Overlapping peri-implantation phenotypes of ZNHIT1 and ZNHIT2 despite distinct functions during early mouse development.

Mammalian preimplantation development culminates in the formation of a blastocyst which undergoes extensive gene expression regulation to successfully implant into the maternal endometrium. Zinc-finger HIT domain-containing (ZNHIT) 1 and 2 are members of a highly conserved family, yet they have been identified as subunits of distinct complexes. Here we report that knockout of either Znhit1 or Znhit2 results in embryonic lethality during peri-implantation stages. Znhit1 and Znhit2 mutant embryos have overlapping phenotypes, including reduced proportion of SOX2-positive ICM cells, a lack of Fgf4 expression and aberrant expression of NANOG and SOX17. Furthermore, we find that the similar phenotypes are caused by distinct mechanisms. Specifically, embryos lacking ZNHIT1 likely fail to incorporate sufficient H2A.Z at the promoter region of Fgf4 and other genes involved in cell projection organization resulting in impaired invasion of trophoblast cells during implantation. In contrast, Znhit2 mutant embryos display a complete lack of nuclear EFTUD2, a key component of U5 spliceosome, indicating a global splicing deficiency. Our findings unveil the indispensable yet distinct roles of ZNHIT1 and ZNHIT2 in early mammalian embryonic development. Comparative gene expression profiling analysis of RNA-seq data for mouse embryos with genotypes of Znhit1 wt, het, mutant or Znhit2 wt, het, mutant.哺乳动物着床前发育以囊胚形成为终末阶段，囊胚需经历广泛的基因表达调控，方可成功植入母体子宫内膜。含锌指HIT结构域（Zinc-finger HIT domain-containing, ZNHIT）家族的ZNHIT1与ZNHIT2属于高度保守的蛋白家族成员，但其被鉴定为不同复合物的亚基。本研究证实，敲除Znhit1或Znhit2均可导致胚胎在围着床阶段发生致死。Znhit1与Znhit2敲除胚胎存在重叠的表型特征：SOX2阳性内细胞团（Inner Cell Mass, ICM）细胞占比降低、Fgf4表达缺失，以及NANOG与SOX17的表达异常。进一步研究发现，二者虽表现出相似的表型，但调控机制却截然不同。具体而言，缺失ZNHIT1的胚胎可能无法在Fgf4及其他参与细胞突起组织调控的基因的启动子区域整合足够量的组蛋白H2A.Z，进而导致着床过程中滋养层细胞的侵袭功能受损。与之相反，Znhit2敲除胚胎完全缺乏细胞核内的EFTUD2——U5剪接体的关键组分，这表明其存在全局性的剪接缺陷。本研究结果揭示了ZNHIT1与ZNHIT2在哺乳动物早期胚胎发育中不可或缺且功能各异的重要作用。本研究对基因型分别为Znhit1野生型（wt）、杂合型（het）、突变型，以及Znhit2野生型（wt）、杂合型（het）、突变型的小鼠胚胎的RNA测序（RNA-seq）数据开展了比较基因表达谱分析。