A nuclear receptor NHR-25 (a homolog of the Ftz-F1 and SF-1 proteins) functions in developmental processes that involve cell-cell contact, cell motility and asymmetric cell division. The stem epidermal seam cells undergo dynamic cell shape changes and the cell-cell interaction is required for their daughters to properly differentiate. We and others have previously shown that NHR-25 plays a critical role in this epidermal differentiation as seam cell contact is perturbed and extra seam cells arise when NHR-25 function is compromised (Chen et al. 2004, Silhankova et al. 2005). Here, we have generated chromosomally integrated transgenic worms that carry
nhr-25 RNAi construct driven by a seam cell specific promoter. As expected the seam cell differentiation and number was altered. The most frequently affected structure in the transgenic worms was the male tail. In the normal male tail, the lineages of the V5, V6 and T seam cells form nine sensory finger-like rays embedded in a cuticle fan and each ray has a distinct set of unique morphogenetic and molecular features. Homozygous
nhr-25(RNAi) worms exhibited severe Mab (male abnormal) phenotype such as partial tail tip retraction, shrunk fan, ray absence or ray fusion, and almost all rays were affected randomly. Animals heterozygous for
nhr-25(RNAi) showed less severe yet more specific anomalies: absence or displacement of ray 1, absence of ray 2, ray 1-2 or 3-4 fusions, or formation of a tenth ectopic ray. Our data therefore strongly suggest that NHR-25 is required for proper male tail differentiation. Male tail morphogenesis is known to involve several signaling pathways, thus opening an opportunity to further explore the regulatory circuitry of the nuclear receptor signaling. Crosstalk between nuclear receptors and signaling pathways is a great interest as the interaction between NHR-25 and Wnt/<font face=symbol>b</font>-catenin singling have been recently demonstrated in C. elegans gonad (Asahina et al. 2006). This work is supported by grants 204/07/0948 and 524/03/H133 from Czech Science Foundation, 2B06129 from the Czech Ministry of Education, and 50/2006/P-BF from GAJU.