Changes in E- and N-cadherin expression in developing rat adenohypophysis.

Recently, we showed that hormone-producing cells express N-cadherin, while folliculo-stellate cells and marginal layer cells express E-cadherin in the adult rat anterior pituitary gland. These cells are believed to originate from a single cell population of the adenohypophyseal placode. In the present study, we immunohistochemically examined the divergence of cadherin types during pituitary histogenesis. Pituitary glands were excised from rats of embryonic day 11 (E11) through postnatal day 60 (P60) and paraffin sections were prepared. E- and N-cadherins were immunostained sequentially using monoclonal and polyclonal primary antibodies and fluorescent secondary antibodies. At E11, E-cadherin was expressed over oral epithelium, while N-cadherin expression was limited to the primordium of Rathke's pouch. When Rathke's pouch was formed at E13, E- and N-cadherin were broadly expressed in the entire cell population. N-cadherin was expressed particularly intensely in the layer of cells that faced the lumen. From E14 through E16, the majority of cells expressed both types of cadherins; however, the cell population to become the pars tuberalis expressed N-cadherin but not E-cadherin. From E18 through E20, when many hormone-producing cells appear, the number of cells that expressed N-cadherin alone increased. However, some cell populations in the pars distalis and multilayered marginal cells still expressed both cadherins. After birth, most of the cells came to express only one of the cadherin types. These results may suggest that undetermined adenohypophyseal cells express both E- and N-cadherin, but come to express either E- or N-cadherin during cytogenesis.