The myelin proteolipid protein (Pip) gene encodes the most abundant protein found in mature CNS myelin. Expression of the gene is regulated spatiotemporally, with maximal expression occurring in oligodendrocytes during the myelination period of CNS development. Pip gene expression is tightly controlled. Misregulation of the gene in humans can result in the dysmyelinating disorder Pelizaeus-Merzbacher disease, and in transgenic mice carrying a null mutation or extra copies of the gene can result in a variety of conditions, from late onset demyelination and axonopathy, to severe early onset dysmyelination. In this study we have examined the effects of Pip intron 1 DNA in mediating proper developmental expression of PIp-lacZ fusion genes in transgenic mice. Our results reveal the importance of Pip intron 1 sequences in instigating the expected surge in PIp-lacZ gene activity during (and following) the active myelination period of brain development. Transgene expression was also detected in the testis (Leydig cells), however, the presence or absence of Pip intron 1 sequences had no effect on the temporal profile in the testis. Surprisingly, expression of the transgene missing Pip intron 1 DNA was always higher in the testis, as compared to the brain, in all of the transgenic lines generated. [ABSTRACT FROM AUTHOR]