Structure and implied functions of truncated B cell receptor mRNAs in early embryo and adult mesenchymal stem cells: C replaces Cµ in µ heavy chain deficient mice

¹ Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel
² QBI Enterprises Ltd., Nes Ziona, Israel

^* To whom correspondence should be addressed. E-mail: dov.zipori{at}weizmann.ac.il.

	Abstract

Stem cells exhibit a promiscuous gene expression pattern. We show herein that the early embryo and adult mesenchymal stem cells (MSC), express B cell receptor component mRNAs. To examine possible bearings of these genes on the expressing cells, we studied immunoglobulin µ chain deficient mice. Pregnant µ chain deficient females were found to produce a higher percentage of defective morulae as compared to control females. Structure analysis indicated that the µ mRNA species found in embryos and in mesenchyme consist of the constant region of the µ heavy chain that encodes a recombinant 50 kDa protein. In situ hybridization localized the constant µ gene expression to loose mesenchymal tissues within the day 12.5 embryo proper and the yolk sac. In early embryo and in adult mesenchyme from µ deficient mice, replaced µ chain, implying a possible requirement of these alternative molecules for embryo development and mesenchymal functions. Indeed, overexpression of the mesenchymal truncated µ heavy chain in 293T cells resulted in specific subcellular localization and in G1 growth arrest. The lack of such occurrence following overexprssion of a complete, rearranged form of µ chain, suggests that the mesenchymal version of this mRNA may possess unique functions.