Could you please advise me what could be the reason of loss of fluorescent protein expression? As a vector I take a lentiviral plasmid pUltra-hot(247629) in which the fluorescent protein mCherry has been replaced with genes encoding bsd resistance. Genes encoding the phytochrome binding protein (PIF) cross-linked to the mCherry protein have been inserted through the T2A peptide under the same promoter. I collect the lentivirus and transduce hek293T cells with it, after 72 some cells start to glow. Next, I start selection starting with a 5ug/ml of Bsd. In the control sample, all cells died after 4 days. In the post-traduction sample, the cells continue to grow after 10 days of selection, but the percentage of cells expressing fluorescent protein(PIF crosslinked with mCherry) decreases. Can you advise what could be the reason for this?