NB 6-4:

NB 6-4 delaminates at S3 in the lateral column.

No information about the lineage derived from NB 6-4 is available from other insects.

At S3, NB 6-4 expresses engrailed (en), muscle-specific homeobox gene-1 (msh-1), gooseberry-distal (gsb-d), and eagle (egl) (Doe, 1992; Broadus et al, 1995; Buescher et al, 1997; Isshiki et al, 1997; Skeath et al, 1995; Higashijima et al, 1997). At S5, it loses gsb-d expression but adds seven-up-lacZ (svp-lacZ) expression (Broadus et al, 1995).

Its lineage was first described by Schmidt et al. (1997) as producing 4-6 dorsally-located interneurons, a medial cell body glia, and the VUM support glia in thoracic segments. In abdominal segments the same glial cells form but the interneuronal components are absent. Higashijima et al. (1996) identified similar NB 6-4 progeny using eagle-kinesin-lacZ transgenes expressed in NB 6-4, and more recently Akiyama-Oda et al (1998,1999) used this marker and others to show that the first daughter cell of thoracic NB 6-4 is a glial precursor (M1) that generates 3 medial glia, while the subsequent 2-3 progeny are GMCs that generate 4-6 interneurons.

A. Interneurons

Thoracic clones contain 4-10 local interneurons. Three axons project in a posterior fascicle of the posterior commissure and appear to "arch anteriorly" within the commissure. Arched commissural projections are also observed in clones derived from NBs 2-3, 5-2, 5-5, 6-2 and 7-3. In addition, 2 or 3 small interneurons (3.8 um; n=7) project posteriorly in a lateral fascicle of the ipsilateral connective. The remaining cells of the larger clones have no detectable projections. Abdominal clones contain 2 cells that may be interneurons with very short axons into the neuropil.

B. Glia

In thoracic segments, we observe 2-4 lateral cell body glia, whereas previous researchers detect only medial-most cell body glia (MM-CBG, Higashijima et al., 1996; Schmidt et al., 1997; Akiyama-Oda et al., 1998,1999). We observe putative MM-CBG in thoracic NB 5-6 clones (Fig. 5-6C). The reason for the different glial positions compared to previous studies is unknown. In abdominal segments, we observe 1-2 sub-perineural glial cells, 1-2 cell body glia, and the 2 MM-CBG. This is similar to previous studies, although we see more cells, perhaps because we assay later in development.

References:

Akiyama-Oda, Y., Hosoya, T., and Hotta, Y. (1998). Alteration of cell fate by ectopic expression of Drosophila glial cells missing in non-neural cells. Dev Genes Evol 208 (10): 578-85.

Akiyama-Oda, Y., Hosoya, T., and Hotta, Y. (1999). Asymmetric cell division of thoracic NB 6-4 to bifurcate glial and neuronal lineage in Drosophila. Development 126(9): 1967-74.

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.

Buescher, M., and Chia, W. (1997). Mutations in lottchen cause cell fate transformations in both neuroblast and glioblast lineages in the Drosophila embryonic central nervous system. Development 124(3): 673-81.

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.

Isshiki, T., Takeichi, M., and Nose, A. (1997). The role of the msh homeobox gene during Drosophila neurogenesis: implication for the dorsoventral specification of the neurectoderm. Development 124(16): 3099-3109.

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.

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.