Iterative oxidation by TET1 is required for reprogramming of imprinting control regions and patterning of mouse sperm hypomethylated regions

Ten-eleven translocation (TET) enzymes iteratively oxidize 5-methylcytosine (5mC) to generate 5-hydroxymethylcytosine (5hmC), 5-formylcytosine, and 5-carboxylcytosine to facilitate active genome demethylation. Whether these bases are required to promote replication-coupled dilution or activate base excision repair during mammalian germline reprogramming remains unresolved due to the inability to decouple TET activities. Here, we generated two mouse lines expressing catalytically inactive TET1 (Tet1-HxD) and TET1 that stalls oxidation at 5hmC (Tet1-V). Tet1 knockout and catalytic mutant primordial germ cells (PGCs) fail to erase methylation at select imprinting control regions and promoters of meiosis-associated genes, validating the requirement for the iterative oxidation of 5mC for complete germline reprogramming. TET1V and TET1HxD rescue most hypermethylation of Tet1-/- sperm, suggesting the role of TET1 beyond its oxidative capability. We additionally identify a broader class of hypermethylated regions in Tet1 mutant mouse sperm that depend on TET oxidation for reprogramming. Our study demonstrates the link between TET1-mediated germline reprogramming and sperm methylome patterning.

Expanding homogeneous culture of human primordial germ cell-like cells maintaining germline features without serum or feeder layers

In vitro expansion of human primordial germ cell-like cells (hPGCLCs), a pluripotent stem cell-derived PGC model, has proved challenging due to rapid loss of primordial germ cell (PGC)-like identity and limited cell survival/proliferation. Here, we describe long-term culture hPGCLCs (LTC-hPGCLCs), which actively proliferate in a serum-free, feeder-free condition without apparent limit as highly homogeneous diploid cell populations maintaining transcriptomic and epigenomic characteristics of hPGCLCs. Histone proteomics confirmed reduced H3K9me2 and increased H3K27me3 marks in LTC-hPGCLCs compared with induced pluripotent stem cells (iPSCs). LTC-hPGCLCs established from multiple human iPSC clones of both sexes were telomerase positive, senescence-free cells readily passaged with minimal cell death or deviation from the PGC-like identity. LTC-hPGCLCs are capable of differentiating to DAZL-positive M-spermatogonia-like cells in the xenogeneic reconstituted testis (xrTestis) organ culture milieu as well as efficiently producing fully pluripotent embryonic germ cell-like cells in the presence of stem cell factor and fibroblast growth factor 2. Thus, LTC-hPGCLCs provide convenient access to unlimited amounts of high-quality and homogeneous hPGCLCs.

Bugs in the program: can pregnancy drugs and smoking disturb molecular reprogramming of the fetal germline, increasing heritable risk for autism and neurodevelopmental disorders?

In a seeming paradox, the prevalence of autism spectrum disorder (ASD) has surged, while at the same time research has pointed to the strong heritability of this neurodevelopmental pathology. Here an autism research philanthropist suggests a biological phenomenon of exogenously induced 'gamete disruption' that could reconcile these seemingly contradictory observations. Mining information from her own family history and that of her fellow autism parents, while also engaging with the scientific community, she proposes that a subset of the autisms may be rooted in a variety of molecular glitches in parental gametes induced by certain acute exposures during the parents' own fetal or neonatal development. These exposures include but are not limited to synthetic hormone drugs, tobacco, and general anesthesia. Consistent with this hypothesis, animal models have demonstrated adverse neurobehavioral outcomes in grandoffspring of gestating dams exposed to hormone-disrupting compounds, tobacco components, and general anesthesia. A recent epidemiological study showed a link between grandmaternal smoking and risk for ASD in grandoffspring through the maternal line. Given the urgency of the autism crisis, combined with the biological plausibility of this mostly unexplored paradigm, the writer contends that questions of nongenetic inheritance should be a priority in autism research.