Sertoli cells, first identified in the adult testis by Enrico Sertoli in the mid-nineteenth century, are known for their role in fostering male germ cell differentiation and production of mature sperm. It was not until the late twentieth century with the discovery of the testis-determining gene SRY that Sertoli cells' new function as the master regulator of testis formation and maleness was unveiled. Fetal Sertoli cells facilitate the establishment of seminiferous cords, induce appearance of androgen-producing Leydig cells, and cause regression of the female reproductive tracts. Originally thought be a terminally differentiated cell type, adult Sertoli cells, at least in the mouse, retain their plasticity and ability to transdifferentiate into the ovarian counterpart, granulosa cells. In this review, we capture the many phases of Sertoli cell differentiation from their fate specification in fetal life to fate maintenance in adulthood. We also introduce the discovery of a new phase of fetal Sertoli cell differentiation via autocrine/paracrine factors with the freemartin characteristics. There remains much to learn about this intriguing cell type that lay the foundation for the maleness.

The regulation of mammalian early-embryonic development is a complex, coordinated process that involves widespread transcriptomic and epigenetic remodeling. The main cause of developmental failure in preimplantation embryos after in vitro fertilization is the irreversible arrested-at-cleavage stage. To deepen our understanding of this embryonic block, we profiled a single-cell multi-omics map of copy number variations (CNVs), the transcriptome, the DNA methylome, and the chromatin state of bovine eight-cell embryos with a two-cell fate that either arrested or developed into blastocysts. To do this, we sequenced a biopsied blastomere and tracked the developmental potential of the remaining cells. Aneuploid embryos inferred by CNVs from DNA- and RNA-library data tended to lose their developmental potency. Analysis of distinct genomic regions of DNA methylation and chromatin accessibility revealed that enrichment of gene function and signaling pathways, such as the MAPK signaling pathway, was altered in arrested euploid eight-cell embryos compared with blastocyst-developed euploid eight-cell embryos. Moreover, the RNA expression and chromatin accessibility of embryonic genome activation-associated genes were lower in arrested euploid embryos than in blastocyst-developed embryos. Taken together, our results indicate that the developmental block of eight-cell embryos can be caused by multiple molecular layers, including CNVs, abnormality of DNA methylation and chromatin accessibility, and insufficient expression of embryonic genome activation-associated genes. Our integrated and comprehensive data set provides a valuable resource to further dissect the exact mechanisms underlying the arrest of bovine eight-cell embryos in vitro.

Summary Sentence

Single-cell biopsy and omics technology reveal that the arrest of bovine eight-cell embryos in vitro involves multi-faceted challenges, including CNVs, abnormal DNA methylation and chromatin accessibility, and insufficient expression of EGA genes.

Graphical Abstract

 https://tidbitapp.io/tidbits/dissecting-the-molecular-features-of-bovine-arrested-eight-cell-embryos-using-single-cell-multi-omics-sequencing-9ea06d4e-2288-4849-9969-4eb6d13e80cf

The mule is the interspecific hybrid of horse and donkey and has hybrid vigor in muscular endurance, disease resistance, and longevity over its parents. Here, we examined adult fibroblasts of mule (MAFs) compared with the cells from their parents (donkey adult fibroblasts and horse adult fibroblasts) (each species has repeated three independent individuals) in proliferation, apoptosis, and glycolysis and found significant differences. We subsequently derived mule, donkey, and horse doxycycline (Dox)-independent induced pluripotent stem cells (miPSCs, diPSCs, and hiPSCs) from three independent individuals of each species and found that the reprogramming efficiency of MAFs was significantly higher than that of cells of donkey and horse. miPSCs, diPSCs, and hiPSCs all expressed the high levels of crucial endogenous pluripotency genes such as POU class 5 homeobox 1 (POU5F1, OCT4), SRY-box 2 (SOX2), and Nanog homeobox (NANOG) and propagated robustly in single-cell passaging. miPSCs exhibited faster proliferation and higher pluripotency and differentiation than diPSCs and hiPSCs, which were reflected in co-cultures and separate-cultures, teratoma formation, and chimera contribution. The establishment of miPSCs provides a unique research material for the investigation of “heterosis” and perhaps is more significant to study hybrid gamete formation.

Summary Sentence

We found that mule adult fibroblasts have significant advantages in reprogramming efficiency compared with donkey and horse adult fibroblasts, and the establishment of mule iPSCs provides an accessible in vitro model to study hybrid gamete formation.

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N⁶-methyladenosine (m6A), an epigenetic modification on RNAs, plays an important role in many physiological and pathological processes. However, the involvement of m6A in goat uterus during early pregnancy remains largely unknown. In this study, we found that the total m6A level was increasing in goat uterus as early pregnancy progressed. Methyltransferase-like 3 (METTL3) is a core catalytic subunit of the m6A methyltransferase. We thus determined the expression and regulation of METTL3 in goat uterus. METTL3 was highly expressed in the luminal and glandular epithelia from day 16 (D16) to D25 of pregnancy, and it could be up-regulated by estrogen and progesterone in goat uterus and primary endometrial epithelial cells (EECs). In EECs, knockdown or overexpression of METTL3 resulted in a significant decrease or increase of cell proliferation, respectively. METTL3 knockdown reduced the m6A level of not only total RNA but also connective tissue growth factor (CTGF) mRNA. Luciferase assay suggested that METTL3 might target the potential m6A sites in the 3'untranslated region (3'UTR) of CTGF mRNA. Moreover, METTL3 positively regulated CTGF expression, and CTGF knockdown significantly counteracted the promoting effect of METTL3 overexpression on EEC proliferation. Collectively, METTL3 is dynamically expressed in goat uterus and can affect EEC proliferation by regulating CTGF in an m6A-dependent manner. Our results will lay a foundation for further studying the crucial mechanism of METTL3-mediated m6A modification in goat uterus during early pregnancy.

Despite stringent quality control checks, some bulls with apparently normal semen quality yield lower than expected pregnancy rates. This study profiled the transcriptome and performed histological analysis of the bovine uterus in response to sperm from high-fertility (HF) and low-fertility (LF) bulls. Postmortem uterine biopsies and uterine explants were collected from heifers 12 h after a fixed time artificial insemination (AI) to a synchronized estrus with frozen–thawed semen from five HF (fertility rate 4.01% ± 0.25) and five LF (fertility rate - 11.29% ± 1.11; mean ± SEM) bulls. Uterine biopsies were also collected from control (CTRL) heifers, which were not inseminated. RNA-sequencing and histological analysis were performed for differential gene expression and neutrophil quantification. In the HF treatment relative to CTRL heifers, there were 376 genes significantly differentially expressed in the endometrium with just one gene differentially expressed in the LF treatment relative to CTRL heifers. Comparing the HF and LF treatments directly, there were 40 significantly differentially expressed genes (P < 0.05). Transcriptomic analysis shows a predominant role for the inflammatory marker Interleukin-1 alpha, which was further confirmed by immunohistochemistry. Quantification of neutrophils in the endometrium showed a significant effect of sperm; however, there was no difference in neutrophil numbers between HF and LF groups. In conclusion, this novel study clearly shows a distinct inflammatory response to sperm in the endometrium and a divergent transcriptomic response to semen from HF and LF bulls.

Summary Sentence

The concept that sperm from high fertility bulls are priming the endometrium for implantation and a subsequent pregnancy merits further investigation.

Graphical Abstract