Mechanisms of adaptive plasticity in feto-placental development

GONZALEZ P.; GASPEROWICZ M.; CROSS J; HALLGRIMSSON B

Congreso; European Evo-Devo Conference; 2012

In mammals, embryonic growth is dependent on maternal supply of nutrients mediated by the placenta. When the availability of nutrients is limited, the mechanisms that regulate resource allocation constitute key determinants of maternal and fetal survival. Thus, adaptive responses in placental phenotype that enhance the robustness of fetal development and increase the chances of maternal survival are expected to be favored by natural selection. This study investigated the responses of feto-placental development to maternal malnutrition. Two weeks before mating, C57BL/6J female mice were assigned to either a low-protein (LP) diet (6% protein) or a control isocaloric diet (20% protein). On days 17.5 and 18.5 of pregnancy conceptuses were dissected and tissue samples prepared for morphometric, stereological and RT-PCR analyses. Our results showed that body and cranial size were significantly reduced in the LP group only at E18.5, while the placentas were significantly lighter than in control animals at both ages. Accordingly, placental efficiency at E17.5, measured as the feto-placental weight ratio, was significantly higher in the LP than in the control group. There was a negative and significant correlation between placental efficiency and fetus weight in all groups except in LP at E18.5. At E17.5 the volume of placenta layer responsible for feto-maternal exchange, the labyrinth, was not changed between LP and control placentas. Interestingly, in LP group placentas, the dramatic and significant volume reduction was observed in another layer - the junctional zone – a layer rich in energy storing glycogen cells. Therefore we propose that junctional zone of the placenta might act as a buffer between maternal supply and fetal demand and play a fundamental role in resource allocation. Finally, we discuss the importance of studying the effects of environmental factors in multiple ontogenetic stages in order to understand the mechanisms of development plasticity that regulate production of phenotypic traits.