Biology Reference
In-Depth Information
Neural stem cells are called neuroblasts (NBs) in
Drosophila
.
Drosophila
NBs usually undergo several rounds of Notch-dependent asymmetric divi-
sions to produce a self-renewed NB, and a smaller daughter cell called gan-
glion mother cell (GMC). GMCs generally divide asymmetrically once to
produce two postmitotic progeny with different fates (reviewed in
Doe,
2008; Karcavich, 2005; Knoblich, 2010; Lin & Lee, 2012
). Several
Drosoph-
ila
NB lineages in the CNS have been partially or completely characterized.
They generate multiple distinct progeny in a birth-order-dependent manner
(
Akiyama-Oda, Hosoya, & Hotta, 1999; Baek & Mann, 2009; Bossing,
Udolph, Doe, & Technau, 1996; Isshiki, Pearson, Holbrook, & Doe, 2001;
Jefferis, Marin, Stocker, & Luo, 2001; Karcavich & Doe, 2005; Lee, Lee, &
Luo, 1999; Lundell & Hirsh, 1998; Pearson & Doe, 2003; Schmid,
Chiba, & Doe, 1999; Schmidt et al., 1997; Skeath & Thor, 2003; Yu,
Chen, Shi, Huang, & Lee, 2009; Yu et al., 2010
).
Drosophila
has recently
become a powerful model system to understand the mechanisms of tem-
poral specification of neurons and there have been several extensive and
excellent reviews on this topic (
Brand & Livesey, 2011; Kao & Lee,
2010; Maurange, 2012; Pearson & Doe, 2004
). This review will therefore
focus on the most recent advances in temporal patterning of NBs in several
systems of
Drosophila
that are now well characterized. Below is a brief
introduction of each system to be described.
1.1. Embryonic and larval ventral nerve cord
Classic work on the temporal patterning of NBs in the
Drosophila
embryonic
ventral nerve cord (VNC) has made it undoubtedly the best-characterized
system. The VNC of
Drosophila
, spanning three thoracic and eight abdom-
inal segments, is the counterpart of the vertebrate spinal cord. During early
embryonic development, NBs delaminate from a neuroectoderm at stereo-
typical positions. Each hemi-segment contains approximately 30 NBs
arranged in seven rows, and each NB is identifiable based on its position
(e.g., NB1-1 is in row1, column1) and molecular markers (
Bhat, 1999b;
Doe, 1992; Skeath & Thor, 2003; Technau, Berger, & Urbach, 2006
).
The distinction between these NBs is achieved by spatial patterning that will
not be discussed in detail here. The neuronal and glial progeny composition
of each embryonic NB lineage have been determined by early Dil NB label-
ing experiments: A single NB can generate multiple neuron types and glia
(
Bossing et al., 1996; Schmid et al., 1999, 1997
). At the embryo to larval
transition, some of these NBs commit to apoptosis, while others enter into
