Foxa2 minimal notochord enhancer element mediates Cre expression in the node and notochord

Abstract

The Cre/loxP system is facilitates excision of DNA sequences located between two loxP sites by the Cre recombinase (Cre) of Bacteriophage P1. Generation of different tissue-specific Cre transgenic mice, which can be used for conditional gene inactivation in specific tissues, is an ideal tool for studying gene function in different tissues in mice. The winged-helix transcription factor, Foxa2, is essential for development of the node and notochord. In mouse, Foxa2 expression is observed in the node, notochord, floor plate and gut epithelium during development. In order to facilitate genetic studies of notochord development, we have used a 520 bp element (mNE) upstream of the Foxa2 gene, which directs specific expression in the node and notochord to generate a mouse line, mNE-Cre, in which the Cre gene was placed under the regulatory control of the mNE and linked to an IRES-lacZ reporter. Staining for b-galactocidase (b-gal) activity revealed that the Cre transgene was expressed from E7.5 to E9.5 specifically in the notochord. Moreover, crossing of the mNE-Cre transgenic mice with the loxP mouse reporter line, Z/EG, resulted in enhanced green fluorescent protein (EGFP) signal specifically in the node and notochord from E8.0 to E9.5. The mNE-Cre mice have been used to conditionally inactivate Smoothened (Smo) in the notochord, and preliminary data revealed that loss of both alleles of Smo in the notochord resulted in embryonic lethality. The mNE-Cre transgenic mice are therefore a useful resource for conditional gene manipulation in the notochord in mice.