Drosophila Oogenesis

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Drosophila Oogenesis

Margaret de Cuevas, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA

Published online: February 2015

DOI: 10.1002/9780470015902.a0001502.pub2

Full Article on Wiley Online Library

Abstract
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Abstract

Oogenesis is the process by which germ cells develop into eggs. Insect ovaries are classified into different types based on the morphology of the mature ovary, but in most insects they follow a common general pattern of development. In the fruitfly Drosophila, oogenesis begins with the formation of a 16‐cell cyst of interconnected germ cells, one of which will become an oocyte and mature into an egg. Cysts are produced by germline stem cells that remain active throughout the lifetime of the fly. The entire process of oogenesis, from germline stem cell to mature egg, takes about a week and depends on complex interactions between the different germ cells in a cyst and between the germ cells and the many different types of somatic cells that surround them. Given here is an overview of the morphology and development of the Drosophila ovary and cyst.

Key Concepts

Insect ovaries are classified on the basis of the morphology of the mature ovary.
Pole cells, the precursors of germ cells, are formed early in embryogenesis.
Germ cell formation depends on pole plasm, a specialised cytoplasm containing proteins that regulate the translation of specific mRNAs.
Drosophila oocytes develop in egg chambers, which are cysts of 16 interconnected germ cells enveloped by somatic follicle cells.
Oocyte differentiation depends on the fusome, a germ‐cell‐specific organelle.
Most of the oocyte's cytoplasm is made in the nurse cells and transported into the oocyte, which allows the oocyte's nucleus to remain quiescent.

Keywords: insect; ovary; oocyte; pole cell; germ cell; fusome

Article Title:	Drosophila Oogenesis
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	Figure 1. Diagram of Drosophila ovary development. Germ cells are depicted in yellow, somatic cells of the ovary are depicted in blue, anterior is to the left, and all stages (not to scale) are shown from a lateral perspective, with only one of the two gonads visible. Pole cells form at the posterior end of the early embryo (a) and migrate inward during gastrulation, where they contact somatic mesodermal cells to form embryonic gonads (b). In the larva (c), the gonads reorganise into individual ovarioles, and germ cells develop into germline stem cells. In the adult fly (d), stem cells divide continuously, producing daughter cells that develop into mature eggs. A typical female fly will lay hundreds of eggs (e) in her lifetime.
	Figure 2. Diagram of a Drosophila ovary (a), ovariole (b), and egg chamber (c), not to scale. Anterior is up, posterior is down. Germ cells are shown in yellow, yolk uptake in the ovariole (b) in red, somatic support cells at the tip of the germarium in green and somatic follicle cells, which envelop germline cysts, in blue. The egg chamber (c) is at stage 8; the oodyte (ooc) has begun to take up yolk but has not yet grown larger than its sibling nurse cells.
	Figure 3. (a) Diagram of a germarium. Anterior is to the left. The three regions of the germarium (1, 2 and 3) and position of an oocyte (ooc) are indicated. Terminal filament (dark green) and cap (light green) cells send signals (arrows) that maintain adjacent germline stem cells (yellow). Dividing cystocytes (light yellow) are wrapped by escort cells (purple). Fusomes (red) are round in stem cells and become elongated and branched in older cysts. Follicle cells (blue) envelop germline cysts. (b) Diagram of a germline cyst showing the pattern of connections between the oocyte and its sibling nurse cells. The direction of transport of materials into the oocyte is indicated (red arrowheads).