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First published online December 22, 2008
doi: 10.1242/10.1242/dev.028407

Development 136, 173-177 (2009)
Published by The Company of Biologists 2009
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Pushing the frontiers of development

Yohanns Bellaïche1 and Edwin Munro2

1 Institut Curie, CNRS, UMR144, 26 rue d'Ulm, 75248 Paris Cedex 05, France.
2 Center for Cell Dynamics, Friday Harbor Labs, University of Washington, 620 University Road, Friday Harbor, WA 98250, USA.


Figure 1
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  		Fig. 1. Interactions between the temporal factor Notch and the transcription factors Tbx6 and Mesp2 in mouse somitogenesis. (A,B) The presomitic mesoderm of mouse embryos at embryonic day (E) 10.5, with anterior towards the left. Interactions between Notch, Tbx6 (a spatial factor) and Mesp2 iteratively define segmental borders and patterning within developing somites. Mesp2 is proposed to be the final output signal in the conversion from temporal to spatial regulation during somitogenesis. At a stage of this process during which Mesp2 transcription is robust, (A) the expression domain of Mesp2 overlaps with that of the Notch intracellular domain (NICD) (Mesp2 in green, NICD in magenta), and (B) with that of Tbx6 (Mesp2 in magenta, Tbx6 in green), with Tbx6 beginning to be repressed. Reproduced, with permission, from Oginuma et al. (Oginuma et al., 2008Go).

 

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  		Fig. 2. The temporal series regulates neuroblast potential and termination. In Drosophila, multipotent neural progenitors called neuroblasts (NBs) divide asymmetrically to self-renew and to generate progeny that differentiate into neurons and/or glia. A single neuroblast can sequentially express a series of temporal transcription factors such as Hunchback (Hb), Kruppel (Kr), Nubbin (Pdm), Castor (Cas), Seven-up (Svp) and probably others, yet unknown. Progression through this series during development schedules the switch from generating Chinmo+ to Broad-complex+ neurons and also terminates neuroblast division, either via Prospero-dependent cell cycle exit (Type-I neuroblasts) or Abdominal-A dependent apoptosis (Type-II neuroblasts). As neuroblasts progress through the temporal series, their properties alter. For example, indirect feed-forward from an early burst of Cas, mediated via a long-lasting switch from Dichaete to Grainyhead, is necessary for the much-later event of termination. Images courtesy of Cedric Maurange and Alex Gould (NIMR, London, UK).

 

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© The Company of Biologists Ltd 2009