HOXA2, HOXD1 AND PAX6 IN THE DEVELOPING MURINE BRAIN AND NEURAL RETINA
Our results demonstrate for the first time novel coordinated expression of Hoxa2, Hoxd1 and Pax6 proteins that coincide with the three developmental stages of the diencephalic mouse brain. During the first stage of diencephalic development (embryonic day (E)10-12) Hoxa2, Hoxd1 and Pax6 (an early marker of the diencephalon) were expressed as early as El 0.5 in prosomeres (p), p2 and p3. All three proteins continue to exhibit overlapping domains of expression at the E12.5-13 (beginning of the second stage) when the primitive cell layer begins to differentiate into the internal germinal, external germinal and mantle layers. Towards the end of the second stage (E15), Pax6 expression was down-regulated whereas Hoxa2 and Hoxd1 continued to exhibit overlapping domains of expression for both protein and mRNA. Hoxd1 expression decreased significantly in the third stage of diencephalic development (E16-postnatal) such that only Hoxa2 expression persisted in the diencephalon of newborn mice. The temporal and spatial expression of these three proteins imply that coordinated waves of Hoxa2, Hoxd1 and Pax6 expression may be required to provide positional information for the specification of the diencephalon. We have also used immunohistochemical and in situ hybridization histochemistry to demonstrate novel Hoxa2 gene expression in the pallium and subpallium of the developing telencephalon. Pax6, which is expressed in the pallium and delineates the pallium/subpallium boundary is co-localized with both Hoxa2 and Hoxd1 in the pallium. As development progresses, Hoxa2 expression within the pallium becomes more restricted to the cortical plate of the telencephalon. Analysis of E11.5 Hoxa2-/- embryos exhibits in some embryos loss of the pallium/subpallium boundary, ectopic Pax6 expression within the subpallium, and the subsequent enlargement and positional shift of the medial ganglionic eminence. Furthermore, an up-regulation of Islet 1 , a marker for striatal projection neurons as well as the marker of developing oligodendrocytes, Olig2 was observed in Hoxa2 -/- mutants. Hence, in addition to the prospective role of Hoxa2 in the dorsal-ventral patterning of the telencephalon, these results implicate a role for Hoxa2 in the specification of striatal neurons and oligodendrocytes. Furthermore, immunohistochemistry, in situ hybridization and RT-PCR analysis was also employed to demonstrate novel Hoxa2 expression within the developing and postnatal murine eye. Hoxa2 is initially expressed within the surface ectoderm and proximal portion of the optic vesicle. During embryonic development, Hoxa2 expression continues in the developing lens and within a subset of differentiating retinal cells. In the postnatal retina, Hoxa2 is expressed in the inner region of the inner nuclear layer as well as in the ganglion cell layer, and gradually ceases in the lens as lens fiber cells differentiate and lose their nuclei. Analyses with cell specific markers, revealed expression of Hoxa2 within the ganglion and amacrine neuronal cells.
Hoxa2, Hoxd1, Pax6, diencephalic development
Doctor of Philosophy (Ph.D.)
Pharmacy and Nutrition
Pharmacy and Nutrition