Scientists at the Albert Einstein College of Medicine of Yeshiva University say that they have discovered two genes responsible for storing fat in cells.
The researchers called these two new genes Fat-Inducing Transcripts 1 (FIT1) and FIT2. Both genes code for proteins that are more than 200 amino acids in length, the team explains. Also, the two genes are 50% similar to each other, they add. The amino acid sequences of the FIT proteins do not resemble any other known proteins found in any species, indicating that the FIT genes comprise a novel gene family, the investigators report.
The researchers say that they conducted several experiments to confirm the roles of FIT1 and FIT2 in fat storage. In one experiment, they overexpressed both FIT1 and FIT2 genes in human cells. While the rate of fat synthesis stayed the same in both overexpressed and control cells, the number of lipid droplets in the overexpressed cells increased dramatically: between four- and six-fold.
The team then knocked down FIT2 in mouse fat cells. FIT1 is not expressed in these cells. Examination of these fat cells for lipid droplets revealed that cells with suppressed FIT2 expression had a drastic reduction in lipid droplets.
Finally, zebrafish eggs were injected with a segment of DNA designed to interfere with FIT2 expression. Then, to induce lipid droplet formation in zebrafish larvae (where it is localized mainly in the liver and intestine), free-swimming, six-day-old larvae were fed a high-fat diet for six hours. Although the larvae had exhibited normal feeding behavior, examination of their livers and intestines revealed a near-absence of lipid droplets.
The findings will appear online in the Proceedings of the National Academy of Sciences.