lag-2 is a member of the Delta/Serrate/LAG-2 (DSL) family of ligands involved mainly in cell fate specification. LIN-12 and GLP-1 are the two Notch receptors identified in C. elegans capable of responding to the LAG-2 signal. During post-embryonic development, Notch signaling has been well characterized in numerous developmental processes while it has recently been implicated in thermotactic behavior. Up to now, no known neuronal function for GLP-1 or LIN-12 has been described in the worm. We noticed that a LAG-2::GFP translational fusion (kindly provided by Judith Kimble) was expressed in 3 pairs of IL-1 neurons in the head region exclusively during dauer and post-dauer development. This suggests that
lag-2 and Notch signaling may be involved in some aspect of dauer development. To test this possibility, we used a dauer constitutive mutation,
daf-7(
e1372), that allowed us to further investigate the function of Notch signaling during the dauer stage. Using a strain that expresses
lag-2 from a transgene (qIs56), we found that dauer formation occurred normally at 25 deg C in a
daf-7 (
e1372ts) background (100%, n=1255). However, 55% of the qIs56;
daf-7 (
e1372) worms recover at restrictive temperature compared to 9% of
daf-7 (
e1372) after 24 hours (~ 6 fold increase).
daf-2, a member of a parallel dauer pathway, is required for this
lag-2 induced recovery since none of the qIs56;
daf-2 (
e1370ts) animals recovered under the same conditions (n=451). Therefore,
lag-2 requires wild type
daf-2 gene product to cause this phenotype. Since extra copies of
lag-2 likely cause this recovery by activating the Notch signaling pathway, we want to confirm if a
lin-12(d) allele (
n302) could phenocopy this effect independent of the LAG-2::GFP transgene. In a different set of experiments, worms carrying an integrated LIN-12 ::GFP (arIs41) transgene (kindly provided by Iva Greenwald) in a
daf-7(
e1372) background also recover to a significantly greater extent then the
daf-7(
e1372) animals (63%, n=154 compare to 9%) . Therefore,
lag-2 likely signals through
lin-12 in order to initiate dauer recovery. We are currently performing antibody staining to determine in which neurons of the head LIN-12 is expressed to support our genetic results. We are also analyzing the promoter region of
lag-2 to determine elements required for its dauer-specific expression. Since this
lin-12 -mediated dauer recovery requires
daf-2 function, we will concentrate on how these two important pathways converge to affect dauer recovery in C. elegans.