Ras/MAPK modifier loci revealed by eQTL inC. elegans

Abstract

12The oncogenic Ras/MAPK pathway is evolutionary conserved across metazoans and is 13 essential for many cellular functions. Mutant screens in the model nematode Caenorhabditis 14 elegans have been invaluable for elucidating Ras/MAPK pathway characteristics and 15 identification of the genes involved. Almost all of these screens have been conducted in a 16 single genetic background. However, phenotypic traits of induced mutations can vary widely 17 depending on the genetic background. At the moment, we lack insight into how different 18 genetic backgrounds modulate Ras/MAPK-signaling and which genetic modifiers are 19 involved. 20 We previously introduced a gain-of-function mutation in the Ras/MAPK pathway 21 gene let-60 in over 200 recombinant inbred lines (mutant introgressed RILs: miRILs) and 22 detected genetic modifiers affecting this pathway by studying variation in vulval 23 development. In the present study, we investigate how gene expression regulation is affected 24 by the let-60 gain-of-function mutation and the genetic background by mapping eQTL using 25 33 miRILs. We found that the majority (~73%) of the 1516 detected cis-eQTL are not specific 26 for the let-60 mutation, whereas most (~76%) of the 898 detected trans-eQTL are associated 27 with the let-60 mutation. We detected 6 eQTL trans-bands that were specific for the 28 interaction between the genetic background and the mutation. One of these eQTL hotspots co-29 localizes with the previously identified polymorphic Ras/MAPK modifier amx-2. Comparing 30 gene expression profiles between transgenic lines expressing either the N2 or the CB4856 31 alleles of amx-2 showed the involvement of amx-2 in 79% of the trans-eQTLs for genes 32 mapping to this trans-band. 33 Together, our results have revealed hidden loci affecting Ras/MAPK signaling using 34 sensitized backgrounds in C. elegans. These loci harbor putative polymorphic modifier genes 35 that would not have been detected using mutant screens in single genetic backgrounds. 37The Ras/MAPK pathway is highly conserved across metazoans and regulates a wide range of 38 physiological responses, such as cell proliferation, apoptosis, cell differentiation, and tissue 39 morphogenesis (GOKHALE AND SHINGLETON 2015). In humans, activating ("gain-of-40 function") mutations in HRas and KRas are strong tumor initiating mutations (PRIOR AND 41 HANCOCK 2012). Activation of MAP kinase components in model organisms has been shown 42 to cause cell transformation and is implicated in tumorigenesis (COWLEY et al. 1994; 43 MANSOUR et al. 1994). As a key pathway in vertebrates and invertebrates, Ras/MAPK-44 signaling has been thoroughly studied in model organisms. Genetic studies in the model 45 nematode Caenorhabditis elegans have provided insight into let-60 Ras/MAPK signaling. 46 Activated LET-60, a member of the GTP-binding RAS family (BEITEL et al. 1990; HAN AND 47 STERNBERG 1990), induces the phosphorylation of LIN-45 (a Raf ortholog), MEK-2 (a 48 MAPK kinase), and MPK-1 (an ERK ortholog) (WU AND HAN 1994). Af...

Tightly linked antagonistic-effect loci underlie polygenic phenotypic variation inC. elegans

“…If epistasis is systematically suppressive Hansen 2013), then the effects of isolated variants will routinely exceed their effects in their native genetic background. Such a pattern has been observed repeatedly in laboratory mice (Shao et al 2008;Tyler et al 2016), and several experiments have pointed to large stores of normally cryptic epistatic variation in C. elegans that can be exposed by genetic perturbations (Paaby et al 2015;Snoek et al 2017;Sterken et al 2017). Whether by repulsion-phase additive effects or tightly linked epistatic variants, C. elegans harbors a store of variation beyond that exposed by ordinary segregation.…”

Photometric Variability of the mCP Star CS Vir: Evolution of the Rotation Period

“…Accordingly, all errors from the maximum times T , reference maximum time T 0 and period P are considered even if the uncertainties of T 0 and P do not significantly affect the result. On the other hand, based on Sterken (2005), the cycle number E is assumed to be error-free since it has been a function of T . Together with the errors, O-C values are shown in Fig.…”

Developmental fidelity imposed by the RGL-1 “Balanced Switch” mediating opposing signals

“…Vulval development has been used to compare mechanisms of induction across nematode species both closely and distantly related to C. elegans (21)(22)(23)(24). Additionally, VPC fate patterning has been used to assess heterogeneity in polymorphic wild C. elegans isolates (22,25), and also developmental robustness in the face of environmental insult: the VPCs are pattered with 99.8% accuracy (26). But this accuracy is compromised by weak mutations in the signaling network that alter the delicate balance of 1˚ and 2˚ inductive signals (27)(28)(29)(30).…”