The body size determination is one of the most fundamental aspects of development but its mechanism remains to be largely unknown. A mutant
gig-1 (
ks16 ) with a body volume of up to twice in adults was isolated previously in our laboratory by Ikue Mori. To elucidate the mechanism of body size determination, we have analyzed this mutant. The
gig-1 is grossly normal in morphology and growths except for weak egg-laying defects, dark intestine and low male mating efficiency. We have mapped
ks16 mutation to a region that is about 50 kbp on the left arm of chromosome IV using single nucleotide polymorphorisms between N2 and CB4856. This region contains a single gene, F55A8.2 encoding a cGMP-dependent kinase (PKG) of 780 amino acids. We were able to rescue the phenotypes with a YAC encoding the PKG and identified a nonsense mutation in this mutant.
ks16 map position was near that of
egl-4 . Both
egl-4 and
ks16 show similar phenotypes, such as egg-laying defects and large body volume. We were not able to complement
egl-4 (
n477 ) with
ks16 , and found missense (
n478 and
n612 ) and frameshift (
n477 ) mutations in the PKG gene of
egl-4 mutants. These results suggest that
gig-1 gene encodes PKG and is the same gene as
egl-4 . The PKG gene have two different start codons; the upstream one for PKGa and the downstream one for PKGb. PKGa is predicted to contain a glycine rich region, a cyclic nucleotide binding domain, and a kinase domain that is highly conserved in Drosophila and human with about 55 % amino acid identity. GFP fused with PKGa promoter was predominantly expressed in many head neurons and hypodermis except for seam cells, while GFP fused with PKGb promoter was expressed in body wall muscles. To investigate PKG function in detail, we produced an anti-PKG antibody that specifically recognizes an 80 KDa protein in a C. elegans lysate. Recently, it was suggested that TGF-b pathway is involved in body size determination, and it was reported that some phenotypes of
egl-4 are suppressed by
daf-3 which is a component of TGF-b pathway (Daniels et. al ., Genetics 156, 123-141, 2000). It is also shown that insulin-like growth factor (IGF) transduces signals that positively regulate growth in Drosophila and mammals. In body size determination, cGMP signaling might crosstalk with TGF-b and IGF pathways. We are trying to analyze the functions of PKG to address the mechanisms of body size determination.