Expression of neuroendocrine secretory protein 7B2 mRNA in the mouse and rat pituitary gland

The secretory polypeptide 7B2 is produced in different endocrine and neuroendocrine cells, where it is presumed to play a role in the hormone secretion mechanism. In this study, we examined a pattern of 7B2 mRNA expression in the mouse and rat pituitary gland. When [35S]-labeled antisense cRNA probes were used for in situ hybridization, 7B2 mRNA transcripts were detected within virtually all endocrine cells of the anterior lobe (gonadotrophs, thyrotrophs, corticotrophs, somatotrophs and lactotrophs) and of the intermediate lobe (melanotrophs). The posterior lobe was negative. By immunocytochemistry, 7B2 accumulation was observed within melanotrophs in the intermediate lobe and within gonadotrophs and thyrotrophs in the anterior lobe. The question of 7B2 production in other pituitary cells, such as corticotrophs, somatotrophs and lactotrophs, was studied under culture conditions. The corticotroph AtT-20 and somatrotroph GH3 cell lines both expressed 7B2 mRNA and contained 7B2 protein detectable by radioimmunoassay. However, this protein could not be visualized by immunocytochemistry. Thus, it is possible that 7B2 is produced in all hormone-synthesizing cells of the pituitary gland, being stored only within some of them and rapidly exported after synthesis from others.