A pulse of the Hox protein Abdominal-A schedules the end of neural proliferation via neuroblast apoptosis. A.P. Gould 1, F. Hirth 2, B. Bello 1. 1) MRC National Inst Medical Res, London, United Kingdom; 2) Institute of Zoology, Biocenter/Pharmacenter, University of Basel, Switzerland.
Most neurons in the adult CNS are generated during larval and pupal life by the division of postembryonic neuroblasts. Their capacity to divide is modulated along the anterior-posterior body axis, but the mechanism underlying this is unclear. Each neuroblast in the thorax produces approximately one hundred progeny, while in the abdomen clone size is less than fifteen cells. We use clonal analysis of identified precursors in the abdomen to show that neuron production stops because the cell death programme is activated in the neuroblast while it is still engaged in the cell cycle. A burst of expression of the Hox protein Abdominal-A (AbdA) during the third larval instar specifies the time at which apoptosis occurs, thereby determining the final number of progeny that each neuroblast generates. We also show that the resident thoracic Hox proteins share the potential to trigger neuroblast apoptosis in a cell-autonomous manner. However, as these proteins are specifically excluded from the postembryonic neuroblast, precursor divisions are able to continue throughout the larval period. These studies identify a mechanism linking the Hox axial patterning system to neural proliferation, and this involves temporal regulation of precursor cell death rather than the cell cycle.