Sexual Maturation Modulates Expression of Nuclear Receptor Types in Laser-Captured Single Cells of the Cichlid (Oreochromis niloticus) Pituitary

Abstract

The role of steroid/thyroid hormones in the regulation of endocrine cells at the level of the pituitary has remained unclear. Therefore, using single-cell quantitative real-time PCR, we examined absolute amounts of transcripts for nuclear receptors [estrogen receptors (ERs) α, β, and γ; androgen receptors (ARs) a and b; glucocorticoid receptors (GRs) 1, 2a, and 2b; and thyroid hormone receptors (TRs) α1, α2, and β] in pituitary cells of immature (IM) and mature (M) male tilapia, Oreochromis niloticus. In the two reproductive stages, ACTH cells expressed only ERβ, whereas all other pituitary cell types expressed ERα + β, and a subpopulation coexpressed ARa, ARb, GR1, GR2b, and TRβ but lacked ERγ, GR2a, TRα1, and TRα2. IM males had high percentages of LH cells (IM 46.0% vs. M 10.0%), GH cells (IM 23.3% vs. M 7.9%), and prolactin cells (IM 68.8% vs. M 6.0%) with ERβ, and TSH cells (IM 19.2% vs. M 0.0%) and MSH cells (IM 25.6% vs. M 0.0%) with ERα + TRβ. A high percentage of FSH cells in IM males expressed ERβ (IM 46.9% vs. M 18.8%), and FSH cells in M males showed significantly high GR1 transcripts (IM 76.0 ± 5.0 vs. M 195.0 ± 10.7 copies per cell; P < 0.05), suggesting that FSH cells are regulated differently in the two reproductive stages. Coexpression of ERα + β in high percentages of cells of the GH family (GH, IM 43.8% vs. M 14.3%; prolactin, IM 8.3% vs. M 59.7%; somatolactin, IM 22.2% vs. M 42.2%) suggests that the expression of both ERs is important for functionality. Thus, differential coexpression of genes for nuclear receptors in subpopulations of pituitary cell types suggests multiple steroid/thyroid hormone regulatory pathways at the level of the pituitary during the two reproductive stages.