L1 and laminin: Their expression during rat hypophysis ontogenesis and in adult neurohemal areas

L1 is a murine multidomain glycoprotein implicated in cell aggregation, fas ciculation, neurite outgrowth and synaptogenesis. Laminin, a trimeric polyp eptide, is implicated in neuronal survival, growth cone guidance, neurite o utgrowth and cell differentiation. Laminin can also interact with the cell adhesion molecule L1. Their expressions were investigated From embryonic da y 15 (E15) to adult in the rat hypophysis, and in adult neurohemal zones. Detected in the neural lobe from E17, the L1 immunoreacticity increased dur ing prenatal development and persisted in adulthood mainly related to the n europeptidergic fibers. Pituicytes were only labelled on the plasmalemma ap posed to axons. In the intermediate lobe, L1 appeared at birth on folliculo -stellate cells extensions, constituting a network which densified during p ostnatal development. L1 is also expressed in all neurohemal areas on neuro nal profiles. Laminin was clearly detectable in the hypophysis at E15 before the fit st b lood vessels penetrate the Rathke pouch. At E20, all the basal membranes of the blood vessels were stained. In the intermediate lobe, a spotted lamini n immunoreactivity was detected at E21. At this stage, we observed the stai ning of intercellular spaces and the intracellular labelling of melanotroph s. concerning reticulum or vesicles. Thr staining of melanotrophs seemed to maintain during adulthood. In contrast with blood vessels of the adult cer ebral tissue, adult capillaries of the neural lobe and the others neuro-hem al zones were intensely labelled a with the anti-laminin antibody. These results suggest that neurite outgrowth and neurite guidance could be promoted be L1 and laminin the neurointermediate lobe. Thr "intercellular t unnels" could also be an important guidance cue for migrating cells in the intermediate lobe. These data also demonstrate that melanotrophic cells, se creting the laminin, have a rule in the ontogenesis of the gland. Finally, we suggest that L1 and laminin can collaborate to reinforce "neurons-capill aries" interactions in neurohemal zones. (C) 1999 ISDN. Published by Elsevi er Science Ltd. All rights reserved.