Cloning of mouse ojoplano, a reticular cytoplasmic protein expressed during embryonic development

Ojoplano ( Opo) is a morphogenetic gene playing an important role during embryogenesis in medaka. This report focuses on the identification and characterization of the mouse Opo gene. We examined Opo expression by whole-mount in situ hybridization and in situ hybridization on sagittal sections during mouse embryogenesis. First expression in whole-mounts was detected at Theiler stages 15–17 (E 9.5–10.5 dpc) as a spotted specific staining in migrating neural crest cells and in placodal structures. A complex expression pattern was observed in Theiler stage 22–23 (E 14.5 dpc) in sagittal sections, including expression in skeletal structures (skull, vertebrae, ribs, bones of the locomotor system), in the nasal region, the heart and the eye. Fusion proteins revealed the localization of OPO within the cytoplasm with a reticular distribution that largely overlapped with the endoplasmic reticulum. Opo shows homology to human transcripts linked to a hereditary craniofacial malformation, orofacial cleft 1 ( OFC1). The expression of mouse Opo in neural crest derivatives and skull elements further supports this link.