Isl1Cre mice express Cre recombinase under the control of the endogenous ISL1 transcription factor, LIM/homeodomain (Isl1) promoter. ISL1 is expressed in undifferentiated cardiac progenitors and hindlimb progenitors. Expression in both locations is downregulated as these cells migrate into the heart or limb, respectively. Isl1 expression is ablolished in this strain. When crossed with a strain containing a loxP site-flanked sequence, Cre-mediated recombination results in deletion of the flanked sequence in cardiac and hindlimb progenitor cells. Heterozygotes are viable and fertile, homozygotes are embryonic lethal.
For example, when bred to mice expressing a floxed version of the bone morphogenetic protein receptor, type 1A (Bmpr1a), lack of BMP signaling in cardiac and hindlimb progenitor cells leads to complete neonatal lethality by E14.5, due to abnormal fetal cardiomyocyte development and persistent truncus arteriosis. These mice also exhibited smaller hindlimb buds and abnormal hindlimb formation.
