| STAT proteins are latent transcription factors activated by tyrosine phosphorylation in response to extracellular signals and have been identified in a variety of organisms, including a single orthologue in C. elegans. I cloned the nematode orthologue of mammalian STATs and characterized its expression pattern. It encodes a protein of 82KD that contains a DNA binding domain, SH2 domain, and site for tyrosine phosphorylation conserved with its mammalian counterparts. Surprisingly, ceSTAT does not contain an N-terminal domain that is highly conserved among mammalian STATs as well as in Drosophila STAT. Using Tc1 transposon mediated reverse genetics, we isolated a ceSTAT mutant that has a 2.1 kb deletion in the gene, resulting in complete loss of full length protein expression. The genetic background of the mutant was cleaned by 10 to 12 outcrossings to Bristol N2 strain.;Immunohistochemistry using affinity-purified rabbit antibody against the endogenous protein showed a staining pattern similar to the expression of a promoter-GFP transgenic line. Confocal microscopy revealed constitutive nuclear staining pattern in a few neuronal cells in the posterior head ganglia in wildtype N2 strain cultured under normal laboratory condition. This pattern suggests that ceSTAT is constitutively active in a subset of amphid neurons, that was lost in mutant worms. Independent mRNA samples were prepared from synchronized young adult wildtype and ceSTAT null worms, growing under normal laboratory conditions. Genome wide gene expression patterns were compared using the Stanford DNA chip, which contains 17,871 genes, representing about 94% of the 18,967 genes currently annotated in the C. elegans genome. Data sets from six chips were analyzed. With p < 0.05, there are about 60 genes which are downregulated more than two fold in ceSTAT knockout worms compared to wildtype worms, whereas there are about 110 genes which are upregulated more than two fold in the same comparison. The fact that there are twice more upregulated as downregulated genes is surprising, since STATs are generally considered to transcription activator, not inhibitors. Further studies using C. elegans model system should provide more evidence on the role of STAT in gene regulation. |
