Genomic structure of the human caldesmon gene

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• High molecular weight caldesmon (h-CaD) is primarily in smooth muscle, while low molecular weight caldesmon (l-CaD) is widespread in non-muscle cells.
• Caldesmon isoform expression changes correlate with smooth muscle cell phenotypic modulation.

Purpose of the Study:

• To investigate the isoform diversity of human caldesmons (CaDs).
• To determine the genomic structure of the human CaD gene and elucidate the molecular mechanisms regulating CaD isoform expression.

Main Methods:

• Cloning of l-CaD cDNAs from HeLa S3 cells.
• Determination of the genomic structure of the human CaD gene.
• Analysis of alternative splicing events in CaD mRNA.

Main Results:

• Identified two l-CaD isoforms (HeLa l-CaD I and II) differing by a 26-amino acid deletion.
• Identified WI-38 l-CaD I with a 26-amino acid insertion compared to WI-38 l-CaD II.
• Mapped the human CaD gene to chromosome 7q33-q34 and found it comprises 14 exons.
• The 26-amino acid insertion/deletion is encoded by exon 4.
• Exon 3 contains splice sites that regulate the expression of h-CaD and l-CaD isoforms.

Conclusions:

• The differential expression of h-CaD and l-CaD isoforms is likely regulated by alternative splicing pathways involving exon 3.
• Understanding these splicing mechanisms provides insight into smooth muscle cell biology and disease states associated with altered CaD expression.