1. ¹Cell Signaling and Developmental Biology Laboratory, Department of Biological Sciences, National University of Singapore, Singapore
2. ²Molecular Biology Laboratory, Department of Biological Sciences, National University of Singapore, Singapore
3. ³Department of Biological Sciences, National University of Singapore, Singapore
4. ⁴Institute of Molecular and Cell Biology, Singapore

Correspondence: Dr BC Low, Cell Signaling and Developmental Biology Laboratory, Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Singapore. E-mail: dbslowbc@nus.edu.sg

Received 3 April 2007; Revised 7 August 2007; Accepted 7 August 2007; Published online 17 September 2007.

Abstract

RhoA small GTPase, as a key regulator for actin cytoskeletal rearrangement, plays pivotal roles during morphogenesis, cytokinesis, phagocytosis and cell migration, but little is known about its signaling mechanism that controls cell survival in vivo. Using zebrafish as a model, we show that non-overlapping antisense morpholinos that block either translation or splicing of rhoA lead to extensive apoptosis during embryogenesis, resulting in overall reduction of body size and body length. These defects are associated with reduced activation of growth-promoting Erk and decreased expression of anti-apoptotic bcl-2. Moreover, ectopic expression of rhoA, Mek or BCL-2 mRNA rescues such phenotypes. Consistently, combined suppression of RhoA and Mek/Erk or Bcl-2 pathways by sub-optimal dose of rhoA morpholino and pharmacological inhibitors for either Mek (U0126) or Bcl-2 (HA 14-1) can induce developmental abnormalities and enhanced apoptosis, similar to those caused by effective RhoA knockdown. Furthermore, U0126 abrogates the rescue by RhoA and MEK but not BCL-2. In contrast, HA 14-1 effectively abolishes all functional rescues by RhoA, MEK or BCL-2, supporting that RhoA prevents apoptosis by activation of Mek/Erk pathway and requiring Bcl-2. These findings reveal an important genetic and functional relationship between RhoA with Mek/Erk and Bcl-2 for cell survival control during embryogenesis.