The DBL-1 pathway, a BMP/TGF-beta related signaling pathway, regulates body size and male morphology in C. elegans. The major components include: ligand DBL-1; two receptors DAF-4, SMA-6; and three Smad proteins SMA-2, SMA-3, and SMA-4 that form a complex upon signal activation and stimulate target gene transcription. Loss of function of the DBL-1 pathway results in a small body size and an abnormal male tail. The gene
sma-9 encodes a zinc finger transcription factor, and regulates body size and male morphology during early larval stages in the DBL-1 pathway. It may function as a transcriptional cofactor of the Smad complex, as its Drosophila homolog schnurri does in the Dpp/BMP pathway. To investigate whether
sma-9 acts as a transcriptional repressor or activator, the new constructs: transcriptional activity domain of vp-16 (transcriptional activator) or engrailed (transcriptional repressor) linked with
sma-9 DNA binding domain were created. Then, these constructs were introduced to wild type and
sma-9 background animals. The results show that engrailed-
sma-9 (en-
sma-9) but not vp-16-
sma-9 rescued body size and male tail defects. Furthermore, using an in vitro yeast system to perform transcriptional activity assay, we confirmed that
sma-9 N-terminal fragment has the transcriptional repressor activity. These results indicate that
sma-9 functions as a transcriptional repressor in the DBL-1 pathway regulated body size and male morphogenesis. DNA microarray analysis was performed using wild type,
sma-9 and
dbl-1 strains at L2 stages. Genes, whose expression level changes above two fold (p value less than 0.001), were considering having high significance. There are more repressed genes than activated genes in the gene list, which is consistent with the above hypothesis. Meanwhile, more genes were found in
dbl-1 background than in
sma-9 background. Thus,
sma-9 regulates a subset of target genes; there are other transcriptional cofactors required in the DBL-1 pathway. Here we showed the first evidence that transcriptional repressor activity can substitute the normal function of Schnurri proteins in BMP/ TGF-betasignal pathway regulated animal development.