Fig. 6. osk mRNA and Osk protein distribution appear normal initially in vls mutant ovaries but Osk protein disappears from the posterior pole after stage 11. (A) In situ hybridization with an osk probe to a vls^null stage 10 egg chamber. osk mRNA is correctly concentrated at the posterior of the oocyte in vls^null mutants. (B-E'') Immunostaining with -Osk antibodies on wild-type and vls mutant ovaries. Osk signal is tightly concentrated at the posterior of stage 9-10 oocytes of wild type (B-B') and vls^null vls⁺ (C-C'), as well as in vls^PG65 (D-D') and vls^null (E-E') females. However, around stage 11, Osk signal appears slightly weaker at the posterior of vls^PG65 (D'') and significantly weaker in vls^null oocytes (E''). This defect is even more pronounced in vls^null after stage 11, where usually no posterior Osk signal is detected (not shown).