[Mosaic expression of the lacZ reporter-gene under control of 5'-regulatory sequences of the alpha-S1-casein gene in transgenic mice].

Phenomenon of mosaic expression at cellular level is widely presented in tissues and organs of transgenic animals. The communication is concerned a study of the mosaics in transgenic mice carrying the lacZ reporter-gene under control of the bovine and goat alpha-S1-casein genes with 5'-flanked sequences of various ex-tent: pCLZ1--721bp, pCLZ2-- 2001 bp and pCLZ3 3409 bp constructs. Five transgenic founders were generated by injection of the recombinant DNA into zygotes: pCLZ 1 - N 16, pCLZ2 - N 37 and pCLZ3 N 7, N 36, and N 48. Positive for J3-galactosidase activity cells were detected in lactating mammary glands of all transgenic females, however, distribution of the positive cells was variable. We observed two types of mosaics: clonal or "lobule" type with positive cells filling the whole of the globule or stochastic type with single positive cells scattered over one or different lobules. Two types of mosaics were characteristic of all the transgenic animals, although, females carrying the pCLZ2 transgene showed "lobule" type more often than transgenic animals with the transgenes pCLZ and pCLZ3. It is suggested that the stochastic type of mosaics occurs in the cells at terminal stage of differentiation, whereas the <> type arises from positive for P-galactosidase proliferating precursors. Analysis of the inheritance of the transgenes in different lines demonstrated that the pCLZl transgene was inserted in the X-chromosome of the founder whereas the other two localized in autosomes. Localization of the pCLZl transgene in the X-chromosome did not influence the mosaicism; it was similar to that of transgenic animals carrying the transgenes in autosomes. Ectopic expression of the reporter-gene was detected in mandibular glands from the offsprings of the founders N 16 and N 37 only, as well as in atrezed follicles in N 37. The weak ectopic expression saggests that the 5 S-flanked regulatory sequences used in the constructs are able to provide perfect tissue-specific expression of the reporter-gene.