ABSTRACT
Genes under a 24-h regulation period may represent drug targets relevant to diseases involving circadian dysfunctions. As a testing model of the circadian clock system, we have used synchronized rat fibroblasts that are known to express at least six genes in a circadian fashion. We have determined the expression patterns of 9957 transcripts every 4 h over a total period of 76 h using high density oligonucleotide microarrays. The spectral analysis of our mRNA profiling data indicated that approximately 2% (85 genes) of all expressed genes followed a robust circadian pattern. We have confirmed the circadian expression of previously known clock or clock-driven genes, and we identified 81 novel circadian genes. The majority of the circadian-regulated gene products are known and are involved in diverse cellular functions. We have classified these circadian genes in seven clusters according to their phase of cycling. Our pathway analysis of the mRNA profiling data strongly suggests a direct link between circadian rhythm and cell cycle.
Subject(s)
Circadian Rhythm , Fibroblasts/metabolism , Gene Expression Profiling/methods , Oligonucleotide Array Sequence Analysis/methods , RNA, Messenger/metabolism , Animals , DNA, Complementary/metabolism , Expressed Sequence Tags , Humans , Kinetics , Rats , Reverse Transcriptase Polymerase Chain Reaction , Ribonucleases/metabolism , Time FactorsABSTRACT
Two proteolipid proteins, PLP and DM20, are the major membrane components of central nervous system (CNS) myelin. Mutations of the X-linked PLP/DM20 gene cause dysmyelination in mouse and man and result in significant mortality. Here we show that mutant mice that lack expression of a targeted PLP gene fail to exhibit the known dysmyelinated phenotype. Unable to encode PLP/DM20 or PLP-related polypeptides, oligodendrocytes are still competent to myelinate CNS axons of all calibers and to assemble compacted myelin sheaths. Ultrastructurally, however, the electron-dense 'intraperiod' lines in myelin remain condensed, correlating with its reduced physical stability. This suggests that after myelin compaction, PLP forms a stabilizing membrane junction, similar to a "zipper." Dysmyelination and oligodendrocyte death emerge as an epiphenomenon of other PLP mutations and have been uncoupled in the PLP null allele from the risk of premature myelin breakdown.
Subject(s)
Central Nervous System/pathology , Central Nervous System/physiopathology , Demyelinating Diseases/genetics , Motor Activity , Myelin Proteolipid Protein/genetics , Myelin Sheath/physiology , Nerve Tissue Proteins , Animals , DNA Primers , Demyelinating Diseases/pathology , Disease Models, Animal , Exons , Humans , Mice , Mice, Transgenic , Myelin Proteins/biosynthesis , Myelin Proteins/isolation & purification , Myelin Proteolipid Protein/biosynthesis , Myelin Sheath/pathology , Myelin Sheath/ultrastructure , Polymerase Chain Reaction , Stem Cells , X ChromosomeABSTRACT
Charcot-Marie-Tooth disease (CMT) is the most common inherited neuropathy in humans and has been associated with a partial duplication of chromosome 17 (CMT type 1A). We have generated a transgenic rat model of this disease and provide experimental evidence that CMT1A is caused by increased expression of the gene for peripheral myelin protein-22 (PMP22, gas-3). PMP22-transgenic rats develop gait abnormalities caused by a peripheral hypomyelination, Schwann cell hypertrophy (onion bulb formation), and muscle weakness. Reduced nerve conduction velocities closely resemble recordings in human patients with CMT1A. When bred to homozygosity, transgenic animals completely fail to elaborate myelin. We anticipate that the CMT rat model will facilitate the identification of a cellular disease mechanism and serve in the evaluation of potential treatment strategies.
