title: Vertebrate Lrig3-ErbB interactions occur in vitro but are unlikely to play a role in Lrig3-dependent inner ear morphogenesis.
abstract: BACKGROUND
  The Lrig genes encode a family of transmembrane proteins that have been implicated in tumorigenesis, psoriasis, neural crest development, and complex tissue morphogenesis. Whether these diverse phenotypes reflect a single underlying cellular mechanism is not known. However, Lrig proteins contain evolutionarily conserved ectodomains harboring both leucine-rich repeats and immunoglobulin domains, suggesting an ability to bind to common partners. Previous studies revealed that Lrig1 binds to and inhibits members of the ErbB family of receptor tyrosine kinases by inducing receptor internalization and degradation. In addition, other receptor tyrosine kinase binding partners have been identified for both Lrig1 and Lrig3, leaving open the question of whether defective ErbB signaling is responsible for the observed mouse phenotypes.
  
  
  RESULTS
  Here, we report that Lrig3, like Lrig1, is able to interact with ErbB receptors in vitro. We examined the in vivo significance of these interactions in the inner ear, where Lrig3 controls semicircular canal formation by determining the timing and extent of Netrin1 expression in the otic vesicle epithelium. We find that ErbB2 and ErbB3 are present in the early otic epithelium, and that Lrig3 acts cell-autonomously here, as would be predicted if Lrig3 regulates ErbB2/B3 activity. However, inhibition of ErbB activation in the chick otic vesicle has no detectable effect on Netrin gene expression or canal morphogenesis.
  
  
  CONCLUSIONS
  Our results suggest that although both Lrig1 and Lrig3 can interact with ErbB receptors in vitro, modulation of Neuregulin signaling is unlikely to contribute to Lrig3-dependent processes of inner ear morphogenesis. These results highlight the similar binding properties of Lrig1 and Lrig3 and underscore the need to determine how these two family members bind to and regulate different receptors to affect diverse aspects of cell behavior in vivo.
authors.affiliation: Department of Neurobiology and Program in Neuroscience, Harvard Medical School, Boston, Massachusetts, United States of America.
authors.forename: Victoria E
authors.initials: VE
authors.lastname: Abraira
authors.forename: Takunori
authors.initials: T
authors.lastname: Satoh
authors.forename: Donna M
authors.initials: DM
authors.lastname: Fekete
authors.forename: Lisa V
authors.initials: LV
authors.lastname: Goodrich
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002642:Chick Embryo; D007758:Ear, Inner / Q000196:embryology / Q000378:metabolism*; D004848:Epithelium / Q000196:embryology / Q000378:metabolism; D005260:Female; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D017403:In Situ Hybridization; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009024:Morphogenesis; D009414:Nerve Growth Factors / Q000235:genetics / Q000378:metabolism; D000075388:Netrin-1; D020880:Neuregulins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D020893:Receptor, ErbB-3 / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C496407:Lrig3 protein, mouse; D008565:Membrane Proteins; C000617351:NTN1 protein, human; D009414:Nerve Growth Factors; D020880:Neuregulins; D025521:Tumor Suppressor Proteins; D000075388:Netrin-1; D020893:Receptor, ErbB-3