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. Domainswapping 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.

Transmembrane helix-helix interactions involved in ErbB receptor signaling

“…15 However, the single TM α-helix of cadherins is able to form oligomers in vivo 16 and is essential for dimerization of truncated cadherin variants. 17,18 Thus, interactions of the single TM α-helix are critical for cadherin signaling and the intracellular cadherin domain prevents individual cadherins from dimer formation, promoted by defined TM helix-helix interactions.…”

Crystal structures of Drosophila N-cadherin ectodomain regions reveal a widely used class of Ca 2+ -free interdomain linkers

“…Whether DN-cadherin also uses a similar surface comprised of multiple EC domains for adhesive interactions remains to be investigated. Interestingly, the CadN gene contains three mutually exclusive exons (MEs) to produce 12 possible alternatively spliced variants (15,32). Alternative splicing at one of these three MEs generates two isoforms with different amino acid compositions in a region encompassing the EC7'-EC8' interdomain linker (32).…”

“…DN-and DE-cadherins serve cell adhesion and tissue patterning functions analogous to their vertebrate counterparts (13,14). Also, like vertebrate classical cadherins, overexpression of DN-cadherin or DE-cadherin in otherwise nonadhesive cells induces Ca 2þ -dependent cell aggregation (13,15). Although DN-and DE-cadherins perform biological roles roughly orthologous to those assumed by classical cadherins in vertebrate species, their ectodomains differ markedly from their vertebrate counterparts both in size and sequence features.…”

Cell adhesion molecules in Drosophila synapse development and function

“…There are 12 isoforms of N-Cad that share the same molecular architecture but have different sequences in their transmembrane and extracellular domains, which mediate homophilic interactions [37][38][39]. N-Cad regulates axonal pattern formation, presumably by regulating axonal fasciculation in the developing embryo [40].…”