Differential expression of methyl CpG-binding domain containing factor MBD3 in the developing and adult rat brain

Using subtractive hybridization screening, the methyl CpG-binding domain containing protein MBD3 was identified as being more prevalently expressed in the embryonic brain than in the adult. In this report, we present the mRNA and protein expression patterns of MBD3 in the developing brain. MBD3 expression was detected in neuroepithelial cells of the developing forebrain, and in peripheral tissues such as liver and intestine during late embryogenesis. This is in contrast to its related family member MBD2, which displayed only minimal expression in the embryonic brain. Immunoblot analysis revealed that the levels of both MBD3 splice forms decrease in the maturing postnatal hippocampus and cortex, although the two forms do not decline at equivalent rates. Immunohistochemical analysis revealed strong MBD3 immunostaining in principal neurons of the hippocampus and cortex, but weak or nondetectable immunostaining in outer cortical layer cells. MBD3 was also selectively expressed in the adult retina, where strong immunoreactivity was detected in cells of the inner nuclear and ganglion cell layers, but no immunoreactivity was detected in cells of the outer nuclear layer. Taken together, these results illustrate that MBD3 displays a selective spatial and temporal pattern of expression in the embryonic and adult brain, thereby strengthening the possibility of MBD3 playing an important role in neuronal development.