PATTERN, TIME OF BIRTH, AND MORPHOGENESIS OF SENSILLUM PROGENITORS INDROSOPHILA

In this paper we describe the spatiotemporal pattern of sensillum prog enitors (SOPs), as well as the way in which these cells segregate from the ectoderm and proliferate. The birthdate of SOPs was determined by applying short heat pulses to embryos carrying the N-intra construct [Struhl et al. (1993), Cell, 74:331-345] which allows the overexpressi on of the active Notch protein at defined developmental stages and the reby eliminates SOPs which would normally segregate during these stage s. Our results show that sensillum progenitors appear in several waves which to some degree respect sensillum modality, as well as dorsovent ral sensillum location. The four early SOPs (stage 10) give rise exclu sively to multiply innervated sensilla, chordotonal organs, and some m ultidendritic neurons. The second wave (early stage 11) produces the r emaining chordotonal organs, some multidendritic neurons, and the dors al singly innervated mechanosensilla. The third wave (late stage 11), in a dorsal-to-ventral succession, gives rise to the lateral and ventr al singly innervated hair and papilla sensilla. Labeling developing SO Ps with specific markers demonstrates that only progenitors of subepid ermally located chordotonal organs and multidendritic neurons delamina te, whereas progenitors of external sensilla are born and proliferate within the ectodermal layer. (C) 1997 Wiley-Liss, Inc.