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Fig. 1. Generation of germline mosaics. (A) Each germline cyst arises from a single
cystoblast through four consecutive rounds of mitosis. Incomplete cytokinesis
after each mitosis results in a stereotyped pattern of cytoplasmic bridges
between the 16 cells of the cyst. Either of the two cells with four ring
canals will become the oocyte. Recombination in the germline stem cell
divisions generates clonal germline cysts (not shown), while mitotic
recombination during the first division of a heterozygous cystoblast results
in a mosaic cyst consisting of eight wild-type cells (green) and eight mutant
cells (blue). In such mosaics, the oocyte nucleus can be either wild type
(left) or mutant (right). (B) Generation of mosaics with the nuclear GFP
marker. Induction of the Flp recombinase (not shown) in heterozygous cells
(left, shown after DNA replication but before mitosis) mediates mitotic
recombination at FRT sites (triangles), resulting in homozygous daughter
cells. grk2B6/grk2B6 cells are marked by the
lack of GFP expression. (C) In the lacO/GFP-LacI system, the starting
heterozygous cells contain the lacO transgene in cis to the
grk2B6 mutation, as well as the GFP-LacI transgene. All
cells exhibit nuclear GFP-LacI fluorescence, and discrete fluorescent foci are
visible in the nuclei of cells with the lacO transgene. Heterozygous females
exhibit a single focus of GFP in the oocyte nucleus and multiple foci in the
polyploid nurse cells. Homozygous wild-type daughter cells lack these foci,
while grk2B6/grk2B6 oocyte nuclei exhibit two
foci.
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