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Fig. 1. The Drosophila germarium. Schematic drawing of the
Drosophila germarium, modified from Zhang and Kalderon
(Zhang and Kalderon, 2001).
Germarial regions 1, 2a, 2b and 3 are indicated above the drawing. At the most
anterior part of the germarium, overlying somatic cells (terminal filament and
cap cells) create a niche to maintain the germline stem cells. Anterior region
1 contains two to three germline stem cells (GSCs); GSC division is asymmetric
and generates both a daughter stem cell and a differentiated daughter cell
called a cystoblast. Each cystoblast undergoes four rounds of mitosis with
incomplete cytokinesis to produce a syncytium of 16 cystocytes, the germline
cyst. One of these 16 cells becomes the oocyte, while the remaining 15 cells
develop as nurse cells. The population of germline cysts during these stages
is surrounded by somatic inner sheath cells. In region 2a/2b, approximately
two somatic stem cells (SSCs), represented in green, give rise to a population
of undifferentiated cells, the prefollicular cells, in blue, which migrate to
envelop each germline cyst individually. These cells diverge soon after to
give rise to: two pairs of polar cells, in pink, which mark the anterior and
posterior poles of the follicle; interfollicular stalk cells, in purple, which
are responsible for follicle budding from the germarium; and epithelial
follicular cells, in yellow, which form a polarized epithelium around each
follicle.
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