NB 2-5 details
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NB 2-5 delaminates as an S1 NB.
No information about the lineage derived from NB 2-5 is available from other insects.
NB 2-5 expresses odd-skipped (odd) and mirror-lacZ (mrr-lacZ) as it delaminates (Doe 1992; Broadus et al, 1995). At S2 it loses odd expression but adds seven-up-lacZ (svp-lacZ) expression . By S5, Klumpfuss (Klu), muscle-specific homeobox gene1 (msh), castor (cas) and runt are detectable, in addition to persistent svp-lacZ and mrr-lacZ expression (Yang et al, 1997; Buescher et al, 1996; Isshiki et al, 1997; Cui and Doe, 1992,1995; Dormand and Brand, 1998).
Schmidt et al (1997) described the 2-5 lineage as consisting of 13-18 neurons including 2 to 5 contralaterally projecting interneurons, 2 to 5 ipsilaterally projecting interneurons, 1 motoneuron and 2 glial cells. They also note that the interneuronal projections can span more than one segment.
A. Motoneurons:
We detect a single ovoid motoneuron (6.2 x 4.6 um; n=6) that projects ipsilaterally into the SNd and makes a forked synapse in the clefts between muscles 15, 16 and 17.
B. Interneurons:
There are an indeterminate number of intersegmental interneurons in this clone: we detect 3-6 contralateral anterior projections that extend all the way to the brain, and 2-4 ipsilateral anterior projections that extend only half as far. It is not clear if each projection derives from a distinct cell body, or if one cell has dual projections (Fig. 2-5). At least two of the intersegmental interneuron cell bodies are large dorsal cells (8.1 um; n=12). Burrows (1996) describes this type of intersegmental interneuron in other insects, but little is known about their function or lineage.
Local interneurons extend to the anterior border in the ipsilateral longitudinal connective (Fig. 2-5A,C, arrows ). The contralateral longitudinal projection extends all the way to the brain in most cases, and generates a large number of small branches into the longitudinal connective; these have the appearance of tiny hairs extending out into the connective at an oblique angle. We found a large dendritic arborization at the base of the contralateral projection in late clones; it is not clear whether these neurites are derived from the medial plurisegmental interneuron or from the more ventral motoneuron (see Fig 2-5A). Local interneurons extended to the anterior border in the ipsilateral longitudinal connective (Fig 2-5C, arrow).
Burrows (1996) summarizes the anatomy of plurisegmental interneurons, (i.e. those extending several segments), as follows: "These (cells) can have cell bodies in the brain and axons that extend to the abdomen, others have cell bodies in the terminal ganglion with their axons extending to the brain, while others may have cells bodies in the subesophageal, thoracic or abdominal ganglia and axons that either ascend or descend. The axons of many of these interneurons run in the connective contralateral to the cell body so that the majority of outputs are made on the side opposite to that on which they receive the majority of their inputs, but others have ipsilateral axons. A small number of intersegmental interneurons have bilateral axons." Little information exists about the functions of these cells and little has been done to characterize individual plurisegmental interneurons.
C. Glia:
We detected glia in only 3/13 clones; clones could contain both segmental nerve and peripheral nerve glia (Fig. 2-5, inset).
D. Other Cells:
We generated 13 NB 2-5 clones and found 3 that produced PNS clones in addition to the primary neuronal clone described above (see Fig 2-5 C). This was a surprising finding, given that 2-5 delaminates as an S1 neuroblast; neurectodermal cell division prior to lineage initiation would be unexpected in a lineage generated at the outset of neurogenesis.
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.
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.
Burrows, M. (1996). Oxford University Press, The Neurobiology of an Insect Brain. New York
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.
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.
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.
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.
Udolph, G., Prokop, A., Bossing, T., and Technau, G.M. (1993). A common precursor for glia and neurons in the embryonic CNS of Drosophila gives rise to segment specific lineage variants. Development 118: 765-775.
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.