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1
Review
Composition of a Neuromere and Its Segmental Diversification under the
Control of Hox Genes in the Embryonic CNS of Drosophila
Gerhard M. Technau, Ana Rogulja-Ortmann, Christian Berger, Oliver Birkholz and Christof Rickert
Institute of Genetics, University of Mainz, Mainz, Germany
Abstract: Studies performed at the level of single, identifed cells in the fruitfy Drosophila have decisively contributed to our
understanding of the mechanisms underlying the development and function of the nervous system. This review highlights some of the
work based on single-cell analyses in the embryonic/larval CNS that sheds light on the principles underlying formation and organization
of an entire segmental unit and its divergence along the anterior-posterior body axis.
Keywords: cell lineage, CNS, Drosophila, Hox genes, single-cell tracing, segmental patterning
A major goal in developmental neurobiology is to
understand how a large number of different neural
cell types is generated and assembled into functional
circuits. As a prerequisite for approaching the mecha-
nisms that orchestrate both formation and function of
neural circuits, the constituent cells of the CNS need
to be individually identified, thoroughly described,
and their origin should be clarified. The relatively
simply structured embryonic/larval ventral nerve cord
(VNC) of Drosophila is a suitable model system to
reach this goal.
Embryonic development of the Drosophila CNS can
be subdivided into four major phases (Figure 1): 1) The
neurogenic regions of the ectoderm are determined in
the blastoderm using the products of early dorso/ventral
and anterior/posterior patterning genes (St Johnston &
Nüsslein-Volhard, 1992; Biehs et al., 1996), the ventral
neurogenic region representing the anlage of the VNC, the
procephalic neurogenic region that of the brain. 2) Within
the neuroectoderm proneural and neurogenic genes con-
trol the selection of cells that will, upon gastrulation,
delaminate as CNS progenitor cells, called neuroblasts
(NBs) (e.g. reviewed by Artavanis-Tsakonas & Simpson,
1991; Campos-Ortega, 1995). 3) NBs typically divide
in a stem cell mode to produce a chain of smaller gan-
glion mother cells, which are generally dividing once to
give rise to two postmitotic progeny cells. 4) Progeny
cells differentiate into specific neuronal and glial cell
types or/and undergo programmed cell death (PCD; e.g.
Rogulja-Ortmann et al., 2007). A subpopulation of the
NBs enters a phase of quiescence and become reactivated
in the larva to produce the cells of the adult CNS; the oth-
ers undergo PCD or terminal differentiation.
These processes take place in a coordinated manner
along the anterior-posterior body axis to form segmental
units of the CNS, called neuromeres. Whereas neuromeres
of the brain, the gnathal, and the most posterior abdomi-
nal (A8–A10) segments are derived to various degrees,
the thoracic (T1–T3) and anterior abdominal neuromeres
(A1–A7) in the embryo are very similar to each other and
resemble the ground state (T2, which does not require
input from any Hox genes; Lewis, 1978) .
In the following, we will give an overview of some
recent work directed towards dissecting the embryonic
(larval) CNS down to the level of single identified cells
and their lineages, and towards analysing the mechanisms
that control patterning of the CNS along the anterior-
posterior body axis.
TYPES AND ARRANGEMENT OF
CONSTITUENT CELLS OF A TYPICAL
NEUROMERE IN THE VNC
In the late embryo a typical neuromere (T1–A7) consists
of approximately 340 postmitotic cells on either side (plus
Received 25 October 2013; accepted 18 November 2013.
Address correspondence to Dr Gerhard M. Technau, Institute of Genetics, University of Mainz, D-55099 Mainz, Germany.
E-mail: technau@uni-mainz.de
J. Neurogenetics, Early Online: 1–10
Copyright © 2014 Informa Healthcare USA, Inc.
ISSN: 0167-7063 print/1563-5260 online
DOI: 10.3109/01677063.2013.868459
GNEG_A_868459.indd 1 GNEG_A_868459.indd 1 6/18/2014 5:01:24 PM 6/18/2014 5:01:24 PM