Bone morphogenetic proteins (BMPs) promote astrocytic differentiation of cultured subventricular zone stem cells. To determine whether BMPs regulate the astrocytic lineage in vivo, transgenic mice were constructed that overexpress BMP4 under control of the neuron-specific enolase (NSE) promoter. Overexpression of BMP4 was first detectable by Western analysis on embryonic day 16 and persisted into the adult. The overexpression of BMP4 resulted in a remarkable 40% increase in the density of astrocytes in multiple brain regions accompanied by a decrease in the density of oligodendrocytes ranging between 11 and 26%, depending on the brain region and the developmental stage. No changes in neuron numbers or the pattern of myelination were detected, and there were no gross structural abnormalities. Similar phenotypes were observed in three independently derived transgenic lines. Coculture of transgenic neurons with neural progenitor cells significantly enhanced astrocytic lineage commitment by the progenitors; this effect was blocked by the BMP inhibitor Noggin, indicating that the stimulation of astrogliogenesis was due to BMP4 release by the transgenic neurons. These observations suggest that BMP4 directs progenitor cells in vivo to commit to the astrocytic rather than the oligodendroglial lineage. Further, differentiation of radial glial cells into astrocytes was accelerated, suggesting that radial glia were a source of at least some of the supernumerary astrocytes. Therefore, BMPs are likely important mediators of astrocyte development in vivo.

Objective Whether febrile status epilepticus (FSE) produces hippocampal sclerosis (HS) and temporal lobe epilepsy (TLE) has long been debated. Our objective is to determine if FSE produces acute hippocampal injury that evolves to HS. Methods FEBSTAT and two affiliated studies prospectively recruited 226 children aged 1 month to 6 years with FSE and controls with simple febrile seizures. All had acute MRIs and follow-up MRIs were obtained at approximately 1 year later in the majority. Visual interpretation by two neuroradiologists informed only of subject age was augmented by hippocampal volumetrics, analysis of the intra-hippocampal distribution of T2 signal, and apparent diffusion coefficients. Results Hippocampal T2 hyperintensity, maximum in Sommer's sector, occurred acutely after FSE in 22 of 226 children in association with increased volume. Follow-up MRIs obtained on 14 of the 22 with acute T2 hyperintensity showed HS in 10 and reduced hippocampal volume in 12. In contrast, follow-up of 116 children without acute hyperintensity showed abnormal T2 signal in only 1 (following another episode of FSE). Furthermore, compared to controls with simple febrile seizures, FSE subjects with normal acute MRIs had abnormally low right to left hippocampal volume ratios, smaller hippocampi initially and reduced hippocampal growth. Interpretation Hippocampal T2 hyperintensity after FSE represents acute injury often evolving to a radiological appearance of HS after one year. Furthermore, impaired growth of normal appearing hippocampi after FSE suggests subtle injury even in the absence of T2 hyperintensity. Longer follow-up is needed to determine the relationship of these findings to TLE.

This prospective study demonstrates that children with FSE are at risk for acute hippocampal injury and that a substantial number also have abnormalities in hippocampal development. Follow-up studies are in progress to determine the long-term outcomes in these children.

The effects of bone morphogenetic protein (BMP) signaling on enteric neuron development were examined in transgenic mice over expressing either the BMP inhibitor, noggin, or BMP4 under control of the neuron specific enolase (NSE) promoter. Noggin antagonism of BMP signaling increased total numbers of enteric neurons and those of subpopulations derived from precursors that exit the cell cycle early in neurogenesis (serotonin, calretinin, calbindin). In contrast, noggin overexpression decreased numbers of neurons derived from precursors that exit the cell cycle late (γ-aminobutyric acid, tyrosine hydroxylase [TH], dopamine transporter, calcitonin gene related peptide, TrkC). Numbers of TH-and TrkC-expressing neurons were increased by overexpression of BMP4. These observations are consistent with the idea that phenotypic expression in the enteric nervous system (ENS) is determined, in part, by the number of proliferative divisions neuronal precursors undergo before their terminal mitosis. BMP signaling may thus regulate enteric neuronal phenotypic diversity by promoting the exit of precursors from the cell cycle. BMP2 increased the numbers of TH-and TrkC-expressing neurons developing in vitro from immunoselected enteric crest-derived precursors; BMP signaling may thus also specify or promote the development of dopaminergic TrkC/NT-3-dependent neurons. The developmental defects in the ENS of noggin overexpressing mice caused a relatively mild disturbance of motility (irregular rapid transit and increased stool frequency, weight, and water content). Although the function of the gut thus displays a remarkable tolerance for ENS defects, subtle functional abnormalities in motility or secretion may arise when ENS defects short of aganglionosis occur during development.

To determine the role of Bone morphogenetic protein (BMP) signaling in murine limb development in vivo, the keratin 14 promoter was used to drive expression of the BMP antagonist Noggin in transgenic mice. Phosphorylation and nuclear translocation of Smad1/5 were dramatically reduced in limbs of the transgenic animals, confirming the inhibition of BMP signaling. These mice developed extensive limb soft tissue syndactyly and postaxial polydactyly. Apoptosis in the developing limb necrotic zones was reduced with incomplete regression of the interdigital tissue. The postaxial extra digit is also consistent with a role for BMPs in regulating apoptosis. Furthermore, there was persistent expression of Fgf8, suggesting a delay in the regression of the AER. However, Msx1 and Msx2 expression was unchanged in these transgenic mice, implying that induction of these genes is not essential for mediating BMP-induced interdigital apoptosis in mice. These abnormalities were rescued by coexpressing BMP4 under the same promoter in double transgenic mice, suggesting that the limb abnormalities are a direct effect of inhibiting BMP signaling.