Morpho-histological and Transcriptome Analysis Reveal the Unreduced Sperm Formation Mechanism in cdk1-Depletion Zebrafish.

Cyclin-dependent kinases (Cdks) are major molecules related to cell cycle regulation. Polyploidy can be caused by the production of unreduced gametes, which is often related to the abnormal cell cycle of germ cells. Here, we successfully constructed a cdk1 mutation line (cdk1+/-) in zebrafish, a commonly used model organism. It showed that cdk1 depletion resulted in the generation of both polyploid and aneuploid embryos of WT♀ × cdk1+/-♂ zebrafish. In addition to normal sperms (1N), the depletion of cdk1 in zebrafish also led to the production of some large-head 2N sperms and higher ploidy sperms. Results of bivalent analysis of testis and ultrastructure analysis of spermatogonia suggested that the production of these large-head sperms was due to spermatogonia chromosome doubling in cdk1+/- zebrafish. Transcriptome analysis revealed aberrant expressions of some cell cycle and DNA replication-related genes in the early testis of cdk1+/- zebrafish relative to WT zebrafish. Through STRING correlation analysis, we further proved that cdk1 depletion affected the mitosis process and endoduplication initiation of spermatogonia by regulating expressions of some proteins related to cell cycle (i.e., Espl1 and Pp1) and DNA replication (i.e., Orc1 and Rnaseh2b), thereby leading to the formation of unreduced sperms. This study provides important information on revealing the molecular mechanisms of unreduced gamete formation caused by cdk1 mutation. Meanwhile, it also provides an important reference for the creation of fish polyploid germplasm.

Mitotic defects lead to unreduced sperm formation in cdk1-/- mutants.

Unreduced gametes, that are important for species evolution and agricultural development, are generally believed to be formed by meiotic defects. However, we found that male diploid loach (Misgurnus anguillicaudatus) could produce not only haploid sperms, but also unreduced sperms, after cyclin-dependent kinase 1 gene (cdk1, one of the most important kinases in regulating cell mitosis) deletion. Observations on synaptonemal complexes of spermatocyte in prophase of meiosis and spermatogonia suggested that the number of chromosomes in some spermatogonia of cdk1-/- loach doubled, leading to unreduced diploid sperm production. Then, transcriptome analysis revealed aberrant expressions of some cell cycle-related genes (such as ppp1c and gadd45) in spermatogonia of cdk1-/- loach relative to wild-type loach. An in vitro and in vivo experiment further validated that Cdk1 deletion in diploid loach resulted in mitotic defects, leading to unreduced diploid sperm formation. In addition, we found that cdk1-/- zebrafish could also produce unreduced diploid sperms. This study provides important information on revealing the molecular mechanisms behind unreduced gamete formation through mitotic defects, and lays the foundation for a novel strategy for fish polyploidy creation by using cdk1 mutants to produce unreduced sperms, which can then be used to obtain polyploidy, proposed to benefit aquaculture.

Transcriptome analyses of betta fish (Betta splendens) provide novel insights into fin regeneration and color-related genes.

The betta fish (Betta splendens), an important ornamental fish, haswell-developed and colorful fins.After fin amputation, betta fish can easily regenerate finssimilar to the originalsin terms of structureand color. The powerful fin regeneration ability and a variety of colors in the betta fish are fascinating. However, the underlying molecular mechanisms are still not fully understood. In this study, tail fin amputation and regeneration experiments were performed on two kinds of betta fish: red and white color betta fish. Then, transcriptome analyseswere conducted to screen out fin regeneration and color-relatedgenes in betta fish. Through enrichment analyses of differentially expressed genes (DEGs), we founda series of enrichment pathways and genes related to finregeneration, including cell cycle (i.e. plcg2), TGF-beta signaling pathway (i.e. bmp6), PI3K-Akt signaling pathway (i.e. loxl2aand loxl2b), Wnt signaling pathway(i.e. lef1), gap junctions (i.e. cx43), angiogenesis (i.e. foxp1), and interferon regulatory factor (i.e. irf8). Meanwhile, some fin color-related pathways and genes were identified in betta fish, especially melanogenesis (i.e. tyr, tyrp1a, tyrp1b, and mc1r) and carotenoid color genes (i.e. pax3, pax7, sox10, and ednrba). In conclusion, this studycan not only enrich the research onfish tissue regeneration, but also has a potential significance for the aquaculture and breeding of the betta fish.