Semaphorin-3D (Sema3D) is a secreted semaphorin expressed during the development of the nervous system []. In zebrafish, Sema3D is expressed in the ventral tectum []. It guides retinal axons along the dorsoventral axis of the tectum and guides the laterality of retinal ganglion cell (RGC) projections. Both Sema3D knockdown or its ubiquitous overexpression induced aberrant ipsilateral projections. Proper balance of Sema3D is needed at the midline for the progression of RGC axons from the chiasm midline into the contralateral optic tract []. Sema3D is a member of the class 3 semaphorin family of proteins. Semaphorins are regulatory molecules in the development of the nervous system and in axonal guidance. They also play important roles in other biological processes, such as angiogenesis, immune regulation, respiration systems and cancer [, ]. The Sema domain is located at the N terminus and contains four disulfide bonds formed by eight conserved cysteine residues. It serves as a receptor-recognition and -binding module.
