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 prolifera tion and differentiation of ectodermal cells in Rathke's pouch to gene rate distinct cell types, each of which produces its corresponding tro phic hormone. Studying pituitary development will therefore reveal nov el aspects of organogenesis. In the present study, we examined by in s itu hybridization the expression of genes for anterior pituitary hormo nes during development of the fetal pig pituitary. We found that the b eta-subunit gene of thyroid-stimulating hormone (TSH beta) was first e xpressed at E40, (E = day of embryonal/fetal life), growth hormone (GH ) mRNA appeared between E40 and E50, and the gonadotrophin genes (LH b eta 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 th e TSH beta and gonadotrophin (LH beta and FSH beta) mRNAs were found i n the central and the basal regions of the anterior lobe, respectively . All of these mRNAs (GH, TSH beta, LH beta, and FSH beta) remained co ncentrated until the end of gestation in the area where they first app eared. The distinctive pattern of developmental expression of these ho rmone genes in the fetal pig anterior pituitary makes this tissue an e xcellent system in which to study tissue-specific gene activation and regulation.