Use of doxycycline-controlled gene expression to reversibly alter milk-protein composition in transgenic mice

A reverse tetracycline transactivator-encoding cDNA under the control of th e mammary specific P-lactoglobulin promoter was linked to a bovine cr-lacta lbumin transcription unit driven by a reverse tetracycline-controlled trans activator/doxycycline-inducible human cytomegalovirus promoter. The constru ct was microinjected into eggs from alpha-lactalbumin-deficient mice. These mice produce a highly viscous lactose-free milli and have a shortened lact ation period. Mice from three out of the nine transgenic Lines investigated expressed reverse tetracycline-controlled transactivator mRNA in their lac tating mammary glands at levels detectable by Northern analysis. Following doxycycline addition to the drinking water, lactation was fully restored in animals from the three lines. Doxycycline removal resulted in a reversal o f phenotype. The observed mammary-specific and high expression of the doxyc ycline inducible reporter gene (up to 5.2 mg of recombinant alpha-lactalbum inm.mL(-1) of milk, i.e. up to 13-fold induction) opens up exciting prospec ts to use the tetracycline system to study the development and functioning of the mammary gland, and to control the production level of active pharmac eutical proteins in the milli of transgenic animals.