Regulation of Somitogenesis by Calcium Signaling

University Of Missouri-Kansas City, Columbia MO

Investigators

Abstract

0091174 Ferrari This project will test the general hypothesis that calcium (Ca 2+ ) transients within the presomitic mesoderm (PSM) and forming somites are necessary for somitogenesis (SMG). The specific aims are to 1) determine if somite formation is directed by Ca 2+ transients and, 2) examine the relationship between somitogenic gene expression and Ca 2+ transients. The morphogenetic movements which produce somites have been described, but the cellular control mechanisms have remained elusive. However, recent observations indicate that several genes are expressed with spatiotemporal patterns corresponding to somite formation. For example, the bHLH transcription factor c-hairy-1, a pair-rule segmentation gene, is transcribed such that the time for a single oscillation equals the time to form one somite. These patterns have generated much excitement, as they are consistent with theoretical models based on a clock and wave somite formation mechanism. However, the biochemical or molecular nature of this segmentation clock remains unknown. This proposal will test the hypothesis that Ca 2+ transients may form part of the clock mechanism and/or serve to entrain cell populations via intercellular Ca 2+ waves. Ca 2+ signaling appears to play an important role in SMG. In both zebrafish and Xenopus, a high degree of Ca 2+ transient activity exists in the PSM and forming somites, and when this activity is blocked SMG is disrupted. Since somites are produced with high regularity, significant correlations between this process and Ca 2+ signals are possible. This regular patterning allows even subtle defects to be detected after experimental manipulation of Ca 2+ signaling. A large array of fluorescent compounds exist for observing and modulating both intra- and intercellular Ca 2+ signals. These fluoroprobes are used in conjunction with high-resolution fluorescence microscopy of living Xenopus embryos and explants. Of particular utility are a number of caged compounds, which can be photoactivated with temporal and spatial specificity to control Ca 2+ dynamics. Using these compounds, experiments are planned to determine if transients are part of an epigenetic signaling pathway responsible for somite patterning. For example, transients will be inhibited in specific regions of the PSM by photoreleasing BAPTA, a high affinty Ca 2+ chelator. These regions will then be examined for the ability to form somites and produce the correct pattern of somitogenic gene expression. The proposed work may further our understanding of how epigenetic signals can control and modify morphogenetic events.