Conventional knock-out approach is a powerful tool to study the role of specific genes but with about 40 ％ of genes inactivation leading to prenatal or early post-natal lethality (1) additional strategies were developed to allow site specific and time controlled inactivation of the gene of interest.The CreloxP system was developed to allow the conditional inactivation of gene of interest and to overcome these limitations.In such strategy, the allele of interest is flanked by loxP recognition sites for the Cre recombinase.