Role of Histone Chaperone APLF in Mammalian Embryo Development

Abstract

Embryonic development involves orchestrated events regulated by a plethora of factors. Epigenetic regulation is one such key aspect regulating embryonic development. We are investigating the role played by Aprataxin and PNK‐like factor (APLF), a histone chaperone, in regulating cellular transitions in the context of embryonic development. APLF is documented as a DNA damage‐specific histone chaperone and has already been studied in our lab in the context of the generation of induced pluripotent stem cells and breast cancer metastasis as a regulator of epithelial to mesenchymal transition.We are looking into the expression profile, functional role, and mechanism of action of APLF in embryonic development. The expression study in pre‐and post‐implantation mouse embryos and mouse trophoblast stem cells (TS) through different days of differentiation showed a dynamic expression pattern of APLF, clearly indicating prospective functional significance. The localization of APLF in mouse embryos was enhanced in trophectoderm (TE) and lineages derived from TE, which contributes to the extraembryonic lineage crucial for developing a proper maternal‐fetal connection. Functional studies by sh RNA mediated knockdown (KD) of Aplf in mouse embryos by microinjection induced the hatching of embryos in vitro at E3.75, with a significant increase in Cadherin 1 (Cdh1) and Caudal‐type homeobox 2 (Cdx2) expression. Hatching is a crucial event whereby the embryo breaks out of the protective sheath called zona pellucida and prepares itself to attach itself to the uterine wall by the process of implantation. The Aplf KD embryos failed to implant in vivo. Rescue experiments neutralized the effects of AplfKD both in vitro and in vivo. We used differentiated TS cells as our model system to understand the mechanism behind the observed phenotype in Aplf KD embryos. Reduced expression of Snail Family Transcriptional Repressor 2 (Snai2) and TEA Domain Transcription Factor 4 (Tead4), and the gain in Cdh1 level, marked the differentiation of AplfKD TS cells. Embryo implantation is one of the pioneer developmental stages where EMT comes into action. Significantly high level of epithelial marker Cdh1 and downregulation of mesenchymal marker Snai2 in Aplf KD TS cells would have impaired the crucial EMT process operational during implantation.Further studies are being conducted to unravel the underlying mechanism completely. Hence, our findings suggest a novel role for APLF during the implantation and post‐implantation development of mouse embryos. As we observed these phenotypes in the mouse embryo, we checked APLF expression in the human placenta, and interestingly, our preliminary studies showed its expression in cytotrophoblast and syncytiotrophoblast cells. As we have seen that a delicate balance of APLF is crucial to achieve implantation and attain proper pregnancy, we anticipate that it would contribute to establishing a felicitous maternal‐fetal connection.