Expression of a midgut-specific cadherin BT-R1 during the development of Manduca sexta larva

The btr-1 gene of Manduca sexta (GenBank AF319973) encodes a cadherin, BT-R(1) (210-kDa), which contains 12 ectodomain modules in association with a number of motifs potentially involved in interactions with cadherin and integrin. The molecule is a target receptor for Bacillus thuringiensis Cry1A toxins that bind to BT-R(1) with high affinity and specificity. BT-R(1) is localized exclusively in the midgut epithelium. The amount of BT-R(1) protein increases dramatically during larval development, paralleling accumulation of its mRNA. The 5'-UTR of the btr-1 gene contains sequence motifs that most likely recruit specific transcription factors, particularly, those that determine posterior patterning and that control intestinal cell proliferation, differentiation and identity during development. The increase in abundance of BT-R(1) may be required to support not only the differentiation of the epithelial cells but also the establishment of physiological function and structural integrity of the midgut during larval development in M. sexta. We believe that BT-R(1) is essential to larval midgut epithelial organization during rapid cell proliferation and tissue growth in M. sexta because disruption of such organization and functionality occasioned by the binding of the Cry1A toxins of B. thuringiensis to BT-R(1) causes death to the insect.