The myelin proteolipid protein gene modulates apoptosis in neural and non-neural tissues

Mutations of the myelin proteolipid protein gene (Plp) are associated with excessive programmed cell death (PCD) of oligodendrocytes. We show for the first time that PLP is a molecule ubiquitously expressed in non-neural tissues during normal development, and that the level of native PLP modulates the level of PCD. We analyze three non-neural tissues, and show that native PLP is expressed in trophoblasts, spermatogonia, and cells of interdigital webbing. The non-neural cells that express high levels of native PLP also undergo PCD. The level of PLP expression modulates the level of PCD because mice that overexpress native PLP have increased PCD and mice deficient in PLP have decreased PCD. We show that overexpression of native PLP causes a dramatic acidification of extracellular fluid that, in turn, causes increased PCD. These studies show that the level of native PLP modulates the amount of PCD during normal development via a pH-dependent mechanism.

Proteolipid protein mRNA stability is regulated by axonal contact in the rodent peripheral nervous system

Proteolipid protein (PLP) and its alternatively spliced isoform, DM20, are the main intrinsic membrane proteins of compact myelin in the CNS. PLP and DM20 are also expressed by Schwann cells, the myelin-forming cells in the PNS, and are necessary for normal PNS function in humans. We have investigated the expression of PLP in the PNS by examining transgenic mice expressing a LacZ transgene under the control of the PLP promoter. In these animals, myelinating Schwann cells expressed beta-galactosidase more prominently than nonmyelinating Schwann cells. PLP/DM20 mRNA levels, but not those of LacZ mRNA, increased during sciatic nerve development and decreased after axotomy, with resultant Wallerian degeneration. PLP/DM20 transcription rates, in nuclear run off experiments, however, did not increase in developing rat sciatic nerve despite robust increases in PLP/DM20 mRNA levels during the same period. In RNAse protection studies, PLP mRNA levels fell to undetectable levels following nerve transection whereas levels of DM20 were essentially unchanged despite both being transcribed from the same promoter. Finally, cotransfection studies demonstrated that PLP-GFP, but not DM20-GFP mRNA is down-regulated in Schwann cells cultured in the absence of forskolin. Taken together these data demonstrate that steady state levels of PLP mRNA are regulated at a posttranscriptional level in Schwann cells, and that this regulation is mediated by Schwann cell-axonal contact. Since the difference between these two mRNAs is a 105-bp sequence in PLP and not in DM20, this sequence is likely to play a role in the regulation of PLP mRNA.

Role and mechanism of action of C. PvuII, a regulatory protein conserved among restriction-modification systems

The PvuII restriction-modification system is a type II system, which means that its restriction endonuclease and modification methyltransferase are independently active proteins. The PvuII system is carried on a plasmid, and its movement into a new host cell is expected to be followed initially by expression of the methyltransferase gene alone so that the new host's DNA is protected before endonuclease activity appears. Previous studies have identified a regulatory gene (pvuIIC) between the divergently oriented genes for the restriction endonuclease (pvuIIR) and modification methyltransferase (pvuIIM), with pvuIIC in the same orientation as and partially overlapping pvuIIR. The product of pvuIIC, C. PvuII, was found to act in trans and to be required for expression of pvuIIR. In this study we demonstrate that premature expression of pvuIIC prevents establishment of the PvuII genes, consistent with the model that requiring C. PvuII for pvuIIR expression provides a timing delay essential for protection of the new host's DNA. We find that the opposing pvuIIC and pvuIIM transcripts overlap by over 60 nucleotides at their 5' ends, raising the possibility that their hybridization might play a regulatory role. We furthermore characterize the action of C. PvuII, demonstrating that it is a sequence-specific DNA-binding protein that binds to the pvuIIC promoter and stimulates transcription of both pvuIIC and pvuIIR into a polycistronic mRNA. The apparent location of C. PvuII binding, overlapping the -10 promoter hexamer and the pvuIICR transcriptional starting points, is highly unusual for transcriptional activators.

Variable subcellular localization of a neuron-specific protein during NTera 2 differentiation into post-mitotic human neurons

The current report describes the molecular characterization of the human (the D4S234 locus) and mouse (the m234) homologs of a gene that was isolated during our genomic analysis of the Huntington disease gene region. Sequence comparisons of full-length cDNA clones revealed that the mouse and human homologs encoded evolutionarily conserved 21-kDa proteins with greater than 90% amino acid sequence identity. Extensive sequence identity between the D4S234 gene and the rat p1A75 gene (a previously identified rat neuron-specific gene) showed that these genes are interspecies homologs. Furthermore, the D4S234 protein exhibited significant amino acid similarity to a 19-kDa mouse protein that localizes to the Golgi apparatus of embryonic neurons. However, nonconservative sequence differences suggested that these genes are independent members of a multigene family. Northern analyses revealed that rodent D4S234 expression occurred predominantly in the brain and included all brain regions. Neuron-specific expression was demonstrated using Northern analysis of cultured glial cells and quinolinic acid-treated rat brain samples. Minimal amounts of the rodent D4S234 mRNA were detected prenatally; however, elevated adult levels were detected within 1 month of birth. Sequence analyses of the human and mouse D4S234 proteins identified an evolutionarily conserved hydrophobic sequence and a consensus nuclear localization signal in both genes. Immunofluorescence microscopy, using an antipeptide antibody, established that the human D4S234 protein preferentially localized to the nucleus of mitotic cultured cells. Since the rat p1A75 protein was previously mapped to the neuronal cytoplasm by in situ hybridization, the subcellular localization of the D4S234 protein was subsequently examined during differentiation of the NTera 2 (NT2) cell line. Following differentiation into postmitotic NT2-N neurons, the D4S234 protein demonstrated cytoplasmic staining and reduced or undetectable nuclear staining in many cells. The variation in the intracellular localization of the D4S234 protein in mitotic and nonmitotic cells suggests that the subcellular localization of this protein is developmentally regulated and provides clues about the biochemical function of this protein.

Transcription of the Huntington disease gene during the quinolinic acid excitotoxic cascade

Although Huntington disease (HD) is characterized by the selective neurodegeneration of the basal ganglia and cerebral cortex, efforts to define the disease pathology have been complicated by the widespread expression of the disease gene (IT15) throughout the body. In this study, we examined IT15 mRNA levels during the quinolinic acid (QA) excitotoxic cascade to determine whether neuronal and/or glial expression is regulated by neurodegeneration. Following an initial increase between 1 h and 6 h, IT15 mRNA levels declined in a pattern homologous to a group of neuron-specific genes. Decreased mRNA levels after 24 h demonstrated that glial transcription is not activated by neurodegeneration or gliosis. The 1 h and 24 h mRNA levels strongly suggest that IT15 transcription preferentially localizes to degenerating neurons.

The mouse plasma membrane Ca2+ pump isoform 1 promoter: cloning and characterization

The expression of plasma membrane Ca2+ pump (PMCA) is regulated by various hormones or agonists via multiple second messenger pathways. Two different 5' segments of the PMCA1 gene (isoform 1) were cloned from a mouse genomic library. While one segment contained the 3' end of intron 1 and exon 2, the other segment was found to encompass the 5'-flanking region of the gene, exon 1, and the 5' portion of intron 1. Sequence analysis of the 5'-flanking region suggested the presence of the putative promoter. Four sites for initiation of transcription (spanning 64 bp) were identified by RNase protection assay and primer extension analysis. The promoter region was very GC-rich, contained no "TATA box," but had a "CAAT box" at -51. Comparison of sequence with known cis-regulatory motifs disclosed that the 5'-flanking region has a number of potential regulatory elements including an AP-1 site at -354, AP-2 binding sites at -267 and -123, Sp1 binding sites at -127, -111, and +3, and a cyclic AMP response element binding protein site at -67. To demonstrate promoter activity, a segment containing 611 bp of the promoter region (from -442 to +169) was subcloned in front of a promoterless chloramphenicol acetyltransferase (CAT) gene. This segment was able to drive the expression of chloramphenicol acetyltransferase in transient transfections of mouse (or human) neuroblastoma cells as well as rat aortic endothelial cells. Deletion analysis demonstrated that a fragment from -256 to +169 showed strong promoter activity, while a fragment from -117 to +169 had CAT activity that was not different from the vector control. The promoter was stimulated threefold by phorbol ester and twofold by cyclic AMP. These results provide further proof indicating up-regulation of the PMCA1 gene by multiple second messenger pathways.

A Sau3A polymorphism in the 5' end of the IT15 gene that nonrandomly segregates with the Huntington disease trinucleotide expansion

Genomic clones encompassing the Huntington disease (HD) mutation were used to isolate a probe that detects size changes in the restriction fragments that contain the HD trinucleotide repeat (TNR). This probe also detects a frequent Sau3A polymorphism (allele sizes 1.8-kb and 2.7kb), which maps approximately 950bp from the TNR. Examination of a number of HD families established that the frequency of the Sau3A alleles did not differ significantly between control and HD populations; however, the HD expansion was always present on a chromosome that contained the 1.8-kb Sau3A allele. This association between a specific allele and the HD TNR expansion was significant and could provide a clue to the chromosomal elements that produce the trinucleotide expansion on the Huntington disease chromosome.

An estimate of the number of genes in the Huntington disease gene region and the identification of 13 transcripts in the 4p16.3 segment

Physical mapping and genetic linkage studies have positioned the Huntington disease (HD) gene to a relatively large genomic region in the distal portion of the short arm of human chromosome 4 (4p16.3). To estimate the number of genes present in this region and to identify candidate disease genes, several clones that map to the 4p16.3 segment have been examined for clusters of CpG-rich restriction sites and transcribed sequences. Thirteen expressed sequences were identified and were shown by pulsed-field gel electrophoresis not to cluster into a small segment of the 4p16.3 band. The frequency of transcripts in these clones suggests that the putative HD gene region contains about 100 genes.

Simultaneous reduction of the sarcolemmal and SR calcium ATPase activities and gene expression in cardiomyopathic hamster

Altered calcium regulation is a prominent feature in the hereditary cardiomyopathy of the Syrian hamster. However, the activity of the two systems necessary for intracellular calcium homeostasis in the heart, the sarcolemmal and sarcoplasmic reticulum calcium ATPase pumps, have not been correlated. Using age- and pair-matched myopathic and control hamsters, a simultaneous reduction in gene expression and enzyme activity for these two pumps has been demonstrated. The concomitant alteration in gene expression as early as 1 month of age, preceding noticeable myocytolysis suggests that the depressed activity in these two calcium ATPase systems is not due to cell necrosis but at least in part due to reduction in their mRNA levels. Reduced capacity of the calcium pumps would result in calcium overload as well as impaired contractility that leads to the eventual heart failure in this animal model.

Phorbol ester induces both gene expression and phosphorylation of the plasma membrane Ca2+ pump

Regulation of the plasma membrane Ca2+ pump in the cell is of critical importance in maintaining calcium homeostasis. Since protein kinase C is known to regulate functions of cellular proteins by direct phosphorylation or by inducing their gene expression, we investigated the possible involvement of protein kinase C in the regulation of the plasma membrane Ca2+ pump. The Ca2+ pump was isolated by immunoprecipitation from [32P]orthophosphate-labeled cultured rat aortic endothelial cells grown in the absence or presence of phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C. PMA treatment of cells led to a rapid increase in the phosphorylation level (1.3-fold) within 5 min and a further increase to 2.9-fold after 3 h. Prolonged PMA treatment also induced the accumulation of the Ca2+ pump mRNA, followed by increased levels of the pump protein. The peak level of the pump mRNA induction occurred at 4 h and was 8-20-fold higher than the control culture without PMA. The rate of the Ca2+ pump protein accumulation was slower, reaching a maximum of 3.5-fold after 6 h. Induction of the pump mRNA was suppressed by the protein kinase C inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine and by down-regulation of protein kinase C. Inactive phorbol ester 4 alpha-phorbol didecanoate also failed to mimic the PMA effect. These results suggest that the induction of Ca2+ pump expression is mediated by a protein kinase C-dependent mechanism. Furthermore, since the induction of the Ca2+ pump mRNA was blocked when cycloheximide and PMA were added together, this suggests that newly synthesized protein factor is needed to produce the mRNA induction. Our results suggest that protein kinase C is involved in the regulation of the Ca2+ pump in endothelial cells. At the protein level, it modifies the Ca2+ pump by phosphorylation, and at the gene level, it stimulates the expression of its mRNA and thereby increases the amount of the pump protein.

Pairwise linkage analysis of 11 loci on human chromosome 4

New RFLPs are described for INP10 and interleukin 2. The 55 pairwise genetic linkage relationships for these two loci and nine additional loci on the long arm of chromosome 4 (4q) are reported. Fifteen new linkages are established, and new data are added to the four previously reported linkages on 4q. Tight linkage of interleukin 2 (T-cell growth factor), epidermal growth factor, and alcohol dehydrogenase is described. Significant differences were observed between male and female recombination rates. The female rate was estimated to be 1.27 times the male rate. On the basis of these pairwise results, the order for the 11 loci is D4S35-GC-(ALB/AFP)-MT2P1-D4S1-INP10-ADH3-( EGF/IL2)-(FBB/FBA/FBG)-MNS. This preliminary order can serve as a starting point for more detailed multipoint analysis.

Assignment of human dihydrofolate reductase gene to band q23 of chromosome 5 and of related pseudogene psi HD1 to chromosome 3

The chromosomal location of the human dihydrofolate reductase (DHFR; EC 1.5.1.3) gene that is amplified in a methotrexate-resistant human cell line has been investigated by screening a number of human-Chinese hamster ovary cell hybrids containing terminal and interstitial deletions in human chromosome 5. A correlation of genomic blotting data with the chromosome 5 constitution of the individual hybrids has allowed the assignment of the human DHFR gene to 5q23. The present work also establishes the location of the related intronless pseudogene psi HD1 in chromosome 3.