Defective folate metabolism causes germline epigenetic instability and distinguishesHiraas a phenotype inheritance biomarker

Abstract

The mechanism behind transgenerational epigenetic inheritance (TEI) is unclear, particularly through the maternal line. We previously showed that disruption of folate metabolism in mice by the Mtrr gt hypomorphic mutation results in TEI of congenital malformations. Either maternal grandparent can initiate this phenomenon, which persists for at least four wildtype generations.Using genome-wide approaches, we reveal genetic stability in the Mtrr gt model and epigenomewide differential DNA methylation in the germline of Mtrr +/gt maternal grandfathers. While epigenetic reprogramming occurs, wildtype grandprogeny and great grandprogeny exhibit memory of germline methylation defects. One such region is associated with misexpression of the Hira gene at least until the F3 generation in a manner that distinguishes the HIRA histone chaperone as a biomarker of maternal epigenetic inheritance.

Disruption of folate metabolism causes poor alignment and spacing of mouse conceptuses for multiple generations

“…In general, the mechanism of TEI of phenotypes is not well understood and will take additional studies to elucidate. However, it is hypothesized that an abnormal epigenetic factor(s) is inherited via the germline to cause epigenetic instability in the offspring and to perpetuate phenotypic inheritance across multiple generations (see below; Blake and Watson, 2016;Blake et al, 2021).…”

“…One-carbon metabolism is involved in thymidine synthesis and cellular methylation reactions (Ducker and Rabinowitz, 2017). Thymidine synthesis is likely unaffected by the Mtrr gt mutation since de novo mutations, which transpire from low thymidine levels resulting in uracil misincorporation into DNA (Blount et al, 1997), occur at a similar frequency in C57Bl/6J control and Mtrr gt/gt mice (Blake et al, 2021). However, considerable alteration in patterns of DNA methylation was identified in adult germ cells and somatic tissues, and in placentas of the Mtrr gt model, with some methylation changes associated with gene misexpression Bertozzi et al, 2021;Blake et al, 2021).…”

“…Thymidine synthesis is likely unaffected by the Mtrr gt mutation since de novo mutations, which transpire from low thymidine levels resulting in uracil misincorporation into DNA (Blount et al, 1997), occur at a similar frequency in C57Bl/6J control and Mtrr gt/gt mice (Blake et al, 2021). However, considerable alteration in patterns of DNA methylation was identified in adult germ cells and somatic tissues, and in placentas of the Mtrr gt model, with some methylation changes associated with gene misexpression Bertozzi et al, 2021;Blake et al, 2021). The broad range of developmental phenotypes observed in the Mtrr gt model suggests that this epigenetic instability occurs stochastically on an inter-individual basis, ultimately leading to disruption of different gene pathways and different phenotypes.…”

“…Besides neural tube closure defects, other developmental phenotypes observed in Mtrr gt/gt conceptuses at E10.5 are growth restriction, developmental delay, cardiac malformations, and placenta phenotypes whereby chorioallantoic attachment appear eccentric upon gross analysis or failed to occur . While the molecular cause and developmental timing of these phenotypes is currently unclear, alterations in genome-wide DNA methylation associated with gene misexpression were apparent in Mtrr gt/gt conceptuses at E10.5 Bertozzi et al, 2021;Blake et al, 2021), implicating an epigenetic mechanism. Interestingly, the Mtrr gt mouse line displays transgenerational epigenetic inheritance (TEI) of developmental phenotypes .…”

“…The mechanism of mammalian TEI is not well understood, though it is hypothesized that an epigenetic factor(s) is inherited via the germline to cause a phenotype in a manner that is independent of DNA base-sequence changes (Blake and Watson, 2016). An Mtrr gt allele in a maternal grandparent (i.e., the F0 generation) was sufficient to disrupt germ cell DNA methylation (Blake et al, 2021) and cause growth defects and congenital malformations at E10.5 in the wildtype grandprogeny, in some cases up to the wildtype F4 generation . This phenomenon occurs when the parents (i.e., the F1 generation) and all subsequent generations are wildtype for Mtrr as determined through robust genetic pedigree analyses.…”