Spatial and temporal patterns of expression of Noggin and BMP4 in embryonic and postnatal rat hippocampus

Recent studies indicate that bone morphogenetic protein-4 (BMP4) and Noggin not only play an important role in the early development of the nervous system, but may also play a role in postnatal central nervous system (CNS) development. In this study, we examined the relative levels and localization of Noggin and BMP4 mRNA in the hippocampus of rats of different developmental stages with reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization (ISH). RT-PCR showed that the temporal changes in the levels of expression of Noggin and BMP4 were different. The peak level of expression of Noggin mRNA was observed at embryonic day 13 (E13), subsequently gradually declined at 1-3 months (P1-3M) postnatal, and was detected only at a low level at P18M. In contrast, the expression of BMP4 mRNA increased gradually during embryonic development, reached a maximal level at 3 weeks (W) postnatal, and declined only slightly through P18M. In situ hybridization revealed that at embryonic stages, Noggin mRNA was localized throughout all hippocampal regions, whereas at early postnatal ages, Noggin mRNA was primarily localized in the anterior subiculum. At embryonic and early postnatal stages, no significant BMP4 mRNA expression was detectable in the hippocampus. At later postnatal ages, however, Noggin and BMP4 mRNA expression was observed in similar patterns. At 1-3 months postnatal, expression of BMP4 was observed mainly in the dentate gyrus and in the CA1-CA3 pyramidal cell layers. Lower hybridization signals were observed in the hilus and subiculum. Taken together, our results demonstrate that Noggin and BMP4 are expressed in embryonic and postnatal hippocampus, and that the temporal and spatial patterns of their expression are developmentally regulated. These data suggest that Noggin and BMP4 play important roles in hippocampal development.