PMC

In wild-type gonads, germ cells exhibit sex-specific divergence during embryogenesis as male germ cells enter mitotic arrest, while female germ cells enter mitosis followed by meiosis. However, in Cyp26b1^SC−/SC− fetuses, Cyp26b1 activity is inactivated after E15.5, thus elevating levels of retinoic acid within the testes. As a result, male germ cells exit from G0 to re-enter the cell cycle and initiate meiotic prophase, which subsequently culminates in loss of male germ cells.

The pro-apoptotic machinery is expressed in the male germ line during meiotic prophase, but CED-3 caspase is not activated. (A) Pathway of germ cell apoptosis in C. elegans []. (B) CED-9 inactivation does not induce apoptosis in the male germ line. Number of apoptotic nuclei per gonad arm measured by AO staining 24h post L4 stage (and 24h post IR). The number of germ lines scored for each genotype is in parenthesis. The data shown are means ± S.E.M. (C) CED-4 and SIR-2.1 are expressed in both hermaphrodite and male germ lines but no SIR-2.1 translocation occurs in male germ cells. Immunolocalization of CED-4 (green) and SIR-2.1 (red) counterstained with DAPI (blue) in pachytene nuclei from wild-type and zim-1(tm1813) hermaphrodite and male germ lines. Arrowheads point to nuclei with more intense CED-4 staining. Scale bars, 5μm. (D) CED-3 is expressed in hermaphrodite and male germ lines but levels do not increase under checkpoint-activating conditions in the male germ line. CED-3 immunolocalization (green) in pachytene nuclei stained with DAPI (blue) of adult worms (24h post L4). Arrowheads indicate apoptotic nuclei that lack CED-3 staining presumably because they have proceeded to a later stage. Scale bars, 5μm. (E) Males do not activate CED-3 caspase. Caspase activity was monitored by fluorescence microscopy following microinjection of SR-FLICA inhibitor in hermaphrodite and male germ lines of N2, zim-1(tm1813) and zim-1(tm1813);ced-3(RNAi) worms. Arrowheads mark some of the caspase-positive cells. Scale bars, 10μm.

Transcriptome-based comparison of developmental stages in chicken germ cells with those in human fetal germ cells (FGCs). (A) UMAP showing the developmental stages of human male (left) and female (right) FGCs. Cells are colored by developmental stage. (B) Scatter plots mapping human male FGCs onto the UMAP plot of chicken male germ cells (top); and human female FGCs onto chicken female germ cells (bottom). Gray points indicate chicken germ cells; colored points, original developmental stages of human FGCs. (C) Bar plots showing proportions of human FGCs in different stages that were mapped onto chicken germ-cell stages, corresponding to (B). (D) Heatmaps showing dynamic patterns of DEGs from chicken male germ cells and human male FGCs (left); and from chicken female germ cells and human female FGCs (right). (E) Heatmaps showing dynamic patterns of germ-plasm-specific genes from chicken male germ cells and human male FGCs (left); and from chicken female germ cells and human female FGCs (right). In D and E, histogram above the heatmaps showing the cell density of each developmental stages in male and female germ cells, and in each species, respectively. Gray lines between gene clusters connect chicken and human orthologs. Notable convergent (blue) and divergent (red) genes are indicated. Gg, Gallus gallus (chicken); Hs, Homo sapiens (human). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Effect of HN on heat-induced male germ cell apoptosis in wild-type and il-27rα or ebi-3 knockout mice. Both wild-type and il-27rα or ebi-3 knockout mice were treated with vehicle (Control), Humanin peptide (HN), heat (Heat), and heat plus HN peptide (Heat + HN) as described in experimental procedures. Male germ cell apoptosis was detected by TUNEL staining and expressed as the number of TUNEL positive germ cells per Sertoli cell. HN prevented heat-induced male germ cell apoptosis in wild-type mice (A and B, left panel, P < 0.05), whereas in il-27rα knockout animals, HN did not significantly prevent heat-induced male germ cell apoptosis (A, right panel, P > 0.05). In ebi-3 knockout animal, HN also did not prevent heat-induced male germ cell apoptosis (B, right panel, P > 0.05).