Analysis of the genic content and differential expression of variants of B chromosome in Psalidodon (Teleostei, Characiformes)

Author(s)

Mateus Rossetto Vidal

• Document type: Master's Dissertation
• Press: Botucatu. 2022-05-02.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Botucatu
• Defense date: 2022-02-21
• Advisor: Fausto Foresti; Duílio Mazzoni Zerbinato de Andrade Silva

Abstract

B chromosomes are supernumerary elements found in the genome of eukaryotes and have several aspects still unknown. Despite its poor composition in protein-coding genes, the description of transcripts from these elements has changed the view that they are inert structures in the genome. Among the fish of the genus Psalidodon, a great diversity of these elements can be observed, with the occurrence of micro to macro B chromosomes, with different morphologies. Previous studies have demonstrated the occurrence of at least 21 genes in the B chromosomes of Psalidodon paranae and Psalidodon scabripinnis, with both species having a greater presence of B chromosomes in females, which suggests their role in sex differentiation pathways. Thus, the present study aimed to investigate the gene content of the BfMa variant of Psalidodon fasciatus to test the hypothesis of a common origin with other variants in the genus, as well as to investigate whether the presence of B chromosomes leads to the different expression of genes in the differentiation pathway of the sex in P. paranae. For this, individuals of P. paranae and P. fasciatus were collected and analyzed and the qPCR analysis allowed the identification of eight protein-coding genes in the BfMa variant of P. fasciatus (amhr2, ccpg1, cia30, g2e3, msh4, nobox, nusap1, and sbno2), being that six of these have already been described in the BfMb variant of the same species. Thus, it is highly likely that both variants have a common origin and have diversified to the point of losing or acquiring unique genes. Still, due to the sharing of five genes between the B chromosomes of Psalidodon already analyzed, it can be supposed that the BfMa variant also shares a common origin with the other variants of the genus, in a process that occurred about 4 million years ago and that its origin was not due to recent interspecific hybridization. RT-qPCR analyzes in P. paranae gonads showed differential expression of three genes in females (cyp19a1a, esr1 and nobox), and two in males (dmrt1 and nobox). The under expression of the cyp19a1a and esr1 genes in females could reflect a dysregulation process caused by the B chromosome, or a response of the A genome to neutralize the B genome, or even a possible functional effect of these chromosomes, which would lead to a distortion of the reproductive period. The overexpression of the nobox gene could reflect the existence of a mechanism of accumulation involving these chromosomes, determining greater efficiency in the oogenesis process and greater reproductive success for +B females. In males, overexpression of the dmrt1 gene could cause an alteration in the reproductive cycle, as has already been observed before in P. scabripinnis. (AU)

• FAPESP's process: 19/15140-9 - Analysis of the genic content and differential expression of variants of B chromosome in Astyanax (Teleostei, Characiformes)
• Grantee: Mateus Rossetto Vidal
• Support Opportunities: Scholarships in Brazil - Master