Cold-shock eliminates female nucleus in fertilized eggs to induce androgenesis in the loach (Misgurnus anguillicaudatus), a teleost fish

Genome-wide DNA methylation and gene expression patterns of androgenetic haploid tiger pufferfish (Takifugu rubripes) provide insights into haploid syndrome

Androgenesis is an important chromosome set manipulation technique used in sex control in aquaculture. Haploid embryos exhibit haploid syndrome with body abnormalities and even die during early embryonic development. In this study, we used whole genome bisulfite sequencing (WGBS) to investigate the genome-wide DNA methylation profiles in haploid females (1n-X) and males (1n-Y), and diploid females (2n-XX) and males (2n-XY) of tiger pufferfish (Takifugu rubripes), an economically important fish in China. A total of 96.32 Gb clean data was produced. Differentially methylated regions (DMRs) were found between haploids and diploids, which may be related to abnormal development and early embryonic death in haploids. There were 3,641 hyper-methylated differentially methylated genes (DMGs) and 2,179 hypo-methylated DMGs in haploid vs. diploid comparisons in both females and males. These DMGs were mainly related to genomic stability maintenance and cell cycle regulation. slf1, actr8, gas2, and pbrm1 genes were selected to validate the methylation sequencing. After combining the methylation data with the corresponding transcriptome data, we identified several genes, including guca2a, myoc, fezf2, rprml, telo2, s100a1, and marveld1, which exhibited differential expression levels modulated by DNA methylation. In conclusion, our study revealed different methylation and expression profiles between haploid and diploid T. rubripes for the first time. Several DMGs were identified between different ploidy levels, which may be related to haploid syndrome formation. The results expand the understanding of the effects of ploidy on the early development of teleosts and provide knowledge about target genes and networks to improve the survival rate of haploids.

An updated review of cold shock and cold stress in fish

Temperature is critical in regulating virtually all biological functions in fish. Low temperature stress (cold shock/stress) is an often-overlooked challenge that many fish face as a result of both natural events and anthropogenic activities. In this study, we present an updated review of the cold shock literature based on a comprehensive literature search, following an initial review on the subject by M.R. Donaldson and colleagues, published in a 2008 volume of this journal. We focus on how knowledge on cold shock and fish has evolved over the past decade, describing advances in the understanding of the generalized stress response in fish under cold stress, what metrics may be used to quantify cold stress and what knowledge gaps remain to be addressed in future research. We also describe the relevance of cold shock as it pertains to environmental managers, policymakers and industry professionals, including practical applications of cold shock. Although substantial progress has been made in addressing some of the knowledge gaps identified a decade ago, other topics (e.g., population-level effects and interactions between primary, secondary and tertiary stress responses) have received little or no attention despite their significance to fish biology and thermal stress. Approaches using combinations of primary, secondary and tertiary stress responses are crucial as a research priority to better understand the mechanisms underlying cold shock responses, from short-term physiological changes to individual- and population-level effects, thereby providing researchers with better means of quantifying cold shock in laboratory and field settings.

How Cold Shock Affects Ploidy Level and Early Ontogenetic Development of the Sterlet, A. ruthenus L

The objective of the present research was to study the effect of cold shock (3 °C and 6 °C) on fertilized eggs of the sterlet, Acipenser ruthenus L. Cold shock was applied for various durations (30, 60 and 90 min) and the ploidy levels, survival, and genotypes of the treated embryos/larvae were recorded. Analysis of ploidy levels confirmed the presence of diploid, triploid, and mosaic (1n/2n, 2n/3n, and 1n/2n/3n) genotypes in experimental groups, while it was strictly diploid in control groups. Microsatellite genotyping confirmed both the incidence of polyspermy and retention of the 2nd polar body in experimental groups. However, patterns of inheritance in all diploid offspring in experimental and control groups revealed classical Mendelian disomic inheritance. Interestingly, the observed mosaic sterlets had normal morphology and were alive. However, some larvae had abnormal morphology which may be due to haploid syndrome. In all treatment groups (treatments: 3 °C-30 min; 3 °C-60 min; 3 °C-90 min; 6 °C-60 min), where the percentage of polyploid/mosaic larvae were high, the mortality was also high. Whereas, in the control groups (where there were only diploid (2n) larvae), the mortality was relatively low.

First report on embryonic and larval development of 2n/3n mosaic sterlet

Mosaicism is frequently observed in aquaculture practices, and it adversely affects the production as well as the restoration programme of the sturgeon. The purpose of the present study was the induction of 2n/3n mosaic in sterlet, Acipenser ruthenus L., and compare their embryonic and larval development with diploid control sterlet. Microsatellite DNA loci genotyping was conducted for the identification of the genotypes and parentage analysis. Embryonic development was monitored in experimental groups at every 24 h interval. Identification of individual stages of embryonic development was recorded based on a 36-degree scale of development. Additionally, the BW and body length (LT) of experimental fishes were taken during 110 days of the rearing period. The Fulton's condition coefficient (F), length-weight parameters, and specific growth rate (SGR) coefficient were calculated. The analysis of embryonic development of the 2n/3n mosaic and the diploid control group did not show differences. However, higher mortality (88%) was observed in 2n/3n mosaic groups in comparison to the diploid control groups (55%). BW and body length of 2n/3n mosaic sterlet were slightly lower than the diploid control sterlet, but the differences were not statistically significant. F analysis did not confirm a lower growth performance of the fishes in the 2n/3n mosaic group. Microsatellite DNA loci genotyping confirmed both the incidence of polyspermy and retention of the second polar body. This paper presents the first report on embryonic development and growth performance of 2n/3n mosaic sturgeons.

Optimization of ultraviolet irradiation of Clarias gariepinus (Burchell, 1822) eggs for androgen production

The optimum distance and duration of ultraviolet (UV) irradiation for the complete inactivation of African catfish Clarias gariepinus egg nucleus was investigated in this study. The UV light was suspended above the unfertilized eggs at four distances (5, 10, 20 and 30 cm) and for five durations (1, 2, 3, 4 and 5 min). Then, the irradiated eggs were activated with sperm from diploid C. gariepinus and cold shocked at 5°C for 5 min just moments before cell cleavage. Ploidy analysis was performed using karyotype chromosome counting. The results obtained suggested that the further the distance, the better the hatchability rate, however prolonged duration seemed to significantly reduced hatchability. All treatments with surviving progenies at the end of the study showed evidence of successfully diploid gynogen (2n = 56) induction at different percentages. However, the optimal protocol that gave a moderately high hatchability/survival rate and completely induced gynogens was exposure of the eggs to UV irradiation at 20 cm for 1 min. It was concluded that the distance and duration of UV irradiation affects gynogenetic induction in African catfish C. gariepinus.

Androgenetic development of X- and Y-chromosome bearing haploid rainbow trout embryos

Haploid fish embryos are important in studies regarding role of the recessive traits during early ontogeny. In fish species with the male heterogamety, androgenetic haploid embryos might be also useful tool in studies concerning role of the sex chromosomes during an embryonic development. Morphologically differentiated X and Y chromosomes have been found in a limited number of fish species including rainbow trout (Oncorhynchus mykiss Walbaum 1792). To evaluate role of the sex chromosomes during rainbow trout embryonic development, survival of the androgenetic haploids in the presence of X or Y sex chromosomes has been examined. Androgenetic haploid rainbow trout were produced by fertilization of X-irradiated eggs with spermatozoa derived from the normal males (XY) and neomales, that is, sex-reversed females (XX) to produce X- and Y-bearing haploids, and all X-bearing haploids, respectively. Survival rates of the androgenetic progenies of normal males and neomales examined during embryogenesis and at hatching did not differ significantly. However, all haploids died within next few days after hatching. Cytogenetic analysis of the androgenetic embryos confirmed their haploid status. Moreover, apart from the intact paternal chromosomes, residues of the irradiated maternal chromosomes observed as chromosome fragments were identified in some of the haploids. Provided results suggested that rainbow trout X and Y chromosomes despite morphological and genetic differences are at the early stage of differentiation and still share genetic information responsible for the proper embryonic development.

Generation of clonal zebrafish line by androgenesis without egg irradiation

Generation of clonal zebrafish will facilitate large-scale genetic screening and help us to overcome other biological and biotechnological challenges due to their isogenecity. However, protocols for the development of clonal lines have not been optimized. Here, we sought to develop a novel method for generation of clonal zebrafish by androgenesis induced by cold shock. Androgenetic zebrafish doubled haploids (DHs) were induced by cold shock of just-fertilized eggs, and the eggs were then heat shocked to double the chromosome set. The yield rate of putative DHs relative to the total number of eggs used was 1.10% ± 0.19%. Microsatellite genotyping of the putative DHs using 30 loci that covered all 25 linkage groups detected no heterozygous loci, confirming the homozygosity of the DHs. Thus, a clonal line was established from sperm of a DH through a second cycle of cold-shock androgenesis and heat-shock chromosome doubling, followed by genetic verification of the isogenic rate confirming the presence of identical DNA fingerprints by using amplified fragment length polymorphism markers. In addition, our data provided important insights into the cytological mechanisms of cold-shock–induced androgenesis.

Genetic inactivation of European sea bass (Dicentrarchus labrax L.) eggs using UV-irradiation: observations and perspectives

Androgenesis is a form of uniparental reproduction leading to progenies inheriting only the paternal set of chromosomes. It has been achieved with variable success in a number of freshwater species and can be attained by artificial fertilization of genetically inactivated eggs following exposure to gamma (γ), X-ray or UV irradiation (haploid androgenesis) and by restoration of diploidy by suppression of mitosis using a pressure or thermal shock. The conditions for the genetic inactivation of the maternal genome in the European sea bass (Dicentrarchus labrax L.) were explored using different combinations of UV irradiation levels and durations. UV treatments significantly affected embryo survival and generated a wide range of developmental abnormalities. Despite the wide range of UV doses tested (from 7.2 to 720 mJ x cm(-2)), only one dose (60 mJ x cm(-2) x min(-1) with 1 min irradiation) resulted in a small percentage (14%) of haploid larvae at hatching in the initial trials as verified by flow cytometry. Microsatellite marker analyses of three further batches of larvae produced by using this UV treatment showed a majority of larvae with variable levels of paternal and maternal contributions and only one larva displaying pure paternal inheritance. The results are discussed also in the context of an assessment of the UV-absorbance characteristics of egg extracts in this species that revealed the presence of gadusol, a compound structurally related to mycosporine-like amino acids (MAAs) with known UV-screening properties.