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Multiple transcripts of the mouse tyrosinase gene are generated by alternative splicing
1Institute of Cell and Tumor Biology, German Cancer Research Center, Heidelberg.
Abstract:
We report the cloning and isolation of the mouse tyrosinase cDNA by screening mouse B16 melanoma cDNA libraries. Independent cDNA clones have been characterized by restriction enzyme analysis, hybridizations with individual subprobes and by partial sequencing analysis. Based on these criteria we have identified multiple transcripts, which in comparison to the major transcript, display deletions of internal sequences and have different 3' termini. The most abundant transcript encodes a functional tyrosinase. The structural gene which encodes five exons separated by large introns and spans a chromosomal region of approximately 70 kb has been isolated. Comparison of the cDNAs with the cloned genomic DNAs and sequencing of the exon/intron boundaries reveal that the multiple transcripts are generated by alternative splicing and putatively by alternate polyadenylation site usage. The alternative splicing mechanisms involve exon skipping as well as internal donor splice site usage. Primer extension analysis shows that the transcripts are produced from two different promoters. Southern blot analysis of DNAs derived from mice carrying the lethal albino deletion mutations demonstrates that the structural gene maps near or at the albino locus. The viable albino mouse BALB/c carries an apparently intact structural gene indicating that the albino phenotype is a consequence of a failure to express the tyrosinase gene or the inability to produce a tyrosinase enzyme.
Insights
Researchers isolated the mouse tyrosinase gene, revealing multiple transcripts due to alternative splicing. This explains the albino mouse phenotype, linked to tyrosinase gene expression issues.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Tyrosinase is crucial for melanin production.
- The genetic basis of the albino mouse phenotype requires detailed investigation.
Purpose of the Study:
- To clone and characterize the mouse tyrosinase gene and its transcripts.
- To elucidate the molecular mechanisms underlying tyrosinase gene expression and its relation to albinism.
Main Methods:
- Screening of mouse melanoma cDNA libraries.
- Restriction enzyme analysis, hybridization, and sequencing of cDNA clones.
- Isolation and characterization of the mouse tyrosinase structural gene.
Main Results:
- Identified multiple tyrosinase transcripts generated by alternative splicing and polyadenylation.
- The major transcript encodes a functional tyrosinase enzyme.
- The mouse tyrosinase gene spans approximately 70 kb and contains five exons.
- Alternative splicing involves exon skipping and internal donor splice site usage.
- Transcripts originate from two distinct promoters.
- The tyrosinase gene maps to the albino locus.
Conclusions:
- Alternative splicing and promoter usage generate diverse tyrosinase transcripts.
- The albino phenotype in BALB/c mice is likely due to impaired tyrosinase gene expression or enzyme function, not a structural defect.