|Other Abstract||It is well known that numerous varieties of goldfish originate from wild crucian carp (Carassius auratus) in China. Eye varieties, such as dragon eye, telescope eye, celestial eye, bubble eye, and cinnabar eye, are main types in the current several hundred varieties. In order to research the molecular mechanism, we firstly compared their eye structures.
In comparison with normal eye, the volume of dragon eye ball is larger; the pupil is smaller; the lens is looser and the volume of the lens for the whole eyeball is smaller. The autochthonous layer is defected in the cornea of the dragon eye. There are eight layers of cells in outer nuclear layer and five layers of cells in inner nuclear layer for normal eye, but in dragon eye the outer nuclear layer is so closer to the inner nuclear layer that outer plexiform layer is hard to be recognized, and about five layers in outer nuclear layer and in inner nuclear. The shape of the nucleus near to pigmented epithelium in outer nuclear layer is long-ellipsoid for normal eye, but the shape of all nucleus is globoid for dragon eye. In contrast to the normal eye, the extending of the pigmented epithelium and the outer segments of rod cells and cone cells are arrayed in disorder in the dragon eye. It is no distinct difference between normal eye and dragon eye during morphogenesis, and similar to other vertebrates. After 1 or 2 months old, the eyeball of dragon eye is larger, and the retina and the chorioidea are thinner than that of the normal eye. This characteristic persists for the dragon eye formed. Based on the previous observation, Six3 was localized in normal eye and dragon eye, and Prox1 was localized in the normal eye during their morphogenesis.
The Six family transcription factors are vertebrate homologues of the Drosophila sine oculis gene, which is required for the development of the Drosophila visual system. Dragon eye goldfish is a goldfish with big size eye extruding out of eye-sockets. The Six3 cDNAs from normal eye and dragon eye goldfishes were cloned, and the predicted amino acid sequences are the same, but exhibiting 97.3% identity to the zebrafish Six3b. During the earlier development stages before hatched, the expression pattern of Six3 protein is quite similar in the two types of eye. But for 2 days old larvae, the expression level of Six3 protein began to increase faster in the cytoplasm of the outer nuclear layer cells in dragon eye than that in normal eye, and the trend persists until the eye expanding. In adult dragon eye, Six3 protein was detected not only in the cytoplasm of the outer nuclear layer, inner nuclear layer and ganglion cell layer, but also remarkable in the nucleus of some cells in retina. The data suggested that dragon eye formation might be related to the higher expression of transcription factor Six3.
In vertebrates, Prox1 is a homologous to the Drosophila transcription factor, prospero gene. The expression levels increased as developmental process. Whole-mount in situ hybridization demonstrated that in the eye Prox1 mRNA is first predominately detected in the lens placode at lens stage. Then the Prox1 mRNA is localized in the whole puerile lens cells and retina germinative zone at heartheat stage. After lens fiber forming, it can be detected predominantly in the optic fiber layer and inner plexiform layer. At the same time, the Prox1 protein expression in the lens epithelium is detected by immunofluorescence histochenistry. In adult goldfish, the Prox1 protein is predominately detected in lens fiber in a hemi-ring region under the lens epithelium. In mouse, Prox1 protein expression showed a pattern from outside to inside in the lens, but in goldfish the process is reverse.|