Identification of an embryonic isoform of myelin basic protein that is expressed widely in the mouse embryo.

We have identified a myelin basic protein (MBP) isoform in mouse embryos that includes an exon upstream of the usual transcription initiation site. This isoform, embryonic-neonatal MBP (E-MBP), is expressed at the protein level in the embryonic nervous system at a time when other MBP isoforms are not detected. In addition to the central and peripheral nervous systems of the embryo and neonate, the thymus, spleen, and testes also express E-MBP at the protein level. The expression of E-MBP in cell types distinct from the nervous system strongly suggests that this MBP isoform has a role apart from the formation of myelin.