Myelin basic protein gene and the function of antisense RNA in its repression in myelin-deficient mutant mouse.

The myelin-deficient (mld) mouse is an autosomal recessive mutant characterized by hypomyelination of the CNS due to reduced expression of the myelin basic protein (MBP) gene. In the mld mutant, the MBP gene is duplicated in tandem. One gene is intact, but a large portion is inverted upstream of the other copy, and its transcription yields the antisense RNA. This antisense RNA was shown to be localized in the nucleus and to form an RNA:RNA duplex with sense RNA. These findings suggested that inhibition of transport from the nucleus or selective degradation of the duplex is responsible for the reduced expression of the MBP gene in the mld mutant. The mechanism of gene rearrangement at the MBP locus was also characterized. Cosmid clones encompassing whole MBP gene loci from control and mld genomic DNA libraries were isolated. The recombination points indicated that the duplication and inversion observed in mld occurred due to nonhomologous recombination.