title: Widespread expression of the mRNA encoding a novel vitamin D/thyroxine dual binding protein in the turtle Trachemys scripta.
abstract: Vitamin D-binding protein (DBP) is the major transport protein for the vitamin D sterols in a variety of mammalian and avian species. The DBP found in the emydid family of turtles is unique in that it exhibits high-affinity binding of both vitamin D and thyroxine (D/TBP). Sequence analysis has revealed that the emydid D/TBP is homologous to mammalian DBP and shares no homology with mammalian thyroxine-binding globulins. Northern blot analysis was used to examine the spatial profile of D/TBP transcription in the turtle Trachemys scripta. In both adults and hatchlings, two transcripts--the expected 1.5-kb full-length transcript and a second 0.8-kb transcript--were present in nearly all of the tissues examined. In adults, highest expression of the 1.5-kb transcript was seen in the kidney, gonad, and spleen, with lower levels in the liver and lung and no transcripts in skeletal muscle. In hatchlings, the full-length transcript was detected in a variety of tissues at similar levels. Injection of hatchlings with thyroxine increased levels of circulating D/TBP and transcript levels. These data are in marked contrast to observations in mammals in which transcription of DBP is confined predominantly to the liver. Further, the increase in circulating D/TBP associated with increased thyroidal activity may result from a direct or indirect activation of D/TBP transcription by thyroxine.
authors.affiliation: Department of Integrative Biology, University of California at Berkeley, 94720, USA. dwhitwor@mail.mdacc.tmc.edu
authors.forename: D J
authors.initials: DJ
authors.lastname: Whitworth
authors.forename: L
authors.initials: L
authors.lastname: Hunt
authors.forename: P
authors.initials: P
authors.lastname: Licht
mesh_terms: D000375:Aging; D000818:Animals; D015152:Blotting, Northern; D001835:Body Weight; D015870:Gene Expression / Q000187:drug effects; D006066:Gonads / Q000737:chemistry; D007668:Kidney / Q000737:chemistry; D008099:Liver / Q000737:chemistry; D008168:Lung / Q000737:chemistry; D018482:Muscle, Skeletal / Q000737:chemistry; D012333:RNA, Messenger / Q000032:analysis*; D013154:Spleen / Q000737:chemistry; D013974:Thyroxine / Q000097:blood / Q000494:pharmacology; D013975:Thyroxine-Binding Proteins / Q000235:genetics*; D014426:Turtles / Q000378:metabolism*; D014809:Vitamin D-Binding Protein / Q000235:genetics*
chemical_list: D012333:RNA, Messenger; D013975:Thyroxine-Binding Proteins; D014809:Vitamin D-Binding Protein; D013974:Thyroxine