Yeast two-hybrid system identifies the ubiquitin-conjugating enzyme mUbc9 as a potential partner of mouse Dac

Using a yeast two hybrid system and pull-down assays we demonstrate that mouse Dac (mDac) specifically binds to mouse ubiquitin-conjugating enzyme mUbc9. In contrast to a direct interaction between Drosophila dachshund (dac) and eyes absent (eya)gene products, we cannot detect by the same methods that mDac binds to mEya2, a functional mouse homologue of the Drosophila Eya. Immunostaining of various cell lines that were transfected with mDac reveals that mDac protein is found predominantly in the nucleus but translocates to the cytoplasm and condensates along the nuclear membrane in a cell-cycle dependent manner. Deletion analysis of mDac show the intracellular localization and protein stability correlates with the binding to mUbc9. The C-terminal half of mDac, which associates with mUbc9, remains cytoplasmic and is degraded in proteasome whereas the non-interacting N-terminus is exclusively nuclear and more stable than the full-length mDac or its C-terminal portion. In situ hybridization on whole-mount embryos or tissue sections detects mUbc9 transcripts in complementary and overlapping areas with mDac expression, particularly in the proliferation zone of the limb buds, the spinal cord and forebrain. Mouse embryos stained with an anti-mDac antibody document that mDac is localized both in the nucleus and the cytoplasm with a cytoplasmic predominance in migrating neural crest cells. In the proliferation zone, visible nuclear envelopes are not formed and mDac is detected throughout the cells.