Abstract

A novel gene was recently discovered using microarray gene profiling of shear stress–induced genes in mouse embryonic stem cells (ESCs), which is located within the intron of the transcription factor Laf4 and therefore designated as Laf4 intron resident gene (Laf4ir). Laf4 and Laf4ir genes use different strands for transcription. Two transcript variants have been identified for Laf4ir with three potential opening reading frames (ORFs). In this study, we intend to characterise the transcriptional/translational expression, regulation, and functions of this novel gene. The experiments with qRT-PCR analysis revealed that Laf4ir mRNA was unregulated transiently by shear stress compared to static conditions in mouse differentiated ESCs. Laf4ir was expressed in late stage of mouse embryos but not in the early stages and Laf4ir was differentially expressed in adult mice organs/tissues. Specific antibodies against peptides from the ORFs confirmed the translation of these ORFs in mouse differentiated ESCs in response to shear stress. Immunofluorescence staining with antibody against ORF2 revealed that the ORF2 was exclusively expressed in the intima of aorta in wild type mice. Over-expression of ORF2 significantly increased CD31 expression in mouse ESC-derived Sca1+ cells, indicating the potential role of Laf4ir in endothelial cell differentiation. Interestingly, high level of ORF2 was detected from intima to the adventitia of aorta in ApoE-/- mice and in the adventitia of femoral artery from platinum wire injured mice. Further detailed and concrete investigation is required to characterise the potential functions of Laf4ir gene products, which may provide some new insights into vascular biology.