The β1 Integrin Distal Promoter is Developmentally Regulated in Transgenic Mice

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Abstract
Transgenic mice harbouring 5′ flanking sequences of the human β1 integrin gene linked to the Escherichia coli lacZ gene have been generated to examine spatial and temporal distribution of the promoter activity during development. Our previous data showed that this regulatory region is composed by two promoters, called distal and proximal, located closely on the human genome. To determine the role of each promoter region during development we generated transgenic mice using these two sequences linked to the lacZ reporter gene. Their analysis shows that these two sequences, as determined by in vitro studies, have different efficiencies in promoting transcription. Actually mice carrying the proximal promoter region exhibit a weak lacZ expression resulting in an undetectable β-galactosidase activity in both embryonic and adult tissues. On the other hand, transgenic mice carrying the distal promoter express β-galactosidase at high efficiency during embryonic development. The pattern of transgene expression is consistent with the localization of β1 protein on mouse embryos evidenced by immunohistochemistry. Moreover the distal promoter is subjected to a temporal modulation since in adult transgenic mice lacZ expression decreases to a level detected only by RT-PCR analysis. We have determined a similar down-regulation analysing by Northern blot β1 mRNA in adult and embryonic organs such as heart and gut.