Comparative transcriptome provides insights into differentially expressed genes between testis and ovary of Onychostoma macrolepis in reproduction period

Analysis of morphology, histology characteristics, and circadian clock gene expression of Onychostoma macrolepis at the overwintering period and the breeding period

Fish typically adapt to their environment through evolutionary traits, and this adaptive strategy plays a critical role in promoting species diversity. Onychostoma macrolepis is a rare and endangered wild species that exhibits a life history of overwintering in caves and breeding in mountain streams. We analyzed the morphological characteristics, histological structure, and expression of circadian clock genes in O. macrolepis to elucidate its adaptive strategies to environmental changes in this study. The results showed that the relative values of O. macrolepis eye diameter, body height, and caudal peduncle height enlarged significantly during the breeding period. The outer layer of the heart was dense; the ventricular myocardial wall was thickened; the fat was accumulated in the liver cells; the red and white pulp structures of the spleen, renal tubules, and glomeruli were increased; and the goblet cells of the intestine were decreased in the breeding period. In addition, the spermatogenic cyst contained mature sperm, and the ovaries were filled with eggs at various stages of development. Throughout the overwintering period, the melano-macrophage center is located between the spleen and kidney, and the melano-macrophage center in the cytoplasm has the ability to synthesize melanin, and is arranged in clusters to form cell clusters or white pulp scattered in it. Circadian clock genes were identified in all organs, exhibiting significant differences between the before/after overwintering period and the breeding period. These findings indicate that the environment plays an important role in shaping the behavior of O. macrolepis, helping the animals to build self-defense mechanisms during cyclical habitat changes. Studying the morphological, histological structure and circadian clock gene expression of O. macrolepis during the overwintering and breeding periods is beneficial for understanding its unique hibernation behavior in caves. Additionally, it provides an excellent biological sample for investigating the environmental adaptability of atypical cavefish species.

A delayed and unsynchronized ovary development as revealed by transcriptome of brain and pituitary of Coilia nasus

Coilia nasus is an anadromous fish that has been successfully domesticated in the last decade due to its high economic value. The fish exhibits a delayed ovary development during the reproductive season, despite breeding and selection for five to six offspring. The molecular mechanism of the delayed ovary development is still unknown, so the obstacles have not been removed in the large-scale breeding program. This study aims to investigate the key genes regulating ovarian development by comparing the transcriptomes of ovarian-stage IV and stage II brain/pituitary of Coilia nasus. Ovarian stages were validated by histological sections. A total of 75,097,641 and 66,735,592 high-quality reads were obtained from brain and pituitary transcriptomes, respectively, and alternatively spliced transcripts associated with gonadal development were detected. Compared to ovarian Ⅱ- brain, 515 differentially expressed genes (DEGs) were upregulated and 535 DEGs were downregulated in ovarian Ⅳ- brain, whereas 470 DEGs were upregulated and 483 DEGs were downregulated in ovarian Ⅳ- pituitary compared to ovarian Ⅱ- pituitary. DEGs involved in hormone synthesis and secretion and in the GnRH signaling pathway were screened. Weighted gene co-expression network analysis identified gene co-expression modules that were positively correlated with ovarian phenotypic traits. The hub genes Smad4 and TRPC4 in the modules were co-expressed with DEGs including Kiss1 receptor and JUNB, suggesting that ovarian development is controlled by a hypothalamic-pituitary-gonadal axis. Our results have provided new insights that advance our understanding of the molecular mechanism of C. nasus reproductive functions and will be useful for future breeding.

Comparative transcriptome analysis of ovaries and testes reveals sex-biased genes and pathways in zebrafish

Zebrafish (Danio rerio) is a widely recognized and extensively studied model organism in scientific research. The regulatory mechanism of gonadal development and differentiation of this species has aroused considerable attention. Nonetheless, the major sex-biased genes and pathways associated with gonadal development remain elusive. Therefore, to comprehend this intricate process, gonadal transcriptome sequencing was carried out to identify differentially expressed genes (DEGs) between the testes and ovaries of adult zebrafish. The preliminary assessment yielded a total of 23,529,272 and 23,521,368 clean reads from the cDNA libraries of ovaries and testes. Afterward, a comparative analysis of the transcriptome revealed 3,604 upregulated and 11,371 downregulated DEGs in the ovaries compared to the testes. Of these genes, 428 were exclusively expressed in females, while 3,516 were exclusively expressed in males. Additionally, further assessments were conducted to explore the functions associated with these DEGs in various biological processes. The data revealed their involvement in sex-biased pathways, such as progesterone-mediated oocyte maturation, oocyte meiosis, cytokine-cytokine receptor interaction, and cardiac muscle contraction. Finally, the expression levels of 14 sex-biased DEGs (cdc20, ccnb1, ypel3, chn1, bmp15, rspo1, tnfsf10, egfra, acta2, cox8a, gsdf, dmrt1, star, and cyp17a1) associated with the enriched pathways were subjected to further validation through qRT-PCR. The data acquired from these investigations offer valuable resources to support further exploration of the mechanisms governing sexual dimorphism and gonadal development in zebrafish.