mir-34 is the founding member of an evolutionarily conserved miRNA family found in diverse species, including humans. Several studies demonstrated that
mir-34 is required for a normal cellular response to DNA damage in vivo resulting in altered cellular survival post-irradiation. To further explore the role of
mir-34 in C. elegans, we have created transgenic lines expressing Pmir-34::gfp to examine the expression pattern at different stages of the animal. In larval stages, Pmir-34::gfp was expressed throughout development in ventral nerve cord, dorsal nerve cord, subsets of head and tail neurons, excretory cell and excretory canal. In adults, Pmir-34::gfp was also detected in vulva and seam cells. Expression was strongly upregulated in dauer larvae, especially in hypodermis, seam cells and amphid neurons. Examination of the reporter expression in
daf-2(insulin receptor),
daf-1(TGF-b receptor) and
daf-7(TGF-b ligand) mutant backgrounds suggests that high
mir-34 expression in dauers is related to the differential gene expression at dauer stage but not to starvation conditions and that
mir-34 expression might be regulated by these signaling pathways. In correlation with its high expression in dauers, 8% of
mir-34(
gk437) formed partial dauers at 27 deg C as compared to 1% in wild type worms, and
mir-34(
gk437) animals showed dauer maintenance defects. DAF-16, the single forkhead box O (FOXO) homologue, functions as the major target of the insulin signaling pathway, which is a determinant of dauer diapause.
daf-16(
mu86);
daf-7(
e1372); Pmir-34::gfp strain, which is dauer constitutive at 25 deg C, lacks the high expression in dauers. Furthermore, GFP expression was seen in the intestine in response to stress conditions (starvation, heat, hypoxia, etc.) in Pmir-34::gfp transgenic lines. This increase, which was also validated by RT-PCR, was more prominent in
daf-16(
mu86) mutants as compared to wild type animals and it was missing in
daf-2(
e1370) mutants. These findings strongly imply the regulation of
mir-34 by insulin signaling pathway.