Developmental pattern of calmodulin-binding proteins in rat jejunal epithelial cells.

Calmodulin-binding proteins have been studied in presumptive rat jejunal epithelial cells and in purified rat brush borders during development. Incubation of nitrocellulose replicas with [125I] calmodulin revealed that, at immature stages (13-15 days of fetal life), only two calmodulin-binding bands were detectable with molecular masses of approximately 145,000 and 135,000 daltons. By fetal day 19, additional calmodulin-binding proteins of 240,000 and 110,000 daltons were observed. The 145,000- and 240,000-dalton calmodulin-binding bands contained polypeptides that were immunologically similar to caldesmon and to the alpha-subunit of the non-erythroid spectrin (fodrin) respectively. Antisera reactive with the 110K subunit of the microvillus 110K-calmodulin complex labelled a 135,000-dalton band which comigrated with one of the calmodulin-binding proteins. This 135,000-dalton immunoreactive polypeptide persisted until birth but was absent in brush borders isolated from adult intestine. In addition, the 110K antisera reacted with an approximately 110,000-dalton subunit by fetal day 19. At birth, numerous lower-molecular-mass 110K immunoreactive bands were also detectable. Immunocytochemical localization of the three calmodulin-binding proteins revealed that, at fetal day 14, caldesmon and fodrin displayed fluorescence lining the periphery of the epithelial cells, whereas staining with the 110K antisera was very weak. At fetal day 19, staining with the three antisera resulted in bright fluorescence localized in the apical part of the epithelial cells, in parallel to the differentiation of brush borders. At this stage, the apical staining of the calmodulin-binding proteins was similar to that of the adult.(ABSTRACT TRUNCATED AT 250 WORDS)