EXPRESSION OF NEURAL CELL-ADHESION MOLECULES, NCAMS, AND THEIR POLYSIALYLATED FORMS, PSA-NCAMS, IN THE DEVELOPING RAT PITUITARY-GLAND

Neural cell adhesion molecules (NCAMs) can undergo post-translational modifications, such as the addition of polysialic acid chains, thus ge nerating PSA-NCAMs, which are expressed mainly during development. Sin ce polysialylation considerably modifies NCAM adhesivity, expression o f NCAMs and PSA-NCAMs has been investigated in the developing hypophys is by immunohistochemistry. At embryonic day 13 (E13), an antibody aga inst NCAM outlined all cellular profiles in the entire Rathke's pouch; this labelling persisted until adulthood. NCAM expression increased i n all lobes during development and concerned all pituitary cell types. In contrast, at E13, PSA-NCAMs were only detected in the neural lobe, solely constituted of pituicytes at this stage, and the tuberal lobe, the only lobe expressing hormonal mRNA at the same stage. PSA-NCAMs e xpression increased in the neural lobe at E17 with the arrival of the neurosecretory fibres and persisted into adulthood. In the anterior lo be, PSA-NCAMs appeared at E15 where their distribution was similar to that of the differentiating corticotrophic cells; at subsequent stages , their expression extended to the whole anterior lobe. Only two cell types, corticotrophic and somatotrophic cells, remained labelled in th e adult gland. In the intermediate lobe, melanotrophic cells never exp ressed PSA-NCAMs but these were expressed on folliculo-stellate cells at birth, preceding the onset of innervation. These results suggest th at NCAMs and PSA-NCAMs play a role in pituitary histogenesis, cell dif ferentiation and neurointermediate lobe innervation.