In both mammals and fishes, this spermiogenic differentiation process typically results in the elimination of cytoplasm and organelles together with the morphogenesis of three major compartments, the head containing a condensed haploid nucleus, a mid-section containing the proximal centriole together with one or more mitochondria, and the terminal region composed of an elongated flagellum or flagella 2, 3. The developmental remodeling of haploid germ cells (HGCs) into highly polarized spermatozoa capable of motility activation and fertilization is an evolutionary conserved mechanism of male gamete formation 1. Our data provide new insight into the mRNA and lncRNA cargos of teleost spermatozoa and uncover the possible involvement of novel endocrine mechanisms during the differentiation and maturation of spermatozoa. Pathway analysis conducted on DEGs identified 37 different signaling pathways enriched in SPZ EJ, including 13 receptor pathways, from which the most predominant correspond to the chemokine and cytokine, gonadotropin-releasing hormone receptor and platelet derived growth factor signaling pathways. The upregulated transcripts are involved in transcriptional and translational regulation, chromatin and cytoskeleton organization, metabolic processes such as glycolysis and oxidative phosphorylation, and also include a number of ion and water channels, exchangers, transporters and receptors. In addition, approximately 9000 long non-coding RNAs (lncRNAs) were found, of which 56% were accumulated or emerged de novo in SPZ EJ. Deep sequencing by RNA-seq identified a total of 7286 differentially expressed genes (DEGs) ( p-value < 0.01) between both cell types, of which nearly half were upregulated in SPZ EJ compared to HCGs. Samples were collected under strict quality controls employing immunofluorescence microscopy as well as by determining the sperm motion kinematic parameters by computer-assisted sperm analysis.
Here, we investigated this process in the marine teleost gilthead seabream ( Sparus aurata) through the examination of the changes in the transcriptome between cell-sorted HGCs and ejaculated sperm (SPZ EJ). In non-mammalian vertebrates, the molecular mechanisms involved in the transformation of haploid germ cells (HGCs) into spermatozoa (spermiogenesis) are largely unknown.
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