NB 5-1 Details
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NB 5-1 delaminates at S5 in the medial column.
In grasshoppers, Shepherd and Laurent (1992) labeled later parts of the NB 5-1 lineage by injecting the already dividing NB 5-1 with a 6% solution of hexaminocobaltic chloride. They isolated and characterized 15 cells from the NB 5-1 lineage and revealed 6 of these to be motoneurons and 9 to be intersegmental interneurons. (They never observed local interneurons to derive from this lineage).
One of these motoneurons has been identified as the 2nd common inhibitory motoneuron (Hale and Burrows, 1985; Wolf, 1990). The second common inhibitory motoneuron, CI2, is known to provide inhibitory innervation to three muscles in the more distal parts of the leg. It is believed that common inhibitory motoneurons function to reduce the force generated by slow motoneurons and to accelerate the rate of muscular relaxation, so that rapid movements are not impeded by the lingering effects of slow innervation (Burrows, 1996).
In Drosophila, NB 5-1 expresses gooseberry-distal (gsb-d) (Skeath et al, 1995), seven-up-lacZ (svp-lacZ) (Broadus et al, 1995), wingless (wg) (Chu-LaGraff et al, 1993; Broadus et al, 1995), castor (cas) (Cui and Doe, 1992,1995), and ventral nervous system defective (vnd) (White et al, 1983; McDonald et al, 1998) from the outset.
Bossing et al (1996) described the NB 5-1 lineage as consisting of 2-4 interneurons that projected as a single fascicle across the midline in the posterior commissure, and a much larger obligate epidermal clone. They observed that despite labeling large number of NBs 5-1, they generated only 4 clones.
A. Interneurons
At stage 17 we detect 6-9 local interneurons with a prominent projection across the posterior commissure, bifurcating at the contralateral connective, similar to that described by Bossing et al. (1996). Two cells are intermediate sized (5.5 um; n=4) and the remainder are the smallest cells observed in any lineage (2.2 um; n=6). Because we did not assay NB 5-1 in the thorax, it is possible that thoracic NB 5-1 generates the Drosophila homolog of CI2 motoneuron described in grasshopper. We cannot comment on the frequency with which NB 5-1 dies. While we also scored only 4 NB 5-1 lineages in this study, it is likely that we missed NB 5-1 lineages because epidermal sub-clones obscured them; we observed a higher-than-average frequency of epidermal lineages from labelings identified as NB 5-1.
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., 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.
Burrows, M. (1996). Oxford University Press, The Neurobiology of an Insect Brain. New York.
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
Hale, J. P., and Burrows, M. (1985). Innervation patterns of inhibitory motor neurons in the thorax of the locust. J. Exp Biol 117: 401-413.
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.
Shepherd, D., and Laurent, G. (1992). Embryonic development of a population of spiking local interneurons in the locust, Schistocerca gregaria. J Comp Neurol 319: 438-53.
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.
Wolf, H., and Lang, D. M. (1994). Origin and clonal relationship of common inhibitory motoneurons CI1 and CI3 in the locust CNS. J. Neurobiol 25: 846-64.