The polymorphic integumentary mucin B.1 from Xenopus laevis contains the short consensus repeat

Area of Science:

• Molecular biology
• Genomics
• Proteomics

Background:

• Frog integumentary mucin B.1 (FIM-B.1) possesses a C-terminal domain homologous to von Willebrand factor.
• Previous discovery of FIM-B.1 was achieved through molecular cloning.

Purpose of the Study:

• To characterize the region 5' to the von Willebrand factor domain in FIM-B.1.
• To investigate the genetic basis and transcript diversity of FIM-B.1.
• To determine the molecular mass and genetic polymorphism of FIM-B.1.

Main Methods:

• Polymerase chain reaction (PCR) for gene characterization.
• Cloning of multiple FIM-B.1 transcripts.
• Genomic sequence analysis of FIM-B.1 in Xenopus laevis.
• Southern blot analysis for genetic polymorphism.
• Western blot analysis using a specific antibody to determine molecular mass.

Main Results:

• A region containing short consensus repeats, typical of complement proteins, was identified 5' to the von Willebrand factor domain.
• Multiple FIM-B.1 transcripts with variable tandem repeats (rep-33 sequences) were cloned from a single animal.
• Evidence suggests transcripts originate from two genes and are generated by alternative splicing of functional cassettes.
• Genomic analysis revealed rep-33 sequences arranged in an interrupted array.
• Southern and Western blot analyses detected genetic polymorphism between animals and a molecular mass greater than 200 kDa for FIM-B.1.

Conclusions:

• FIM-B.1 exhibits significant transcript diversity generated through alternative splicing of tandem repeat units.
• Genetic polymorphism in the tandem repeat region contributes to variations in FIM-B.1 between individuals.
• FIM-B.1 is a large mucin with a complex genetic structure, suggesting important biological functions in frog integument.