BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Talks.cam//talks.cam.ac.uk// X-WR-CALNAME:Talks.cam BEGIN:VEVENT SUMMARY:"\;Pathways specifying cell fates in the Drosophila CNS”. - Stefan Thor\, Linkoping University\, Sweden DTSTART:20160307T163000Z DTEND:20160307T180000Z UID:TALK62802@talks.cam.ac.uk CONTACT:Lyn Dakin DESCRIPTION:Baumgardt\, M.\, Miguel-Aliaga\, I.\, Karlsson\, D.\, Ekman\, H.\, Thor\, S. (2007). Specification of neuronal identities by feedforwar d combinatorial coding. PLos Biol 5(2): e37. doi:10.1371/journal.pbio.0050 037.\n\nNeuronal specification is often seen as a multistep process: earli er regulators confer broad neuronal identity and are followed by combinato rial codes specifying neuronal properties unique to specific subtypes. How ever\, it is still unclear whether early regulators are re-deployed in sub type-specific combinatorial codes\, and whether early patterning events ac t to restrict the developmental potential of postmitotic cells. Here\, we use the differential peptidergic fate of two lineage-related peptidergic n eurons in the Drosophila ventral nerve cord to show how\, in a feedforward mechanism\, earlier determinants become critical players in later combina torial codes. Amongst the progeny of neuroblast 5–6 are two peptidergic neurons: one expresses FMRFamide and the other one expresses Nplp1 and the dopamine receptor DopR. We show the HLH gene collier functions at three d ifferent levels to progressively restrict neuronal identity in the 5–6 l ineage. At the final step\, collier is the critical combinatorial factor t hat differentiates two partially overlapping combinatorial codes that defi ne FMRFamide versus Nplp1/DopR identity. Misexpression experiments reveal that both codes can activate neuropeptide gene expression in vast numbers of neurons. Despite their partially overlapping composition\, we find that the codes are remarkably specific\, with each code activating only the pr oper neuropeptide gene. These results indicate that a limited number of re gulators may constitute a potent combinatorial code that dictates unique n euronal cell fate\, and that such codes show a surprising disregard for ma ny global instructive cues.\n\nBaumgardt\, M.\, Karlsson\, D.\, Terriente\ , J.\, Dı´az-Benjumea\, F.J.\, Thor\, S. Neuronal subtype specification within a lineage by opposing temporal feed-forward loops.\ndoi:10.1016/ j. cell.2009.10.032\n\nNeural progenitors generate distinct cell types at dif ferent stages\, but the mechanisms controlling these temporal transitions are poorly understood. In the Drosophila CNS\, a cascade of transcription factors\, the ‘‘temporal gene cascade\,’’ has been identified that acts to alter progenitor competence over time. However\, many CNS lineage s display broad temporal windows\, and it is unclear how broad windows pro gress into subwindows that generate unique cell types. We have addressed t his issue in an identifiable Drosophila CNS lineage and find that a broad castor temporal window is subdivided by two different feed-forward loops\, both of which are triggered by castor itself. The first loop acts to spec ify a unique cell fate\, whereas the second loop suppresses the first loop \, thereby allowing for the generation of alternate cell fates. This mecha nism of temporal and ‘‘subtemporal’’ genes acting in opposing feed -forward loops may be used by many stem cell lineages to generate diversit y.\n\n LOCATION:The Hodgkin Huxley Seminar Room\, Department of Physiology Develo pment and Neuroscience END:VEVENT END:VCALENDAR