplete lineage sorting and genomic introgressions: complete fixation of allospecific mitochondrial DNA in a sexually reproducing fish (Cobitis; Teleostei), despite clonal reproduction of hybrids.

PubMed

Choleva, Lukas; Musilova, Zuzana; Kohoutova-Sediva, Alena; Paces, Jan; Rab, Petr; Janko, Karel

2014-01-01

Distinguishing between hybrid introgression and incomplete lineage sorting causing incongruence among gene trees in that they exhibit topological differences requires application of statistical approaches that are based on biologically relevant models. Such study is especially challenging in hybrid systems, where usual vectors mediating interspecific gene transfers--hybrids with Mendelian heredity--are absent or unknown. Here we study a complex of hybridizing species, which are known to produce clonal hybrids, to discover how one of the species, Cobitis tanaitica, has achieved a pattern of mito-nuclear mosaic genome over the whole geographic range. We appplied three distinct methods, including the method using solely the information on gene tree topologies, and found that the contrasting mito-nuclear signal might not have resulted from the retention of ancestral polymorphism. Instead, we found two signs of hybridization events related to C. tanaitica; one concerning nuclear gene flow and the other suggested mitochondrial capture. Interestingly, clonal inheritance (gynogenesis) of contemporary hybrids prevents genomic introgressions and non-clonal hybrids are either absent or too rare to be detected among European Cobitis. Our analyses therefore suggest that introgressive hybridizations are rather old episodes, mediated by previously existing hybrids whose inheritance was not entirely clonal. Cobitis complex thus supports the view that the type of resulting hybrids depends on a level of genomic divergence between sexual species.

Identification of hemiclonal reproduction in three species of Hexagrammos marine reef fishes.

PubMed

Kimura-Kawaguchi, M R; Horita, M; Abe, S; Arai, K; Kawata, M; Munehara, H

2014-08-01

Natural hybrids between the boreal species Hexagrammos octogrammus and two temperate species Hexagrammos agrammus and Hexagrammos otakii were observed frequently in southern Hokkaido, Japan. Previous studies revealed that H. octogrammus is a maternal ancestor of both hybrids; the hybrids are all fertile females and they frequently breed with paternal species. Although such rampant hybridization occurs, species boundaries have been maintained in the hybrid zone. Possible explanations for the absence of introgressions, despite the frequent backcrossing, might include clonal reproduction: parthenogenesis, gynogenesis and hybridogenesis. The natural hybrids produced haploid eggs that contained only the H. octogrammus genome (maternal ancestor) with discarded paternal genome and generated F1 -hybrid type offspring by fertilization with the haploid sperm of H. agrammus or H. otakii (paternal ancestor). This reproductive mode was found in an artificial backcross hybrid between the natural hybrid and a male of the paternal ancestor. These findings indicate that the natural hybrids adopt hybridogenesis with high possibility and produce successive generations through hybridogenesis by backcrossing with the paternal ancestor. These hybrids of Hexagrammos represent the first hybridogenetic system found from marine fishes that widely inhabit the North Pacific Ocean. In contrast with other hybridogenetic systems, these Hexagrammos hybrids coexist with all three ancestral species in the hybrid zone. The coexistence mechanism is also discussed. © 2014 The Fisheries Society of the British Isles.

Complete depletion of primordial germ cells in an All-female fish leads to Sex-biased gene expression alteration and sterile All-male occurrence.

PubMed

Liu, Wei; Li, Shi-Zhu; Li, Zhi; Wang, Yang; Li, Xi-Yin; Zhong, Jian-Xiang; Zhang, Xiao-Juan; Zhang, Jun; Zhou, Li; Gui, Jian-Fang

2015-11-18

Gynogenesis is one of unisexual reproduction modes in vertebrates, and produces all-female individuals with identical genetic background. In sexual reproduction vertebrates, the roles of primordial germ cells on sexual dimorphism and gonadal differentiation have been largely studied, and two distinct functional models have been proposed. However, the role of primordial germ cells remains unknown in unisexual animals, and it is also unclear whether the functional models in sexual reproduction animals are common in unisexual animals. To solve these puzzles, we attempt to utilize the gynogenetic superiority of polyploid Carassius gibelio to create a complete germ cell-depleted gonad model by a similar morpholino-mediated knockdown approach used in other examined sexual reproduction fishes. Through the germ cell-depleted gonad model, we have performed comprehensive and comparative transcriptome analysis, and revealed a complete alteration of sex-biased gene expression. Moreover, the expression alteration leads to up-regulation of testis-biased genes and down-regulation of ovary-biased genes, and results in the occurrence of sterile all-males with testis-like gonads and secondary sex characteristics in the germ cell-depleted gynogenetic Carassius gibelio. Our current results have demonstrated that unisexual gynogenetic embryos remain keeping male sex determination information in the genome, and the complete depletion of primordial germ cells in the all-female fish leads to sex-biased gene expression alteration and sterile all-male occurrence.

Comparative morphology, biology and histology of reproductive development in three lines of Manihot esculenta Crantz (Euphorbiaceae: Crotonoideae).

PubMed

Perera, P I P; Quintero, M; Dedicova, B; Kularatne, J D J S; Ceballos, H

2013-01-01

Cassava (Manihot esculenta), a major food staple in the tropics and subtropics, thrives even in environments undergoing threatening climate change. To satisfy the increasing demand for crop improvement and overcome the limitations of conventional breeding, the introduction of inbreeding techniques such as the production of doubled haploid lines via androgenesis or gynogenesis offers advantages. However, comprehensive studies on cassava flower bud biology or structural development are lacking and precise structural and biological information is a prerequisite to enhance the efficiency of these techniques. The floral biology of three selected cassava lines was studied, focusing on morphology, phenology and pollen biology (quantity, viability and dimorphism). Histological studies were also conducted on microsporogenesis/microgametogenesis and megasporogenesis/megagameto-genesis to generate precise developmental data for these lines. Male and female cyathia have distinct developmental phases. Pollen viability was high during immature stages of plant development; however, pollen mortality was common at later stages. Pollen trimorphism in male gametophytes towards the larger or smaller pollen size, as compared with normal size, was observed. Ten characteristic events were identified in male gametogenesis and six in female gametogenesis that were correlated with flower bud diameter. Male gametophyte diameter at different developmental stages was also determined. Results indicate that the three lines did not differ significantly, except regarding a few morphological aspects such as plant height, flower colour and number of male cyathia. Pollen grains were initially viable, but viability decreased drastically at later stages of growth. Abnormal meiosis or mitosis triggered pollen trimorphism. The demonstrated sequential events of reproductive development generated valuable information at the cellular level, which will help close the current information gap for cassava improvement via breeding programmes and doubled haploid plant production.

The role of HIRA and maternal histones in sperm nucleus decondensation in the gibel carp and color crucian carp.

PubMed

Zhao, Zhan-Ke; Li, Wei; Wang, Meng-Yu; Zhou, Li; Wang, Jia-Lin; Wang, Yu-Feng

2011-02-01

The histone H3.3 chaperone HIRA is essential for chromatin assembly during male pronucleus formation in Drosophila. However, the role of HIRA during fertilization in vertebrates remains unclear. The gibel carp (Carassius auratus gibelio) is a unique gynogenetic crucian carp (gyno-carp). Heterologous sperm nuclei cannot decondense when incorporated in the egg, thus the eggs produce a clonal lineage of all females by typical gynogenesis. In contrast, after entering the egg, homologous sperm can undergo decondensation and sexual reproduction is activated, which may produce both female and male offspring. Therefore, this fish is a useful model for studying the mechanisms of fertilization. Herein, we first compared HIRA expression during embryogenesis between gyno-carp and the gonochoristic color crucian carp (Carassius auratus; gono-carp). In gono-carp, a dramatic reduction of HIRA protein occurs shortly after fertilization, whereas HIRA protein is consistently expressed during embryogenesis of gyno-carp. Next, we used immunodepletion and an in vitro sperm decondensation system, and found that complete removal of HIRA inhibited sperm decondensation in both of the fish. Immunofluorescence localization showed that in the condensed sperm nuclei of gono-carp incubated in gyno-carp egg extracts, HIRA was detected, but neither the histone H2A variant H2af1o nor acetylated histone H4 was observed. These results suggest that HIRA may be a critical factor required for sperm nucleus decondensation, while the defect in deposition of some maternal histones in the sperm nucleus could be one reason why heterologous sperm cannot decondense in the gibel carp egg. Copyright © 2011 Wiley-Liss, Inc.

Induction of gynogenetic and androgenetic haploid and doubled haploid development in the brown trout (Salmo trutta Linnaeus 1758).

PubMed

Michalik, O; Dobosz, S; Zalewski, T; Sapota, M; Ocalewicz, K

2015-04-01

Gynogenetic and androgenetic brown trout (Salmo trutta Linnaeus 1758) haploids (Hs) and doubled haploids (DHs) were produced in the present research. Haploid development was induced by radiation-induced genetic inactivation of spermatozoa (gynogenesis) or eggs (androgenesis) before insemination. To provide DHs, gynogenetic and androgenetic haploid zygotes were subjected to the high pressure shock to suppress the first mitotic cleavage. Among haploids, gynogenetic embryos were showing lower mortality when compared to the androgenetic embryos; however, most of them die before the first feeding stage. Gynogenetic doubled haploids provided in the course of the brown trout eggs activation performed by homologous and heterologous sperm (rainbow trout) were developing equally showing hatching rates of 14.76 ± 2.4% and 16.14 ± 2.90% and the survival rates at the first feeding stage of 10.48 ± 3.48% and 12.78 ± 2.18%, respectively. Significantly, lower survival rate was observed among androgenetic progenies from the diploid groups with only few specimens that survived to the first feeding stage. Cytogenetic survey showed that among embryos from the diploid variants of the research, only gynogenetic individuals possessed doubled sets of chromosomes. Thus, it is reasonable to assume that radiation employed for the genetic inactivation of the brown trout eggs misaligned mechanism responsible for the cell divisions and might have delayed or even arrested the first mitotic cleavage in the androgenetic brown trout zygotes. Moreover, protocol for the radiation-induced inactivation of the paternal and maternal genome should be adjusted as some of the cytogenetically surveyed gynogenetic and androgenetic embryos exhibited fragments of the irradiated chromosomes. © 2015 Blackwell Verlag GmbH.

Recovery and characterization of a Citrus clementina Hort. ex Tan. 'Clemenules' haploid plant selected to establish the reference whole Citrus genome sequence.

PubMed

Aleza, Pablo; Juárez, José; Hernández, María; Pina, José A; Ollitrault, Patrick; Navarro, Luis

2009-08-22

In recent years, the development of structural genomics has generated a growing interest in obtaining haploid plants. The use of homozygous lines presents a significant advantage for the accomplishment of sequencing projects. Commercial citrus species are characterized by high heterozygosity, making it difficult to assemble large genome sequences. Thus, the International Citrus Genomic Consortium (ICGC) decided to establish a reference whole citrus genome sequence from a homozygous plant. Due to the existence of important molecular resources and previous success in obtaining haploid clementine plants, haploid clementine was selected as the target for the implementation of the reference whole genome citrus sequence. To obtain haploid clementine lines we used the technique of in situ gynogenesis induced by irradiated pollen. Flow cytometry, chromosome counts and SSR marker (Simple Sequence Repeats) analysis facilitated the identification of six different haploid lines (2n = x = 9), one aneuploid line (2n = 2x+4 = 22) and one doubled haploid plant (2n = 2x = 18) of 'Clemenules' clementine. One of the haploids, obtained directly from an original haploid embryo, grew vigorously and produced flowers after four years. This is the first haploid plant of clementine that has bloomed and we have, for the first time, characterized the histology of haploid and diploid flowers of clementine. Additionally a double haploid plant was obtained spontaneously from this haploid line. The first haploid plant of 'Clemenules' clementine produced directly by germination of a haploid embryo, which grew vigorously and produced flowers, has been obtained in this work. This haploid line has been selected and it is being used by the ICGC to establish the reference sequence of the nuclear genome of citrus.

Sex Determination and Polyploid Gigantism in the Dwarf Surfclam (Mulinia Lateralis Say)

PubMed Central

Guo, X.; Allen-Jr., S. K.

1994-01-01

Mulinia lateralis, the dwarf surfclam, is a suitable model for bivalve genetics because it is hardy and has a short generation time. In this study, gynogenetic and triploid. M. lateralis were successfully induced. For gynogenesis, eggs were fertilized with sperm irradiated with ultraviolet light and subsequently treated with cytochalasin B to block the release of the second polar body (PB2). Triploidy was induced by blocking PB2 in normally fertilized eggs. The survival of gynogenetic diploids was very low, only 0.7% to 8 days post-fertilization (PF), compared with 15.2% in the triploid groups and 27.5% in the normal diploid control. Larvae in all groups metamorphosed at 8-10 days PF, and there was no significant post-larval mortality. At sexual maturation (2-3 months PF), all gynogenetic diploids were female, and there was no significant difference (P > 0.05) in sex ratio between diploids and triploids. These results suggested that the dwarf surfclam may have an XX-female, XY-male sex determination with Y-domination. Compared with diploids, triploids had a relative fecundity of 59% for females and 80% for males. Eggs produced by triploid females were 53% larger (P < 0.001) in volume than those from diploid females. In both length and weight measurements at three months PF, the gynogenetic diploids were not significantly (P > 0.33) different from normal diploid females, suggesting that inbreeding depression was minimal in meiosis II gynogens. Triploid clams were significantly larger (P < 0.001) than normal diploids. We hypothesize that the increased body-size in triploids was caused by a polyploid gigantism due to the increased cell volume and a lack of cell-number compensation. PMID:7896101

Effects of hydrostatic pressure on microtubule organization and nucleus changes in gynogenetically activated eggs of olive flounder (Paralichthys olivaceus).

PubMed

Lin, Zhengmei; Zhu, Xiangping; Zhang, Tingrong; You, Feng; Wu, Zhihao; Cao, Yuanshui

2016-06-01

Fluorescent double-labeled technique was used to investigate the effects of hydrostatic pressure on microtubule organization and nucleus in gynogenetically activated eggs of olive flounder (Paralichthys olivaceus). The parameter of hydrostatic pressure treatment was 600 kg/cm(2) for 6 minutes at prometaphase of the first mitosis. The data showed that nucleus and microtubule changes of the diploid control were basically similar to those of the haploid one (5 minutes behind those of the diploid control). Nuclear diameter of the haploid embryo was significantly smaller than that of the diploid one (P < 0.01). The ploidy of chromosome set could be determined basing on nuclear diameter. The results of nuclear diameter measurement and the ratio of developmentally delayed embryo showed that the chromosome set was not doubled during the second cell cycle, the first cleavage proceeded normally; but that of about 80% treated embryo was doubled during the third cell cycle, the second cleavage was inhibited. Microtubules were disassembled, and nucleation capacity of centrosome was just temporarily inhibited by pressure treatment. Centrosome renucleated microtubule, and a bipolar spindle reassembled 15 minutes after treatment, leading to occurrence of the first cleavage. During the second cell cycle, about 80% treated embryo had a single centrosome and formed a unipolar spindle in both blastomeres. After prometaphase, chromosomes spread around for about 20 minutes instead of aligning on the equatorial plane, then assembled and formed one large nucleus without anaphase separation. The second cleavage was inhibited, and the chromosome set was doubled. The data indicated that the chromosome set doubling of mitogynogenetic diploid induced by hydrostatic pressure treatment, which performed at prometaphase of the first mitosis, mainly resulted from the inhibition of the second cleavage rather than the first one. This study is the first to adapt fluorescent double-labeled technique to investigate the mechanism on chromosome set doubling of mitotic gynogenesis induction. This study will offer theoretical support for mitogynogenetic diploid induction in marine fish. Copyright © 2016 Elsevier Inc. All rights reserved.

no privacy, a Xenopus tropicalis mutant, is a model of human Hermansky-Pudlak Syndrome and allows visualization of internal organogenesis during tadpole development.

PubMed

Nakayama, Takuya; Nakajima, Keisuke; Cox, Amanda; Fisher, Marilyn; Howell, Mary; Fish, Margaret B; Yaoita, Yoshio; Grainger, Robert M

2017-06-15

We describe a novel recessive and nonlethal pigmentation mutant in Xenopus tropicalis. The mutant phenotype can be initially observed in tadpoles after stage 39/40, when mutant embryos display markedly reduced pigmentation in the retina and the trunk. By tadpole stage 50 almost all pigmented melanophores have disappeared. Most interestingly, those embryos fail entirely to make pigmented iridophores. The combined reduction/absence of both pigmented iridophores and melanophores renders these embryos virtually transparent, permitting one to easily observe both the developing internal organs and nervous system; accordingly, we named this mutant no privacy (nop). We identified the causative genetic lesion as occurring in the Xenopus homolog of the human Hermansky-Pudlak Syndrome 6 (HPS6) gene, combining several approaches that utilized conventional gene mapping and classical and modern genetic tools available in Xenopus (gynogenesis, BAC transgenesis and TALEN-mediated mutagenesis). The nop allele contains a 10-base deletion that results in truncation of the Hps6 protein. In humans, HPS6 is one of the genes responsible for the congenital disease HPS, pathological symptoms of which include oculocutaneous albinism caused by defects in lysosome-related organelles required for pigment formation. Markers for melanin-producing neural crest cells show that the cells that would give rise to melanocytes are present in nop, though unpigmented. Abnormalities develop at tadpole stages in the pigmented retina when overall pigmentation becomes reduced and large multi-melanosomes are first formed. Ear development is also affected in nop embryos when both zygotic and maternal hsp6 is mutated: otoliths are often reduced or abnormal in morphology, as seen in some mouse HPS mutations, but to our knowledge not described in the BLOC-2 subset of HPS mutations nor described in non-mammalian systems previously. The transparency of the nop line suggests that these animals will aid studies of early organogenesis during tadpole stages. In addition, because of advantages of the Xenopus system for assessing gene expression, cell biological mechanisms, and the ontogeny of melanosome and otolith formation, this should be a highly useful model for studying the molecular mechanisms underlying the acquisition of the HPS phenotype and the underlying biology of lysosome-related organelle function. Copyright © 2016 Elsevier Inc. All rights reserved.

CLONAL INHERITANCE OF A DIPLOID NUCLEAR GENOME BY A HYBRID FRESHWATER MINNOW (PHOXINUS EOS-NEOGAEUS, PISCES: CYPRINIDAE).

PubMed

Goddard, Kathryn Ann; Dawley, Robert M

1990-07-01

Hybrids between the minnows Phoxinus eos and Phoxinus neogaeus coexist with a population of P. eos in East Inlet Pond, Coos Co., New Hampshire. Chromosome counts and flow cytometric analysis of erythrocyte DNA indicate that these hybrids include diploids, triploids, and diploid-triploid mosaics. The mosaics have both diploid and triploid cells in their bodies, even within the same tissues. All three hybrid types are heterozygous at seven putative loci for which P. eos and P. neogaeus are fixed for different allozymes, indicating that the hybrids carry one eos and one neogaeus haploid genome. The diploid hybrids are therefore P. eos-neogaeus, whereas the triploids and mosaics are derived from P. eos-neogaeus but have an extra eos or neogaeus genome in all or some of their cells. Diploid, triploid, and mosaic hybrids accept tissue grafts from diploid hybrids, indicating that all individuals carry the identical eos-neogaeus diploid genome. Thus, one P. eos-neogaeus clone exists at East Inlet Pond. Grafts among the triploids and mosaics or from these individuals to diploid hybrids are rejected, indicating that the third genome is different in each triploid and mosaic individual. In this study, diploid and mosaic hybrids, carrying the clonal eos-neogaeus genome, were bred in the laboratory with males of P. eos or P. neogaeus. Both diploid and mosaic hybrids produced diploid, triploid, and mosaic offspring, revealing the source of the three hybrid types present at East Inlet Pond. These offspring accepted grafts from P. eos-neogaeus individuals, indicating that they all had inherited the identical eos-neogaeus genome. Most grafts among triploid and mosaic progeny, or from these individuals to their diploid broodmates, were rejected, indicating that the third genome was different in each triploid and mosaic (as was observed in the wild hybrids) and was contributed by sperm from males of P. eos or P. neogaeus. Diploid progeny are produced if sperm serves only to stimulate embryogenesis; triploid or mosaic progeny are produced if the sperm genome is incorporated. Although based on a mode of reproduction that by definition results in a genetically identical community of individuals, i.e., gynogenesis, reproduction in hybrid Phoxinus results in a variety of genetically distinct individuals by the incorporation of sperm into approximately 50% of the diploid ova produced. © 1990 The Society for the Study of Evolution.