Retinoic acid-dependent upregulation of mouse folate receptor-alpha expression in embryonic stem cells, and conservation of alternative splicing patterns.

The action of retinoic acid (RA) in normal development and differentiation is mediated by changes in the expression of RA-responsive target genes. We used differential display reverse transcriptase polymerase chain reaction (RT-PCR) to identify RA-responsive genes expressed in embryonic stem (ES) cells and found that murine folate receptor-alpha (FR-alpha) expression is rapidly induced by RA treatment. The observed increase in FR-alpha expression occurs within 3h, is independent of protein synthesis and does not occur when ES cells are differentiated by removal of leukaemia inhibitory factor (LIF), evidence that the response to RA is both direct and specific. Two messenger RNA (mRNA) isoforms of FR-alpha featuring novel sequence in the 5' untranslated region (UTR) were cloned, and both were found to be upregulated by RA. Other splice variants in both the 5' UTR and 3' UTR of FR-alpha mRNA were also identified. There is a striking similarity between these splicing patterns and those reported for human FR-alpha, which also generates multiple isoforms by alternative splicing in the 5' and 3' UTR. The conservation of these splicing patterns in the non-coding regions of the FR-alpha gene between mouse and human suggests that these regions, and in particular the 5' UTR, play an important role in regulating expression of this gene.