Nucleolar protein that acts as a modulator of rRNA synthesis. Plays a central role during organogenesis, including thymus development. Ubiquitously expressed. Death between 8 and 10 dpf due to multiple defects in organogenesis. Thymus primordium fails to accumulate lymphoid cells. The head, the eyes, the liver and the gall bladder are smaller. Pharyngeal arches are abnormally shaped and lower jaws are malformed. In contrast, hematopoiesis and development of the gills and the gut, as well as body axis formation, are not disturbed at 7 dpf. Belongs to the WD repeat WDR55 family.