The Fads3 gene encodes for three different FADS3 proteins in rodent tissues
Résumé
Marquardt et al., described in 2000 the genomic structure of the fatty acid desaturase (FADS) cluster in human. This cluster includes the FADS1 and FADS2 genes encoding respectively for the D5- and D6-desaturases involved in the polyunsaturated fatty acid biosynthesis. A third gene named FADS3 was newly identified revealing 62% and 70% nucleotide sequence identity with FADS1 and FADS2 respectively. Further studies underlined the correlation between the FADS3 polymorphism and lipid markers in human. The FADS3 gene expression was also tested in mouse embryo implantation or during human neurogenic differentiation, but still no functional role is attributed to the putative FADS3 protein, even if protein datasearch identified FADS3 as a classical front-end membrane-bound fatty acid desaturase. The translation from the transcript into the protein has never been described. Thus the question is: does FADS3 exist? To answer that query, we investigated the FADS3 occurrence in rat somatic and germinal tissues by western-blot. We used two specific polyclonal antibodies directed against the N terminal and C terminal ends of FADS3. Our results showed three potential protein isoforms of FADS3. One protein displayed a 51kDa molecular mass, as predicted by the peptide sequence of FADS3, and was mainly present in liver, kidney, heart and brown adipose tissue. A 75kDa protein was also observed but only in few tissues and was specifically abundant in lung. The third protein found at 37kDa was located in many tissues and particularly in abdominal and skeletal muscles. In this study, we reported that FADS3 does exist. Three potential isoforms were identified in rats in a tissue-dependent manner, with a similar profile between males and females. The occurrence of these FADS3 isoforms did not depend on the mRNA level determined in parallel by real-time PCR. Furthermore, mouse tissues were also tested and showed the presence of the same three FADS3 isoforms but with a different tissue distribution. Finally, the FADS3 isoform exhibiting the predicted 51kDa molecular mass was preponderant in liver, underlining a putative function as a fatty acid desaturase, function we have now to further investigate