Deregulated Rac1 Activity in Neural Crest Controls Cell Proliferation, Migration and Differentiation During Midbrain Development

Apurva Gahankari,Garrett Bartoletti,Maria Galazo,Fenglei He,Chunmin Dong

doi:10.3389/fcell.2021.704769

Abstract

Mutations in RAC1 allele are implicated in multiple brain tumors, indicating a rigorous control of Rac1 activity is required for neural tissue normal development and homeostasis. To understand how elevated Rac1 activity affects neural crest cells (NCCs) development, we have generated Rac1CA;Wnt1-Cre2 mice, in which a constitutively active Rac1G12V mutant is expressed specifically in NCCs derivatives. Our results revealed that augmented Rac1 activity leads to enlarged midbrain and altered cell density, accompanied by increased NCCs proliferation rate and misrouted cell migration. Interestingly, our experimental data also showed that elevated Rac1 activity in NCCs disrupts regionalization of dopaminergic neuron progenitors in the ventral midbrain and impairs their differentiation. These findings shed light on the mechanisms of RAC1 mutation correlated brain tumor at the cellular and molecular level.

Highlights

Small GTPases are essential for embryonic development and homeostasis
To examine the role of increased related C3 botulinum toxin substrate 1 (Rac1) activity in neural crest cells (NCCs) development, Rac1CA has been crossed to Wnt1-Cre2 to generate Rac1CA;Wnt1-Cre2 mice (Srinivasan et al, 2009; Lewis et al, 2013)
In Rac1CA;Wnt1-Cre2 mice, we have identified EGFP expression in Rac1CA;Wnt1-Cre2 embryos in the craniofacial mesenchyme, midbrain, and dorsal neural tube at both E10.5 and E13.5 (Figures 1A–F, n = 5 at each stage), in a pattern recapitulated by Wnt1-Cre2 triggered reporter expression in NCC derived cells (Lewis et al, 2013)

Summary

Introduction

Small GTPases are essential for embryonic development and homeostasis. Ras-related C3 botulinum toxin substrate 1 (Rac1), which encodes a small GTPase of the Ras superfamily, is implicated in multiple processes including actin cytoskeleton rearrangement, cell migration, and cell cycle progression (Didsbury et al, 1989; Ridley, 2001; Wittmann et al, 2003; Hall, 2005; Bosco et al, 2009; Hua et al, 2015). Rac protein shuttles between two states, the GTP-bound active state and GDP-bound inactive form. Rac1GTP can be inactivated by GTPase activating proteins (GAPs), which hydrolyze Rac bound GTP to GDP (Jaffe and Hall, 2005). GEFs and GAPs recognize and bind to specific amino acids of Rac and modulate its activity. Mutation in these amino acids causes deregulated Rac activity. G12V mutation of Rac impairs its interaction with GAP, and causes its constitutive activation in a Rac1-GTP form (Kobayashi et al, 1998). Mutation in RAC1 and its regulators have been implicated in abnormal development and tumorigenesis (Khalil and El-Sibai, 2012). The mechanisms underlying excessive Rac activity in regulation of neuronal tissues and brain development have not been fully elucidated

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