MLC1
Membrane protein MLC1 [KIAA0027] [WKL1]
PublicationsПравить
The rat myosin light chain (MLC)1/3 gene locus contains a potent muscle-specific enhancer, located downstream of the coding region, greater than 24 kilobases away from the MLC1 transcription start site. To assess the role of this enhancer in the activation of MLC expression during development, transgenic mice were generated carrying multiple copies of a MLC1 promoter-chloramphenicol acetyltransferase (CAT) transcription unit linked to a genomic fragment including the enhancer. CAT expression was detected in four mouse lines, up to 1000-fold higher in skeletal muscles than in other tissues. Activation of endogenous MLC1 transcription in these animals 4 days before birth was reflected in the onset of CAT transgene expression. This study identifies the transcriptional control elements necessary to activate the 21-kilobase MLC1/3 locus at the appropriate fetal stage and indicates that the MLC enhancer is sufficient to induce developmentally regulated expression from the MLC1 promoter exclusively in skeletal muscle cells.
MeSH Terms
- Aging
- Animals
- Blotting, Northern
- Blotting, Southern
- Cells, Cultured
- Chloramphenicol O-Acetyltransferase
- Enhancer Elements, Genetic
- Female
- Fibroblasts
- Gene Expression Regulation
- Genes
- Genetic Vectors
- Kinetics
- Mice
- Mice, Transgenic
- Muscle Development
- Muscles
- Myosin Subfragments
- Plasmids
- Rats
- Transfection
Expression of the two isoforms of cardiac myosin heavy chain (MHC), MHC alpha and MHC beta, in mammals is regulated postnatally by a variety of stimuli, including serum hormone levels. Less is known about the factors that regulate myosin gene expression in rapidly growing cardiac muscle in embryos. Using isoform-specific 35S-labeled cRNA probes corresponding to the two MHC genes and the two myosin alkali light chain (MLC) genes expressed in cardiac muscle, we have investigated the temporal and spatial pattern of expression of these different genes in the developing mouse heart by in situ hybridization. Between 7.5 and 8 d post coitum (p.c.), the newly formed cardiac tube begins to express MHC alpha, MHC beta, MLC1 atrial (MLC1A), and MLC1 ventricular (MLC1V) gene transcripts at high levels throughout the myocardium. As a distinct ventricular chamber forms between 8 and 9 d p.c., MHC beta mRNAs begin to be restricted to ventricular myocytes. This process is complete by 10.5 d p.c. During this time, MHC alpha mRNA levels decrease in ventricular muscle cells but continue to be expressed at high levels in atrial muscle cells. MHC alpha transcripts continue to decrease in ventricular myocytes until 16 d p.c., when they are detectable at low levels, but then increase, and finally replace MHC beta mRNAs in ventricular muscle by 7 d after birth. Like MHC beta, MLC1V transcripts become restricted to ventricular myocytes, but at a slower rate. MLC1V mRNAs continue to be detected at low levels in atrial cells until 15.5 d p.c. MLC1A mRNA levels gradually decrease but are still detectable in ventricular cells until a few days after birth. This dynamic pattern of changes in the myosin phenotype in the prenatal mouse heart suggests that there are different regulatory mechanisms for cell-specific expression of myosin isoforms during cardiac development.
MeSH Terms
- Aging
- Animals
- Base Sequence
- Gene Expression Regulation
- Genes
- Gestational Age
- Heart
- Mice
- Mice, Inbred BALB C
- Mice, Inbred C3H
- Molecular Sequence Data
- Myosins
- Oligonucleotide Probes
- Transcription, Genetic
In order to study muscle gene expression during ageing, we examined both protein and total cellular RNA from Wistar F455 rat soleus and extensor digitorum longus (EDL) muscles at a variety of chronological ages. We found no evidence of the reappearance of the fast protein isoform of myosin light chain 1 [[[MLC1]]] in the slow soleus muscle during ageing previously reported by Syrovy and Gutmann, Pflügers Arch., 369 (1977) 85-89. We used both SDS-PAGE analysis of MLC1 proteins and slot blot RNA analysis with a probe specific for rat fast MLC1 mRNA (pC91), and found no changes in fast MLC1 expression during ageing in soleus or EDL muscles from these rats. These results indicate that re-expression of the fast MLC1 isoform is not a universal property of ageing soleus muscle.
MeSH Terms
- Aging
- Animals
- Female
- Gene Expression
- Male
- Muscles
- Myosins
- RNA
- Rats
- Rats, Inbred Strains