BIRTH TIMES OF NEURONS IN LABELLAR TASTE SENSILLA OF THE BLOWFLY PHORMIA-REGINA

We studied the birth times of neurons of labellar taste sensilla in bl owflies using incorporation of the thymidine analogue 5-bromodeoxyurid ine (BrdU) as an indicator of birth time. We found that one of the two main sensillum types, the taste papillae, arise according to a clear spatial gradient of birth times, whereas the other sensillum type, tas te hairs, arise without any apparent spatial ordering. Within each sen sillum type, there was a strong tendency for either all or none of the neurons to have incorporated BrdU. Among those rare sensilla in which only some of the neurons incorporated BrdU, there were clear patterns of the distribution of labeled and unlabeled neurons per sensillum. T hese results suggest that subsets of the neurons of a sensillum are si blings, and thus argue against the possibility that the several neuron s of a sensillum arise from a single stem cell precursor through repea ted asymmetrical divisions. (C) 1995 John Wiley and Sons, Inc.