Single-cell transcriptome analyses reveal critical regulators of spermatogonial stem cell fate transitions

BACKGROUND

Spermatogonial stem cells (SSCs) are the foundation cells for continual spermatogenesis and germline regeneration in mammals. SSC activities reside in the undifferentiated spermatogonial population, and currently, the molecular identities of SSCs and their committed progenitors remain unclear.

RESULTS

We performed single-cell transcriptome analysis on isolated undifferentiated spermatogonia from mice to decipher the molecular signatures of SSC fate transitions. Through comprehensive analysis, we delineated the developmental trajectory and identified candidate transcription factors (TFs) involved in the fate transitions of SSCs and their progenitors in distinct states. Specifically, we characterized the Asingle spermatogonial subtype marked by the expression of Eomes. Eomes+ cells contained enriched transplantable SSCs, and more than 90% of the cells remained in the quiescent state. Conditional deletion of Eomes in the germline did not impact steady-state spermatogenesis but enhanced SSC regeneration. Forced expression of Eomes in spermatogenic cells disrupted spermatogenesis mainly by affecting the cell cycle progression of undifferentiated spermatogonia. After injury, Eomes+ cells re-enter the cell cycle and divide to expand the SSC pool. Eomes+ cells consisted of 7 different subsets of cells at single-cell resolution, and genes enriched in glycolysis/gluconeogenesis and the PI3/Akt signaling pathway participated in the SSC regeneration process.

CONCLUSIONS

In this study, we explored the molecular characteristics and critical regulators of subpopulations of undifferentiated spermatogonia. The findings of the present study described a quiescent SSC subpopulation, Eomes+ spermatogonia, and provided a dynamic transcriptional map of SSC fate determination.

Single-cell transcriptomic characterization of sheep conceptus elongation and implantation

Bidirectional communication between the developing conceptus and endometrium is essential for pregnancy recognition and establishment in ruminants. We dissect the transcriptomic dynamics of sheep conceptus and corresponding endometrium at pre- and peri-implantation stages using single-cell RNA sequencing. Spherical blastocysts contain five cell types, with 68.62% trophectoderm cells. Strikingly, elongated conceptuses differentiate into 17 cell types, indicating dramatic cell fate specifications. Cell-type-specific gene expression delineates the features of distinctive trophectoderm lineages and indicates that the transition from polar trophectoderm to trophoblast increases interferon-tau expression and likely drives elongation initiation. We identify 13 endometrium-derived cell types and elucidate their molecular responses to conceptus development. Integrated analyses uncover multiple paired transcripts mediating the dialogues between extraembryonic membrane and endometrium, including IGF2-IGF1R, FGF19-FGFR1, NPY-NPY1R, PROS1-AXL, and ADGRE5-CD55. These data provide insight into the molecular regulation of conceptus elongation and represent a valuable resource for functional investigations of pre- and peri-implantation ruminant development.

Pancreatic lipase-related protein 2 is selectively expressed by peritubular myoid cells in the murine testis and sustains long-term spermatogenesis

Spermatogenesis is a complicated process of germ cell differentiation that occurs within the seminiferous tubule in the testis. Peritubular myoid cells (PTMCs) produce major components of the basement membrane that separates and ensures the structural integrity of seminiferous tubules. These cells secrete niche factors to promote spermatogonial stem cell (SSC) maintenance and mediate androgen signals to direct spermatid development. However, the regulatory mechanisms underlying the identity and function of PTMCs have not been fully elucidated. In the present study, we showed that the expression of pancreatic lipase-related protein 2 (Pnliprp2) was restricted in PTMCs in the testis and that its genetic ablation caused age-dependent defects in spermatogenesis. The fertility of Pnliprp2 knockout animals (Pnliprp2-/-) was normal at a young age but declined sharply beginning at 9 months. Pnliprp2 deletion impaired the homeostasis of undifferentiated spermatogonia and severely disrupted the development and function of spermatids. Integrated analyses of single-cell RNA-seq and metabolomics data revealed that glyceride metabolism was changed in PTMCs from Pnliprp2-/- mice. Further analysis found that 60 metabolites were altered in the sperm of the Pnliprp2-/- animals; notably, lipid metabolism was significantly dysregulated. Collectively, these results revealed that Pnliprp2 was exclusively expressed in PTMCs in the testis and played a novel role in supporting continual spermatogenesis in mice. The outcomes of these findings highlight the function of lipid metabolism in reproduction and provide new insights into the regulation of PTMCs in mammals.

ARHGEF15 is expressed in undifferentiated spermatogonia but is not required for spermatogenesis in mice

Spermatogenesis is a continual process that relies on the activities of undifferentiated spermatogonia, which contain spermatogonial stem cells (SSCs) that serve as the basis of spermatogenesis. The gene expression pattern and molecular control of fate decisions of undifferentiated spermatogonia are not well understood. Rho guanine nucleotide exchange factor 15 (ARHGEF15, also known as EPHEXIN5) is a guanine nucleotide-exchange factor (GEF) that activates the Rho protein. Here, we reported that ARHGEF15 was expressed in undifferentiated spermatogonia and spermatocytes in mouse testes; however, its deletion did not affect spermatogenesis. Arhgef15-/- mice were fertile, and histological examination of the seminiferous tubules of Arhgef15-/- mice revealed complete spermatogenesis with the presence of all types of spermatogenic cells. Proliferation and differentiation of the undifferentiated spermatogonia were not impacted; however, further analysis showed that Arhgef15 deletion resulted in decreased expression of Nanos2, Lin28a and Ddx4. Together, these findings suggest that ARHGEF15 was specifically enriched in undifferentiated spermatogonia and regulated gene expression but dispensable for spermatogenesis in mice.

Ldha-Dependent Metabolic Programs in Sertoli Cells Regulate Spermiogenesis in Mouse Testis

Sertoli cells play indispensable roles in spermatogenesis by providing the advanced germ cells with structural, nutritional, and regulatory support. Lactate is regarded as an essential Sertoli-cell-derived energy metabolite that nurses various types of spermatogenic cells; however, this assumption has not been tested using genetic approaches. Here, we have reported that the depletion of lactate production in Sertoli cells by conditionally deleting lactate dehydrogenase A (Ldha) greatly affected spermatogenesis. Ldha deletion in Sertoli cells significantly reduced the lactate production and resulted in severe defects in spermatogenesis. Spermatogonia and spermatocytes did not show even mild impairments, but the spermiogenesis of Ldha conditional knockout males was severely disrupted. Further analysis revealed that 2456 metabolites were altered in the sperm of the knockout animals, and specifically, lipid metabolism was dysregulated, including choline, oleic acid, and myristic acid. Surprisingly, choline supplementation completely rescued the spermiogenesis disorder that was caused by the loss of Ldha activities. Collectively, these data have demonstrated that the interruption of Sertoli-cell-derived lactate impacted sperm development through a choline-mediated mechanism. The outcomes of these findings have revealed a novel function of lactate in spermatogenesis and have therapeutic applications in treating human infertility.

Theabrownin Induces Cell Apoptosis and Cell Cycle Arrest of Oligodendroglioma and Astrocytoma in Different Pathways

Theabrownin (TB), a natural compound present in the fresh leaves of green tea, is a potential antitumor agent. However, so far whether and how TB affects glioma is unclear. In this study, we investigated the effect of TB on astroglioma and oligodendroglioma cells. Surprisingly, TB significantly reduced the viabilities of HOG and U251 cells in a dose-dependent manner, which was accompanied by the upregulation of active-Casp-3, Bax, and PTEN; meanwhile, the antiapoptotic gene Bcl-2 was downregulated. In addition, TB treatment induced cell cycle arrest at the G1 and G2/M phases in HOG and U251 cells, respectively. TB treatment caused the downregulating of c-myc, cyclin D, CDK2, and CDK4 and upregulating of p21 and p27 in the HOG cell, while TB increased P53, p21, and p27 levels and decreased the levels of cell cycle regulator proteins such as CDK and cyclin A/B in the U251 cells. Therefore, the c-myc- and P53-related mechanisms were proposed for cell cycle arrest in these two glioma cell lines, respectively. Overall, our findings indicated that TB could be a novel candidate drug for the treatment of gliomas.

Intermolecular disulfide bonds link specific high-molecular-weight glutenin subunits in wheat endosperm

A detergent wash extracted soluble proteins from wheat flour, leaving a residue enriched with insoluble glutenin aggregates. Digestion of this residue with endoproteinase Lys-C, which showed a limited specificity for glutenin subunits, produced several peptides with apparent molecular weights close to those of intact high-molecular-weight glutenin subunits. N-terminal sequencing indicated that the isolated peptides were composed of high-molecular-weight glutenin subunit fragments joined by an intermolecular disulfide bond. In two of these peptides, only two components were found, one from an x-type subunit and the other from a y-type subunit. The isolated peptides all contained at least one x-type C-terminal region and one y-type N-terminal region, suggesting a specific orientation to the intermolecular disulfide linkage.

Partial amino acid sequence of potato solanidine UDP-glucose glucosyltransferase purified by new anion-exchange and size exclusion media

Solanidine UDP-glucose glucosyltransferase (SGT) is involved in the biosynthesis of steroidal glycoalkaloids in potatoes. This enzyme is present at an extremely low level, is inherently unstable, and copurifies with the major storage protein patatin during isolation. We describe an improved method for isolating SGT from greening potato peel using two new chromatographic supports, Macro-Prep 50 Q anion-exchange and Superdex 75HR size exclusion media, under medium-pressure conditions at room temperature. The enzyme preparation was further resolved by SDS-PAGE and the proteins transferred to PVDF membrane (Immobilon-P). Two protein bands corresponding to active forms of SGT (36 and 37 kDa) were excised and cleaved with cyanogen bromide in trifluoroacetic acid. The resultant peptide mixtures were then separated by Tricine-SDS-PAGE and transferred to a PVDF membrane (Pro-Blott). The two major peptide bands observed in both digests (17 and 19 kDa) were sequenced. Identical N-terminal sequences were obtained from the 19-kDa peptides from both digests.

Germin-Like Polypeptides Increase in Barley Roots during Salt Stress

The 26 kilodalton, isoelectric point 6.3 and 6.5 (Gs1 and Gs2) polypeptides that increase in barley (Hordeum vulgare L.) roots during salt stress were isolated and identified. Both Gs1 and Gs2 had high sequence similarity to germin, a protein that increases significantly in germinating wheat seeds. Like germin, Gs1 and Gs2 were resistant to proteases and were glycosylated. Immunoblots were probed with antibodies to Gs1 and Gs2 to determine the distribution of these polypeptides among organs and cell-free fractions. Gs1 and Gs2 were present in roots and coleoptiles, but absent from leaves. In roots, Gs1 and Gs2 were present in the mature region, but not the tip. Gs1 and Gs2 increased in roots, but decreased in coleoptiles in response to salt stress. Gs1 and Gs2 were distributed among the soluble, microsomal, and cell wall fractions of roots, but the majority of Gs1 and Gs2 was present in the soluble fraction. Although Gs1 and Gs2 were heat stable, their synthesis was not affected by abscisic acid treatment. Gs2 accumulated during abscisic acid treatment, whereas Gs1 did not. However, a 25.5 kilodalton, isoelectric point 6.1 polypeptide that was immunologically related to Gs1 did accumulate with abscisic acid treatment.

Amphiphilic cationic peptides mediate cell adhesion to plastic surfaces

Four amphiphilic peptides, each with net charges of +2 or more at neutrality and molecular weights under 4 kilodaltons, were found to mediate the adhesion of normal rat kidney fibroblasts to polystyrene surfaces. Two of these peptides, a model for calcitonin (peptide 1, MCT) and melittin (peptide 2, MEL), form amphiphilic alpha-helical structures at aqueous/nonpolar interfaces. The other two, a luteinizing hormone-releasing hormone model (peptide 3, LHM) and a platelet factor model (peptide 4, MPF) form beta-strand structures in amphiphilic environments. Although it contains only 10 residues, LHM mediated adhesion to surfaces coated with solutions containing as little as 10 pmoles/ml of peptide. All four of these peptides were capable of forming monolayers at air-buffer interfaces with collapse pressures greater than 20 dynes/cm. None of these four peptides contains the tetrapeptide sequence Arg-Gly-Asp-Ser, which has been associated with fibronectin-mediated cell adhesion. Ten polypeptides that also lacked the sequence Arg-Gly-Asp-Ser but were nonamphiphilic and/or had net charges less than +2 at neutrality were all incapable of mediating cell adhesion (Pierschbacher and Ruoslahti, 1984). The morphologies of NRK cells spread on polystyrene coated with peptide LHM resemble the morphologies on fibronectin-coated surfaces, whereas cells spread on surfaces coated with MCT or MEL exhibit strikingly different morphologies. The adhesiveness of MCT, MEL, LHM, and MPF implies that many amphiphilic cationic peptides could prove useful as well defined adhesive substrata for cell culture and for studies of the mechanism of cell adhesion.