Zac1 regulates an imprinted gene network critically involved in the control of embryonic growth.

Genomic imprinting is an epigenetic mechanism of regulation that restrains the expression of a small subset of mammalian genes to one parental allele. The reason for the targeting of these approximately 80 genes by imprinting remains uncertain. We show that inactivation of the maternally repressed Zac1 transcription factor results in intrauterine growth restriction, altered bone formation, and neonatal lethality.