We describe the expression pattern of cSix3, a chick homologue of the murine Six3. cSix3 transcripts are expressed from presomitic stages in the most anterior portion of the neural plate. As the neural tube folds and the optic vesicles evaginate, cSix3 is expressed in the optic vesicle and the rostroventral forebrain. At later stages, cSix3 is found in most of the structures derived from the anterior neural plate, i.e. olfactory epithelium, septum, adenohypophysis, hypothalamus and preoptic areas. During eye development, cSix3 expression is first found in the entire optic vesicle and the overlying ectoderm but soon becomes restricted to the prospective neural retina and to the lens placode. In the developing neural retina, cSix3 is expressed in the entire undifferentiated neuroepithelium but is rapidly downregulated, first in the postmitotic photoreceptors and later in the majority of retinal ganglion cells.
