Nomenclature: C57BL/6–Ext1^tm1.1Tac

• The targeting strategy allows the generation of a conditional Knock-Out (KO) and a constitutive KO of the Ext1 gene. This model carries the conditional (floxed) allele.
• Ext1 exon 1 contains the translation initiation codon. Part of exon 1 (including 230 bp of the 5' untranslated region (UTR) and the coding part of exon 1) has been flanked by loxP sites (size of loxP-flanked region is 1.5 kb).
• The constitutive KO allele can be obtained after in vivo Cre-mediated recombination. Deletion of the part of exon 1 will remove the translation initiation site as well as the splice donor of exon 1 and should result in the loss of function of the Ext1 gene. Note that efficiency of in vivo Cre-mediated deletion depends on the genomic locus and the Cre mouse strain used.
• Insertion of the proximal loxP site into the 5' UTR may alter the expression levels of the Ext1 gene in the conditional configuration
• After Cre-mediated recombination, a truncated protein may be produced. Ext1 mRNA may still be produced as well since the transcription initiation regulatory elements are not intended to be modified. This transcript may not be as stable as wild type transcript. Due to the lack of the translation initiation site, any transcript produced may not be translated into protein. Any truncated protein produced shall not be as functional as full length, wild type protein as the deletion has removed the transmembrane domain and the glycosylation site close to the N terminus. Production of mRNA or protein has not been evaluated in this model.