Abnormal labyrinthine zone in the Hectd1-null placenta

Together these defects indicate that Hectd1 is required for development of the labyrinthine zonethe mouse placenta.

The structure of the mutant placenta was compared to wildtype littermates using histological methods. The expression of cell type specific markers was examined by immunohistochemistry and in situ hybridization.

Hectd1 is expressed in the labyrinthine zone throughout development and the protein is enriched in syncytiotrophoblast layer type I cells (SynT-I) and Sinusoidal Trophoblast Giant cells (S-TGCs) in the mature placenta. Mutation of Hectd1 results in pale placentas with frequent hemorrhages along with gross abnormalities in the structure of the labyrinthine zone including a smaller overall volume and a poorly elaborated fetal vasculature that contain fewer fetal blood cells. Examination of molecular markers of labyrinthine trophoblast cell types reveals increased Dlx3 positive cells and Syna positive SynT-I cells, along with decreased Hand1 and Ctsq positive sinusoidal trophoblast giant cells (S-TGCs).