Homozygous females defective in proliferation, differentition, or maturation of the germ line, depending on the
level of activity of the particular allele. So-called quiescent alleles (QUI) produce ovarioles lacking in germ cells;
oncogenic alleles (ONC) produce cystocytes that continue
dividing and form tumors; differentiated alleles (DIF) produce
chambers containing only "pseudonurse" cells (PNCs) or nurse
cell/oocyte (NC/O) syncytia. In these, transport of nurse
cell cytoplasm to the oocyte is inhibited and chambers are
arrested at a pseudo-12 stage [Bishop and King, 1984, J. Cell
Sci. 67: 87-119 (fig.)]. Mutant nurse cells that fail to
pump their cytoplasm into the oocytes are also unable to form
a system of actin microfilament bundles in their cortical
cytoplasm during stage 10B (Storto and King, 1988, Dev. Genet.
9: 91-120). The proportions of ovarioles with the different
phenotypes appear to reflect the level of function of the particular allele; homozygotes are less severely affected than
hemizygotes (80% of ovarioles of females carrying otu1, otu4,
otu5, or otu7 in combination with an otu deficiency lack germ
cells, whereas 5% of the ovarioles of homozygotes lack germ
cells); similarly, the levels of function of certain alleles
decline as the developmental temperature is raised. Thus otu1
behaves like a DIF allele at 18, an ONC allele at 23, and a
QUI allele at 28.
The ovarian tumors which give the mutant gene its name are
made up of large numbers of single cystocytes and small
numbers of clones of 2-4 interconnected cells [King, 1979,
Int. J. Insect Morphol. Embryol. 8: 297-309 (fig.)]. Most
cystocytes undergo complete cytokinesis, and there are defects
in the construction and functioning of the polyfusomal system
during the cycles of cystocyte divisions [Storto and King,
1989, Dev. Genet. 10: 70-86 (fig.)]. Drosophila nurse cells
normally undergo nine or ten cycles of DNA replication (Mulligan and Rasch, 1985, Histochemistry 82: 233-47), and the
chromatids dissociate so that each nucleus is filled with a
jumbled mass of oligotene threads. In otu PNCs, the chromatids remain in register, generating banded polytene chromosomes [Dabbs and King, 1980, Int. J. Insect Morphol. Embryol.
9: 215-29 (fig.)]. Homologues pair and rearrangement configurations can be discerned [King, Riley, Cassidy, White, and
Paik, 1981, Science 212: 441-43 (fig.)]. The largest
polytenes have undergone 12 cycles of endonuclear replication
(Rasch, King, and Rasch, 1984, Histochemistry 81: 105-10).
The banding pattern of PNC polytenes is similar to that of the
polytenes from larval salivary gland cells (Sinha, Mishra, and
Lakhotia, 1987, Chromosoma 95: 108-16; Heino, 1989, Chromosoma 97: 363-73).
At 25, otu11 behaves as an ONC allele, the cells dividing to
form tumors, but at 18, homozygous females produce oocytes
that reach a pseudo-14 stage, contain beta yolk spheres and
can undergo early embryogenesis. In the case of DIF alleles
such as otu4, females generate pseudo-12 eggs which lack beta
yolk spheres and never initiate development. When otu11 is
combined with alleles from the QUI class such as otu2, the
heteroallelic females are sterile. Heteroalleles between
otu11 and certain DIF alleles show various degrees of fertility [Storto and King, 1987, Roux's Arch. Dev. Biol.
196: 210-21 (fig.)]. otu11/otu14 females are fully fertile
although the nurse cells, unlike those of wild-type females,
contain banded chromosomes (Storto and King, 1988).
Oocyte differentiation is destabilized in certain otu
alleles; for example, the presumptive oocytes in about 20% of
otu7 homozygotes resemble nurse cells in their polytenization,
although they lag behind the remaining nurse cells by at least
one replication cycle [King, Rasch, Riley, O'Grady, and
Storto, 1985, Histochemistry 82: 131-34 (fig.)]. Germ line
autonomy has been demonstrated for otu3, otu4, and otu7
(Wieschaus, Audit, and Masson, 1981, Dev. Biol. 88: 92-103;
unpublished work cited in King et al., 1986).