Muchow Michael, Bossis Ioannis, Porter Tom E
Department of Animal and Avian Sciences, University of Maryland, College Park, Maryland 20742, USA.
J Endocrinol. 2005 Feb;184(2):407-16. doi: 10.1677/joe.1.05944.
Increased thyroid hormone production is essential for hatching of the chick and for the increased metabolism necessary for posthatch endothermic life. However, little is known about the ontogeny and distribution of pituitary thyrotrophs during this period or whether pituitary thyroid-stimulating hormone (TSH) production is regulated by endogenous thyroid hormones during chick embryonic development. This study assessed the abundance and location of pituitary thyrotrophs and the regulation of TSH(beta) peptide and mRNA levels by endogenous thyroid hormones prior to hatching. TSH(beta)-containing cells were first detected on embryonic day (e) 11, and the thyrotroph population increased to maximum levels on e17 and e19 and then decreased prior to hatching (d1). Thyrotroph distribution within the cephalic lobe of the anterior pituitary was determined on e19 by whole-mount immunocytochemistry for TSH(beta) peptide and by whole-mount in situ hybridization for TSH(beta) mRNA. Thyrotroph distribution within the cephalic lobe was heterogeneous among embryos, but most commonly extended from the ventral medial region to the dorsal lateral regions, along the boundary of the cephalic and caudal lobes. Inhibition of endogenous thyroid hormone production with methimazole (MMI) decreased plasma thyroxine (T4) levels and increased pituitary TSH(beta) mRNA levels on e19 and d1. However, control pituitaries contained significantly more TSH(beta) peptide than MMI-treated pituitaries on e17 and e19, suggesting higher TSH secretion into the blood in MMI-treated groups. We conclude that thyrotroph abundance and TSH production increase prior to hatching, that thyrotrophs are localized heterogeneously within the cephalic lobe of the anterior pituitary at that time, and that TSH gene expression and secretion are under negative feedback regulation from thyroid hormones during this critical period of development.
甲状腺激素分泌增加对于雏鸡孵化以及孵化后维持内温性生命所需的新陈代谢增强至关重要。然而，在此期间垂体促甲状腺细胞的个体发生和分布情况，以及在雏鸡胚胎发育过程中垂体促甲状腺激素（TSH）的分泌是否受内源性甲状腺激素调控，目前所知甚少。本研究评估了孵化前垂体促甲状腺细胞的数量和位置，以及内源性甲状腺激素对TSH（β）肽和mRNA水平的调控。含TSH（β）的细胞在胚胎第11天首次被检测到，促甲状腺细胞数量在胚胎第17天和第19天增加到最高水平，然后在孵化前（第1天）减少。通过对TSH（β）肽进行全片免疫细胞化学和对TSH（β）mRNA进行全片原位杂交，在胚胎第19天确定了垂体前叶头部促甲状腺细胞的分布。胚胎之间垂体前叶头部促甲状腺细胞的分布存在异质性，但最常见的是沿着头部和尾部叶的边界，从腹内侧区域延伸至背外侧区域。用甲巯咪唑（MMI）抑制内源性甲状腺激素分泌，可降低胚胎第19天和第1天的血浆甲状腺素（T4）水平，并增加垂体TSH（β）mRNA水平。然而，在胚胎第17天和第19天，对照垂体中的TSH（β）肽含量显著高于MMI处理组的垂体，这表明MMI处理组中TSH向血液中的分泌量更高。我们得出结论，促甲状腺细胞数量和TSH分泌在孵化前增加，此时促甲状腺细胞在前垂体头部叶内分布不均一，并且在这个关键发育时期，TSH基因表达和分泌受甲状腺激素的负反馈调节。
