S100 calcium binding proteins have long been known to express in the adult nervous system, but their distribution in the developing brain, especially the human fetal brain, is largely unknown. We used an immunohistochemical method to determine the expression of three S100 proteins, namely S100A4, S100A5, and S100A13, in the human fetal hippocampus and temporal cortex from 12 to 33 weeks of gestation. At 12 weeks, S100A5 was strongly expressed in the cells and fibers of the polymorphic, pyramidal, and molecular layers of the hippocampus. Thereafter, its expression decreased with age. In the temporal cortex, S100A5 expression was detected from 12 weeks onwards, peaked at 20 to 24 weeks, and then decreased with age. The horizontal fibers of the marginal zone were immunoreactive at all stages examined. S100A13 immunoreactivity was also detected in both cells and fibers of the hippocampus at 12 weeks, became slightly stronger at 20 weeks, and then decreased with age. In the temporal cortex, S100A13 immunoreactivity was also strong in all cellular layers at 12 to 24 weeks before it declined with age from 28 weeks onwards. Among the three proteins examined, S100A4 showed the weakest expression, which was detected in the cells and fibers of the hippocampus and the temporal cortex at all stages examined. Our results have demonstrated for the first time, in the human fetal hippocampus and temporal cortex, specific spatio-temporal patterns of expression of these proteins, all of which are likely to have different roles to play during development despite their pronounced sequence homology.

No abstract

Nuclear factor-kappa B (NF-ĸB) is a transcription factor, which is ubiquitously distributed in the adult nervous system and is thought to be crucially involved in the neuronal and glial functions. However, during development, the spatiotemporal expression pattern of NF-ĸB has not been well characterized, especially in developing primates and humans. In the present study, we used an immunohistochemical method to determine the distribution of NF-ĸB in the developing rhesus monkey (Macaca mulatta) brain at different developmental stages. Immunoreactive products were not observed at 25 days of pregnancy but were detected at 40 days mainly in the perinuclear region, and then, gradually more positive signals were found inside the nucleus of cells in different brain regions. At this stage, when various primitive brain structures had just started to form, a low level of immunoreactivity was detected in the presumptive areas of the thalamus, hypothalamus, caudate nucleus and parietal cortex. The immunoreactive cells were scattered and large, usually with a prominent nucleus. In the developing choroid plexus, moderate immunoreactivity was observed in the epithelial lining of the ventricle and also in the underlying mesenchymal tissues. By 55 days, immunoreactivity became stronger, and brain regions were more easily identified. Both the number of the immunoreactive cells and the intensity of positive signals were increased, and cells were more differentiated. Some of these cells extended cytoplasmic processes. Positive cells were also scattered without any specific pattern of distribution in all the brain regions examined. The columnar epithelium of the choroid plexus showed intense immunoreactivity. Our findings show that NF-ĸB starts to express in many regions of the early developing monkey brain, and the immunoreactivity of NF-ĸB increases with time.