Fig. 6.

Model summarizing SPG MET and BBB formation. (A) Formation of polarized domains in SPG. In contrast to columnar primary epithelia, SPG form a squamous epithelium and lack classical apical polarity complexes. Dystroglycan (Dg) shows polarized distribution in the glia prior to epithelial formation, suggesting that initial apical-basal polarity is established by contact to the basal lamina. Moody polarity depends on the presence of SJs. (B) SPG growth is regulated by GPCR pathway activity and there is an increase in the number of retractions in GPCR pathway mutants.