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Summary of Hox/Pbx/Meis and temporal control of NB 5–6 development.

The NB 5–6 lineage is generated in all CNS segments, but the genetic pathway leading to Ap cluster formation is only triggered in the NB 5-6T lineages. Three separate mechanisms act to ensure this segment-specific event. 

In abdominal segments, the Pbx/Meis genes hth and exd act with Bx-C Hox genes to truncate the NB 5-6A lineage by triggering neuroblast cell cycle exit within an early temporal (Pdm) window. This occurs prior to generation of Ap cluster cells, and prior to progression into the Cas/Grh late temporal window. 

In thoracic segments, the absence of Bx-C expression in the NB 5-6T neuroblast allows it to progress further and generate a larger lineage, thereby generating the Ap cluster cells. Importantly, this also allows for the lineage to progress into the Cas/Grh late temporal window. Combined with the expression of the thoracic Hox gene Antp, and increasing levels of Hth, this allows for integration of anteroposterior and temporal cues and the specification of Ap cluster cells into Ap cluster neurons, primarily by the activation of the critical Ap cluster determinant col. Grh plays a postmitotic role in specifying the Ap4/FMRFa cell fate. 

In anterior segments, the NB 5–6 lineage, although varying in size when compared to thoracic segments, does contain a Cas window. However, the absence of Antp expression, coupled with weak or absent expression of the late temporal gene grh, prevents specification of Ap cluster neurons.

Figure 12. Journal.pbio.1000368.g012.png


<pubmed>20485487</pubmed>

Citation: Karlsson D, Baumgardt M, Thor S (2010) Segment-Specific Neuronal Subtype Specification by the Integration of Anteroposterior and Temporal Cues. PLoS Biol 8(5): e1000368. doi:10.1371/journal.pbio.1000368

Academic Editor: William A. Harris, University of Cambridge, United Kingdom

Received: October 12, 2009; Accepted: April 1, 2010; Published: May 11, 2010

Copyright: © 2010 Karlsson et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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