PARENT SESSION

(152) TRANSCRIPTION FACTOR AP-2 IS NECESSARY THROUGHOUT MOUSE EMBRYONIC DEVELOPMENT.

Guttormsen, Jillian¹, Williams, Trevor ², Winger, Quinton¹, ¹ Utah Sate University, Logan, UT² University of Colorado Health Sciences Center, Denver, CO

ABSTRACT- Mouse embryos lacking AP-2 die at around 7.5 dpc due to defects in extraembryonic trophoblast cell lineages. This early embryonic lethal mutation makes it difficult to study the role of AP-2 in the placenta or the embryo at later developmental stages. Therefore, little is known about the role of AP-2 in development after 7.5 dpc. This study uses a conditional gene targeting strategy to investigate the later developmental stages. Mice expressing Cre recombinase were used to produce the conditional mutation of an AP-2 floxed allele. The first mouse, Sox2-Cre, expresses Cre in the epiblast and in the extraembryonic derivatives, the yolk sac mesoderm and the amnion beginning at 6.5 dpc, the onset of gastrulation. The second mouse, Cre-ERTM, contains a ubiquitously expressed, tamoxifen-inducible form of Cre. This Cre is not active until combined with the drug tamoxifen, which can be injected into pregnant mothers to study the effect of the AP-2 deletion on embryos at late stages of pregnancy. Embryos that contained the Sox2-Cre mutation did not survive. We dissected and genotyped embryos at 8.5, 10.5 and 12.5 dpc to determine when the mutant embryos fail. Embryos containing the mutation were detected at all three days of development with no abnormal phenotype when compared to embryos without the mutation. Embryos collected at 10.5 and 12.5 dpc showed complete recombination of the AP-2 floxed allele while the corresponding yolk sacs were only partially recombined. The Sox2-Cre mutant embryos must fail some time after 12.5 dpc and before birth. To mutate AP-2 after day 14.5 of embryonic development we injected females pregnant with Cre-ERTM embryos three times at embryonic days 14.5, 16.5 and 18.5 dpc with tamoxifen (3 mg/40 g body weight of mother) and then evaluated the pups. Pups that contained the Cre-ERTM genotype were born but died at birth while littermate controls without the Cre survived. These results do not clarify whether the effect of the mutation was entirely within the placenta or if it may also have a role within the embryo. However, they prove that AP-2 has a critical role during the entire period of embryonic development.

KEY WORDS: AP-2, mouse, Cre-recombinase, embryo