A potential dual apical pathway in polarized regenerative cells of the midgut of Manduca sexta

Two novel proteins with apparent molecular weight of 38 (Manduca sexta midg ut MsM38) and 46kDa (MsM46) were isolated from midgut homogenates in wander ing stage Manduca sexta larvae and both of them were found to be present ex clusively in this tissue on Western blots. Immunocytochemical studies revea led that both proteins are expressed in the regenerative cells however, the ir distribution pattern is clearly different. MsM38 is localized in the cyt oplasm of resting regenerative cells during the feeding period, and is accu mulated in the calcospherits at the beginning of the wandering period. Alon g with the delamination of the larval epithelium, this protein is released apically from these vesicles. The antiserum labels an additional 76 kDa pro tein in the wandering larval midgut homogenates. The appearance of this 76 kDa protein coincides with the accumulation of the immunopositive material in the calcospherits. MsM46 is similarly distributed during the feeding per iod in the cytoplasm of regenerative cells. At the beginning of the wanderi ng period it accumulates around the newly forming large apical vacuoles, th at are released at the time of complete delamination of the larval epitheli um. In parallel with this process MsM46, and another 40 kDa protein, that b ecomes labeled from this period on Western blots appeares on the apical mic rovillar projections. Thus both isolated proteins are directed apically fro m different compartments, that raises the possibility of a dual apical rout ing pathway in regenerative cells.