DNA fragments from the promoter region of the C. elegans UL6 gene which are capable of functioning as promoters directing gene expression in the excretory cell of C. elegans are provided and also expression vectors and transgenic C. elegans containing these fragments. Also provided are screening methods performed in C. elegans for identifying compounds or mutations which have an affect on the morphology of the excretory canal. Compounds identified using these screening methods may have therapeutic potential in the treatment of a range of diseases for which the C. elegans excretory canal serves as a model.