A novel transmembrane protein with epidermal growth factor and follistatin domains expressed in the hypothalamo-hypophysial axis of Xenopus laevis.

Through the use of a screening strategy designed to isolate novel cDNAs encoding proteins concerned with pituitary secretion in Xenopus laevis, we discovered clone X7365, which encodes a transmembrane protein with a signal peptide, two follistatin modules, a unique epidermal growth factor domain, and a short cytoplasmic region. RNA expression analyses indicated that the X7365 transcript is enriched in neuroendocrine tissues. Immunohistochemical studies demonstrated that, in addition to being expressed in the optic tectum and in astrocytes in the optic nerve, the X7365 protein is concentrated in a discrete population of hypothalamic magnocellular neurons. Axons projecting to the median eminence and the neurointermediate lobe of the pituitary were also immunopositive, suggesting that X7365 functions in the regulation of magnocellular neurosecretion.