NB 6-1 Details
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NB 6-1 delaminates during S3 in the medial column.
No information about the lineage derived from NB 6-1 is available from other insects.
At S3, NB 6-1 expresses castor (cas) (Cui and Doe, 1992), engrailed (en) (Broadus et al, 1995), ventral nervous system defective (vnd) (White et al, 1983; McDonald et al, 1998) and gooseberry distal (gsb-d) (Skeath et al, 1995; Broadus et al, 1995). At S4, it adds Klumpfuss (Klu) and mirror-lacZ (mrr-lacZ) expression (Yang et al, 1997; Broadus et al, 1995; McNeill et al, 1997).
Its lineage was described as containing 10-16 interneurons, and an occasional epidermal subclone (Bossing et al., 1996).
A. Motoneurons
A motoneuron was only observed in the first thoracic segment (Fig. 6-1 E, single arrow). It projects out the posterior root of the ISN, not yet forming a synapse at the time we assayed (mid-stage 17). One type of interneuron, with posterior contralateral projections (see below) is specifically absent in this segment (Fig. 6-1E, double arrow).
B. Interneurons
There are three distinct intersegmental interneuron projection patterns: (1) 3 or more axons project across the posterior commissure and then extend anteriorly; (2) 1-2 axons project across the posterior commissure but then extend posteriorly (these are absent in T1); and (3) 3 or more axons project posteriorly in the ipsilateral connective. In addition, there are local interneurons that project anteriorly and posteriorly in the ipsilateral connective (Fig. 6-1D). In general, dorsal cells project ipsilaterally, and ventral cells project contralaterally. The interneuronal projections form extremely complex endings in the CNS. The cells fall into two size categories: about one-third are large (5.1 um; n=20), and two-thirds are small (3.0 um; n=20)
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.
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.
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.
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.
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.