Paralogous vitamin D receptors in teleosts: transition of nuclear receptor function.

Published

Journal Article

The availability of multiple teleost (bony fish) genomes is providing unprecedented opportunities to understand the diversity and function of gene duplication events using comparative genomics. Here we describe the cloning and functional characterization of two novel vitamin D receptor (VDR) paralogs from the freshwater teleost medaka (Oryzias latipes). VDR sequences were identified through mining of the medaka genome database in which gene organization and structure was determined. Two distinct VDR genes were identified in the medaka genome and mapped to defined loci. Each VDR sequence exhibits unique intronic organization and dissimilar 5' untranslated regions, suggesting they are not isoforms of the same gene locus. Phylogenetic comparison with additional teleosts and mammalian VDR sequences illustrate that two distinct clusters are formed separating aquatic and terrestrial species. Nested within the teleost cluster are two separate clades for VDRalpha and VDRbeta. The topology of teleost VDR sequences is consistent with the notion of paralogous genes arising from a whole genome duplication event prior to teleost radiation. Functional characterization was conducted through the development of VDR expression vectors including Gal4 chimeras containing the yeast Gal4 DNA binding domain fused to the medaka VDR ligand binding domain and full-length protein. The common VDR ligand 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)(2)D(3)] resulted in significant transactivation activity with both the Gal4 and full-length constructs of medaka (m) VDRbeta. Comparatively, transactivation of mVDRalpha with 1alpha,25(OH)(2)D(3) was highly attenuated, suggesting a functional divergence between these two nuclear receptor paralogs. We additionally demonstrate through coactivator studies that mVDRalpha is still functional; however, it exhibits a different sensitivity to 1alpha,25(OH)(2)D(3), compared with VDRbeta. These results suggest that in mVDRalpha and VDRbeta have undergone a functional divergence through a process of sub- and/or neofunctionalization of VDR nuclear receptor gene pairs.

Full Text

Duke Authors

Cited Authors

  • Howarth, DL; Law, SHW; Barnes, B; Hall, JM; Hinton, DE; Moore, L; Maglich, JM; Moore, JT; Kullman, SW

Published Date

  • May 2008

Published In

Volume / Issue

  • 149 / 5

Start / End Page

  • 2411 - 2422

PubMed ID

  • 18258682

Pubmed Central ID

  • 18258682

Electronic International Standard Serial Number (EISSN)

  • 1945-7170

International Standard Serial Number (ISSN)

  • 0013-7227

Digital Object Identifier (DOI)

  • 10.1210/en.2007-1256

Language

  • eng