Cardiac Cre Lineage Maps
I love lineages, and I am fascinated by in vivo biological studies using loss and gain of function models, but it is good (essential, actually) to know where and when, exactly, your Cre of choice is active. I've included images from a few of the more utilized Cre lines below after crossing them into the Rosa-mTmG reporter line. All embryos were harvested at E14.5 and imaged live, then the hearts were removed and fixed overnight and processed for vibratome embedding and sectioning. The images are of "live" fluorescence, and are not immunostained or amplified. The sections are 150 micron vibratome sections (in the transverse plane) from the dissected hearts. They proceed from the ventral surface of the heart (on the left) to the dorsal surface (on the far right), with several sections in between not shown for the sake of space. If this is of interest please check back, as I will add other Cre lines to the panel.
For those who aren't aware:
Isl1-Cre/+ (MGI#3623159, Yang et al., Development, 2006) has variable recombinase activity. This can be seen here. While rare, you can absolutely get any one of those various activities in your embryos, although the activity shown below (on this page) is the dominant pattern you will see. Accordingly, you must have a reporter in the background to verify the extent of the allele's activity in order to make confident inferences about phenotypes observed using this Cre.
The Tg(Mef2c-AHF-Cre) (and the Dre allele) line has activity in the female germline, and it acts as a universal deleter Cre. Thus, it is a good idea to maintain this Cre in males (unless you want to make a global null allele-which we often use this line for, since the offspring don't have to inherit the Cre to be KO/+, and this can save a generation of mating if you're lucky).
Tbx5-CreER-IRES-2XFLAG/+ (Devine et al., Elife, 2014) is a hypomorphic allele. Irfan Kathiriya in the Bruneau lab is studying the exact mechanism and phenotype of these mice. The images below were pulsed with tamoxifen at E7.5.