Mitosis is a highly coordinated process that assures the fidelity of chromosome segregation. Errors in this process result in aneuploidy which can lead to cell death or oncogenesis. In this paper we describe a putative mammalian protein kinase, AIM-1 (Aurora and Ipl1-like midbody-associated protein), related to Drosophila Aurora and Saccharomyces cerevisiae Ipl1, both of which are required for chromosome segregation. AIM-1 message and protein accumulate at G 2 /M phase. The protein localizes at the equator of central spindles during late anaphase and at the midbody during telophase and cytokinesis. Overexpression of kinase-inactive AIM-1 disrupts cleavage furrow formation without affecting nuclear division. Furthermore, cytokinesis frequently fails, resulting in cell polyploidy and subsequent cell death. These results strongly suggest that AIM-1 is required for proper progression of cytokinesis in mammalian cells.
A molecular oscillator regulates the pace of vertebrate segmentation. Here, we show that the oscillator (clock) controls cyclic initiation of transcription in the unsegmented presomitic mesoderm (PSM). We identify an evolutionarily conserved 2.3 kb region in the murine Lunatic fringe (Lfng) promoter that drives periodic expression in the PSM. This region includes conserved blocks required for enhancing and repressing cyclic Lfng transcription, and to prevent continued expression in formed somites. We also show that dynamic expression in the cycling PSM is lost in the total absence of Notch signaling, and that Notch signaling acts directly via CBF1/RBP-Jkappa binding sites to regulate Lfng. These results are consistent with a model in which oscillatory Notch signaling underlies the segmentation clock and directly activates and indirectly represses Lfng expression.
Abstract-At the border zone of myocardial infarcts, surviving cardiomyocytes achieve drastic remodeling of cell-cell and cell-extracellular matrix interactions. Spatiotemporal changes in these interactions are likely related to each other and possibly have significant impact on cardiac function. To elucidate the changes, we conducted experimental infarction in rats and performed 3-dimensional analysis of the localization of gap junctions (connexin43), desmosomes (desmoplakin), adherens junctions (cadherin), and integrins ( 1 -integrin) by immunoconfocal microscopy. After myocardial infarction, changes in the distribution of gap junctions, desmosomes, and adherens junctions showed a similar but nonidentical tendency. In the early phase, gap junctions almost disappeared at stumps (longitudinal edges of cardiomyocytes facing the infarct), and, although desmosomes and adherens junctions decreased, they still remained. In the healing phase, at stumps, connexin43, desmoplakin, and cadherin were closely associated between multiple cell processes originating from a single cardiomyocyte. Electron microscopy confirmed the presence of junctional complexes between the cell processes.  1 -Integrin at the cell process increased during the formation of papillary myotendinous junction-like structures. Abnormal localization of connexin43 was often accompanied by desmoplakin and cadherin on lateral surfaces of surviving cardiomyocytes. These findings suggested that remodeling of gap junction distribution was closely linked to changes in desmosomes and adherens junctions and that temporary formation of intracellular junctional complexes was an element of the remodeling of cell-cell and cell-extracellular matrix interactions after myocardial infarction. Moreover, the remodeling of the intercalated disk region at the myocardial interface with area of scar tissues was associated with the acquisition of extracellular matrix and  1 -integrin. (Circ Res. 1999;85:1046-1055.)
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