Hypodermal expression of Caenorhabditis elegans TGF-beta type I receptor SMA-6 is essential for the growth and maintenance of body length.

There are several transforming growth factor-beta (TGF-beta) pathways in the nematode Caenorhabditis elegans. One of these pathways regulates body length and is composed of the ligand DBL-1, serine/threonine protein kinase receptors SMA-6 and DAF-4, and cytoplasmic signaling components SMA-2, SMA-3, and SMA-4. To further examine the molecular mechanisms of body-length regulation in the nematode by the TGF-beta pathway, we examined the regional requirement for the type-I receptor SMA-6. Using a SMA-6::GFP (green fluorescent protein) reporter gene, sma-6 was highly expressed in the hypodermis, unlike the type-II receptor DAF-4, which is reported to be ubiquitously expressed. We then examined the ability of SMA-6 expression in different regions of the C. elegans body to rescue the sma-6 phenotype (small) and found that hypodermal expression of SMA-6 is necessary and sufficient for the growth and maintenance of body length. We also demonstrate that GATA sequences in the sma-6 promoter contribute to the hypodermal expression of sma-6.