CADHERIN-6 EXPRESSION TRANSIENTLY DELINEATES SPECIFIC RHOMBOMERES, OTHER NEURAL-TUBE SUBDIVISIONS, AND NEURAL CREST SUBPOPULATIONS IN MOUSEEMBRYOS

Mammalian cadherin-6 (K-cadherin, cad6) was originally identified by m eans of the polymerase chain reaction, but its biological functions ha ve not yet been determined. We analyzed the expression pattern of the mouse homologue of this cadherin during development and found that it was transiently expressed in restricted rhombomeres and in other subdi visions of the neural plate and tube. In the midbrain and anterior hin dbrain of E8.0-8.5 embryos, cad6 was expressed only in neural crest-ge nerating regions. In contrast, in the posterior hindbrain and contiguo us spinal cord of these embryos, cad6 occurred throughout the neural p late, forming a sharp anterior limit at the future rhombomere 4 and 5 boundary. Subsequently, this neural plate expression became confined t o rhombomere 6, although most of the neural crest-generating areas rem ained positive throughout the body. Neural crest cells expressing cad6 migrated out of the neural tube, and subsequently accumulated mainly along peripheral nerves. We then studied the effect of Hoxa-1 mutation on the expression of cad6, as their expressions spatiotemporally over lapped with each other in the early posterior hindbrain. In E8.0-8.5 H oxa-1 mutants, cad6 expression was suppressed in the region of rhombom eres 4 to 6, although that in the other regions was not essentially af fected. At later stages, however, cad6-positive crest cells appeared a nd migrated out of rhombomeres 4 to 6, indicating that the suppression of cad6 expression was transient and restricted to early stages. Impo rtantly, this effect of the Hoxa-1 mutation concurred with the timing of the expression of this gene. We also studied Hoxa-3 mutants, but fo und no effect of this mutation on the cad6 expression pattern. These f indings suggest that cad6 may contribute to the formation of the segme ntal structure of the early brain through its ability to confer specif ic adhesiveness on cells and that Hoxa-1 may be required for early cad 6 expression in the posterior hindbrain. (C) 1997 Academic Press.