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Regular Article |
a Departments of Physiology, Obstetrics and Gynaecology, and Paediatrics, The University of Western Ontario, London, Ontario, Canada N6A 5C1
b Child Health Research Institute, London, Ontario, Canada N6C 2V5
c Department of Biology, The University of York, York, United Kingdom
d Institute of Anatomy, University Hospital of Essen, Essen, Germany
e Institute of Genetics, The University of Bonn, Bonn, Germany
Gap junctional intercellular coupling allows cells to share low molecular weight metabolites and second messengers, thus facilitating homeostatic and developmental processes. Gap junctions make their appearance very early in rodent development, during compaction in the eight-cell stage. Surprisingly, preimplantation mouse embryos lacking the gap junction protein connexin 43 develop normally and establish full-term pregnancies despite severely reduced gap junctional coupling. It was suggested that this might be explained by the presence of at least five additional connexins known to be expressed in blastocysts. In the present study, we set out to clarify the number of connexins present in preimplantation rodent embryos and the role of gap junctional coupling, if any, in blastocyst development. We provide evidence from reverse transcription-polymerase chain reaction analysis that the genes encoding 3 additional connexins (connexin 30 or ß6, connexin 36 or 
9, and connexin 57 or 10) are also transcribed in preimplantation mouse embryos. Furthermore, we show that multiple connexins are expressed in rat preimplantation embryos, indicating that multiplicity of connexin expression may be a common feature of early mammalian embryogenesis. We could detect no up-regulation of any of 3 coexpressed connexins examined in mouse embryos lacking connexin 43. Impaired intercellular coupling caused either by the loss of connexin 43 or by treatment of cultured embryos with the gap junctional coupling blocker 18-glycyrrhetinic acid (AGA) had no discernable effect on either apoptosis or glucose utilization, parameters known to be affected by gap junctional coupling in other contexts. These results, taken together with the reported inability of AGA to perturb blastocyst formation, imply that gap junctional coupling is not essential during this developmental period. We propose that connexin expression and the assembly of multiple types of gap junction channels in preimplantation embryos facilitates the diversification of communication pathways that will appear during postimplantation development. New evidence of this diversification is presented using rat blastocyst outgrowths.
1 This research was supported by grants from the Natural Sciences and Engineering Research Council of Canada (6863-98 to G.M.K.), the U.K. Medical Research Council (G9813883 to H.J.L.), and the Deutsche Forschungsgemeinschaft (Wi 774/10-3 to E.W.).
2 Correspondence: Gerald M. Kidder, Department of Physiology, The University of Western Ontario, Dental Sciences Building, dock 15, London, ON, Canada N6A 5C1. FAX: 519 661 3827; gerald.kidder{at}fmd.uwo.ca
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