Cup Blocks the Precocious Activation of the Orb Autoregulatory Loop
Figure 5
orb mRNA is mislocalized in cup mutants.
In wild type, orb mRNA can first be detected in the germarium (panel A). It appears concentrated in a single cell that is thought to correspond to the presumptive oocyte. During the previtellogenic stages (panel A), orb mRNA is localized at the posterior end of the oocyte, while there are only low levels in the nurse cell cytoplasm. After the onset of vitellogenesis (panel B), orb mRNA accumulates along the anterior margin of the oocyte. In many cup8 chambers orb mRNA is not properly localized and reduced in level (arrowheads in C). Sometimes a single cell can be seen which has high levels of orb mRNA (D & E); however, this cell is not always positioned correctly (arrow in D). Mislocalized orb mRNA is also seen in cup3. In the examples shown in F and G the level of orb mRNA in the nurse cells is high, while the level in the presumptive oocyte is relatively low (compare levels of orb mRNA in nurse cells and oocyte in the wild type (arrow in panel A) and mutant (arrow in F and G) chambers). The pattern of orb mRNA accumulation in cup1355 chambers (panels H and I) more closely resembles wild type; however, in older chambers the mRNA is not properly localized to the anterior margin and higher than normal levels are seen in the nurse cells (panel I).