Abstract
Spermatogenesis relies on complex molecular mechanisms, essential for the genesis and differentiation of the male gamete. Germ cell differentiation starts at the testicular parenchyma and finishes in the epididymis, which has three main regions: head, body, and tail. RNA-sequencing data of the testicular parenchyma (TP), head epididymis (HE), and tail epididymis (TE) from four bulls (three biopsies per bull: 12 samples) were subjected to differential expression analyses, functional enrichment analyses, and co-expression analyses. The aim was to investigate the co-expression and infer possible regulatory roles for transcripts involved in the spermatogenesis of Bos indicus bulls. Across the three pairwise comparisons, 3,826 differentially expressed (DE) transcripts were identified, of which 384 are small RNAs. Functional enrichment analysis pointed to gene ontology (GO) terms related to ion channel activity, detoxification of copper, neuroactive receptors, and spermatogenesis. Using the regulatory impact factor (RIF) algorithm, we detected 70 DE small RNAs likely to regulate the DE transcripts considering all pairwise comparisons among tissues. The pattern of small RNA co-expression suggested that these elements are involved in spermatogenesis regulation. The 3,826 DE transcripts (mRNAs and small RNAs) were further subjected to co-expression analyses using the partial correlation and information theory (PCIT) algorithm for network prediction. Significant correlations underpinned the co-expression network, which had 2,216 transcripts connected by 158,807 predicted interactions. The larger network cluster was enriched for male gamete generation and had 15 miRNAs with significant RIF. The miRNA bta-mir-2886 showed the highest number of connections (601) and was predicted to down-regulate ELOVL3, FEZF2, and HOXA13 (negative co-expression correlations and confirmed with TargetScan). In short, we suggest that bta-mir-2886 and other small RNAs might modulate gene expression in the testis and epididymis, in Bos indicus cattle.
Highlights
Spermatozoid is the most specialized cell in mammalian organisms
Spermatogenesis starts with the multiplication of spermatogonial stem cells followed by their meiotic division into spermatids, which differentiate into spermatozoa that are released into the lumen of seminiferous tubules in the testis (Staub and Johnson, 2018)
Samples from the head and tail epididymis (HE and TE) and the testicular parenchyma (TP) of Bos indicus bulls were used for RNA sequencing
Summary
Spermatozoid is the most specialized cell in mammalian organisms. Spermatogenesis, the differentiation of male germ cells, relies on a complex network of specialized molecular mechanisms that are critical to male fertility (MacLean and Wilkinson, 2005; Marengo, 2008; Hermann et al, 2018). Three sequential phases of cell proliferation and differentiation occur, where there is an extensive multiplication and proliferation of spermatogonial stem cells, followed by a meiotic division, and a remodeling of the nuclear and cellular components forming sperm cells (Abou-Haila and Tulsiani, 2000). Spermatogenesis starts with the multiplication of spermatogonial stem cells followed by their meiotic division into spermatids, which differentiate into spermatozoa that are released into the lumen of seminiferous tubules in the testis (Staub and Johnson, 2018). Spermatozoa leaving the testis transit through the epididymis, where they further mature, acquiring motility and the ability to fertilize the egg (Cornwall, 2009). The spermatozoa from the testis pass to the epididymis, which contributes to their maturation (Belleannée et al, 2012). Formed mature sperm cells emerge from the tail epididymis and are stored until the ejaculation event in the vas deferens
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