Characterization of lh and tsh expression in the saccus vasculosus of the neotropical cichlid fish Cichlasoma dimerus

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

Mar del Plata

Congreso; REUNIÓN ANUAL DE LAS SOCIEDADES DE BIOCIENCIAS; 2023

Sociedad Argentina de Biología

The saccus vasculosus (SV) is a highly vascularized organ of gnathostomefishes, located ventral to the hypothalamus and posteriorto the pituitary gland. It is characterized by a folded neuroepitheliumcomposed mainly of coronet and supporting cells, but its functionremains controversial. In 2013, Nakane et al. proposed that the SVcould be homologous to the pars tuberalis, being involved in thecontrol of seasonal reproduction since they detected the expressionof genes involved in this function: thyrotropin (tsh) and its receptor(tshr) and rhodopsin family genes in the SV of Oncorhynchusmasou. In addition, the authors observed that isolated SV of thisspecies could respond to photoperiod and that their removal suppressedthe gonadal response to these signals. Furthermore, inthe last six years, studies in different fish species have shown theexpression of neuropeptides and receptors related to reproduction.Previously, in our laboratory, we characterized the SV of Cichlasomadimerus and detected the innervation of gonadotropin inhibitory hormone(Gnih) in adults and ontogeny, a neuropeptide whose role inreproduction has been widely discussed. This study aims to characterizethe expression of Lh and Tsh in the SV of adults of C. dimerusand to evaluate the effect of Gnih on lh expression in vitro. Adult SVwere sampled and processed for immunohistochemistry, PCR, andin vitro assays. β-Tsh immunoreactivity was observed in the vesiclesof the apical processes of the coronet cells in both sexes, and wedetected the mRNA expression of both β-tsh and β-lh by PCR. Regardingthe in vitro assays, preliminary results indicate that the β-lhmRNA expression was stimulated by the presence of Gnih syntheticpeptide, especially in females. The present work is the first reportshowing the expression of β-tsh and β-lh in a freshwater speciesand is the starting point for future experiments on the role of SV inreproductive function.