In the catfish, vasotocin and isotocin precursor (pro-VT and pro-IT) transcripts were localized in brain and ovary by RNA in situ hybridization and estrogen control of gene expression studied by qRT-PCR. Both pro-VT and pro-IT transcripts were detected in nucleus preopticus (NPO) of the brain. Within the NPO, the VT and IT neurons displayed distinct spatial distribution and neuronal organization. Apart from the NPO, pro-VT transcripts were also detected in the anterior nucleus lateralis tuberis. In the ovary, the follicular envelope (theca and granulosa layers) of ovarian follicles showed strong positive transcript signals, which was reported for the first time in teleosts. The regulation of expression of pro-VT and pro-IT genes by estrogen was investigated in vitro using brain preoptic area and ovarian slices in presence of exemestane, a known endogenous estrogen (E2) synthesis blocker, alone or in co-incubation with E2. Exemestane elicited differential effects on the nonapeptide expression in the brain and ovary. Exemestane mildly downregulated pro-IT expression but did not influence the pro-VT expression in the brain. In the ovary, exemstane inhibited both pro-VT and pro-IT expression about 4 folds higher than the control groups. The E2 supplementation increased the expression of both pro-VT and pro-IT in the brain differentially with the high E2 dose eliciting about 3-fold stimulation of the pro-VT expression. In the ovary, only the high dose of E2 supplementation restored and increased the pro-VT and pro- IT expression compared to the exemstane group. The steroid-induced expression was still significantly lower than the control level. The presence of pro-VT and pro-IT transcripts in the follicular envelope points to de novo synthesis of the neuropeptides in the ovary, which is influenced by the locally synthesized E2. The pro-VT and pro-IT neurons seem to be responsive to the E2 feedbacks rather than to the locally produced E2.
Banerjee P, Chaube R, Joy KP
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