Distinct requirements for energy metabolism in mouse primordial germ cells and their reprogramming to embryonic germ cells

Abstract

Primordial germ cells (PGCs), undifferentiated embryonic germ cells, are the only cells that have the ability to become gametes and to reacquire totipotency upon fertilization. It is generally understood that the development of PGCs proceeds through the expression of germ cell-specific transcription factors and characteristic epigenomic changes. However, little is known about the properties of PGCs at the metabolite and protein levels, which are directly responsible for the control of cell function. Here, we report the distinct energy metabolism of PGCs compared with that of embryonic stem cells. Specifically, we observed remarkably enhanced oxidative phosphorylation (OXPHOS) and decreased glycolysis in embryonic day 13.5 (E13.5) PGCs, a pattern that was gradually established during PGC differentiation. We also demonstrate that glycolysis and OXPHOS are important for the control of PGC reprogramming and specification of pluripotent stem cells (PSCs) into PGCs in culture. Our findings about the unique metabolic property of PGCs provide insights into our understanding of the importance of distinct facets of energy metabolism for switching PGC and PSC status.primordial germ cell | metabolome | proteome | glycolysis | oxidative phosphorylation I n mouse, germ cells first develop as primordial germ cells (PGCs) from a subset of cells in late epiblasts consisting of primed pluripotent stem cells (PSCs) that differentiate from naïve PSCs, designated primitive ectoderm or early epiblast, at around embryonic day 7.25 (E7.25) in the extraembryonic mesoderm (1). Several cytokines (2) and transcription factors (3-5) have critical roles in the emergence of PGCs. Following their initial appearance, PGCs migrate and colonize the genital ridges at ∼E10.5, subsequently exhibiting sexual differentiation at ∼E11.5. After their initial development, PGCs undergo characteristic epigenetic reprogramming, including the global reduction of histone H3 lysine 9 dimethylation (H3K9me2) and DNA methylation (6-8). As a result of the dynamic changes in gene regulation and epigenetic states that occur in the course of PGC differentiation, PGCs have developmental potential distinct from that of PSCs. Notably, PGCs show dormant totipotency, although PGCs are monopotential cells for the generation of gametes. Nonetheless, PGCs and PSCs remain closely related: both cell types share the expression of several pluripotency-associated transcription factors (9-12), and PGCs are easily reprogrammed into naïve PSCs, designated embryonic germ cells (EGCs), in culture (13,14). Therefore, the intrinsic mechanisms that control the distinct developmental potential of these two cell types are of great interest.Recent studies have focused primarily on the transcriptome and epigenome to explain the functional difference between PSCs and PGCs. However, the differences in metabolites and proteins in these cells, which may be closely linked to their distinct developmental potential, have not been examined. Recently, exhaustive analyses of metabolites, especially re...

Alpha‐ketoglutarate: a “magic” metabolite in early germ cell development

“…Using single‐cell RNA‐Seq over a developmental time course referred to as a “pseudotime analysis”, they show a transition from mainly oxidative (OXPHOS) to glycolytic metabolism with progression from mESCs to EpiLCs. On conversion of EPiLCs to PGCLCs, OXPHOS increases and glycolysis decreases, consistent with a prior study (Hayashi et al , ). Repressing glycolysis or elevating αKG levels favors retention of mESC self‐renewal over exit from naïve pluripotency.…”

Assessing the fitness consequences of mitonuclear interactions in natural populations

“…Together, this provides two levels by which selection might screen for best‐functioning mitochondria. Emerging evidence supports the contention that the mitochondria are active within primordial germ cells and developing oocytes (Ge et al ., ; Kasashima, Nagao & Endo, ; Hayashi et al ., ). Thus, we hypothesize that only those oocytes with full capacity for efficient respiratory function, requiring compatible mitonuclear genotypes, reach maturity (Dumollard, Duchen & Carroll, ; Stewart & Larsson, ).…”

Metabolic regulation of pluripotency and germ cell fate through α‐ketoglutarate

“…Consistently, we find that PGCLCs express higher levels of Cox7a1 and Idh2 transcripts, suggesting a boost in mitochondrial oxidative metabolism. Accordingly, activation of mitochondrial oxidative metabolism by 2-DG supplementation results in enhanced PGCLC induction (Hayashi et al, 2017). The molecular mechanisms underlying the promotion of PGC fate through stimulation of oxidative metabolism, however, remain to be discovered.…”