DDX21 is a p38-MAPK-sensitive nucleolar protein necessary for mouse preimplantation embryo development and cell-fate specification

Abstract

Successful navigation of the mouse preimplantation stages of development, during which three distinct blastocyst lineages are derived, represents a prerequisite for continued development. We previously identified a role for p38-mitogen-activated kinases (p38-MAPK) regulating blastocyst inner cell mass (ICM) cell fate, specifically primitive endoderm (PrE) differentiation, that is intimately linked to rRNA precursor processing, polysome formation and protein translation regulation. Here, we develop this work by assaying the role of DEAD-box RNA helicase 21 (DDX21), a known regulator of rRNA processing, in the context of p38-MAPK regulation of preimplantation mouse embryo development. We show nuclear DDX21 protein is robustly expressed from the 16-cell stage, becoming exclusively nucleolar during blastocyst maturation, a localization dependent on active p38-MAPK. siRNA-mediated clonal Ddx21 knockdown within developing embryos is associated with profound cell-autonomous and non-autonomous proliferation defects and reduced blastocyst volume, by the equivalent peri-implantation blastocyst stage. Moreover, ICM residing Ddx21 knockdown clones express the EPI marker NANOG but rarely express the PrE differentiation marker GATA4. These data contribute further significance to the emerging importance of lineage-specific translation regulation, as identified for p38-MAPK, during mouse preimplantation development.

Journey of the mouse primitive endoderm: from specification to maturation

“…Notably, p38-MAPK mutation prevents the specification of ICM cells into Epi and PrE as is apparent by sustained uncommitted cell populations [91,136]. The effect of p38-MAPK on mechanical properties and cell fate specification is likely due to its involvement in protein translation through mTOR in mouse embryos [138]. A recent study suggests that prospective PrE cells in isolated ICMs exhibit surface fluctuations and possess higher surface tension as compared to prospective Epi cells, and that these physical properties are key to lineage sorting [139].…”

Spatial positioning of preimplantation mouse embryo blastomeres is regulated by mTORC1 and 7mG-cap dependent translation at the 8- to 16-cell transition

“…The phenocopy of mTORi mediated deficits in primary ICM cell formation using p38-MAPKi (Fig. S5e) is also notable, as we previously identified DDX21 as a p38-MAPK effector protein in early mouse blastocysts development and a verified component of PrE specification [78]. Enhanced mTOR mediated translation of Ank2 transcripts, in proximity to condensing chromosomes and forming meiotic spindles, is reported in maturing mouse oocytes and ensures appropriate and highly asymmetric cell divisions generating the first polar body [54, 55]; implying potential mechanistic similarities that generate primary, but not secondary, populations of blastocyst ICM founders.…”

Paracrine interactions through FGFR1 and FGFR2 receptors regulate the development of preimplantation mouse chimaeric embryo

“…However, it is worth noting that Yang et al [36] induced knockdown later in development (at the blastocyst stage) and used a transfection method rather than the microinjection of zygote method applied in our study, which could contribute to these discrepancies. Interestingly, p38 MAPK signalling involved in the regulation of expanded blastocyst formation has also been shown to be important for early PE specification from uncommitted ICM progenitors [41][42][43][44], which further speaks to the similarity between the specifications of both extraembryonic lineages: the TE and PE.…”