Laminin, a major basement membrane protein, comprises three subunit chains: α, β, and γ
chains. Among these chains, only the laminin α chain is capable of signaling via laminin
receptors. Although laminin isoforms containing the α5 chain were reported to be the first
laminin produced during rat anterior pituitary gland development, the functions of these
isoforms are unknown. We used immunohistochemical techniques to localize the laminin α5
chain and its specific receptor, basal cell adhesion molecule (BCAM), in fetal and adult
pituitary gland. Laminin α5 chain immunoreactivity was observed in the basement
membrane of the primordial adenohypophysis at embryonic days 12.5 to 19.5. Double
immunostaining showed that BCAM was present and co-localized with the laminin α5 chain
in the tissue. Quantitative analysis showed that the laminin α5 chain and BCAM were
expressed in the anterior pituitary gland during postnatal development and in adulthood
(postnatal day 60). In the adult gland, co-localization of the laminin α5 chain and BCAM was
observed, and BCAM was detected in both the folliculo-stellate cells and endothelial cells.
These results suggest that laminin α5 chain signaling via BCAM occurs in both the fetal
adenohypophysis and adult anterior pituitary gland.