analysis-retinoic-acid-induced-neural-differentiation-mouse-embryonic

Analysis of Retinoic Acid-induced Neural Differentiation of Mouse Embryonic Stem Cells in Two and Three-dimensional Embryoid Bodies

Mouse embryonic stem cells (ESCs) isolated from the inner mass of the blastocyst (typically at day E3.5), can be used as in vitro model system for ...

Sidney Kimmel Medical College, Thomas Jefferson University

Spontaneous neural differentiation of embryonic stem cells is induced by Noggin-mediated inhibition of bone morphogenetic protein 4 (BMP4) signaling. RhoA is a guanosine triphosphatase (GTPase) that regulates cytoskeletal dynamics and gene expression, both of which control stem cell fate. We found that disruption of Syx, a gene encoding a RhoA-specific guanine nucleotide exchange factor, accelerated retinoic acid-induced neural differentiation in murine embryonic stem cells aggregated into embryoid bodies. Cells from Syx(+/+) and Syx(-/-) embryoid bodies had different abundances of proteins implicated in stem cell pluripotency. The differentiation-promoting proteins Noggin and RARγ (a retinoic acid receptor) were more abundant in cells of Syx(-/-) embryoid bodies, whereas the differentiation-suppressing proteins SIRT1 (a protein deacetylase) and the phosphorylated form of SMAD1 (the active form of this transcription factor) were more abundant in cells of Syx(+/+) embryoid bodies. These differences were blocked by the overexpression of constitutively active RhoA, indicating that the abundance of these proteins was maintained, at least in part, by RhoA activity. The peripheral stress fibers in cells from Syx(-/-) embryoid bodies were thinner than those in Syx(+/+) cells. Furthermore, less Noggin and fewer vesicles containing Rab3d, a GTPase that mediates Noggin trafficking, were detected in cells from Syx(-/-) embryoid bodies, which could result from increased Noggin exocytosis. These results suggested that, in addition to inhibiting Noggin transcription, RhoA activity in wild-type murine embryonic stem cells also prevented neural differentiation by limiting Noggin secretion.

RhoA inhibits neural differentiation in murine stem cells through multiple mechanisms.

In this commentary we discuss a paper we published recently on the activities of the GTPase RhoA during neural differentiation of murine embryonic stem cells, and relate our findings to previous studies. We narrate how we found that RhoA impedes neural differentiation by inhibiting the production as well as the secretion of noggin, a soluble factor that antagonizes bone morphogenetic protein. We discuss how the questions we tried to address shaped the study, and how embryonic stem cells isolated from a genetically modified mouse model devoid of Syx, a RhoA-specific guanine exchange factor, were used to address them. We detail several signaling pathways downstream of RhoA that are hindered by the absence of Syx, and obstructed by retinoic acid, resulting in an increase of noggin production; we explain how the lower RhoA activity and, consequently, the sparser peri-junctional stress fibers in Syx(-/-) cells facilitated noggin secretion; and we report unpublished results showing that pharmacological inhibition of RhoA accelerates the neuronal differentiation of human embryonic stem cells. Finally, we identify signaling mechanisms in our recent study that warrant further study, and speculate on the possibility of manipulating RhoA signaling in combination with other pathways to drive the differentiation of neuronal subtypes.

Article	Year
RhoA inhibits neural differentiation in murine stem cells through multiple mechanisms. Science signaling\| PubMed ID: 27460990	2016
The versatility of RhoA activities in neural differentiation. Small GTPases\| PubMed ID: 28125332	2017

Junning Yang

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