NB 3-2 details
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NB 3-2 delaminates as an S1 NB in the anterior-most row of the intermediate column; it later moves slightly posteriorly to become part of the row 3 NBs.
No information is available from other insects about the lineage derived from NB 3-2.
NB 3-2 expresses mirror-lacZ (mrr-lacZ) and intermediate neuroblasts defective (ind) as it forms at S1 (Broadus et al, 1995; McNeill et al, 1997), adds seven-up-lacZ (svp-lacZ) expression at S2 (Broadus et al, 1995), runt at S3 (Doe, 1992; Dormand and Brand, 1998),Klumpfuss (Klu) at S4 (Yang et al, 1997), and castor (cas) expression at S5 (Cui and Doe, 1992,1995).
Previous studies (Bossing et al., 1996; Landgraf et al., 1997) describe the clone as containing 10-18 cells: 3-6 motoneurons projecting to muscles 18,11,19 and 20, 23 and 24, plus a group of local interneurons with contralateral projections.
A. Motoneurons:
At stage 14, we observed a labeled NB surrounded by a cluster of 6 motoneurons that have begun to extend axons (Fig. 3-2A); the clone does not appear to contain local interneurons, suggesting that motoneurons are born first in this lineage (similar to many other NB lineages). All 6 motoneurons are round and increase in size from 4.9 to 7.0 um between stage 15 and 17. At stage 16 two motoneurons are positioned at the anterior ventral edge of the clone; these project via the SNa to muscles 24, 18 and 4 (we cannot rule out the possibility that muscle 23 may be innervated by these cells as well, as observed by Landgraf et al., 1997). The other four motoneurons are at the medial dorsal position of the clone; these project via the ISN to muscles 10, 2, 11, 19 and 20. Differences between our results and Landgraf et al. (1997) are that they propose that an ISN projection innervates muscle 18, which we do not observe; and that they do not observe innervation to muscles 2 or 10, which we see 100% of the time at stage 17.
Innervation of muscle 4 by SNa is a unique finding. Nevertheless we see this projection consistently and believe that this innervation has been missed in previous studies because the projection of SNa beyond its major branch point is delicate and complex. We see the branch to muscle 4 as occurring at the external surface of the muscle (i.e., beneath the surface presented in dissection; see Fig. 3-2).
B. Interneurons:
All of the interneurons are local, with a robust projection in three fascicles across the anterior commissure, before bifurcating at the contralateral longitudinal connective and extending to the anterior and posterior segment borders. By stage 17, half the cells are small (2.4 um) and half are larger (4.0 um; n=36).
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.
Bossing, T., Technau, G. M., and Doe, C.Q. (1995). Huckebein is required for glial development and axon pathfinding in the NB 1-1 and NB 2-2 lineages in the Drosophila central nervous system. Mech Dev 55: 53-64.
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.
Dormand, E.L., and Brand, A.H. (1998). Runt determines cell fate in the Drosophila embryonic CNS. Development 125(9):1659-67.
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.
Sink, H., and Whitington, P. (1991a). Location and connectivity of abdominal motoneurons in the embryo and larvae of Drosophila melanogaster. J. Neurobiol 22: 298-311.
Sink, H., and Whitington, P. (1991b). Pathfinding in the central nervous system and periphery by identified embryonic Drosophila motor axons. Development 112(1): 307-16.
Weiss, J., VonOhlen, T., Mellerick, D., Dressler, G., Doe, C. Q., and Scott, M.P. (1998). Dorsoventral patterning in the Drosophila central nervous system: the intermediate neuroblasts defective homeobox gene specifies intermediate column identity. Genes Dev 12:3591-3602.
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.