The Variable Transmembrane Domain of Drosophila N-Cadherin Regulates Adhesive Activity

Abstract

Drosophila N-cadherin (CadN) is an evolutionarily conserved classic cadherin which has a large, complex extracellular domain and a catenin-binding cytoplasmic domain. The CadN locus contains three modules of alternative exons (7a/b, 13a/b, and 18a/b) and undergoes alternative splicing to generate multiple isoforms. Using quantitative transcript analyses and green fluorescent protein-based cell sorting, we found that during development CadN alternative splicing is regulated in a temporal but not cell-type-specific fashion. In particular, exon 18b is predominantly expressed during early developmental stages, while exon 18a is prevalent at the late developmental and adult stages. All CadN isoforms share the same molecular architecture but have different sequences in their extracellular and transmembrane domains, suggesting functional diversity. In vitro quantitative cell aggregation assays revealed that all CadN isoforms mediate homophilic interactions, but the isoforms encoded by exon 18b have a higher adhesive activity than those by its alternative, 18a. Domain-swapping experiments further revealed that the different sequences in the transmembrane domains of isoforms are responsible for their differential adhesive activities. CadN alternative splicing might provide a novel mechanism to fine-tune its adhesive activity at different developmental stages or to restrict the use of high-affinity 18b-type isoforms at the adult stage.

Supplemental material for this article may be found at http://mcb.asm.org/.

We thank Tadashi Uemura and James Clemens for providing reagents, without which this project could not be completed. We give special thanks to Aiyi Liu for advice on statistics. We thank Larry Zipursky and Thomas Clandinin for communicating results prior to publication and Benjamin White, Alan Hinnebusch, Mark Lemmon, and Henry Levin for helpful discussions. We thank Margaret Dieringer for manuscript handling and editing.

This work is supported by the Intramural Research Program of the NIH, National Institute of Child Health and Human Development (grant HD008748-03 to C.-H.L.) S.Y. is a fellow of the Japan Society for the Promotion of Science.