Alternative splicing of VWFA modules generates variants of type VI collagen α3 chain with a distinctive expression pattern in embryonic chicken tissues and potentially different adhesive function

Roberto Doliana, Maria Teresa Mucignat, Daniela Segat, Stefania Zanussi, Carla Fabbro, T. R M Lakshmi, Alfonso Colombatti

Research output: Contribution to journalArticle

Abstract

Type VI collagen, a ubiquitous extracellular cell adhesion molecule, is formed by heterotrimeric monomers which associate into dimers and tetramers and assemble into larger oligomers constituting the 100 nm-long periodic microfilaments of connective tissues. One distinctive structural characteristic of type VI collagen is represented by an α3 chain with a much larger molecular mass compared to the other two chains and with an extensive size heterogeneity, exemplified by the separation into up to five polypeptides in SDS-PAGE. There is evidence that the α3(VI) mRNA can undergo alternative splicing of three VWFA modules at the 5'-end, potentially resulting in the expression of protein variants. Here we report that alternative splicing of α3(VI) mRNA in chicken embyro did not result in the absolute predominance of a particular α3(VI) form in any tissue; instead, the expression of variants including exons A9, A8 and A6 increased with age. In addition, these variants had a more restricted tissue distribution pattern compared to variants including only constitutive exons: A9+ were the rarest and were present almost exclusively in skin and skeletal muscle; A6+ were expressed in several of the examined tissues with local variations; A8+ had intermediate levels and were less widely distributed than A6+ variants. Quantitative densitometric scanning of immunoblots of type VI collagen purified from gizzard and stained with VWFA module-specific antibodies indicated that the polymorphic migration pattern of α3(VI) polypeptides is contributed by concurrent or independent splicing of two exons (A8 and A6) and probably by processing and/or proteolysis at the N- and C-terminus. Three exon-specific recombinant polypeptides were examined in cell adhesion assays, and A6 appeared to be the most active, particularly at low substrate concentrations. The adhesion to the recombinant modules was not abrogated by EDTA nor by mAbs against the integrin β1 or α2 subunits. Over all, these results suggest that the splicing of the α3(VI) mRNA and the tissue distribution pattern of type VI collagen variants, apart from promoting cell adhesion to different ex tents, might also affect additional structural as well as functional properties of this molecule, including microfilament formation and interaction with other extracellular matrix molecules.

Original languageEnglish
Pages (from-to)427-442
Number of pages16
JournalMatrix Biology
Volume16
Issue number7
DOIs
Publication statusPublished - Feb 1998

Keywords

  • Alternative splicing
  • Cell adhesion
  • Tissue variants
  • Type VI collagen

ASJC Scopus subject areas

  • Molecular Biology

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