Objective: Cardiac morphogenesis in the mouse embryo occurs over a short period of time. More specifically, cardiac outflow tract and aortopulmonary septum formation occur between E9.5 and E13.5, concurrent with cardiac neural crest migration, which is required for conotruncal septation. The purpose of this study is to identify known and novel genes that participate in cardiac development either directly or indirectly through regulation of cardiac neural crest migration.

Methods: Representational difference analysis (a method of subtractive hybridization), was used to compare mRNAs expressed in the heart at E10.5 to those expressed a day later. Clones identified by this method were sequenced and tested for differential expression by northern dot blot screening. To date, we obtained 23 different sequences from 57 clones. Of 12 clones screened by dot blot, 6 were truly differentially expressed at E11.5, when compared to E10.5. Of these, two cardiac specific genes (a cardiac troponin T and an alpha-cardiac actin isoform), two non-cardiac genes (alpha and epsilon globin), a mitochondrial gene and one unknown were identified.In situ hybridization confirmed denovo expression or significant upregulation of the cardiac troponin T isoform and the mitochondrial sequence at E11.5. Other sequences with homology to F1Fo-ATP synthase, YB-1 protein, mouse cyclin B1, titin, an actin polymerization factor and two unknowns remain to be tested for differential expression at E11.5.

Conclusions: We have successfully isolated cardiac specific genes expressed at E11.5. The specific roles of these genes in cardiac development will be the subject of our further studies.