Abstract 20990: Targeted Deletion of Heparan Sulfate Modifying Enzyme, EXT1, Leads to Cardiac Abnormalities and Embryonic Lethality
Background and Objective: EXT1 (exostosin 1, positioned on human chromosome 8), and EXT2 are responsible for the polymerization of heparan sulfate attached to proteoglycan core proteins. The role of EXT1 and heparan sulfate are thought to be critically important in development given that EXT1−/− mice die between E6.5 and E9.5 due to defects in mesoderm formation. Heparan sulfate proteoglycans are necessary co-receptors for a number of ligands including FGF and Wnt that are critical for cardiac development. The role of EXT1 in heart is not understood. An array CGH analysis identified a de novo interstitial deletion in chromosome 8q in a newborn that contained the EXT1 gene, resulting in apical and ventral septal defects, and early death.
Methods and Results: To begin to define the role of EXT1 in the heart we analyzed a benchmark microarray dataset in cardiac development in C57BL/6 mice. This dataset revealed strongest expression of EXT1 at E10.5 and E11.5 compared to E12.5-E18.5. EXT1 expression was roughly 4 fold greater than EXT2. To define the role of EXT1 in cardiac development, we utilized a targeted cre-lox approach to delete EXT1 using the SM22a promoter which turns on in the heart and the vasculature at ∼E8.5. Out of the 5 litters born, no pups with the genotype SM22acre+EXT1−/− were observed. Littermates with other expected genotypes were viable and healthy and followed Mendelian ratios. Histological examination of E16.5 SM22acre+EXT1−/− embryos paraffin embedded sections revealed severe cardiac abnormalities. Staining with smooth muscle specific alpha actin revealed abnormal aorta size and structure in these embryos. The cardiovascular phenotype observed in the SM22acre+EXT1−/− embryos partially mimics the FGF8 deletion.
Conclusion: Expression of the heparan sulfate polymerizing enzyme, EXT1 is highest between E10.5-E11.5 in C57BL/6 mice. Targeted deletion of EXT1 with the SM22a promoter resulted in severe cardiac malformation at E16.5, embryonic lethality, and abnormal aortic size and structure. Further characterization is underway.
- © 2010 by American Heart Association, Inc.