Segment-specific expression of connexin31 in the embryonic hindbrain is regulated by Krox20

Communication and interaction between cells has been shown to be important during the embryonic development of the vertebrate hindbrain, which becomes transiently subdivided into segments called rhombomeres (r). One gene family allowing intercellular communication and possibly being involved in the control of hindbrain development is the connexin family encoding gap junction channels. Here, we have characterized in detail the previously observed (Dahl et al., 1997) expression of one particular connexin gene, connexin31 (Cx31), in the mouse embryonic hindbrain and compared it with that of Cx43 and Cx36. We found transient Cx31 expression from approximately embryonic day (E) E8-E11 in two small lateral/dorsal subgroups of cells in the hindbrain. We could show that these spots of expression corresponded to r3 and r5 and that Cx31 expression in r3 and r5 was controlled by the transcription factor Krox20. In contrast, expression of Cx43 and Cx36 started later (from E9.5 and E10.5, respectively) and was confined to longitudinal stripes of expression. In addition, from E10.5-E11.5, Cx31 was expressed by a column of cells in ventral r4, most likely representing contralateral vestibulo-acoustic efferent neurons, immediately anterior to a ventral column expressing Cx36 at the same stage. From E11.5 onward, another site of Cx31 expression was detected in the boundary cap cells in the entry/exit points of all mixed sensory/motor and in the entry points of pure sensory nerves. This expression was not present in the boundary cap cells of the exit points of pure motor nerves. So far, our analysis of the hindbrain area of Cx31-deficient embryos in terms of projections of sensory or motor neurons or in the generation or migration of neurons has not yet revealed any obvious defects.