NB 4-2 Details
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NB 4-2 delaminates at S2 in the intermediate column.
In Schistocerca, late-born progeny of NB 4-2 include a large population of intersegmental interneurons with ipsilateral projections (Shepherd and Laurent, 1992; these most closely resemble Drosophila NB 4-1 interneurons, see NB 4-1); Schistocerca does have an even-skipped+ RP2 motoneuron with axon morphology similar to the Drosophila RP2 motoneuron, but its parental NB has not been determined (Goodman et al., 1984; Patel et al, 1987; Snow et al, 1987).
In Drosophila NB 4-2 expresses huckebein (hkb) and intermediate neuroblasts defective (ind) as it is born at S2 (Doe et al, 1988; Broadus et al, 1995; Weiss et al, 1998). It expresses Klumpfuss (Klu) at S4 (Yang et al, 1997), and adds seven-up-lacZ (svp-lacZ) expression at S5 (Doe, 1992; Broadus et al, 1995).
The first GMC derived from NB 4-2 is hkb+, pdm1+, pdm2+, eve+ and ftz+ (Broadus et al, 1995). This GMC, GMC 4-2a, generates the eve+ RP2 motoneuron and the smaller RP2 sibling cell (known as the RP2-sib), which is only transiently eve+, losing eve-expression by stage 16 (Doe et al, 1988; Broadus et al, 1995; Bhat et al, 1995; Doe, 1992).
Both RP2 and the RP2-sib express fushi tarazu (ftz) transiently, losing ftz expression at stage 16 (Doe and Goodman, 1985). The second GMC in the NB 4-2 lineage (GMC4-2b) replaces eve-expression with Klumpfuss (Klu) expression (Yang et al, 1997).
DiI lineage analysis of NB 4-2 was done by Chu-LaGraff et al. (1995) and Bossing et al. (1996); they observe 10-16 cells including the RP2 motoneuron and at least one "cousin of RP2" (CoR) motoneuron (described in detail below), as well as a pool of local interneurons with contralateral projections.
A. Motoneurons:
There are at least 4 motoneurons in this clone, and possibly an additional thoracic motoneuron that extends an axon late in stage 17 (Fig. 4-2B). The well characterized RP2 motoneuron is a large round cell (7.4 um; n=19) that migrates dorsally and medially from the clone; it lies at the extreme dorsal surface of the CNS above the junction of the anterior commissure and the longitudinal connective (Fig 4-2, white circles). The RP2 axon projects ipsilaterally via the posterior root of the ISN and travels in the ISN until forming a synapse at muscle 2; it has branches at muscles 11 and 20 ("first branchpoint") and at muscles 3 and 19 ("second branchpoint) (Fig. 4-2D).
In addition, there are three CoR motoneurons which are also dorsally located, but lateral, posterior, and smaller (6.9 um; n=36) than RP2 (Fig 4-2). The CoRs project ipsilaterally and comprise the entirety of the SNc root innervating muscles 26, 27, and 29 (Fig. 4-2D). Landgraf et al (1997) back-filled motoneurons from neuromuscular junctions and identified the CoR motoneurons as innervating targets we believe to be innervated by the RP1, 3, 4, 5 motoneurons (derived from NB 3-1). However, they did backfill motoneurons innervating muscles 26,27 and 29 matching the sizes, shapes and positions of the CoR motoneurons. Each of the motoneurons in this clone appears to be associated with a smaller cell, typified by the RP2/RP2sib pair of siblings.
B. Interneurons:
There are ~19 small (4.4 um; n=126) interneurons by stage 17. Two or three interneurons have axon projections into anterior commissure with bifurcations in an intermediate fascicle of the contralateral connective. In addition, the teardrop-shaped RP2sib has a very short projection into the neuropil (Fig. 4-2B,C,D). The majority of cells in this clone appear axonless and in close contact with the much larger motoneurons. This arrangement is consistent with findings in other systems, in which small, axonless local interneurons function to modify motoneuronal function (Pearson et al. 1975; Burrows, 1996). It is interesting to speculate that this one-to-one relationship is due to a sibling relationship between motoneurons and axonless interneurons, as appears to be the case for RP2/RP2sib.
C. Other cells:
In 5 of 12 stage 17 clones we observe a cluster of epidermal cells in close apposition to the RP2 motoneuronal fascicle (Fig. 4-2, inset). It is interesting that these epidermal subclones are always in an identical position, in close contact with the RP2 axon, at about 50% of its trajectory.
References:
Bhat, K.M., Poole, S.J., and Schedl, P (1995). The miti-mere and pdm1 genes collaborate during specification of the RP2/sib lineage in Drosophila neurogenesis. Mol Cell Biol 15(8): 4052-63.
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 Bio 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.
Burrows, M. (1996). Oxford University Press, The Neurobiology of an Insect Brain. New York
Chu-LaGraff, Q., Schmid, A., Leidel, J., Broenner, G., Jaeckle, H., and Doe, C. Q. (1995). huckebein specifies aspects of CNS precursor identity required for motoneuron axon pathfinding. Neuron 15: 1041-1051.
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., and Goodman, C. S. (1985). Neurogenesis in grasshopper and fushi tarazu Drosophila embryos. in Cold Spring Harbor Quant Review of Biology.
Doe, C. Q., Smouse, D., and Goodman, C. S. (1988). Control of neuronal fate by the Drosophila segmentation gene even-skipped. Nature 333:376-8.
Doe, C. Q. (1992) Molecular markers for identified neuroblasts and ganglion mother cells in the Drosophila central nervous system. Development 116: 855-863.
Goodman, C. S., Bastiani, M., Doe, C. Q., du Lac, S., Helfand, S. L., Kuwada, J. Y., and Thomas, J. B. (1984). Cell recognition during neuronal development. Science 225: 1271-79.
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.
Patel, N.H., Snow, P.M., and Goodman, C.S. (1987).Characterization and cloning of fasciclin III: a glycoprotein expressed on a subset of neurons and axon pathways in Drosophila. Cell 48(6):975-88.
Pearson, K.G., and Fourtner, C. R. (1975). Non-spiking interneurons in walking system of the cockroach. J. Neurophysiol 38: 33-52.
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.
Snow, P.M., Patel, N.H., Harrelson, A.L., and Goodmans, C.S. (1987). Neural-specific carbohydrate moiety shared by many surface glycoproteins in Drosophila and grasshopper embryos. J Neurosci 7(12): 4137-44.
Spana, E.P., Kopczynski, C., Goodman, C.S., and Doe, C.Q. (1995). Asymmetric localization of numb autonomously determines sibling neuron identity in the Drosophila CNS. Development 121(11):3489-94.
Weiss, J., VonOhlen, T., Mellerick, D., Dressler, G., Doe, C. Q., and Scott, M.P. (1998). Dorsoventral patterning in the Drosophila central nervous system: the intermediate neuroblasts defective homeobox gene specifies intermediate column identity. Genes Dev 12:3591-3602.
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.