['The YPEL (Yippee-like) gene family comprises five highly conserved members (YPEL1-5), but their biological function remains largely unknown. Early studies of YPEL1 function suggested that it plays a role in the development of structures derived from the pharyngeal arches. Human YPEL1 localises to distal chromosome 22q11.2 and copy number changes at this locus lead to diverse phenotypes that include facial dysmorphism, facial asymmetry, and palatal anomalies comprising the distal 22q11.2 deletion/duplication syndromes (OMIM 611867). We therefore investigated the role of chick YPEL1 in craniofacial development using ex vivo and in vivo approaches in the avian model.', 'We found that retroviral-mediated in vivo overexpression of YPEL1 causes abnormal mandibular morphogenesis associated with increased apoptosis and involvement of the BMP/MSX pathway.'] Does yPEL1 overexpression in early avian craniofacial mesenchyme cause mandibular dysmorphogenesis by up-regulating apoptosis?