NB 3-3 Details
videos
NB 3-3 delaminates at S4 in an intermediate column of NBs.
No information about the NB 3-3 lineage is available from other insects.
NB 3-3 expresses castor (cas) and eagle (egl) as it forms, adding seven-up-lacZ (svp) and Klumpfuss (Klu) at S5 (Cui and Doe, 1992, 1995; Higashijima et al, 1996; Broadus et al, 1995; Yang et al, 1997). By S5, muscle-specific homeobox gene 1 (msh) can be faintly detected in NB 3-3, as well as in NB 3-5, although this appears not to be due to de novo msh expression, but to residual expression from its synthesis in the neurectodermal progenitor from which the NB derives (T. Isshiki, personal communication). A recent paper reports NB 3-3 to be runt-positive at S4, and throughout the rest of neurogenesis (Dormand and Brand, 1998). The lineage in Drosophila was partially described by Higashijima et al. (1994) who showed that an eagle-kinesin-lacZ gene expressed in NB 3-3 revealed a cluster of interneurons that projected across the anterior commissure. These data were confirmed by DiI labeling of NB 3-3 (Schmidt et al., 1997), who document 10-13 interneurons with similar projections. Both studies show that the lateral even-skipped-positive (EL) cells come from this lineage, but neither study detected a motoneuron in the clone.
A. Motoneurons:
In 2 out of 3 abdominal clones, we detect a single oval motoneuron (6.4 x 5 um) positioned midway along the dorsoventral extent of the clone, but displaced slightly laterally and posteriorly; it projects out the SNa and forms a distinctive, robust synapse on muscle 5. The NB 3-3 derived motoneuron forms only in abdominal segments, and its muscle 5 target also forms only in abdominal segments. Cash et al. (1992) and Landgraf et al. (1997) both describe muscles 5 and 8 as being innervated by a single motoneuron that exits the CNS via SNa, but did not identify the clonal origin of this motoneuron. The neuron these groups describe matches the motoneuron we find in this lineage, both in the position of its cell body within the hemisegment and in the pattern of its neurite extensions (Fig. 3-3). However, it does not innervate muscle 8. We find muscle 8 to be innervated by an abdominal 2-4 derived motoneuron and a thoracic NB 5-3 derived motoneuron (Figs. 2-4, 5-3).
B. Interneurons:
At stage 17 we observe at least 3 intersegmental interneurons that project across the anterior commissure and then turn anteriorly in an intermediate fascicle of the contralateral connective. Two of these interneurons are distinctive egg-shaped cells lying at the medial side of the clone; just lateral to this pair are as many as 8 additional large round cells (5.4 um; n=12). The number of local interneurons is variable, ranging from 4-10 at stage 17. They are small (3.2 um; n=5) and project across the midline in the anterior commissure before extending anteriorly to the segment boundary. We could often detect more than ten loosely-bundled axons. Every NB 3-3 clone contained DiI-labeled cellular debris associated with cell death; in addition, there was always a large droplet of DiI at the lateral extent of the CNS (asterisks in Fig 3-3) that appeared to be a dying cell.
References:
Broadus, J., Skeath, J.B., Spana, E. P., Bossing, T., Technau, G.M., and Doe, C.Q. (1995). New neuroblast markers and the origin of the aCC/pCC neurons in the Drosophila central nervous system. Mech Dev 53: 393-402.
Cash, S., Chiba, A., and Keshishian, H. S. (1992). Alternate neuromuscular target selection following the loss of single muscle fibers in Drosophila. J. Neurosci 12(6): 2051-64.
Cui, X., and Doe, C.Q. (1992). ming is expressed in neuroblast sublineages and regulates gene expression in the Drosophila central nervous system. Development 116(4): 943-52.
Cui, X., and Doe, C.Q. (1995). The role of the cell cycle and cytokinesis in regulating neuroblast sublineage gene expression in the Drosophila CNS. Development 121(10): 3233-43
Doe, C. Q. (1992). Molecular markers for identified neuroblasts and ganglion mother cells in the Drosophila central nervous system. Development 116: 855-863.
Higashijima, S-i., Shishido, E., Matsuzaki, M., and Saigo, K. (1996). eagle, a member of the steroid receptor gene superfamily is expressed in a subset of neuroblasts and regulates the fate of their putative progeny in the Drosophila melanogaster CNS. Development 122: 527-36.
Landgraf, M., Bossing, T., Technau, G. M., and Bate, M. (1997). The origin, location and projections of the embryonic abdominal motoneurons of Drosophila melanogaster. J. Neurosci 17(24): 9642-55.
McNeill, H., Yang, C.H., Brodsky, M., Ungos, J., and Simon, M.A. (1997). Mirror encodes a novel PBX-class ofhomeoprotein that functions in the definition of the dorsal-ventral border in the Drosophila eye. Genes Dev 11(8): 1073-82.
Schmidt, H., Rickert, C., Bossing, T., Vef, O., Urban, J., and Technau, G. M. (1997). The embryonic Central Nervous System lineages of Drosophila melanogaster II. Neuroblast lineages derived from the dorsal part of the neurectoderm. Dev Biol 189: 186-204.
Yang, X., Bahri, S., Klein, T., and Chia, W. (1997). Klumpfuss, a putative Drosophila zinc finger transcription factor, acts to differentiate between the identities of two secondary precursor cells within one neuroblast lineage. Genes Dev 11(11):1396-1408.