Various transcripts are generated from the VCSA1 gene by alternative splicing and poly(A) processing in the rat...

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• The variable coding sequence (VCS) multigene family exhibits significant evolutionary divergence in protein-coding regions.
• The VCSA1 gene in Rattus norvegicus submandibular gland (SMG) encodes the SMR1-VA1 preproprotein via a major 0.7-kb mRNA (VCSA1*1T1).

Purpose of the Study:

• To clone and characterize additional VCSA1 cDNAs and their corresponding mRNAs expressed in the rat SMG.
• To investigate the functional implications of alternative splicing and polyadenylation in VCSA1 gene expression.

Main Methods:

• cDNA cloning and sequencing
• Analysis of mRNA 3' untranslated regions (UTR) and polyadenylation sites
• Comparison of transcript levels during post-natal development
• Polysomal fractionation to assess in vivo translation
• Run-on transcription assays

Main Results:

• Four new VCSA1 cDNAs (VCSA1*1T2 to *1T5) were identified in the SMG.
• VCSA1*1T1 to *1T4 mRNAs differ in their 3' UTRs due to alternative polyadenylation site usage.
• VCSA1*1T5 mRNA results from alternative splicing, incorporating an additional exon (exon 4) and lacking the final exon.
• VCSA1*1T1, VCSA1*1T4, and VCSA1*1T5 transcripts are translated in vivo.
• The VCSA1*1T5 transcript encodes a distinct 68-amino acid protein (P2-VA1), likely a glycosylated secretory protein with a different function than SMR1-VA1.
• VCSA1*1T1 mRNA is the most abundant transcript in the male rat SMG.

Conclusions:

• The VCSA1 gene generates multiple mRNA isoforms through alternative polyadenylation and splicing.
• These isoforms encode distinct proteins, including P2-VA1, suggesting diverse functional roles for VCSA1 products.
• Alternative RNA processing plays a significant role in regulating VCSA1 gene expression in the rat SMG.