Fig. 1. The germarium, a niche for germline stem cells. (A) A wild-type ovariole showing the germarium (anterior tip; bracket) and a string of developing egg chambers, all of which derive from the activity of stem cells in the germarium. The oocyte is the cell located at the posterior of the cysts that accumulates most of the green staining. The dashed line labels the anterior half of the germarium hosting the germline stem cells represented in B and pictured in C and E. Red: F-actin staining to show the shape and arrangement of somatic and germline cells. (B) The scheme represents different cell types present in a wild-type germarium. Terminal filament cells, cap cells and inner sheath cells are of somatic origin (the dpp gene is expressed in the cap cells); the differentiating germline cells are the cystoblast (daughter of a stem cell) and the cystocytes, which form part of 2-, 4-, 8- and 16-cell cysts. The organelle in red is the fusome, which acquires a spherical shape in germline stem cells and in cystoblasts in interphase, and a branched appearance in developing cysts. (C) Wild-type germarium stained with F-actin to visualise the shape of somatic cells (red); germline cells are stained in green. The large cells in contact with the cap cells are germline stem cells. Note the apposition of both cell types. (D) Wild-type germarium showing the localisation of the Armadillo protein in the junctions between cap cells, and between the cap cells and the germline stem cells. This focal plane depicts only three cap cells. (E) Wild-type germarium showing the apical localisation of the spherical fusome present in germline stem cells. Asterisks label cap cells.

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