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lacZ sequences prevent regulated expression of housekeeping genes

Abstract : In order to dissect the MHC class I H-2K gene regulatory sequences, we p reviously generated transgenic mice containing various H-2K/lacZ fusion genes. However contrary to transgenes where H-2K sequences were fused to other coding sequences, none of the lacZ fusion transgenes was widely ex pressed like H-2K gene. We now show that this silencing also occurs when lacZ is inserted into a larger H-2K genomic construct including promoter and other regulatory elements. Because the 5'H-2K region contains a CpG island, we suspected that the presence of lacZ coding sequences was inte rfering with the mechanism by which the H-2K promoter region is normally unmethylated and transcriptionally active. Indeed, we show that in high ( >10) copy number transgenic mice, insertion of lacZ sequences in the v icinity of the H-2K promoter results in partial or complete methylation of the H-2K CpG island. However, in low (1-3) copy number transgenic mic e no methylation was observed but the transgene was still silent, sugges ting that the silencing effect of lacZ does not only rely on abnormal CpG methylation. Intriguingly, when the H -2/lacZ construct was introduced via embryonic stem (ES) cells, regulate d transgene expression was observed in several chimaeric embryos derived from independent ES clones, but never in adult chimeras. Combined with t he fact that, despite much effort, it has been very difficult to generat e 'blue' mice, our results highlight the transcription-silencing effect of lacZ sequences when they are associated with regulatory sequences of ubiquitously expressed genes.
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https://hal-pasteur.archives-ouvertes.fr/pasteur-02075550
Contributor : Michel Cohen-Tannoudji <>
Submitted on : Thursday, March 21, 2019 - 2:45:11 PM
Last modification on : Wednesday, October 14, 2020 - 3:47:48 AM

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Michel Cohen-Tannoudji, Sandrine Vandormael-Pournin, Michel Drezen, Pascale Mercier, Charles Babinet, et al.. lacZ sequences prevent regulated expression of housekeeping genes. Mechanisms of Development, Elsevier, 2000, 90 (1), pp.29-39. ⟨10.1016/S0925-4773(99)00226-9⟩. ⟨pasteur-02075550⟩

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