GSE130895
Transcriptome of tambaqui Colossoma macropomum during gonad differentiation: different molecular signals leading to sex identity
Purpose: The gene molecular network involved in teleost fish sex determination and differentiation is highly variable among species and even in some cases among populations of the same species. The objectives of the present study were to identify the period of gonadal sex differentiation in tambaqui juveniles, as well as the genes and pathways potentially involved in this process. Methods: Histological analysis of juveniles was carried out to establish a timeline of the gonadal differentiation in tambaqui. Based on that knowledge, ten juveniles were selected before the first evidence of histological sex differentiation and total RNA was extracted from their trunks and used for RNA-Sequencing and a subsequent de novo transcriptome assembly. Principal Component Analysis (PCA) of the whole transcriptome data was used to cluster samples into two distinct groups: putative males and putative females. Differential gene expression, functional annotation and gene enrichment were used to identify genes and pathways related to sex  differentiation in tambaqui to which was applied the Mann-Whitney non-parametric t test (p <0.05) confirming the statistical significance of the expression dimorphism between the groups. Results: The first sign of histological sex differentiation in tambaqui was the formation of the ovarian cavity detected in individuals measuring about 40 mm in total length. Before the differentiation period, components of the Wnt / ß-catenin pathway, fox and fst genes (p <0.05) suggest female sex development in the putative females, whereas antagonistic pathways (gsk3b, wt1 and fgfr2), sox9 and genes for androgen synthesis (p <0.05) are indicative of a male-like differentiation. Conclusions: Tambaqui juveniles prior to the morphological ovarian differentiation present the Wnt / ß-catenin pathway exerting putative role on the sex differentiation target, either upregulated in female-like individuals, or antagonized in male-like individuals. Thus, the present work provides a molecular basis for future studies on the application of tambaqui monosex cultivation. Overall design: Ten juveniles were selected before the first evidence of histological sex differentiation and total RNA was extracted from their trunks and used for RNA-Sequencing.