Dynamic patterned expression of orphan nuclear receptor genes RORα and RORβ in developing mouse forebrain

As a step toward using two closely related members of the nuclear receptor family, RORα and RORβ,as markers and tools for genetic manipulations in mouse forebrain, we have used in situ hybridization to analyze their expression from E10.5 to P7. At later embryonic and early postnatal ages, RORα expression in dorsal thalamus is mainly limited to robust expression throughout the principal sensory nuclei. RORβ is expressed in a similar set of dorsal thalamic nuclei as RORα, but exhibits a more limited expression within the principal sensory nuclei. RORα is expressed as early as E12.5 in dorsal thalamus by presumptive ventro-posterior neurons, whereas RORβ expression is not detected until later embryonic ages. RORβ is highly expressed in embryonic neocortex, and exhibits strongly graded rostrocaudal and lateromedial patterns of expression. Over the first postnatal week, the graded expression of RORβ gradually acquires a disjunctive pattern largely restricted to layers 4 and 5 of the primary sensory areas. In contrast, very weak RORα expression is first detected in the neocortex just around birth, and is limited to the middle layer of the cortical plate of the putative somatosensory area. Later, a limited and very weak RORα expression is evident mainly in layer 4 of more caudal areas. To determine whether patterned retinal input is required for the proper postnatal expression and patterning of RORα and RORβ, we performed neonatal bilateral enucleations. We did not detect any significant differences between normal and enucleated mice in expression in visual areas. Although TCA input may be required for proper regulation of the postnatal expression of RORα and RORβ, these findings suggest that aspects of the dynamic postnatal expression and patterning of these genes are regulated independently of patterned visual activity relayed by geniculocortical afferents. The patterned expression of RORα in dorsal thalamus suggests that this gene locus may be useful to genetically modify the development of dorsal thalamus and thalamocortical projections.