In the developing Drosophila embryonic central nervous system (CNS), the pattern of neural stem cells – neuroblasts (NBs) – is highly stereotyped, both between individuals and, in the truncal ventral nerve cord, between segments. Over the past decades, multiple studies have mapped the spatio-temporal origin and gene expression signature of the embryonic NBs in the brain, thorax and abdomen. On p. , Rolf Urbach and colleagues provide the final piece to this puzzle by providing a comprehensive map of the NBs in the gnathal (labial, maxillary and mandibular) segments of the embryo. In doing so, they are able to compare the NBs complement of each segment to identify homologies between NBs in different embryonic origins. Their work demonstrates the progressive loss of NBs from trunk to progressively anterior gnathal segments and analyses its cause. Despite the reduced NB number, homologies in developmental origin and expression pattern are clearly recognisable, and can also be traced into posterior brain segments. The wealth of data in this and related papers provide an essential foundation to understand the molecular and evolutionary basis of segmental diversification of the CNS.
