The extracellular matrix components laminin, fibronectin, and collagen IV are present among the epithelial cells forming Rathke's pouch.

Cell-matrix interactions probably play a cooperative role with cell-hormone interactions to ensure normal differentiation of the adenohypophysis. The extracellular matrix (ECM) surrounding adult adenohypophysial cells contains laminin but its embryonic development has not been described. This study was carried out to test the hypothesis that adenohypophysial cells are associated with components in the ECM prior to cellular differentiation in the adenohypophysis. Fetuses were removed from Golden Syrian hamsters every 12 h from embryonic days 8.5-14. Coronal and sagittal 5-microns-thick sections of paraplast-embedded embryos were stained for fibronectin, laminin, or collagen IV using avidin-biotin immunoperoxidase staining. The adenohypophysial anlage was observed initially as a group of epithelial cells (Rathke's pouch) in the roof of the stomatodeum in contact with a basement membrane. The basement membrane stained positively for laminin, collagen IV and fibronectin. Lighter staining for laminin, fibronectin and collagen IV was observed between the developing adenohypophysial cells in Rathke's pouch. Proliferative activity was apparent in the antero-inferior region of Rathke's pouch and resulted in the formation of the bulk of the adenohypophysis. Mesenchyme infiltrates the region between the base of Rathke's pouch and the oral epithelium, thus separating the two. The basement membrane surrounding the pouch appears to become discontinuous in the regions of high proliferative activity. These results show that ECM components appear early during the development of adenohypophysial cells prior to their cellular differentiation into hormone-containing cells. This association between ECM components and developing adenohypophysial cells provides the anatomical basis for cell-ECM interactions to influence adenohypophysial development and differentiation.