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Characterization of the mRNAs encoding the gene 2 sarcoplasmic/endoplasmic-reticulum Ca2+ pump in pig smooth muscle
J A Eggermont1, F Wuytack, R Casteels
1Laboratorium voor Fysiologie, K.U. Leuven, Belgium.
Abstract:
The gene 2 sarcoplasmic/endoplasmic-reticulum (SR/ER) Ca2+ pump is expressed in slow skeletal and cardiac muscle, smooth muscle and non-muscle tissues. We have analysed the gene 2 Ca2+ pump mRNAs using a panel of anti-sense RNA probes which recognize either the muscle (class 1) or the non-muscle (class 2) transcript, or both. In pig smooth muscle, we confirmed the presence of the class 1 and class 2 mRNAs of 4.4 kb length and we also detected a third mRNA of 8.0 kb which reacted with both the class 1 and class 2 riboprobes. A 4.2 kb cDNA corresponding to the 3' part of the 8.0 kb mRNA was cloned from a pig gastric smooth muscle cDNA library. Nucleotide sequence analysis of this clone revealed that the 8.0 kb mRNA (class 3 transcript) contained both the non-muscle-specific and the muscle-specific exons separated by a 2.4 kb intron which has not been removed. The class 3-mRNA-encoded SR/ER Ca2+ pump is identical to the class 2-encoded non-muscle isoform. Northern blot analysis demonstrated that, in cardiac muscle, the class 1 mRNA (encoding the muscle isoform) is the predominant messenger, whereas in non-muscle tissues the class 2 and 3 mRNAs (encoding the non-muscle isoform) predominate. In smooth muscle all three mRNA types are present. The tissue distribution of the mRNA types suggests a tissue-dependent processing of the primary transcript of the sarcoplasmic/endoplasmic reticulum Ca2+ pump gene 2.
Insights
The sarcoplasmic/endoplasmic reticulum Ca2+ pump gene 2 produces different mRNA types. Tissue-specific processing of this gene generates distinct muscle and non-muscle isoforms, influencing Ca2+ pump function.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- The sarcoplasmic/endendoplasmic reticulum Ca2+ pump (SERCA) gene 2 is crucial for calcium ion (Ca2+) regulation.
- This gene expresses multiple mRNA transcripts, including muscle (class 1) and non-muscle (class 2) forms.
Purpose of the Study:
- To investigate the different mRNA transcripts of the SERCA gene 2.
- To analyze the tissue-specific expression and processing of these transcripts.
Main Methods:
- Analysis of SERCA gene 2 mRNAs using anti-sense RNA probes.
- Northern blot analysis to detect mRNA sizes and distribution.
- cDNA cloning and nucleotide sequencing of a novel mRNA transcript.
Main Results:
- A third mRNA transcript (class 3) of 8.0 kb was identified in pig smooth muscle, containing both muscle and non-muscle exons with an unspliced intron.
- The class 3 transcript encodes a non-muscle isoform identical to the class 2 isoform.
- Cardiac muscle predominantly expresses class 1 mRNA, non-muscle tissues express class 2 and 3 mRNAs, and smooth muscle expresses all three types.
Conclusions:
- SERCA gene 2 undergoes tissue-dependent alternative splicing or processing.
- This differential processing generates distinct Ca2+ pump isoforms tailored for specific tissue functions.
- The findings highlight the complexity of gene expression regulation in calcium homeostasis.