UO-44 is a novel protein of unknown function which was described in uterus, medium-size ovarian follicles, oviduct and pancreas of different mammalian species. Using differential display analysis in preimplantation rat uteri, Chen et al. 1999 cloned and described it as an estradiol responsive gene named estrogen regulated gene 1 (ERG-1). Subsequent characterization showed that its expression was modified through pregnancy. The human ortholog (HuUO-44) was cloned and characterized by Leong et al. in 2004 and various splice variants were described. Multiple Tissue Northern blots and immunohistochemistry revealed rather specific expression in pancreas and ovaries. The full length cDNA, when expressed as a GFP-fusion protein, was shown to be associated with the cell membrane.
We prepared total RNA from human fetal osteoblasts (hFOB), telomerase-immortalized human mesenchymal stem cells (hMSC-TERT) and four different strains of primary human mesenchymal stem cells (hMSC). Whole genome microarray (Affymetrix, HG-U133 2.0 plus) analysis of hMSC-TERT expression pattern revealed HuUO44 to be expressed in these cells. Results were confirmed by RT-PCR. Using framing primer oligonucleotides for RT-PCR in hMSC-TERT cells, we obtained two distinct full length bands. Cloning and consequent sequence analysis verified presence of two different splice variants of HuUO44 in hMSC-TERT. RT-PCR using cDNA preparations from primary hMSCs and hFOBs depicted expression of HuUO44 in these cells.
In summary we have demonstrated the expression of two splice variants of the estrogen responsive gene of unknown function UO-44 in human cells of mesenchymal origin.