Induction of androgenetic development of the brook charr (Salvelinus fontinalis)× Arctic charr (Salvelinus alpinus) hybrids in eggs derived from the parental species

Quality of fish eggs and production of androgenetic and gynogenetic doubled haploids (DHs)

Induced development of haploid embryos (H) with only paternal (androgenesis) or maternal (gynogenesis) chromosomes requires irradiation of eggs before fertilization or activation of eggs with irradiated spermatozoa, respectively. To provide doubled haploids (DHs), androgenetic and gynogenetic haploid zygotes need to be subjected to the thermal or high hydrostatic pressure (HHP) shock to suppress the first mitotic cleavage and to double paternal or maternal haploid set of chromosomes. Androgenesis and mitotic gynogenesis (mito-gynogenesis) result in the generation of fully homozygous individuals in a single generation. DHs have been utilized in selective breeding programs, in studies concerning the phenotypic consequences of recessive alleles and to evaluate the impact of sex chromosomes on the early ontogeny. Moreover, the use of DHs for the NGS approach radically improves de novo the assembly of the genomes. However, reduced survival of the doubled haploids limits the wide application of androgenotes and gynogenotes. The high mortality of DHs may be only partly explained by the expression of recessive traits. Observed inter-clutch variation in the survival of DHs developing in eggs originating from different females make it necessary to take a closer look at the quality of the eggs used during induced androgenesis and gynogenesis. Moreover, the developmental competence of eggs that are subjected to irradiation before fertilization in order to deactivate maternal chromosomes when undergoing induced androgenesis and exposed to the physical shock after fertilization that leads to the duplication of the zygotes in both mito-gynogenesis and androgenesis may be also altered as irradiation and sublethal values of temperatures and hydrostatic pressure are considered as harmful for the cell organelles and biomolecules. Here, recently provided results concerning the morphological, biochemical, genomic, and transcriptomic characteristics of fish eggs showing high and low competence for androgenesis and mito-gynogenesis are reviewed.

Telomerase Activity in Androgenetic Rainbow Trout with Growth Deficiency and in Normally Developed Individuals

Role of telomerase in specimens with retarded growth (dwarfs) has not been thoroughly examined to date. Considering that some of the fish species show correlation between somatic growth and activity of telomerase, it has been tempting to assume that pattern of telomerase activity in specimens with retarded growth and these with normal growth rate may vary. In the present research, telomerase activity has been examined in liver, skin, and muscles in the androgenetic rainbow trout (Oncorhynchus mykiss) with growth deficiency and their normally developed siblings. Among the examined organs, the liver showed the highest telomerase activity in all studied fish, what may be linked to the enormous regeneration capacity of the liver tissue. Although dwarf specimens examined here displayed significantly lower body size and weight they did not exhibit any significant differences in the telomerase activity measured in liver and muscle when compared to the rainbow trout without growth deficiency. In turn, telomerase activity in skin was significantly upregulated in the normally developed androgenotes. The present study indicates that dwarfism in the androgenetic rainbow trout is neither associated with ceased telomerase activity nor its decrease throughout the ontogenetic development.

Telomere length variation does not correspond with the growth disturbances in the rainbow trout (Oncorhynchus mykiss)

Somatic growth is considered to affect pace of the telomere attrition in vertebrates. As normally developed and dwarf fish differ in the body size we have decided to compare telomere length in the rainbow trout (Oncorhynchus mykiss) with normal growth and with growth reduced due to the dwarf condition. Examined 1-year-old fish with normal and dwarf appearance were siblings originated from androgenetic fully homozygous doubled haploid (DH) line of rainbow trout. Particular dwarf individuals had body deformities such as humpback, kyphosis, and lordosis. Somatic cells of examined rainbow trout had an average telomere length between 17 and 20 kb, comparable in females and males. Dwarf rainbow trout exhibited significantly lower body length and weight than their normally developed siblings even though no differences in the telomere length were found between these fishes. Statistical analysis did not exhibit any correlation between body size and the telomere length. Equal length of telomeres observed in the studied normal and dwarf rainbow trout suggests morphological and physiological differences in fish with different growth rates do not affect dynamics of telomeric DNA. Or any variation in the telomere length might have been levelled by telomerase that in rainbow trout is active in all tissues irrespective of the individual developmental stage.

Production of triploid, doubled haploid (DH) and meiogynogenetic brook trout (Salvelinus fontinalis) – efficiency and development of body deformities

In the present research we produced triploid, mitogynogenetic (doubled haploid; DH) and meiogynogenetic brook trout (Salvelinus fontinalis) to examine efficiency of these technologies and potential susceptibility of chromosome set manipulated individuals for the spinal disorders. Triploidy was induced by shocking (High Hydrostatic Pressure – HHP) of fertilized eggs 30 min. after insemination. In turn, gynogenetic development was induced by activation of eggs with UV-irradiated sperm. Activated eggs were then exposed to HHP shock applied 30 and 420 minutes after insemination to provide meiogynogenotes and gynogenetic DHs, respectively. When compared to non-manipulated diploids, the highest survival rates were observed among triploid brook trout while DHs showed the highest mortality. Malformation rates in the diploid larvae from the control groups did not exceed 7.0% while percentage of malformed triploid individuals equaled 19.1%. Drastically increased number of deformed larvae (> 30%) was observed in both DH and meiogynogenetic individuals. Intensification of kyphosis and scoliosis was clearly demonstrated in the gynogenetic and triploid brook trout. Genetic factors such as increased number of sets of chromosomes in triploids and expression of lethal alleles in the gynogenetic fish plus side effects of HHP shock utilized for retention of the second polar body or inhibition of the first cell cleavage when induced triploid and gynogenetic development have been discussed to affect survival rates and prevalence for the skeletal deformities in the chromosome set manipulated brook trout.

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.

Cytogenetic investigation of Arctic char × brook trout F1, F2 and backcross hybrids revealed remnants of the chromosomal rearrangements

Arctic char (Salvelinus alpinus) and brook trout (Salvelinus fontinalis) hybridize and their offspring is viable and fertile. This may be a real treat for the native European stocks of Arctic char which gene pools might be unintendedly contaminated with the genetic elements of brook trout. On the other hand, hybrids of these two species are appreciated by customers and have some potential for the aquaculture. Moreover, Salvelinus hybrids and backcross individuals are interesting models in the research focused on influence of hybridization on the genomic organization and chromosome rearrangements. Thus, the main goal of the present study was to examine chromosomes of Arctic char × brook trout F₁, F₂ hybrids and backcross individuals and compare with genomic information concerning parental species to recognize karyotypic changes provoked by the hybridization events. Application of conventional and molecular (FISH) techniques allow to identify characteristic chromosomes for both parental species in the hybrid progeny and show multiplicity of cytotypes among different types of crosses with variability in structure and number of chromosome (81–85) and chromosome arm (99–101). Chromosome fragment was detected in the karyotype of one F₁ and one backcross individual and the presence of one triploid (3n) fish was documented. Occurrence of chromosomes containing internally located telomeric sequences (ITS) inherited after brook trout or both parental species was shown in F₁ and backcross progeny. Moreover, additional CMA₃-positive signal on chromosome from Arctic char pair no. 2 in F₁ fish and interstitially located active NOR visible on subtelo-acrocentric (F₂ hybrid) and acrocentric (Sf × H individual) chromosomes were detected. Described polymorphic chromosomes together with specific, interstitial location of CMA₃-positive found in F₂ and Sf × H hybrids and DAPI-positive regions observed in H × Sa fish at different uniarmed chromosomes pair presumably are remnants of chromosomal rearrangements. Provided results strongly indicate that the hybridization process influenced the genome organization in the Salvelinus hybrid progeny.

Preliminary Identification of Candidate Genes Related to Survival of Gynogenetic Rainbow Trout (Oncorhynchus mykiss) Based on Comparative Transcriptome Analysis

In the present research, the eggs from four rainbow trout females were used to provide four groups of gynogenetic doubled haploids (DHs). The quality of the eggs from different clutches was comparable, however, interclutch differences were observed in the gynogenetic variants of the experiment and the survival of DH specimens from different groups varied from 3% to 57% during embryogenesis. Transcriptome analysis of the eggs from different females exhibited inter-individual differences in the maternal genes' expression. Eggs originating from females whose gynogenetic offspring had the highest survival showed an increased expression of 46 genes when compared to the eggs from three other females. Eggs with the highest survival of gynogenetic embryos showed an up-regulation of genes that are associated with cell survival, migration and differentiation (tyrosine-protein kinase receptor TYRO3-like gene), triglyceride metabolism (carnitine O-palmitoyltransferase 1 gene), biosynthesis of polyunsaturated fat (3-oxoacyl-acyl-carrier-protein reductase gene), early embryogenic development (protein argonaute-3 gene, leucine-rich repeat-containing protein 3-like gene), 5S RNA binding (ribosome biogenesis regulatory protein homolog) as well as senescence and aging (telomerase reverse transcriptase, TERT gene), among others. Positive correlation between the genotypic efficiency and egg transcriptome profiles indicated that at least some of the differentially expressed genes should be considered as potential candidate genes for the efficiency of gynogenesis in rainbow trout.

Hybrid between Danio rerio female and Danio nigrofasciatus male produces aneuploid sperm with limited fertilization capacity

In the Danio species, interspecific hybridization has been conducted in several combinations. Among them, only the hybrid between a zebrafish (D. rerio) female and a spotted danio (D. nigrofasciatus) male was reported to be fertile. However, beyond these investigations, by means of reproductive biology, gametes of the hybrid have also not been investigated genetically. For this study, we induced a hybrid of the D. rerio female and D. nigrofasciatus male in order to study its developmental capacity, reproductive performance and gametic characteristics. Its hybrid nature was genetically verified by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis of the rhodopsin gene. Almost all the hybrids (36/37) were males, and only one was female. Developing oocytes were observed in the hybrid female, but ovulated eggs have not been obtained thus far. Microscopic observation revealed various head sizes of sperm in the hybrid males. Flow cytometry showed that the hybrid males generated aneuploid sperm with various ploidy levels up to diploidy. In backcrosses between D. rerio females and hybrid males, fertilization rates were significantly lower than the control D. rerio, and most resultant progeny with abnormal appearance exhibited various kinds of aneuploidies ranging from haploidy to triploidy, but only one viable progeny, which survived more than four months, was triploid. This suggested the contribution of fertile diploid sperm of the hybrid male to successful fertilization and development.

Induced androgenetic development in rainbow trout and transcriptome analysis of irradiated eggs

Ionizing radiation is administered to damage nuclear genome in fish eggs during induced androgenesis. In this study, we examined whether 350 Gy of X-ray applied to damage chromosomes in the rainbow trout eggs affects maternal RNA. Shortly after irradiation, we did not find any symptoms of RNA degradation in the treated eggs. Significant (p < 0.01) differences between non-irradiated and irradiated eggs concerned only a few transcripts including increased expression of immediate early response 2 (IER2) and early growth response 1 (EGR1) genes observed in the irradiated eggs. Both genes belong to the group of “immediate early genes” that respond quickly to the diverse extracellular stimuli. Elevated expression of these genes was accompanied by decreased level of ssa-miR-10b-5p and ssa-miR-21b-5p (p < 0.05), for which IER2 and EGR1 are target genes. The level of RNA in the fertilized irradiated eggs was highly significantly lower than in the non-irradiated eggs (p < 0.001) and in the unfertilized irradiated eggs (p < 0.0001). However, transcriptome profiles of fertilized non-irradiated eggs and fertilized irradiated eggs did not differ significantly. Thus, we assume that reduced abundance of mRNA in the fertilized irradiated eggs was associated with post-translational degradation and clearance of the maternal transcripts rather than from the irradiation of eggs.

High Rate of Deformed Larvae among Gynogenetic Brown Trout (Salmo trutta m. fario) Doubled Haploids

Mitotic gynogenesis results in the production of fully homozygous individuals in a single generation. Since inbred fish were found to exhibit an increased frequency of body deformations that may affect their survival, the main focus of this research was to evaluate the ratio of individuals with spinal deformities among gynogenetic doubled haploids (DHs) brown trout as compared to nonmanipulated heterozygous individuals. Gynogenetic development was induced by the activation of brown trout eggs by UV-irradiated homologous and heterologous (rainbow trout) spermatozoa. The subsequent exposure of the activated eggs to the high hydrostatic pressure disturbed the first cleavage in gynogenetic zygotes and enabled duplication of the maternal haploid set of chromosomes. The survival rate was significantly higher among gynogenetic brown trout hatched from eggs activated with the homologous UV-irradiated spermatozoa when compared to DHs hatched from eggs activated by the heterologous spermatozoa. More than 35% of the gynogenetic larvae exhibited body deformities, mostly lordosis and scoliosis. The percentage of malformed brown trout from the control group did not exceed 15%. The increased number of deformed larvae among DHs brown trout suggested rather a genetic background of the disease related to the fish spine deformities; however, both genetic and environmental factors were discussed as a cause of such conditions in fish.

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.

Activation of the Albino Sterlet Acipenser ruthenus Eggs by UV-Irradiated Bester Hybrid Spermatozoa to Provide Gynogenetic Progeny

Meiotic gynogenesis was induced in the albino form of sterlet Acipenser ruthenus by activation of eggs with UV-irradiated bester (Huso huso x Acipenser ruthenus) spermatozoa followed by inhibition of the second meiotic division performed by a heat shock. Obtained putative gynogenetic progeny were all albinos. The genetic verification based on three microsatellite DNA markers confirmed the only maternal inheritance of the progeny from the gynogenetic experimental groups. Cytogenetic analysis proved the gynogenetic sterlets were diploids. Application of the albino phenotype together with the molecular and the cytogenetic diagnostic approaches enabled to evaluate the efficiency of the spermatozoa irradiation and application of the heat shock to restore diploid state in the gynogenetic zygotes.

Use of eggs derived from the interspecific charr hybrids to induce androgenetic development of the brook charr (Salvelinus fontinalis Mitchill 1814)

Although, brook charr (Salvelinus fontinalis Mitchill 1814) and Arctic charr (Salvelinus alpinus Linnaeus 1758) are able to cross and give fertile offspring, their androgenetic nucleocytoplasmic hybrids are not viable. To overcome incompatibility between the egg cytoplasm of one charr species and the sperm nucleus of another charr species, application of F1 interspecific hybrids as egg donors for the purpose of androgenesis has been proposed. Here, androgenetic development of the brook charr was successfully induced in the brook charr eggs and the eggs derived from the reciprocal brook charr × Arctic charr F1 hybrids. A working androgenesis protocol included inactivation of the maternal nuclear DNA achieved by irradiation of the eggs with 420 Gy of X-rays, insemination of such treated eggs with the haploid sperm cells and exposition of the haploid androgenetic zygotes to the high hydrostatic pressure shock (51.711 MPa for 4 min) applied 420 min after insemination. Androgenetic larvae that hatched from the brook charr and the hybrid eggs were shown to be homozygous brook charr individuals. Androgenetic individuals exhibited 84 chromosomes and 100 chromosome arms (FN), values characteristic for the brook charr diploid cells. Strategy hybridize first than induce androgenesis should be tested in order to provide androgenetic offspring in other salmonids that are able to cross and produce fertile offspring.