Distinct cis-essential modules direct the time-space pattern of the Pax6 gene activity

Pax6 is a regulatory gene with restricted expression and essential functions in the developing eye and pancreas and distinct domains of the CNS. In this study we report the identification of three conserved transcription start sites (P0, P1, alpha) in the murine Pax6 locus. Furthermore, using transgenic mouse technology we localized independent cis-regulatory elements controlling the tissue-specific expression of Pax6. Specifically, a 107-bp enhancer and a 1.1-kb sequence within the 4.6-kb untranslated region upstream of exon 0 are required to mediate Pax6 expression in the lens, cornea, lacrimal gland, conjunctiva, or pancreas, respectively. Another 530-bp enhancer fragment located downstream of the Pax6 translational start site is required for expression in the neural retina, the pigment layer of the retina, and the iris. Finally, a 5-kb fragment located between the promoters P0 and P1 can mediate expression into the dorsal telencephalon, the hindbrain, and the spinal cord. The identified Pax6/cis-essential elements are highly conserved in pufferfish, mouse, and human DNA and contain binding sites for several transcription factors indicative of the cascade of control events. Corresponding regulatory elements from pufferfish are able to mimic the reporter expression in transgenic mice. Thus, the results indicate a structural and functional conservation of the Pax6 regulatory elements in the vertebrate genome.