![]() ![]() Afferent fibers from the thalamus, which will innervate the cortical plate, arrive early, before their target neurons have migrated, and “wait” in the subplate ( Luskin and Shatz, 1985). Two of these, the subplate and marginal zone, contain the earliest-generated neurons of the cortex ( Luskin and Shatz, 1985 Chun et al., 1987), which are largely eliminated in the early postnatal period ( Chun and Shatz, 1989 Woo et al., 1991 Wood et al., 1992). This may represent a novel maternal contribution to fetal neural development and implicates Ig molecules as potential mediators of cortical developmental events.ĭuring fetal development, the mammalian cerebral cortex consists of transient histological zones distinct from those of the adult ( Boulder Committee, 1970). We conclude that maternally derived Ig light chain is present in the fetal murine CNS. In confirmation of this, Ig-ir could be partially reproduced by intraperitoneal injection of pregnant RAG-1 −/− females with normal mouse serum. No Ig-ir was detected in the brains of RAG-1 +/− embryos carried by a −/− female, suggesting a maternal source of the immunoreactive molecule. This result could be replicated with an antiserum specific for Ig κ light chain, but not with antisera specific for Ig γ or μ heavy chain. Western blot analyses of wild-type brains from embryonic day 12 through birth identified a 25 kDa protein that co-migrated with Ig light chain and was absent from RAG-1 or RAG-2 −/− brain samples. In three independently derived mouse strains lacking the recombination activating genes RAG-1 or RAG-2, which are essential for Ig production, Ig-ir was absent from the fetal CNS. Immunohistochemistry using several antisera recognizing IgG revealed intense immunoreactivity in the subplate and marginal zone of embryonic day 16 cortex, as well as in the hindbrain and spinal cord, particularly within ventral fiber tracts. Toward identifying molecules involved in cell–cell interactions during cerebral cortical development, we have investigated the nature of immunoglobulin-like immunoreactivity (Ig-ir) in the murine cortex.
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