DEVELOPMENTAL REGULATION OF VARIOUS ANNEXINS IN THE EMBRYONIC PALATE OF THE MOUSE - DEXAMETHASONE AFFECTS EXPRESSION OF ANNEXIN-1

The annexins are a group of structurally related proteins implicated i n a number of cellular processes, including growth, membrane fusion, a nd the effects of glucocorticoids on cellular physiology, signal trans duction, and regulation of activities of phospholipase A(2). Though th eir exact role in cellular physiology is not clear, their properties m ake them candidate proteins for signal transduction pathways by which growth factors and glucocorticoids modulate development of the palate. We have determined the exact cellular location and developmental expr ession of various annexins in the embryonic murine palate as a first s tep in assessing their developmental function, Western blot analysis r evealed an increased accumulation of selected annexins in elevated pal ates compared to vertical (unelevated) ones. This was particularly str iking for lipocortin I-1 (annexin I), whose mRNA accumulated as well. Lipocortin I was expressed primarily in the apical portion of the pala tal epithelium at early stages of development, but throughout the epit helium at later stages. Also, there was increased immunoreactivity for lipocortin I in the mesenchyme as development proceeded. Immunoreacti vity for the endonexins (annexins IV and V) was found in the palatal e pithelium and mesenchyme, whereas immunoreactivity for the 67-kDa cale lectrin (annexin VI) was found only in the mesenchyme. Treatment of pr egnant A/J strain mice with a cleft-palate inducing regimen of dexamet hasone stimulated accumulation of lipocortin I protein and mRNA, but n ot lipocortin II (annexin II) protein. In contrast, the same regimen o f dexamethasone did not affect levels of lipocortin I protein in palat es of the glucocorticoid-less sensitive C57BL/6J strain mouse embryo. These data permit the suggestion that lipocortin I plays some critical , but as yet undefined, role in modulating ontogeny of the murine pala te.