Spermatogenesis requires intricate interactions between the germline and somatic cells. Within a given cross section of a seminiferous tubule, multiple germ and somatic cell types co-occur. This cellular heterogeneity has made it difficult to profile distinct cell types at different stages of development. To address this challenge, we collected single-cell RNA sequencing data from ∼35,000 cells from the adult mouse testis and identified all known germ and somatic cells, as well as two unexpected somatic cell types. Our analysis revealed a continuous developmental trajectory of germ cells from spermatogonia to spermatids and identified candidate transcriptional regulators at several transition points during differentiation. Focused analyses delineated four subtypes of spermatogonia and nine subtypes of Sertoli cells; the latter linked to histologically defined developmental stages over the seminiferous epithelial cycle. Overall, this high-resolution cellular atlas represents a community resource and foundation of knowledge to study germ cell development and in vivo gametogenesis.

The genetic structure of the indigenous hunter-gatherer peoples of southern Africa, the oldest known lineage of modern human, is important for understanding human diversity. Studies based on mitochondrial1 and small sets of nuclear markers2 have shown that these hunter-gatherers, known as Khoisan, San, or Bushmen, are genetically divergent from other humans1,3. However, until now, fully sequenced human genomes have been limited to recently diverged populations4–8. Here we present the complete genome sequences of an indigenous hunter-gatherer from the Kalahari Desert and a Bantu from southern Africa, as well as protein-coding regions from an additional three hunter-gatherers from disparate regions of the Kalahari. We characterize the extent of whole-genome and exome diversity among the five men, reporting 1.3 million novel DNA differences genome-wide, including 13,146 novel amino acid variants. In terms of nucleotide substitutions, the Bushmen seem to be, on average, more different from each other than, for example, a European and an Asian. Observed genomic differences between the hunter-gatherers and others may help to pinpoint genetic adaptations to an agricultural lifestyle. Adding the described variants to current databases will facilitate inclusion of southern Africans in medical research efforts, particularly when family and medical histories can be correlated with genome-wide data.

Spermatogenesis is a highly regulated process that produces sperm to transmit genetic information to the next generation. Although extensively studied in mice, our current understanding of primate spermatogenesis is limited to populations defined by state-specific markers defined from rodent data. As between-species differences have been reported in the process duration and cellular differentiation hierarchy, it remains unclear how molecular markers and cell states are conserved or have diverged from mice to man. To address this challenge, we employ single-cell RNA-sequencing to identify transcriptional signatures of major germ and somatic cell-types of the testes in human, macaque and mice. This approach reveals differences in expression throughout spermatogenesis, including the stem/progenitor pool of spermatogonia, classical markers of differentiation, potential regulators of meiosis, the kinetics of RNA turnover during spermatid differentiation, and germ cell-soma communication. These datasets provide a rich foundation for future targeted mechanistic studies of primate germ cell development and in vitro gametogenesis.

Although heme iron is an important form of dietary iron, its intestinal absorption mechanism remains elusive. Our previous work revealed that (−)-epigallocatechin-3-gallate (EGCG) and grape seed extract (GSE) markedly inhibited intestinal heme iron absorption by reducing the basolateral iron export in Caco-2 cells. The aims of this study were to examine whether small amounts of EGCG, GSE and green tea extract (GT) could inhibit heme iron absorption, and to test whether the inhibitory action of polyphenols could be offset by ascorbic acid. A heme-55Fe absorption study was conducted by adding various concentrations of EGCG, GSE and GT to Caco-2 cells in the absence and presence of ascorbic acid. Polyphenolic compounds significantly inhibited heme-55Fe absorption in a dose-dependent manner. The addition of ascorbic acid did not modulate the inhibitory effect of dietary polyphenols on heme iron absorption when the cells were treated with polyphenols at a concentration of 46 mg/L. However, ascorbic acid was able to offset or reverse the inhibitory effects of polyphenolic compounds when lower concentrations of polyphenols were added (≤ 4.6 mg/L). Ascorbic acid modulated the heme iron absorption without changing the apical heme uptake, the expression of the proteins involved in heme metabolism and basolateral iron transport, and heme oxygenase activity, indicating that ascorbic acid may enhance heme iron absorption by modulating the intracellular distribution of 55Fe. These results imply that the regular consumption of dietary ascorbic acid can easily counteract the inhibitory effects of low concentrations of dietary polyphenols on heme iron absorption but cannot counteract the inhibitory actions of high concentrations of polyphenols.

Because dietary polyphenolic compounds have a wide range of effects in vivo and vitro, including chelation of metals such as iron, it is prudent to test whether the regular consumption of dietary bioactive polyphenols impair the utilization of dietary iron. Because our previous study showed the inhibitory effect of (-) -epigallocatechin-3-gallate (EGCG) and grape seed extract (GSE) on nonheme iron absorption, we investigated whether EGCG and GSE also affect iron absorption from heme. The fully differentiated intestinal Caco-2 cells grown on microporous membrane inserts were incubated with heme (55)Fe in uptake buffer containing EGCG or GSE in the apical compartment for 7 h. Both EGCG and GSE decreased (P < 0.05) transepithelial transport of heme-derived iron. However, apical heme iron uptake was increased (P < 0.05) by GSE. Despite the increased cellular levels of heme (55)Fe, the transfer of iron across the intestinal basolateral membrane was extremely low, indicating that basolateral export was impaired by GSE. In contrast, EGCG moderately decreased the cellular assimilation of heme (55)Fe, but the basolateral iron transfer was extremely low, suggesting that the basolateral efflux of heme iron was also inhibited by EGCG. Expression of heme oxygenase, ferroportin, and hephaestin protein was not changed by EGCG and GSE. The apical uptake of heme iron was temperature dependent and saturable in fully differentiated Caco-2 cells. Our data show that bioactive dietary polyphenols inhibit heme iron absorption mainly by reducing basolateral iron exit rather than decreasing apical heme iron uptake in intestinal cells.