EcollacZrho-R1.1 expression is spatially and temporally restricted compared to expression of the endogenous rho gene. Whereas rho mRNA is expressed initially in a 'saddle'-shaped domain encompassing all the dorsal-appendage-forming cells starting at oogenesis stage 9 (FBrf0057902), EcollacZrho-R1.1 is expressed exclusively in floor cells, starting at oogenesis stage 10B. While the majority of the floor cells express EcollacZrho-R1.1, some do not due to variability of marker expression. The authors report that this is "random from one egg chamber to the next and thus is not likely to be significant".