MEC-8 is a nuclear protein that contains two RNA recognition motifs, and is involved in RNA processing [Lundquist et al. (1996) Development 122: 1601-1610]. The initial
mec-8 mutations were identified because they produce touch insensitivity, and we have identified
mec-2 as a target of
mec-8-dependent processing. Wild-type animals express two
mec-2 mRNAs,
mec-2a and
mec-2b;
mec-2a contains 13 exons and encodes a protein of 481 amino acids.
mec-2b is identical to
mec-2a through exon 9 followed by an alternative exon contained in intron 9 and a polyA tail. The splicing of
mec-2 intron 9 is dependent on
mec-8, since
mec-2b mRNA, but not
mec-2a mRNA, is present in
mec-8 animals.
mec-2 is not the only gene whose transcript is processed in a
mec-8-dependent fashion. Touch insensitivity from a
mec-2 null allele, but not from a
mec-8 null allele, is rescued by
mec-2 genomic DNA lacking intron 9. Because the rescue was incomplete, although readily apparent, we do not know if
mec-2b is important for touch receptor function. Inclusion of
mec-2 intron 9 is sufficient to convey
mec-8-dependent regulation. We placed intron 9 before the gfp in a construct driven from the touch cell-specific
mec-18 promoter (Pmec-18intron9::gfp), and obtained fluorescence in wild-type touch receptor neurons, but not in
mec-8 touch neurons. As a further modification, we used a temperature-sensitive allele of
mec-8,
u218, to regulate gene expression in a temperature-dependent manner.
mec-8(
u218); Pmec-18intron9::gfp animals had fluorescent touch receptor neurons at 15<
sym05>C, but not at 25<
sym05>C. Because
mec-8 is expressed in a variety of cells (including several types of neurons and the hypodermis) and is also ubiquitously expressed in the embryo,
mec-8 and
mec-2 intron 9 should produce temperature-sensitive expression for many genes. As a further application of this method, we have produced a strain that has temperature-dependent RNAi, which can be used, for example, to study the function of embryonic lethal genes. To make the strain, we transformed
mec-8(
u218);
rde-1 (
ne219) animals with wild-type
rde-1 genomic DNA in which the
mec-2 intron 9 had been inserted just before the first ATG. The resulting transformants are mutant when grown on bacteria making dsRNA for
unc-22,
unc-52, and
rpl-3 at 15<
sym05>C but not at 25<
sym05>C.