| Abstrakt: |
Communication via gap junctions provides a mechanism for the cell–cell transfer and coordination of developmental signals. The spatial restriction of gap junctions may also serve to organize cells into domains of coordinated behavior. To investigate the role of gap junctions during embryogenesis, we have characterized the expression of a member of the gap junction gene family, zebrafishconnexin43.4,a homolog ofconnexin45in chicken and mammals. Expression ofconnexin43.4was induced in the early gastrula, coincident with the first definitive assignments of axial cell fate and the onset of the cell movements comprising convergence and extension in zebrafish.In situhybridization and immunohistochemistry revealed that during gastrulationconnexin43.4mRNA and protein were progressively enriched in the germ ring and in the notochord primordia on the dorsal side of the embryo. Later in developmentconnexin43.4expression was detected in the notochord, the paraxial mesoderm, and the tail bud but was not observed after the differentiation of these tissues. Inno tailmutant embryos which are defective in tail formation and proper morphogenesis of the notochord,connexin43.4expression was absent during gastrulation from the caudal embryonic shield and notochord primordia. During somite stages inno tailembryos,connexin43.4expression remained absent in the notochordal precursor cells and was lost in the tail bud. Thus, theno tailgene product, a transcription factor, was required for the expression ofconnexin43.4in both the notochord and tail bud during morphogenesis. By microinjection of mRNA coding for a connexin43.4/green fluorescent protein fusion in the 1-cell zebrafish embryo, we showed that connexin43.4 is capable of assembling into structures reminiscent of gap junctions. The progressively restricted, developmental expression of the zebrafishconnexin43.4gene suggests that this gap junctional protein participates in the coordination of gastrulation and the formation of the notochord and tail. |
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