Myelin proteolipid protein (Plp) intron 1 DNA is required to temporally regulate Plp gene expression in the brain

Abstract

The myelin proteolipid protein (Plp) 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. Plp 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 Plp intron 1 DNA in mediating proper developmental expression of Plp-lacZ fusion genes in transgenic mice. Our results reveal the importance of Plp intron 1 sequences in instigating the expected surge in Plp-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 Plp intron 1 sequences had no effect on the temporal profile in the testis. Surprisingly, expression of the transgene missing Plp intron 1 DNA was always higher in the testis, as compared to the brain, in all of the transgenic lines generated.

Separate Proteolipid Protein/DM20 Enhancers Serve Different Lineages and Stages of Development

“…Specifically, the strong oligodendrocyte and Schwann cell enhancers identified within intron 1, wmN1 and wmN2, respectively, are contained within randomly inserted transgenes that appropriately reflect their regulatory activity (Spassky et al, 1998;Fuss et al, 2000). The proximal promoter sequence extending to Ϫ2.5 kb has no independent targeting ability (Li et al, 2002), but addition of the wmN1 and wmN2 containing intron 1 sequence leads to strong transgene expression in both oligodendrocytes and Schwann cells (Mallon et al, 2002). A Cre-containing transgene regulated by plp/DM20 sequences extending 5Ј to Ϫ3.74 kb and the same intron 1 sequence demonstrated a similar expression program (Delaunay et al, 2008).…”

“…Consequently, plp/DM20 regulation has been investigated extensively, and long sequence domains capable of directing expression to oligodendrocytes, Schwann cells, and neuronal precursors have been identified (Nadon et al, 1994;Readhead et al, 1994;Fuss et al, 2000;Li et al, 2002;Mallon et al, 2002;Delaunay et al, 2008). However, the location and function of plp/DM20 enhancers remain essentially unknown.…”

Where, when and how much: regulation of myelin proteolipid protein gene expression

“…The Plp gene is abundantly expressed in oligodendrocytes, although much lower levels of expression have been detected in a variety of cell types, including Schwann cells [57 -60], olfactory nerve ensheathing cells [61], cardiac myocytes [62], cells of the immune system [63,64], certain types of neurons [52,65], human amniotic epithelial cells [66], and in the testis [64], presumably in Leydig cells [67]. By reverse transciptionpolymerase chain reaction (RT-PCR) analysis, DM20-specific products have been noted in even a wider range of tissues from the mouse [68].…”

“…2) of this positive regulatory region from the mouse gene has been compared to those from other species and shows extensive identity to the rat sequence (95 %) and moderate identity to the human (71 %), pig (56 %) and cow (63 %) sequences, although the latter three sequences show higher identity when compared among themselves. The positive regulatory region likely mediates the dramatic upswing of Plp gene activity in oligodendrocytes during the active myelination period since mice, which harbor a Plp-lacZ transgene containing Plp genomic sequences from the proximal 2.4 kb of 5¢-flanking DNA downstream to an internal site in exon 2, express the reporter gene in a temporal (and spatial) manner consistent with that of the endogenous Plp gene in the brain with peak expression occurring during the myelination stage of CNS development [67,110]. However, expression from a similar transgene, which does not contain any Plp intron 1 sequences, remained low and static throughout CNS development [67].…”

Expression of a Myelin Proteolipid Protein (Plp)-lacZ Transgene is Reduced in both the CNS and PNS of Plp jp Mice

“…The PLP(+)Z transgene contains the proximal 2.4 kb of 5′-flanking DNA, exon 1, intron 1 and the first 37 bp of exon 2 of the Plp gene, and encodes a fusion protein between the first 13 amino acids of PLP and β-galactosidase (β-gal), which is trafficked to the myelin membrane [12]. A series of transgenic animals have subsequently been derived that further corroborate the ability of these Plp sequences to promote transgene expression, and to serve as a reliable readout of endogenous Plp gene activity [13][14][15][16][17][18], with inclusion of Plp intron 1 sequences being important [19]. In the current studies, the PLP(+)Z transgene was crossed into the Plp jp background and used to monitor the effects of the Plp jp mutation on Plp promoter activity via lacZ reporter gene expression.…”