Fig. 6. aub is required for normal pole cell formation. Embryos produced by aub heterozygous (A-D) or aub mutant (E-H) females expressing an osk-bcd transgene. (A-C,E-G) Projections of multiple z-sections showing the location of Osk (fluorescence). (A-C) Transgenic Osk protein can be found at the anterior (A) in addition to the endogenous Osk at the posterior pole (B) of precellularized embryos. After cellularization, Osk can be found in pole cells at the anterior (C) and posterior (data not shown). (D) Pole cells (arrowheads) can be identified by their round cell bodies and nuclei while those of other cells at the surface of the blastoderm have become elongated. (E,F) In early stage embryos maternally mutant for aub, only the transgenic, anterior Osk (E) accumulates to high levels. Posterior Osk (F) is absent or greatly reduced. Note that anterior localization of nos mRNA in such early stage embryos is defective, despite the anterior accumulation of Osk protein (Wilson et al., 1996). Thus, the nos mRNA localization defect cannot be attributed to the subsequent dispersal of Osk protein seen in G. (G) By the time of cellularization in embryos from aub mutant females, local concentrations of Osk at the anterior are greatly diminished, and Osk often appears dispersed from the anterior pole. Osk occasionally is found in cells along the cortex, but only rarely do these have the morphological characteristics of pole cells. Osk protein is not maintained in these cells, as we never see Osk in late embryos from aub mutants, while it persists in both ectopic and native pole cells in embryos from aub heterozygotes (not shown). (H) No obvious pole cells are found at the anterior of an embryo maternally mutant for aub.
