EARLY EYE MORPHOGENESIS IN THE ZEBRAFISH, BRACHYDANIO-RERIO

Early eye morphogenesis in the zebrafish between 12 and 36 hours postf ertilization was studied by light- and scanning electron microscopy. O verall, early eye morphogenesis in the zebrafish is similar to that of other vertebrates even though the optic primordia evaginate from the forebrain as solid masses of cells. After initial evagination (6-7 som ite stage [SS]), the optic primordia take on a wing-like shape (8-9 SS ). Subsequently, they bend ventrally and rotate slightly in an anterio r direction (10-12 SS). These changes serve to bring the primordia fro m a horizontal to a more vertical orientation in relation to the embry onic neural axis. Invagination commences from the center of each primo rdium (14 SS) and progresses symmetrically out towards the periphery ( 14-20 SS). The choroid fissure forms by an involution along the anteri or region of the eyecup (18-20 SS). By 24 hours postfertilization (pf) the eyecups are well formed. Between 24 and 36 hours pf, the eyes rot ate further in relation to the axis of the embryo, and this reposition s the choroid fissue to a typical ventral location by 36 hours pf. Bec ause of the two rotations of the eye during early morphogenesis, parti cularly the later one, the anterior-posterior orientation of the emerg ing optic primordium ultimately becomes the ventral-dorsalaxis of the completed eyecup. (C) 1994 WiIey-Liss, Inc.