Figure 4
From: A streamlined implementation of the glutamine synthetase-based protein expression system
Stability of the sorted cell populations. eGFP expression (A, gated on live cells) and FcERα yield (B) of FcERα-IRES-eGFP-GS-pOPINEE12G transfected CHO cells are stable for the first month after sorting, but then decrease over time. Cells were passaged in 75 cm2 flasks, split twice weekly. Every two weeks, 4×106 cells were used to seed a 75 cm2 flask. Forty-eight hours later, supernatants were collected for FcERα titre determination by competition ELISA, and for testing eGFP expression by flow cytometry. The levels of expression are lower than those in Figure 3 owing to the shorter period for accumulation of the protein. Error bars indicate standard errors for triplicate ELISA readings. “Freeze/thaw” denotes cells frozen at week 1 and thawed at week 11.