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Differential Regulation of the Expression of the Two Thyrotropin Beta Subunit Paralogs by Salmon Pituitary Cells In Vitro

Abstract : We recently characterized two paralogs of the thyrotropin (TSH) beta subunit in Atlantic salmon, tshba and tshbb, issued from teleost-specific whole genome duplication. The transcript expression of tshbb, but not of tshba, peaks at the time of smoltification, which revealed a specific involvement of tshbb paralog in this metamorphic event. Tshba and tshbb are expressed by distinct pituitary cells in salmon, likely related to TSH cells from the pars distalis and pars tuberalis, respectively, in mammals and birds. The present study aimed at investigating the neuroendocrine and endocrine factors potentially involved in the differential regulation of tshba and tshbb paralogs, using primary cultures of Atlantic salmon pituitary cells. The effects of various neurohormones and endocrine factors potentially involved in the control of development, growth, and metabolism were tested. Transcript levels of tshba and tshbb were measured by qPCR, as well as those of growth hormone (gh), for comparison and validation. Corticotropin-releasing hormone (CRH) stimulated tshba transcript levels in agreement with its potential role in the thyrotropic axis in teleosts, but had no effect on tshbb paralog, while it also stimulated gh transcript levels. Thyrotropin-releasing hormone (TRH) had no effect on neither tshb paralogs nor gh. Somatostatin (SRIH) had no effects on both tshb paralogs, while it exerted a canonical inhibitory effect on gh transcript levels. Thyroid hormones [triiodothyronine (T3) and thyroxine (T4)] inhibited transcript levels of both tshb paralogs, as well as gh, but with a much stronger effect on tshba than on tshbb and gh. Conversely, cortisol had a stronger inhibitory effect on tshbb than tshba, while no effect on gh. Remarkably, insulin-like growth factor 1 (IGF1) dose-dependently stimulated tshbb transcript levels, while it had no effect on tshba, and a classical inhibitory effect on gh. This study provides the first data on the neuroendocrine factors involved in the differential regulation of the expression of the two tshb paralogs. It suggests that IGF1 may be involved in triggering the expression peak of the tshbb paralog at smoltification, thus representing a potential internal signal in the link between body growth and smoltification metamorphosis.
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Submitted on : Monday, December 14, 2020 - 10:00:37 PM
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Mitchell Fleming, Gersende Maugars, Patrick Martin, Sylvie Dufour, Karine Rousseau. Differential Regulation of the Expression of the Two Thyrotropin Beta Subunit Paralogs by Salmon Pituitary Cells In Vitro. Frontiers in Endocrinology, Frontiers, 2020, ⟨10.3389/fendo.2020.603538⟩. ⟨hal-03065703⟩



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