Transcriptomic changes during the onset of spermatogenesis in the European sea bass

Abstract

Pubertal development in males starts with the onset of spermatogenesis and implies the division of spermatogonia and their subsequent entry into meiosis. Meiosis is essential for the initiation of spermatogenesis, triggering the transition from the immature gonad into the mature one. The present study characterizes the expression of several genes involved in the onset of spermatogenesis in the European sea bass, focusing on the appearance of spermatocytes and thus the first meiotic divisions. Histological assessment and 11- ketotestosterone plasma levels were used as indicators of the gonadal maturation stage. A transcriptomic study using a sea bass specific microarray resulted in a number of genes differentially expressed during the onset of spermatogenesis, indicating that they could be used as potential molecular markers for this process. Based on the analysis of their go-terms, the genes were classified into different categories among which cell-cycle progression, microtubule assembly during meiosis or retinoic acid (RA) metabolic pathway, were the most relevant. The study deepens on the possible role that genes involved in the RA pathway could have on pubertal development. With this purpose, sequences of some of these genes, including that of cyp26, the enzyme involved in the metabolism of RA, were cloned to study their tissue-specific expression and to quantify their levels during testicular development by qRT-PCR. The results obtained validated those of the microarray suggesting that a decrease in the expression of cyp26 is needed to facilitate the presence of RA in the gonad and thus initiate meiosis