NB 3-1 Details
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NB 3-1 delaminates as an S3 NB.
No information about the lineage of NB 3-1 is available from other insects.
zinc finger homeodomain 1 (zfh-1) (Fortini et al, 1991; Skeath et al, 1998), ventral nervous system defective (vnd) (White et al, 1983; McDonald et al, 1998) and runt (Dormand, et al 1998) are first detected in NB 3-1 as it forms. Klumpfuss (Klu) is not detected until S4 (Yang, et al 1997), and seven up-lacZ (svp-lacZ) and castor (cas) are first expressed at S5 (Doe, 1992; Cui and Doe, 1992, 1995). No specific information is currently available about the expression of these markers in the progeny of NB 3-1.
The lineage of NB 3-1 was first described by Bossing et al. (1996) as producing the well-characterized RP1, 3, 4, and 5 motoneurons that project contralaterally out the SNb to innervate ventral muscles; the clone also includes a group of local interneurons that project across the anterior commissure before bifurcating in the connective.
The RP motoneurons are the most thoroughly studied cells of the Drosophila CNS (e.g. Halpern et al., 1991; Fernandes et al., 1996, 1998; Halfon et al., 1997; Halfon and Keshishian, 1998; Desai et al., 1996; Krueger et al., 1996; Cash et al., 1993; Broadie and Bate, 1993; Keshishian et al., 1995, 1996).Other insects have similar RP neurons (Jacobs and Goodman, 1989b; Sink and Whitington, 1991a,b), but their parental NB has not been identified. The "RP" name derives from the observation by Michael Bate and Corey Goodman that the large dorsal RP motoneurons are easily poked, and in that way reminded the two of "raw prawns", an Australian term of endearment (Haig Keshishian, personal communication). These RP motoneurons are the most thoroughly studied cells of the Drosophila CNS. They are used primarily as a model system for pathfinding: their cell bodies are easily located, between the anterior and posterior commissures at the dorsal surface of the CNS, their trajectory is of a convenient length for pathfinding studies, and SNb is located on the interior surface of the body wall musculature, completely visible and accessible in simple fillets.
A. Motoneurons:
The RP1, RP3, RP4, and RP5 motoneurons are all large cells (7.4 x 5.7 um; n=27). RP4 and RP1 most dorsal; ventral and lateral to them is RP3, followed by RP5. The RP motoneurons project to the ventral muscles 12, 13, 14, 15, 28, 30, 6 and 7 in abdominal segments (Fig. 3-1E-G), in complete agreement with Sink and Whitington (1991a,b), who used Lucifer Yellow injections into RP cell bodies to conclude that RP1 innervates muscle 13, RP4 innervates muscles 13 and 6, RP3 innervates muscles 6 and 7, and RP5 innervates muscles 15,16,7,6,13 and 12. Our results, and those of Sink and Whitington (1991a,b), differ from those of Landgraf et al. (1997), who did DiI backfills from synaptic contacts and found that the RPs innervate only muscles 12,13,6 and 7. In addition, both Sink and Whitington (1991a,b) and this study observe RP dendrites projecting anteriorly in a medial fascicle of the contralateral connective (Fig 3-1 C,D single dashed arrow).
B. Interneurons:
We found the number of interneurons in this lineage to be highly variable; there can be as few as 2 or as many as 18 at stage 17. Bossing et al. (1996) speculated that cell death leads to the variability in the number of interneurons; we do not observe differences in cell death between small or large clones, and propose instead that the variable number of interneurons is due to differences in the time at which NB 3-1 stops dividing. There are about twice as many intersegmental interneurons as there are local interneurons; both project across the anterior commissure in three axon bundles and then extend in a lateral fascicle of the contralateral connective, with the local projections turning anterior and the intersegmental projections turning posterior (Fig. 3-1, C,D,E,G large arrows). The majority of the interneurons are medium sized (4.8 um; n=46) which may be the intersegmental interneurons, but there are always several small cells (3.0 um; n=7), which may be local interneurons.
References:
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Cash, S., Chiba, A., and Keshishian, H. S. (1992). Alternate neuromuscular target selection following the loss of single muscle fibers in Drosophila. J. Neurosci 12(6): 2051-64.
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
Desai, G. J., Gindhart, J. G., Goldstein, S. B., and Zinn, K. (1996). Receptor tyrosine phosphatases are required for motoraxon guidance in the Drosophila embryo. Cell 84: 599-609.
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Skeath, J. B. (1998). The Drosophila EGF-Receptor controls the formation and specification of NBs along the dorso-ventral axis of the Drosophila embryo. Development 125: 3301-12.
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