Association of Rex-1 to target genes support its interaction with polycomb function
Rex-1/Zfp42 was identified originally due to its restricted expression in the ICM of preimplantation embryos, primary spermatocytes, and undifferentiated mouse embryonic stem cells. We have analyzed the expression pattern of Rex-1 protein in blastocyst, demonstrating expression in both trophectoderm and ICM. Similarly, we demonstrate expression of Rex-1 both in embryonic (ES) and (TS) trophectoderm stem cells. Defining the transcriptionally circuits operating in ES cells contributes to understanding the molecular nature of pluripotency, selfrenewal and reprogramming. To understand the contribution of Rex-1 to the adquisition of selfrenewal and pluripotency, we identified Rex-1 target genes in ESC. Surprisingly , Rex-1 doesn´t seem to share target genes with its close relative YY1, despite the presence of almost identical Zinc Fingers in both genes. We found association of Rex-1 to several genes identified previously as either co-expressed in Rex-1 expressing subpopulations of ES cells or induced in subpopulations devoid of Rex-1. We hypothesized that Rex-1 may contribute to PcG function, considering its homology to YY1, a gene identified genetically as Polycomb in D. Melanogaster. Indeed, we found association of Rex-1 to several genes described as regulators of differentiation and repressed by PcG in mouse and human ESC. Support for this hypothesis is also provided by the intaraction of Rex-1 with Ring1 proteins and RYBP/YAF2, proteins identified in PcG-associated complexes. We conclude that Rex1 might contribute to pluripotency through gene regulation in conjunction with Polycomb.