Polymorphisms in the CPB2 gene are maintained by balancing selection and result in haplotype-preferential splicing of exon 7

Rachele Cagliani, Matteo Fumagalli, Stefania Riva, Uberto Pozzoli, Marco Fracassetti, Nereo Bresolin, Giacomo P. Comi, Manuela Sironi

Research output: Contribution to journalArticle

Abstract

The CPB2 gene encodes thrombin-activatable fibrinolysis inhibitor (TAFI), a hepatically secreted zymogen acting as a molecular link among coagulation, fibrinolysis, and inflammation. Variants in CPB2 have been associated with several human conditions. We resequenced and analyzed the two regions carrying previously known nonsynonimous single-nucleotide polymorphisms (Ala147Thr and Ile325Thr) and variants affecting transcript stability. Our data indicate that whereas the gene portion extending from exon 9 to the 3′ untranslated region fits a model of neutral evolution, variants in the region encompassing exons 6-7 have been maintained by balancing selection. Indeed, we verified that the region displays high nucleotide diversity, many intermediate frequency variants, and an excess of polymorphism compared with interspecific divergence. Consistently, haplotype analysis indicated the presence of two major haplotype clades separated by deep branches. Transcript analysis revealed that in both HepG2 cells and human liver samples, CPB2 exon 7 undergoes haplotype- preferential skipping. Therefore, we indicate that balancing selection has been maintaining functional variants that promote alternative exon 7 splicing. Although transcripts lacking exon 7 represent a minority of total CPB2 products, the effect on antifibrinolytic activity might be much greater as the intrinsic instability of TAFI is a major determinant of its antifibrinolytic potential.These data highlight the contribution of population genetics approaches to the analysis of functional genetic variation and may orient further biochemical and genetics studies on the pathophysiolgic role of CPB2 gene products.

Original languageEnglish
Pages (from-to)1945-1954
Number of pages10
JournalMolecular Biology and Evolution
Volume27
Issue number8
DOIs
Publication statusPublished - 2010

Keywords

  • alternative splicing
  • balancing selection
  • CPB2
  • thrombin-activatable fibrinolysis inhibitor

ASJC Scopus subject areas

  • Genetics
  • Molecular Biology
  • Ecology, Evolution, Behavior and Systematics
  • Medicine(all)

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