Tet-Free FBS — Tetracycline-Free FBS for Tet-On / Tet-Off Inducible Systems | SeamlessBio
FBS Tet-Free — Tetracycline-Free FBS for Tet-On & Tet-Off Inducible Expression Systems
Standard FBS contains tetracycline residues from antibiotic use in bovine feed and veterinary treatment — typically 1–10 ng/mL, occasionally higher. This is sufficient to partially suppress tetracycline-responsive promoters in Tet-On and Tet-Off inducible expression systems, causing leaky baseline expression in Tet-Off systems and reduced inducibility in Tet-On systems. Tet-Free FBS is specifically tested and certified to contain less than 1 ng/mL tetracycline, ensuring full dynamic range of inducible expression.
The problem in practice: Researchers using Tet-On/Off systems with standard FBS frequently observe baseline leakiness or reduced induction fold-change. Switching to Tet-Free FBS typically restores the expected dynamic range. If your Tet-Off system shows expression even without doxycycline addition, tetracycline contamination in the serum is the most likely cause.
Why Tetracycline in Standard FBS is a Problem
| System | How it Works | Effect of Tetracycline Contamination |
|---|
| Tet-Off (tTA system) | tTA activates promoter in ABSENCE of tetracycline/dox. Adding dox → gene OFF. | Tetracycline in FBS partially occupies tTA → baseline expression suppressed even without dox addition. System appears "leaky OFF". |
| Tet-On (rtTA system) | rtTA activates promoter in PRESENCE of doxycycline only. No dox → gene OFF. | Tetracycline in FBS partially activates rtTA → low-level baseline expression without dox. Reduces fold-induction because baseline is elevated. |
| CRISPR dCas9-TetO CRISPRi/a | Tet-responsive transcriptional activators/repressors | Same problem as Tet-On — tetracycline background reduces dynamic range of gene activation/repression |
Applications
| Application | Cell Lines / Systems |
|---|
| Tet-On inducible gene expression (doxycycline-inducible) | HEK293 Tet-On, HeLa Tet-On, U2OS Tet-On, any stable or transient Tet-On line |
| Tet-Off inducible systems | Any tTA-based cell line where dox removes expression |
| CRISPR interference / activation (CRISPRi/CRISPRa) with Tet-inducible components | dCas9-KRAB-TetR or dCas9-VP64-TetO systems |
| Inducible shRNA / siRNA systems (Tet-inducible) | pTRIPZ, pSLIK, or any Tet-responsive shRNA vector system |
| Inducible Cre recombinase systems | Tet-Cre mouse-derived cell lines, inducible Cre-ERT2 with Tet component |
Specifications
| Parameter | Specification |
|---|
| Tetracycline content | <1 ng/mL — tested by HPLC or ELISA per lot |
| Sterile filtration | 0.1 µm |
| Endotoxin | Tested per lot (LAL) |
| Mycoplasma | Tested — negative |
| BVDV | Tested — negative |
| Growth performance | Validated on reference cell lines — comparable to standard FBS |
| Origin | EU and/or US |
| Volumes | 100 mL, 500 mL | Bulk on request |
| Storage | −20°C | Batch reservation available |
| Documentation | CoA with tetracycline test result, CoO, MSDS |
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