Preparation and delivery of 4-hydroxy-tamoxifen for clonal and polyclonal labeling of cells of the surface ectoderm, skin, and hair follicle.

To study the cell behavior during morphogenesis of mouse surface ectoderm, skin, and hair follicles, we (1-3) have developed a new method to temporally induce clones that is based on a tamoxifen-dependent Cre recombinase. The classical protocol consisting in dissolving 4-hydroxy-tamoxifen or tamoxifen in corn oil to perform intraperitoneal (ip) injections (4) is not optimal to control the pharmacokinetic parameters of the induction as it leads to experimental variability in terms of timing and level of induction. We have developed a new protocol that consists in solubilizing 4-OHT or tamoxifen in an aqueous solvent using Cremophor(®) EL (5). This allows for intravenous (iv) and intraperitoneal injections.