Tamoxifen (TAM) inducible Cre recombinase system is an essential tool to study gene function when early ablation or overexpression can cause developmental defects or embryonic lethality. However, there remains a lack of consensus on the optimal route and dosage of TAM administration in vivo. Here, we assessed dosage and delivery of TAM for activation of Cre in immune cell subsets assessed longitudinally and spatially using transgenic mice with ubiquitously expressed Cre/ER and the Cre-inducible fluorescent reporter YFP. After comparing two TAM delivery methods (intraperitoneal versus oral gavage) and different doses, we found that 3 mg of TAM administered orally for five consecutive days provides maximal reporter induction with minimal adverse effects in vivo. Serum levels of TAM peaked 1 week after initiating treatment then slowly decreased, regardless of dosing and delivery methods. TAM concentration in specific tissues (liver, spleen, lymph nodes, and thymus) was also dependent on delivery method and dose. Cre induction was highest in myeloid cells and B cells and substantially lower in T cells, and double-positive thymocytes had a notably higher response to TAM. In addition to establishing optimal dose and administration of TAM, our study reveals a disparate activity of Cre in different cell immune populations when using Cre/ER models.

当早期消融或过度表达会导致发育缺陷或胚胎致死时，他莫昔芬 (TAM) 诱导型 Cre 重组酶系统是研究基因功能的重要工具。然而，关于体内 TAM 给药的最佳途径和剂量仍缺乏共识。在这里，我们使用具有普遍表达的 Cre/ER 和 Cre 诱导型荧光报告基因 YFP 的转基因小鼠，评估了 TAM 的剂量和递送以激活免疫细胞亚群中的 Cre。在比较了两种 TAM 递送方法（腹膜内与口服管饲）和不同剂量后，我们发现连续五天口服 3 mg TAM 可提供最大的报告基因诱导，而体内副作用最小。TAM 的血清水平在开始治疗后 1 周达到峰值，然后缓慢下降，无论给药方式和给药方式如何。特定组织（肝脏、脾脏、淋巴结和胸腺）中的 TAM 浓度也取决于递送方法和剂量。Cre 诱导在骨髓细胞和 B 细胞中最高，在 T 细胞中显着降低，双阳性胸腺细胞对 TAM 的反应明显更高。除了确定 TAM 的最佳剂量和给药方式外，我们的研究还揭示了使用 Cre/ER 模型时不同细胞免疫群体中 Cre 的不同活性。