The influx of calcium into the postsynaptic neuron is likely to be an important event in memory formation. Among the mechanisms that nerve cells may use to alter the time course or size of a spike of intracellular calcium are cytosolic calcium binding or "buffering" proteins. To consider the role in memory formation of one of these proteins, calbindin D28K, which is abundant in many neurons, including the CAl pyramidal cells of the hippocampus, transgenic mice deficient in calbindin D28K have been created. These mice show selective impairments in spatial learning paradigms and fail to maintain long-term potentiation. These results suggest a role for calbindin D28K protein in temporally extending a neuronal calcium signal, allowing the activation of calciumdependent intracellular signaling pathways underlying memory function.

No abstract

We have established the complete coding sequence of the human vimentin gene. It had 91% homology to the coding sequence of the Syrian hamster vimentin gene (Quax et al., Cell 35:215-223, 1983)

Mesoangioblasts are vessel-derived stem cells that can be induced to differentiate into different cell types of the mesoderm such as muscle and bone. The gene expression profile of four clonal derived lines of mesoangioblasts was determined by DNA micro-array analysis: it was similar in the four lines but different from 10T1/2 embryonic fibroblasts, used as comparison. Many known genes expressed by mesoangioblasts belong to response pathways to developmental signalling molecules, such as Wnt or TGFβ/BMP. Interestingly, mesoangioblasts express receptors of the TGFβ/BMP family and several Smads and, accordingly, differentiate very efficiently into smooth muscle cells in response to TGFβ and into osteoblasts in response to BMP. In addition, insulin signalling promotes adipogenic differentiation, possibly through the activation of IGF-R. Several Wnts and Frizzled, Dishevelled and Tcfs are expressed, suggesting the existence of an autocrine loop for proliferation and indeed, forced expression of Frzb-1 inhibits cell division. Mesoangioblasts also express many neuro-ectodermal genes and yet undergo only abortive neurogenesis, even after forced expression of neurogenin 1 or 2, MASH or NeuroD. Finally, mesoangioblasts express several pro-inflammatory genes, cytokines and cytokine receptors, which may explain their ability to be recruited by tissue inflammation. Our data define a unique phenotype for mesoangioblasts, explain several of their biological features and set the basis for future functional studies on the role of these cells in tissue histogenesis and repair.

The Myocyte Enhancer Factor 2C (MEF2C) transcription factor plays a critical role in skeletal muscle differentiation, promoting muscle-specific gene transcription. Here we report that in proliferating cells MEF2C is degraded in mitosis by the Anaphase Promoting Complex/Cyclosome (APC/C) and that this downregulation is necessary for an efficient progression of the cell cycle. We show that this mechanism of degradation requires the presence on MEF2C of a D-box (R-X-X-L) and 2 phospho-motifs, pSer98 and pSer110. Both the D-box and pSer110 motifs are encoded by the ubiquitous alternate a1 exon. These two domains mediate the interaction between MEF2C and CDC20, a co-activator of APC/C. We further report that in myoblasts, MEF2C regulates the expression of G2/M checkpoint genes (14-3-3g, Gadd45b and p21) and the sub-cellular localization of CYCLIN B1. The importance of controlling MEF2C levels during the cell cycle is reinforced by the observation that modulation of its expression affects the proliferation rate of colon cancer cells. Our findings show that beside the well-established role as pro-myogenic transcription factor, MEF2C can also function as a regulator of cell proliferation.