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 deve lopment (6-8 developmental weeks), PAX6 was expressed in the ventricular zo ne of telencephalon and diencephalon, and in the ventricular and ventral in termediate zones of medulla oblongata and spinal cord. PAX6 expression was detected in both layers of the optic cup, optic stalk and prospective corne al epithelium. Infundibulum and Rathke's pouch of the pituitary gland showe d hybridization signal as well. In the early fetal period (9 developmental weeks) PAX6 expression increased in the spinal cord. In the eye, hybridizat ion signal characterized the corneal and lens epithelium, pigmented and neu ral retina, while it was missing in the optic disc and nerve. In a 6-week h uman 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 spina l cord. In the 8-9-week fetus, PAX3 expression increased in dorsal parts of the spinal cord. PAX3 characterized ectomesenchyme of the upper and tower jaw, and tongue. During early human development, PAX6 and PAX3 genes seem t o be involved in the brain regionalization and establishment of dorso-ventr al polarity of the spinal cord. Additionally, PAX6 participates in organoge nesis of the eye and the pituitary gland, and PAX3 in the development of fa ce and neck mesenchyme.