Abstract
BackgroundFatty acid oxidation plays an important role in a variety of developing and mature organ systems. However, the role of this metabolic pathway in different stages of testis development remains unknown. Here, we elucidate the mechanisms by which fatty acid oxidation regulates the maintenance and differentiation of gonocytes and spermatogonial stem cells.ResultsDuring E13.5-E15.5, male germ cells gradually enter the mitotic arrest phase, while the expression of CPT1A, a rate-limiting enzyme for fatty acid oxidation, gradually increases. Therefore, we treated pregnant mice (E13.5 to E15.5) with etomoxir, which is an inhibitor of CPT1A. Etomoxir-treated mice showed no difference in embryonic morphology; however, etomoxir-treated male gonocytes exited mitotic arrest, and cells of the gonad underwent apoptosis. In addition, etomoxir-treated mice at P7 displayed impaired homing of spermatogonia and increased cell apoptosis. We further demonstrated that inhibition of fatty acid oxidation in gonads was associated with gonocyte differentiation events and the histone modification H3K27ac.ConclusionsInhibiting fatty acid oxidation can specifically reduce the level of H3K27ac in the reproductive crest, which may be the cause of the down-regulation of male differentiation-specific gene expression, which ultimately leads to the male primordial germ cells exited from mitotic arrest. Our work uncovers metabolic reprogramming during male gonadal development, revealing that it plays an important role in the maintenance of gonocytes in a differentiated and quiescent state during foetal testis development.
Highlights
Fatty acid oxidation plays an important role in a variety of developing and mature organ systems
Nanos C2HC-type zinc finger 2 (Nanos2) is expressed after the loss of Cytochrome P450 (Cyp26b1), and it plays an important role in promoting male primordial germ cell differentiation
Gonocytes of Nanos2 KO mice undergo normal mitotic arrest but reenter mitosis and undergo apoptosis at E15.5 [8]; further, they are unable to correctly express male differentiation genes including stimulated by retinoic acid gene 8 (Stra8), synaptonemal complex protein 3 (Sycp3), and dosage suppressor of Mck1 homolog (Dmc1), at which point they begin to enter meiosis
Summary
Fatty acid oxidation plays an important role in a variety of developing and mature organ systems. By E13.5, Retinoic acid (RA) present in the female gonads induces the germ cells to enter the prophase of the first meiotic division. Between E12.5 and E14.5, PGCs in the female embryonic gonad enter meiosis following signaling by retinoic acid. Nanos is expressed after the loss of Cyp26b1, and it plays an important role in promoting male primordial germ cell differentiation. Gonocytes of Nanos KO mice undergo normal mitotic arrest but reenter mitosis and undergo apoptosis at E15.5 [8]; further, they are unable to correctly express male differentiation genes including stimulated by retinoic acid gene 8 (Stra8), synaptonemal complex protein 3 (Sycp3), and dosage suppressor of Mck homolog (Dmc1), at which point they begin to enter meiosis. Fgf inhibits male gonocyte entry into meiosis by downregulating Stra, acting in a complementary manner to that of the Cyp26b1/RA pathway [9], while FGF9 has a sex-specific effect on germ cell survival: Fgf knockout mice cause gender reversal and induce male germ cell death at E12.5 [10]
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