Is a knockdown using shRNA permanent?

Whether or not knockdowns from shRNA gene silencing are permanent depends on the exact vector used. Delivery by (non integrase-deficient) lentivirus should be permanent on a theoretical basis, as the shDNA integrates into the cell's genome. However, continued transduction or other frequent treatments that edit or mutate the cell's DNA might have varying effects on the knockdown. While the probability should be low you could consider confirming the status of your knockdown in intervals of weeks to months, if you continue such experiments.

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shRNA transfection itself gives transient gene knockdown. shRNA mediated knockdown is normally more stable and longer than siRNA's which provide efficient silencing for up to a few days.However, you can integrate the shRNA sequence into a plasmid vector which in turn can integrate into the cell genome thereby providing stable long-term effects.

You usually have 48-36 hours of k.o. or k.d. after transfection, you can use Cas9 plasmid with the lentiviral delivery system to get stable k.o. or overexpression of your targets. If the process of vectors design and application is not well established in your lab. I suggest you contact Millipore Sigma or Thermofisher for initial constructs to establish the workflow. Then you can increase the complexity and design your own.

Whether or not knockdowns from shRNA gene silencing are permanent depends on the exact vector used. Delivery by (non integrase-deficient) lentivirus should be permanent on a theoretical basis, as the shDNA integrates into the cell's genome. However, continued transduction or other frequent treatments that edit or mutate the cell's DNA might have varying effects on the knockdown. While the probability should be low you could consider confirming the status of your knockdown in intervals of weeks to months, if you continue such experiments.