100: Disruption of Igf2 signaling in rat hemochorial placental development results in fetal growth restriction

Abstract

Insulin-like growth factor 2 (Igf2) is a maternally imprinted gene, which has been implicated in the regulation of hemochorial placental development. This study characterized fetal and placental weights in rat litters produced by wildtype versus heterozygous Igf2 mutant breeding pairs across various time points. Igf2 null rats were generated using Crispr/Cas9 genome editing by deleting a 1751 bp region in the Igf2 locus, resulting in a frameshift and premature stop codon. A founder male pup with the deletion was then backcrossed with a wildtype female to produce heterozygous rats. Given Igf2 is paternally expressed, two breeding schemes were utilized. First wildtype females were crossed with heterozygous Igf2 males. Secondly, heterozygous Igf2 females were crossed with wildtype males. Fetal and placental weights were obtained for gestational days 15.5, 18.5 and 20.5. Placentas were then separated so that the labyrinth and junctional zones could be independently weighed. IHC of placentation sites was also performed. Igf2+/pat pups were significantly smaller compared to their wildtype siblings at all time points. The overall placental weights were also found to be significantly smaller, primarily due to the decrease in the weights of the labyrinth zone. At gestational days 18.5 and 20.5, the labyrinth zone to junctional zone ratio was found to be significantly lower for Igf2+/pat compared to controls. IHC also demonstrated a reduced thickness of the labyrinth zone in Igf2+/pat pups compared to their wildtype litter mates. No difference in fetal or placental weights was seen in Igf2mat/+ compared to Igf2+/+. Maternally-inherited Igf2 mutation lead to the development of small placentas and growth restricted pups. A reduction in the size of the labyrinth zone was the primary reason for the reduction in placental size. Given that the labyrinth zone is analogous to human villous trophoblasts, it is possible that the fetal growth restriction seen here is secondary to an impairment of nutrient transfer to the rat fetuses.View Large Image Figure ViewerDownload Hi-res image Download (PPT)