RT Journal Article
SR Electronic
T1 Developmental fidelity imposed by the RGL-1 “Balanced Switch” mediating opposing signals
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 381012
DO 10.1101/381012
A1 Hanna Shin
A1 Christian Braendle
A1 Kimberly B. Monahan
A1 Rebecca E.W. Kaplan
A1 Tanya P. Zand
A1 F. Sefakor Mote
A1 DeSean R. Craig
A1 Eldon Peters
A1 David J. Reiner
YR 2018
UL http://biorxiv.org/content/early/2018/07/31/381012.abstract
AB The six C. elegans vulval precursor cells (VPCs) are induced to form the 30-30-20-Γ-20-3° pattern of cell fates with high fidelity. In response to EGF signal, the LET-60/Ras-LIN-45/Raf-MEK-2/MEK-MPK-1/ERK canonical MAP kinase cascade is necessary to induce 1° fate and synthesis of DSL ligands. In turn, LIN-12/Notch signal is necessary to induce neighboring cells to become 2°. We previously showed that, in response to lower dose of EGF signal, the modulatory LET-60/Ras-RGL-1/RalGEF-RAL-1/Ral signal promotes 2° fate in support of LIN-12. In this study we identify two key differences between RGL-1 and RAL-1 functions. First, deletion of RGL-1 confers no overt developmental defects, while previous studies showed RAL-1 to be essential for viability and fertility. From this observation we hypothesize that the developmentally essential functions of RAL-1 are independent of upstream activation. Second, RGL-1 plays opposing and genetically separable roles in VPC fate patterning. RGL-1 promotes 2° fate via canonical GEF-dependent activation of RAL-1 and 1° fate via a non-canonical GEF-independent activity. Our genetic epistasis experiments are consistent with RGL-1 functioning in the modulatory 1°-promoting AGE-1/PI3-Kinase-PDK-1-AKT-1 cascade. Additionally, animals without RGL-1 experience 15-fold higher rates of VPC patterning errors compared to the wild type. Yet VPC patterning in RGL-1 deletion mutants is not more sensitive to environmental perturbations. We propose that RGL-1 functions as a “Balanced Switch” that orchestrates opposing 1°- and 2°-promoting modulatory cascades to decrease inappropriate fate decisions. We speculate that such switches are broadly conserved but mostly masked by paralog redundancy or essential genes.