Ex vivo reconstitution of fetal oocyte development in humans and cynomolgus monkeys

ヒト・サルの胎児卵巣から原始卵胞を体外で作出することに成功. 京都大学プレスリリース. 2022-08-01.New egg recipe to boost fertility research. 京都大学プレスリリース. 2022-08-14.In vitro oogenesis is key to elucidating the mechanism of human female germ-cell development and its anomalies. Accordingly, pluripotent stem cells have been induced into primordial germ cell-like cells and into oogonia with epigenetic reprogramming, yet further reconstitutions remain a challenge. Here, we demonstrate ex vivo reconstitution of fetal oocyte development in both humans and cynomolgus monkeys (Macaca fascicularis). With an optimized culture of fetal ovary reaggregates over three months, human and monkey oogonia enter and complete the first meiotic prophase to differentiate into diplotene oocytes that form primordial follicles, the source for oogenesis in adults. The cytological and transcriptomic progressions of fetal oocyte development in vitro closely recapitulate those in vivo. A comparison of single-cell transcriptomes among humans, monkeys, and mice unravels primate-specific and conserved programs driving fetal oocyte development, the former including a distinct transcriptomic transformation upon oogonia-to-oocyte transition and the latter including two active X chromosomes with little X-chromosome upregulation. Our study provides a critical step forward for realizing human in vitro oogenesis and uncovers salient characteristics of fetal oocyte development in primates

The Run-in Process for Stable Friction Fade-Out and Tribofilm Analyses by SEM and Nano-Indenter

It was shown in previous reports by authors that friction coefficients of the level of 0.0001 were achieved when ZrO2 (Y-PSZ: yttria partially stabilized zirconia) pins were slid against diamond-like carbon (DLC) films in H2-gas environment under heavy applied load of 63.7 N (friction fade-out, FFO). It was also shown that FFO continued long when the main H2-gas flow was mixed with a small amount of aqueous-alcohol vapor. A tribofilm was formed at the contact area of ZrO2 surface, and it was considered that the aqueous-alcohol vapor made the tribofilm strong. In the present research, the run-in process for achieving more stable FFO is investigated by varying the run-in pattern consisting of load step-up and aqueous-alcohol vapor addition, and the stable FFO continuing several hours is realized reproducibly. Then, before and after the FFO onset, the contact area on ZrO2 surface is observed by SEM, and nano-indentation hardness of tribofilm is measured. It will be shown that a substance made of hydrocarbons with low melting temperature, low electrical conductivity and low nano-indentation hardness such as hydrocarbon polymers is formed on the tribofilm, suggesting the evolution of hydrocarbon gas at the sliding surface

Evolution of tribo-induced interfacial nanostructures governing superlubricity in a-C:H and a-C:H:Si films

Hydrogenated amorphous carbon (a-C:H) is capable of providing a near-frictionless lubrication state when rubbed in dry sliding contacts. Nevertheless, the mechanisms governing superlubricity in a-C:H are still not well comprehended, mainly due to the lack of spatially resolved structural information of the buried contact surface. Here, we present structural analysis of the carbonaceous sliding interfaces at the atomic scale in two superlubricious solid lubricants, a-C:H and Si-doped a-C:H (a-C:H:Si), by probing the contact area using state-of-the-art scanning electron transmission microscopy and electron energy-loss spectroscopy. The results emphasize the diversity of superlubricity mechanisms in a-C:Hs. They suggest that the occurrence of a superlubricious state is generally dependent on the formation of interfacial nanostructures, mainly a tribolayer, by different carbon rehybridization pathways. The evolution of such anti-friction nanostructures highly depends on the contact mechanics and the counterpart material. These findings enable a more effective manipulation of superlubricity and developments of new carbon lubricants with robust lubrication properties