Zfat expression in ZsGreen reporter gene knock-in mice: Implications for a novel function of Zfat in definitive erythropoiesis

Zinc finger and AT-hook domain containing (Zfat) is a transcriptional regulator harboring an AT-hook domain and 18 repeats of a C2H2 zinc-finger motif, which binds directly to the proximal region of transcription start sites in Zfat-target genes. It was previously reported that deletion of the Zfat gene in mice yields embryonic lethality by embryonic day 8.5 and impairs primitive hematopoiesis in yolk sac blood islands. In addition, Zfat has been reported to be involved in thymic T-cell development and peripheral T-cell homeostasis. In the present study, in order to obtain a precise understanding of the expression and function of Zfat, a knock-in mouse strain (Zfat(ZsG/+) mice), which expressed ZsGreen in the Zfat locus, was established. ZsGreen signals in tissues and cells of Zfat(ZsG/+) mice were examined by flow cytometric and histological analyses. Consistent with our previous studies, ZsGreen signals in Zfat(ZsG/+) mice were detected in the embryo and yolk sac blood islands, as well as in thymocytes, B and T cells. In the Zfat(ZsG/+) thymus, ZsGreen(+) cells were identified not only in T-cell populations but also in thymic epithelial cells, suggesting the role of Zfat in antigen-presenting cells during thymic T-cell development. ZsGreen signals were observed in definitive erythroid progenitor cells in the fetal liver and adult bone marrow of Zfat(ZsG/+) mice. The proportion of ZsGreen(+) cells in these tissues was highest at the early stage of erythroid differentiation, suggesting that Zfat serves particular roles in definitive erythropoiesis. Histological studies demonstrated that ZsGreen signals were detected in the pyramidal cells in the hippocampal CA1 region and the Purkinje cells in the cerebellum, suggesting novel functions of Zfat in nervous tissues. Taken together, these results indicated that the Zfat(ZsG/+) reporter mouse may be considered a useful tool for elucidating the expression and function of Zfat.