Efficient Array-based Identification of Novel Cardiac Genes through Differentiation of Mouse ESCs

Cardiac disease accounts for the largest proportion of adult mortality and morbidity in the industrialized world. However, progress toward improved clinical treatments is hampered by an incomplete understanding of the genetic programs controlling early cardiogenesis. To better understand this process, we set out to identify genes whose expression is enriched within early cardiac fated populations, obtaining the transcriptional signatures of mouse embryonic stem cells (mESCs) differentiating along a cardiac path. We compared the RNA profiles of cardiac precursors cells (CPCs) with time-matched non-CPCs and undifferentiated mESCs, using a transgenic mESC line harboring an Nkx2-5 cardiac-specific regulatory sequence driving green fluorescent protein (GFP) to facilitate selection of CPCs. Approximately 24% (43/176) of the transcripts enriched in the CPC population have known roles in cardiac function or development. Importantly, we evaluated the biological relevance of a subset 31/133 (23%) of the remaining candidate genes by in situ hybridization and report that all were expressed in key cardiac structures during cardiogenesis (embryonic day, E7.5 - 9.5), many of which were previously uncharacterized. These data demonstrate the power of mESC differentiation to model specific developmental processes and provide a valuable resource that may be mined to further elucidate the genetic programs underlying cardiogenesis. Keywords: time course, differentiated cardiac cell fate Transgenic mouse embryonic stem cell line (Nkx2-5-GFP, PMID:9834187) contains an Nkx2-5 cardiac-specific transcription factor driving expression of green fluorescent protein (GFP). Cells were differentiated through embryoid body formation (hanging droplet technique) as described in PMID:8155574. Following primary mouse embryonic fibroblasts (PMEF) feeder subtraction, mESCs were dissociated and resuspended in differentiation medium. Cells at this time point were designated as day 0. Following incubation for two days, the EBs were transferred, in suspension, to poly-HEMA coated tissue culture dishes to prevent cell attachment and grown in medium containing ascorbic acid PMID:12668514) which was replenished every 3 days thereafter. Cells were harvested on days 0, 4 and 6 in three biological replicates each (1a, 2a and 3a), washed in PBS for 30 minutes at 37ºC then resuspended in 0.25% trypsin for 7 minutes. Cells from day 6 were then sorted using the BD Biosciences FACSAria™ Cell sorting system into GFP+ and GFP- fractions into RLT buffer (RNeasy, Qiagen). This sorting separates cells into two groups reflecting their differentiation into those fated to a non-cardiac lineage (GFP negative) and to a cardiac lineage (GFP positive).