Expression pattern of PAX3 and PAX6 genes during human embryogenesis.

The expression of human PAX6 and PAX3 genes was investigated in 6 human 6-9 week old conceptuses by in situ hybridization. During human embryonic development (6-8 developmental weeks), PAX6 was expressed in the ventricular zone of telencephalon and diencephalon, and in the ventricular and ventral intermediate zones of medulla oblongata and spinal cord. PAX6 expression was detected in both layers of the optic cup, optic stalk and prospective corneal epithelium. Infundibulum and Rathke's pouch of the pituitary gland showed hybridization signal as well. In the early fetal period (9 developmental weeks) PAX6 expression increased in the spinal cord. In the eye, hybridization signal characterized the corneal and lens epithelium, pigmented and neural retina, while it was missing in the optic disc and nerve. In a 6-week human embryo, transcripts of PAX3 gene were observed in the ventricular zone at the mesencephalic-rhombencephalic border, and in the dorsal part of the ventricular zone and the roof plate of the medulla oblongata and the spinal cord. In the 8-9-week fetus, PAX3 expression increased in dorsal parts of the spinal cord. PAX3 characterized ectomesenchyme of the upper and lower jaw, and tongue. During early human development, PAX6 and PAX3 genes seem to be involved in the brain regionalization and establishment of dorso-ventral polarity of the spinal cord. Additionally, PAX6 participates in organogenesis of the eye and the pituitary gland, and PAX3 in the development of face and neck mesenchyme.