Developmental competence of eggs produced by rainbow trout Doubled Haploids (DHs) and generation of the clonal lines

Transcript level of telomerase reverse-transcriptase (TERT) gene in the rainbow trout (Oncorhynchus mykiss) eggs with different developmental competence for gynogenesis

Expression of the telomerase reverse-transcriptase (TERT) gene and activity of telomerase have been reported in the somatic tissues and gonads in fish irrespective of their age and size. Nevertheless, little is known about TERT expression in the fish eggs. In the current study, the presence of the TERT transcripts was confirmed in the rainbow trout ovulated eggs before and after activation with nonirradiated and UV-irradiated (gynogenesis) sperm. Eggs originating from eight females had high and comparable quality expressed by similar hatching rates. However, survival of the gynogenetic larvae that hatched from eggs activated with UV-irradiated sperm and further exposed to the high hydrostatic pressure (HHP) shock for duplication of the maternal chromosomes varied between females from 2.1 ± 0.4 to 40.5 ± 2.2%. Increased level of TERT transcripts was observed in eggs originating from two females, and gametes from only one of them showed improved competence for gynogenesis (27.3 ± 1.9%). In turn, eggs from the female that exhibited the highest survival after gynogenetic activation were characterized by the lowest expression of the TERT gene. Telomerase in rainbow trout eggs may compensate erosion of the telomeres during early embryonic development; however, its upregulation does not assure better development after gynogenetic activation.

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.

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.

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.