Vasa-Cre (Ddx4-Cre) transgenic mice express Cre recombinase under the direction of the mouse Ddx4 promoter.
In Goodwin et al. 2019 Genome Res. 29:494, analysis of the Ddx4-Cre parental strain (Stock No. 006954) identified more than 20 transgene copies integrated on chromosome 18 that caused a 1098 kbp deletion encompassing two loci - neuropilin (NRP) and tolloid (TLL)-like 1 (Neto1) and cerebellin 2 precursor protein (Cbln2). The deletion results in a functional knock-out of both genes in homozygous mice.
Mice hemizygous for this Ddx4-Cre transgene are viable and fertile. Transgenic cre activity is directed to male and female germ cells starting at embryonic day (e)15-e18. When bred with mice containing a loxP-flanked sequence of interest, Cre-mediated recombination will result in deletion of the flanked sequence. In such breedings, occasional hemizygous mice may exhibit variegated cre expression in skin epithelium or global cre expression (<20% incidence). Differential parent-of-origin transgene expression is observed. When the mother harbors Ddx4-Cre, virtually all progeny undergo global Cre-mediated recombination, even those that do not inherit the transgene (which may be useful in converting a "floxed" allele to a null while obviating the need to perform additional crosses to remove the transgene). To achieve germ-line specific Cre-mediated recombination in offspring, paternal Ddx4-Cre mice should be used.
In crosses with some floxed alleles, global recombination may occur even when males are used as the Dxd4-Cre carriers. The basis of this "paternal" effect is not known, but may relate to the presence of Cre protein in sperm. This global recombination can occur more frequently with older males. Thus, when paternal-effect global recombination is observed, it is recommended that the youngest available Ddx4-Cre males be used for breeding (ideally 5-6 weeks, but less than 9 weeks of age). Once a male has proven to repeatedly give rise to globally-recombined progeny, he should no longer be used as a breeder.
These Ddx4-Cre mice may be useful in generating conditional germ cell knock-outs in both males and females for studies including infertility, gonadogenesis, gametogenesis, and the assembly, activation, and growth of primordial follicles.
While another germ line cre-expressing strain, ZP3-Cre (see Stock No. 003651), permits recombination/deletion of loxP-flanked genes in growing follicles, Ddx4-Cre mice have additional cre expression in primordial follicles (early oogenesis) and in the male germline.
If the recombinase activity pattern of this allele is further characterized by the Genetic Resource Science group at The Jackson Laboratory, such findings will be reported on the Mouse Genome Informatics (MGI) Allele Detail entry (Tg(Ddx4-cre)1Dcas). This same information would also be found searching the MGI Recombinase Activity database.
In an attempt to offer alleles on well-characterized or multiple genetic backgrounds, alleles are frequently moved to a genetic background different from that on which an allele was first characterized. This is the case for the strain above. It should be noted that the phenotype could vary from that originally described. We will modify the strain description if necessary as published results become available.
