Expression of GH, TSH beta, LH beta and FSH beta genes during fetal pituitary development in the pig.

The development of the anterior pituitary gland involves the proliferation and differentiation of ectodermal cells in Rathke's pouch to generate distinct cell types, each of which produces its corresponding trophic hormone. Studying pituitary development will therefore reveal novel aspects of organogenesis. In the present study, we examined by in situ hybridization the expression of genes for anterior pituitary hormones during development of the fetal pig pituitary. We found that the beta-subunit gene of thyroid-stimulating hormone (TSH beta) was first expressed at E40, (E = day of embryonal/fetal life), growth hormone (GH) mRNA appeared between E40 and E50, and the gonadotrophin genes (LH beta and FSH beta) were expressed at E50. The transcripts for TSH beta, LH beta and FSH beta were abundantly expressed at about E80, while GH mRNA continued to be richly expressed until after birth. The GH gene was first expressed in the mantle layer of the anterior lobe, while the TSH beta and gonadotrophin (LH beta and FSH beta) mRNAs were found in the central and the basal regions of the anterior lobe, respectively. All of these mRNAs (GH, TSH beta, LH beta, and FSH beta) remained concentrated until the end of gestation in the area where they first appeared. The distinctive pattern of developmental expression of these hormone genes in the fetal pig anterior pituitary makes this tissue an excellent system in which to study tissue-specific gene activation and regulation.