A Germline-Specific Regulator of Mitochondrial Fusion is Required for Maintenance and Differentiation of Germline Stem and Progenitor Cells

Endogenous biosynthesis of docosahexaenoic acid (DHA) regulates fish oocyte maturation by promoting pregnenolone production

Omega-3 polyunsaturated fatty acids (n-3 PUFAs), particularly docosahexaenoic acid (22:6n-3, DHA), play crucial roles in the reproductive health of vertebrates, including humans. Nevertheless, the underlying mechanism related to this phenomenon remains largely unknown. In this study, we employed two zebrafish genetic models, i.e., elovl2 -/- mutant as an endogenous DHA-deficient model and fat1 (omega-3 desaturase encoding gene) transgenic zebrafish as an endogenous DHA-rich model, to investigate the effects of DHA on oocyte maturation and quality. Results show that the elovl2 -/- mutants had much lower fecundity and poorer oocyte quality than the wild-type controls, while the fat1 zebrafish had higher fecundity and better oocyte quality than wild-type controls. DHA deficiency in elovl2 -/- embryos led to defects in egg activation, poor microtubule stability, and reduced pregnenolone levels. Further study revealed that DHA promoted pregnenolone synthesis by enhancing transcription of cyp11a1, which encodes the cholesterol side-chain cleavage enzyme, thereby stabilizing microtubule assembly during oogenesis. In turn, the hypothalamic-pituitary-gonadal axis was enhanced by DHA. In conclusion, using two unique genetic models, our findings demonstrate that endogenously synthesized DHA promotes oocyte maturation and quality by promoting pregnenolone production via transcriptional regulation of cyp11a1.

Induced formation of primordial germ cells from zebrafish blastomeres by germplasm factors

The combination of genome editing and primordial germ cell (PGC) transplantation has enormous significance in the study of developmental biology and genetic breeding, despite its low efficiency due to limited number of donor PGCs. Here, we employ a combination of germplasm factors to convert blastoderm cells into induced PGCs (iPGCs) in zebrafish and obtain functional gametes either through iPGC transplantation or via the single blastomere overexpression of germplasm factors. Zebrafish-derived germplasm factors convert blastula cells of Gobiocypris rarus into iPGCs, and Gobiocypris rarus spermatozoa can be produced by iPGC-transplanted zebrafish. Moreover, the combination of genome knock-in and iPGC transplantation perfectly resolves the contradiction between high knock-in efficiency and early lethality during embryonic stages and greatly improves the efficiency of genome knock-in. Together, we present an efficient method for generating PGCs in a teleost, a technique that will have a strong impact in basic research and aquaculture.

The mitochondrial protein Sod2 is important for the migration, maintenance, and fitness of germ cells

To maintain a range of cellular functions and to ensure cell survival, cells must control their levels of reactive oxygen species (ROS). The main source of these molecules is the mitochondrial respiration machinery, and the first line of defense against these toxic substances is the mitochondrial enzyme superoxide dismutase 2 (Sod2). Thus, investigating early expression patterns and functions of this protein is critical for understanding how an organism develops ways to protect itself against ROS and enhance tissue fitness. Here, we report on expression pattern and function of zebrafish Sod2, focusing on the role of the protein in migration and maintenance of primordial germ cells during early embryonic development. We provide evidence that Sod2 is involved in purifying selection of vertebrate germ cells, which can contribute to the fitness of the organism in the following generations.

Quantitative proteomics and phosphoproteomics reveal insights into mechanisms of ocnus function in Drosophila testis development

BACKGROUND

Testis is the only organ supporting sperm production and with the largest number of proteins and tissue-specific proteins in animals. In our previous studies, we have found that knockdown of ocnus (ocn), a testis-specific gene, resulted in much smaller testis with no germ cells in Drosophila melanogaster. However, the molecular consequences of ocn knockdown in fly testes are unknown.

RESULTS

In this study, through iTRAQ quantitative proteomics sequencing, 606 proteins were identified from fly abdomens as having a significant and at least a 1.5-fold change in expression after ocn knockdown in fly testes, of which 85 were up-regulated and 521 were down-regulated. Among the differential expressed proteins (DEPs), apart from those proteins involved in spermatogenesis, the others extensively affected biological processes of generation of precursor metabolites and energy, metabolic process, and mitochondrial transport. Protein-protein interaction (PPI) analyses of DEPs showed that several kinases and/or phosphatases interacted with Ocn. Re-analyses of the transcriptome revealed 150 differential expressed genes (DEGs) appeared in the DEPs, and their changing trends in expressions after ocn knockdown were consistent. Many common down-regulated DEGs and DEPs were testis-specific or highly expressed in the testis of D. melanogaster. Quantitative RT-PCR (qRT-PCR) confirmed 12 genes appeared in both DEGs and DEPs were significantly down-regulated after ocn knockdown in fly testes. Furthermore, 153 differentially expressed phosphoproteins (DEPPs), including 72 up-regulated and 94 down-regulated phosphorylated proteins were also identified (13 phosphoproteins appeared in both up- and down-regulated groups due to having multiple phosphorylation sites). In addition to those DEPPs associated with spermatogenesis, the other DEPPs were enriched in actin filament-based process, protein folding, and mesoderm development. Some DEPs and DEPPs were involved in Notch, JAK/STAT, and cell death pathways.

CONCLUSIONS

Given the drastic effect of the ocn knockdown on tissue development and testis cells composition, the differences in protein abundance in the ocn knockdown flies might not necessarily be the direct result of differential gene regulation due to the inactivation of ocn. Nevertheless, our results suggest that the expression of ocn is essential for Drosophila testis development and that its down-regulation disturbs key signaling pathways related to cell survival and differentiation. These DEPs and DEPPs identified may provide significant candidate set for future studies on the mechanism of male reproduction of animals, including humans.

Identification of fish spermatogenic cells through high-throughput immunofluorescence against testis with an antibody set

Image-based identification and quantification of different types of spermatogenic cells is of great importance, not only for reproductive studies but also for genetic breeding. Here, we have developed antibodies against spermatogenesis-related proteins in zebrafish (Danio rerio), including Ddx4, Piwil1, Sycp3, and Pcna, and a high-throughput method for immunofluorescence analysis of zebrafish testicular sections. By immunofluorescence analysis of zebrafish testes, our results demonstrate that the expression of Ddx4 decreases progressively during spermatogenesis, Piwil1 is strongly expressed in type A spermatogonia and moderately expressed in type B spermatogonia, and Sycp3 has distinct expression patterns in different subtypes of spermatocytes. Additionally, we observed polar expression of Sycp3 and Pcna in primary spermatocytes at the leptotene stage. By a triple staining of Ddx4, Sycp3, and Pcna, different types/subtypes of spermatogenic cells were easily characterized. We further demonstrated the practicality of our antibodies in other fish species, including Chinese rare minnow (Gobiocypris rarus), common carp (Cyprinus carpio), blunt snout bream (Megalobrama amblycephala), rice field eel (Monopterus albus) and grass carp (Ctenopharyngodon idella). Finally, we proposed an integrated criterion for identifying different types/subtypes of spermatogenic cells in zebrafish and other fishes using this high-throughput immunofluorescence approach based on these antibodies. Therefore, our study provides a simple, practical, and efficient tool for the study of spermatogenesis in fish species.