Gene expression of the IGF binding proteins during post-implantation embryogenesis of the mouse; comparison with the expression of IGF-I and -II and their receptors in rodent and human

The IGF binding proteins (IGFBPs) comprise at least six distinct species which may modulate the action of IGFs. IGFs are important regulators of fetal growth and differentiation. We have studied the mRNA expression of the six IGFBPs during post-implantation embryogenesis (day 11-18) by in situ hybridization techniques. Expression of IGFBP-1 was detected in mouse conceptuses after day 12 of gestation and seemed restricted to the liver. Transcripts for IGFBP-2, -4 and -5 were detected in various tissues and were found in all stages tested. In contrast, expression of IGFBP-3 and -6 could be detected only weakly in late gestational embryos. Comparison of the expression pattern of IGFBP-2, -4 and -5, which were found widely distributed in mouse conceptuses, revealed that IGFBP-2 was expressed mainly in the ectodermal layer and also in the mesoderm derived part of the tongue (day 13.5). Transcripts for IGFBP-4 however, only were detected in the mesoderm derived tissues, whereas expression of IGFBP-5 was restricted to the ectodermal layer. A similar distribution pattern was observed in the lung. In general, expression of IGFBP-2 and -5 was detected in the same cells, whereas IGFBP-4 and -5 were expressed mainly in different cell types. In rodents as in the human there is widespread expression of the genes coding IGFs, the IGFBPs and the receptors during pre- and postimplantation embryogenesis. These data support the assumption that the IGFs play an important role during embryogenesis.