NB 5-2 Details
videos
NB 5-2 delaminates at S1 in the medial column.
No information about the lineage derived from NB 5-2 is available from other insects.
NB 5-2 expresses seven-up-lacZ (svp-lacZ), gooseberry-distal (gsb-d), ventral nervous system defective (vnd) (White et al, 1983; McDonald et al, 1998) and wingless (wg) as it forms (Chu-LaGraff et al, 1995; Skeath et al, 1996; Broadus, et al, 1995). By S3, it has added castor (cas) (Cui and Doe, 1992, 1995) and Klumpfuss (Klu) expression (Yang et al, 1997).
Its lineage was described by Bossing et al. (1996) as containing 17-26 cells: a large group of interneurons with contralateral projections, and a motoneuron projecting contralaterally out the ISN, and occasionally reaching muscle 13. Subsequently, the motoneuron target was shown to be muscle 12 (Landgraf et al., 1997). We find that by stage 17 the clone consists of 30-40 neurons in thoracic segments and 16-24 neurons in abdominal segments. It generates a motoneuron, several intersegmental interneurons, and a large number of local interneurons.
A. Motoneurons
The motoneuron is a large (6.5 um; n=8) cell and located 1-2 cell diameters from the dorsal surface of the clone (Fig. 5-2D, white circle). It projects across the posterior commissure, turns posteriorly to exit the CNS in SNb, and forms a bifurcated ending on muscle 12. In one case, we also observed a branching projection from this motoneuron to muscle 5 (data not shown).
B.Interneurons:
There are 4 distinct intersegmental interneuronal projections. One crosses the anterior commissure, follows the median nerve for a short distance, and turns anteriorly in a medial fascicle of the contralateral connective. This projection is established by stage 15 and originates from the dorsal-most cell of the clone (4.8 um; yellow circle in Fig. 5-2D). Two other projections cross the anterior commissure, with one turning anteriorly and another turning posteriorly in a medial fascicle of the longitudinal connective. The fourth projection is across the posterior commissure with an anterior turn in a lateral fascicle of the contralateral connective. We also observed an ipsilateral anterior intersegmental projection in about 25% of the clones (Fig. 5-2C). There are a large number of local interneurons, and most or all project across the posterior commissure and then turn anteriorly, forming an extensive arborizations (see Fig. 5-2 movies). These interneurons comprise the majority of the posterior commissure at stage 17. The interneurons fall into two size classes: about half are medially-located and medium sized (4.5 um, including the intersegmental interneurons) and half are laterally-located and very small (2.8 um).
References:
Bossing, T., Udolph, G., Doe, C. Q., and Technau, G. M. (1996). The Embryonic CNS lineages of Drosophila melanogaster I. Neuroblast lineages derived from the ventral half of the neurectoderm. Dev Biol 179: 41-64.
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.
Chu-LaGraff, Q., and Doe, C.Q. (1993). Neuroblast specification and formation regulated by wingless in the Drosophila CNS. Science 261(5128): 1594-7.
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
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.
McDonald, J.A., Holbrook, S., Isshiki, T., Weiss, J., Doe, C.Q., and Mellerick, D.M. (1998). Dorsoventral patterning in the Droosphila central nervous system: the vnd homeobox gene specifies ventral column identity. Genes Dev 12: 3603-12.
Skeath, J. B., Zhang, Y., Holmgren, R., Carroll, S. B., and Doe, C. Q. (1995). Specification of neuroblast identity in the Drosophila embryonic central nervous system by gooseberry-distal. Nature 376: 427-430.
White, K., DeCelles, N.L., and Enlow, T.C. (1983). Genetic and developmental analysis of the locus vnd in Drosophila melanogaster. Genetics 104(3): 433-48.
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.