Characterization of Lh and Tsh expression in the saccus vasculosus of the neotropical cichlid fish Cichlasoma dimerus

SALLEMI, JULIETA E.; DI YORIO, MARÍA P.; BRECCIA, ANDRÉS; VISSIO, PAULA G.

Mar del Plata

Congreso; Reunión conjunta SAIC SAB AAFE AACYTAL 2023. XXV Jornadas Anuales de la Sociedad Argentina de Biología (SAB).; 2023

SAIC SAB AAFE AACYTAL

The saccus vasculosus (SV) is a highly vascularized organ of gnathostome fishes, located ventral to the hypothalamus and posterior to the pituitary gland. It is characterized by a folded neuroepithelium composed mainly of coronet and supporting cells, but its function remains controversial. In 2013, Nakane et al. proposed that the SV could be homologous to the pars tuberalis, being involved in the control of seasonal reproduction since they detected the expression of genes involved in this function: thyrotropin (tsh) and its receptor (tshr) and rhodopsin family genes in the SV of Oncorhynchus masou. In addition, the authors observed that isolated SV of this species could respond to photoperiod and that their removal suppressed the gonadal response to these signals. Furthermore, in the last six years, studies in different fish species have shown the expression of neuropeptides and receptors related to reproduction. Previously, in our laboratory, we characterized the SV of Cichlasoma dimerus and detected the innervation of gonadotropin inhibitory hormone (Gnih) in adults and ontogeny, a neuropeptide whose role in reproduction has been widely discussed. This study aims to characterize the expression of Lh and Tsh in the SV of adults of C. dimerus and to evaluate the effect of Gnih on lh expression in vitro. Adult SV were sampled and processed for immunohistochemistry, PCR, and in vitro assays. β-Tsh immunoreactivity was observed in the vesicles of the apical processes of the coronet cells in both sexes, and we detected the mRNA expression of both β-tsh and β-lh by PCR. Regarding the in vitro assays, preliminary results indicate that the β-lh mRNA expression was stimulated by the presence of Gnih synthetic peptide, especially in females. The present work is the first report showing the expression of β-tsh and β-lh in a freshwater species and is the starting point for future experiments on the role of SV in reproductive function.