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 generating PSA-NCAMs, which are expressed mainly during development. Since polysialylation considerably modifies NCAM adhesivity, expression of NCAMs and PSA-NCAMs has been investigated in the developing hypophysis by immunohistochemistry. At embryonic day 13 (E13), an antibody against NCAM outlined all cellular profiles in the entire Rathke's pouch; this labelling persisted until adulthood. NCAM expression increased in 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 expression increased in the neural lobe at E17 with the arrival of the neurosecretory fibres and persisted into adulthood. In the anterior lobe, 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 the adult gland. In the intermediate lobe, melanotrophic cells never expressed PSA-NCAMs but these were expressed on folliculo-stellate cells at birth, preceding the onset of innervation. These results suggest that NCAMs and PSA-NCAMs play a role in pituitary histogenesis, cell differentiation and neurointermediate lobe innervation.