Multigenerational effects of abnormal folate metabolism on embryo growth and development

Change log
Menelaou, Katerina 

It has been known for decades that maternal folate deficiency impairs fetal development. However, the molecular mechanism of folate metabolism remains unclear. To explore this, we study a mouse model of abnormal folate metabolism whereby the gene Mtrr was mutated causing a knockdown effect. MTRR is a key enzyme required for the progression of folate and methionine metabolism, which are important for DNA synthesis and cellular methylation. The Mtrrgt mutation disrupts folate metabolism, alters global and locus-specific DNA methylation, and causes a wide spectrum of developmental phenotypes including growth defects and congenital malformations. Remarkably, the Mtrrgt mouse line is a model of transgenerational epigenetic inheritance since the congenital malformations persist at least up to four wildtype generations after an Mtrr+/gt maternal grandparent. In contrast, the growth phenotypes only appear until the F2 generation and have been attributed to an atypical uterine environment in the wildtype F1 generation as determined by a blastocyst transfer experiment. This thesis aims to examine how the Mtrrgt mutation influences uterine biology and fetoplacental growth. First, the effects of intrinsic and parental Mtrr deficiency on uterine structure and function at estrus and decidualisation at gestational day (GD) 6.5 were determined. We found that a paternal Mtrrgt allele was sufficient to alter the cellular structure of the uterine epithelium and outer myometrium at estrus. Furthermore, decidualisation was abnormal at GD6.5 based on mRNA expression analysis of key decidual markers. Next, to determine how an atypical uterine environment caused by the Mtrrgt mutation might influence fetoplacental growth, an unbiased transcriptome analysis of placentas at embryonic day (E)10.5 with specific growth phenotypes and from specific Mtrrgt pedigrees was completed. The Mtrrgt/gt mutation altered the placental transcriptome in a phenotype-specific manner. Genes involved in embryo growth and placental transport were differentially expressed between Mtrrgt/gt and C57Bl/6 placentas. This result suggests that intrinsic Mtrr deficiency affects the placental transcriptome and potentially fetal growth. However, transcriptomes of C57Bl/6 placentas and placentas of wildtype conceptuses derived from an Mtrr+/gt maternal grandfather were similar. This suggests that the F1 uterine phenotype caused by abnormal folate metabolism in F0 does not affect the placental transcriptome of the F2 generation at E10.5. Simultaneously, RNA-seq was performed on F2 Mtrr+/+ placentas after blastocyst transfer to determine whether programming effects of the F1 maternal environment become apparent in the F2 offspring after a normal uterine environment was provided. While fetal growth enhancement in transferred F2 conceptuses was more frequent in these litters, only six genes were upregulated in placentas of transferred growth enhanced, but not phenotypically normal F2 Mtrr+/+ compared to transferred C57Bl/6 conceptuses. One remarkable finding was that the blastocyst transfer procedure affected placental gene expression and development, indicating a potential influence of blastocyst transfer, as part of assisted reproductive technology procedures in humans, on fetoplacental growth. Overall, these results indicate that while the Mtrrgt mutation in mice is sufficient to impair the uterine structure and function in their wildtype daughters, this does not substantially alter the placental transcriptome of their wildtype grandprogeny. However, Mtrr deficiency in the placenta cells themselves alters the transcriptome. In summary, abnormal folate metabolism caused by the Mtrrgt mutation affects the uterine environment, which potentially affects placental development. Normal folate metabolism is required to establish a normal maternal-fetal interface. If disrupted, the effects persist for multiple generations.

Watson, Erica D.
Colledge , William H.
folate, embryo growth, fetal growth restriction, placenta transcriptome, epigenetics, uterine function
Doctor of Philosophy (PhD)
Awarding Institution
University of Cambridge