Inositol Trisphosphate Mediates a RAS-Independent Response to LET-23 Receptor Tyrosine Kinase Activation in C. elegans

Abstract

Activity of LET-23, the C. elegans homolog of the epidermal growth factor receptor, is required in multiple tissues. RAS activation is necessary and sufficient for certain LET-23 functions. We show that an inositol trisphosphate receptor can act as a RAS-independent, tissue-specific positive effector of LET-23. Moreover, an inositol trisphosphate kinase negatively regulates this transduction pathway. Signals transduced by LET-23 control ovulation through changes in spermathecal dilation, possibly dependent upon calcium release regulated by both IP3 and IP4. Our results demonstrate that one mechanism by which receptor tyrosine kinases can evoke tissue-specific responses is through activation of distinct signal transduction cascades in different tissues.

Regulated Disruption of Inositol 1,4,5-Trisphosphate Signaling inCaenorhabditis elegansReveals New Functions in Feeding and Embryogenesis

“…Substitution of the equivalent residue in the mouse type 1 receptor, R441, by glutamine results in a twofold increase in binding (Yoshikawa et al, 1996), whereas conversion to cysteine produces a fivefold increase in affinity (Hirota, personal communication). This substitution is identical to that found in the gain-of-function allele, itr-1 (sy290) (Clandinin et al, 1998).We confirmed that the IP 3 sponge constructs showed the predicted binding to IP 3 in vitro, by using GST fusion proteins of these binding domains. As Figure 1B shows, the wild-type sponge exhibits properties identical to those reported previously for the ITR-1 IP 3 binding domain (Baylis et al, 1999), whereas the super-sponge construct exhibits an approximately twofold increase in affinity.…”

“…Substitution of the equivalent residue in the mouse type 1 receptor, R441, by glutamine results in a twofold increase in binding (Yoshikawa et al, 1996), whereas conversion to cysteine produces a fivefold increase in affinity (Hirota, personal communication). This substitution is identical to that found in the gain-of-function allele, itr-1 (sy290) (Clandinin et al, 1998).…”

“…Genetic analysis implicates itr-1 in ovulation (Clandinin et al, 1998) and itr-1 is clearly expressed in the spermatheca and uterine sheath cells (Baylis et al, 1999;Dal Santo et al, 1999;Gower et al, 2001). Furthermore, depletion of ITR-1 by RNAi results in the predicted endomitotic (Emo) phenotype (Gower and Baylis, unpublished data).…”

“…This effect may be the result of poor expression from the hsp16-2 promoter in the relevant somatic gonad cells. However, expression of the same sponge constructs under the control of the hsp16-41 promoter (in pPD49.83; Mello and Fine, 1995), which has been used to disrupt ovulation via overexpression of LFE-2 (Clandinin et al, 1998), also had no effect. In addition, inducing expression earlier in development, by commencing heat shock at the first larval stage, had no effect on brood size or ovulation (our unpublished data).…”

Structural components of the nonstriated contractile apparatuses in the Caenorhabditis elegans gonadal myoepithelial sheath and their essential roles for ovulation

“…The rrf-1 mutants are defective with RNAi in the somatic cells but not in the germ cells (Sijen et al, 2001). Thus, if function of an RNAi target is important in the somatic gonad (either sheath contraction [McCarter et al, 1997] or spermathecal dilation [Clandinin et al, 1998;Aono et al, 2004]), ovulation will be defective in wild-type but normal in the rrf-1 background.…”