Limits...
Male-killing symbiont damages host's dosage-compensated sex chromosome to induce embryonic apoptosis

View Article: PubMed Central - PubMed

ABSTRACT

Some symbiotic bacteria are capable of interfering with host reproduction in selfish ways. How such bacteria can manipulate host's sex-related mechanisms is of fundamental interest encompassing cell, developmental and evolutionary biology. Here, we uncover the molecular and cellular mechanisms underlying Spiroplasma-induced embryonic male lethality in Drosophila melanogaster. Transcriptomic analysis reveals that many genes related to DNA damage and apoptosis are up-regulated specifically in infected male embryos. Detailed genetic and cytological analyses demonstrate that male-killing Spiroplasma causes DNA damage on the male X chromosome interacting with the male-specific lethal (MSL) complex. The damaged male X chromosome exhibits a chromatin bridge during mitosis, and bridge breakage triggers sex-specific abnormal apoptosis via p53-dependent pathways. Notably, the MSL complex is not only necessary but also sufficient for this cytotoxic process. These results highlight symbiont's sophisticated strategy to target host's sex chromosome and recruit host's molecular cascades toward massive apoptosis in a sex-specific manner.

No MeSH data available.


Bridge and breakage of the male X chromosome during mitosis.(a) Epidermal cells of an uninfected male embryo at stage 11, in which pH2Av, MSL1 and DNA are visualized in green, magenta and blue as in Fig. 3a. (b,c) Magnified images of boxed regions in a, whose single-channelled images are shown in b′–b′′′ and c′–c′′′, respectively. Dotted circles highlight dividing cells in telophase. In b–b′′′, sister chromatids are normally segregating to daughter cells, whereas in c–c′′′, MSL1-labelled X chromatids seem to be segregating slightly slower than the other chromatids (arrows). (d) An image similar to a of a Spiroplasma-infected male embryo, exhibiting many pH2Av signals. (e,f) Magnified images of boxed regions in d, whose single-channelled images are shown in e′–e′′′ and f′–f′′′, respectively. Dotted circles highlight dividing cells in telophase, while arrows indicate inter-nuclear bridges overlapping with MSL1 and focal pH2Av signals, indicating that damaged male X chromatids constitute inter-nuclear bridges. (g,h) Two examples of anaphase chromatin bridges in infected male embryos at stage 9, wherein chromosomal DNA (green) and MSL1 representing X chromatids (magenta) are shown. Single-channelled images are shown in g′, g′′ and h′, h′′. Arrows and arrowheads in h–h′′ indicate an abnormally tangled DNA mass and asymmetrically segregated X chromatids, respectively. (i) Categorization of anaphase chromatin bridges in infected male embryos at stage 8–10. In total 140 anaphase bridges from 35 embryos were inspected. The categories ‘only X', ‘with X' and ‘without X' indicate complete, partial and no overlap between chromatin bridges and MSL1 signals. For more detail, see text. Scale bars, 20 μm (a,d) and 5 μm (b–c′′′, e–f′′′ and g–h′′).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5036004&req=5

f4: Bridge and breakage of the male X chromosome during mitosis.(a) Epidermal cells of an uninfected male embryo at stage 11, in which pH2Av, MSL1 and DNA are visualized in green, magenta and blue as in Fig. 3a. (b,c) Magnified images of boxed regions in a, whose single-channelled images are shown in b′–b′′′ and c′–c′′′, respectively. Dotted circles highlight dividing cells in telophase. In b–b′′′, sister chromatids are normally segregating to daughter cells, whereas in c–c′′′, MSL1-labelled X chromatids seem to be segregating slightly slower than the other chromatids (arrows). (d) An image similar to a of a Spiroplasma-infected male embryo, exhibiting many pH2Av signals. (e,f) Magnified images of boxed regions in d, whose single-channelled images are shown in e′–e′′′ and f′–f′′′, respectively. Dotted circles highlight dividing cells in telophase, while arrows indicate inter-nuclear bridges overlapping with MSL1 and focal pH2Av signals, indicating that damaged male X chromatids constitute inter-nuclear bridges. (g,h) Two examples of anaphase chromatin bridges in infected male embryos at stage 9, wherein chromosomal DNA (green) and MSL1 representing X chromatids (magenta) are shown. Single-channelled images are shown in g′, g′′ and h′, h′′. Arrows and arrowheads in h–h′′ indicate an abnormally tangled DNA mass and asymmetrically segregated X chromatids, respectively. (i) Categorization of anaphase chromatin bridges in infected male embryos at stage 8–10. In total 140 anaphase bridges from 35 embryos were inspected. The categories ‘only X', ‘with X' and ‘without X' indicate complete, partial and no overlap between chromatin bridges and MSL1 signals. For more detail, see text. Scale bars, 20 μm (a,d) and 5 μm (b–c′′′, e–f′′′ and g–h′′).

Mentions: During the immunohistochemical experiments, we frequently observed inter-nuclear chromatin bridges in infected male embryos (Fig. 4d–f and Supplementary Fig. 3a). Notably, MSL1 signals frequently overlapped with chromatin bridges, suggesting that the male X chromosome may be involved in these abnormal structures (35/45 chromatin bridges observed in infected male embryos; Fig. 4e,f). To see more details, we analyzed 35 infected male embryos stained for both DNA and MSL1, and collected 140 mitotic cell images during anaphase, in which sister chromatids are about to separate and moving toward the opposite cell poles with a chromosomal bridge (Fig. 4g–i and Supplementary Fig. 3b–f). According to the extent of overlap between chromosomal bridges and MSL1 signals, we classified the images into three categories: only X, in which the chromosomal bridge and the MSL1 signal completely overlapped (116/140=83%; Fig. 4g–i and Supplementary Fig. 3c); with X, in which the chromosomal bridge and the MSL1 signal partially overlapped, or MSL1-labelled and unlabelled chromosomal bridges were observed simultaneously (21/140=15%; Supplementary Fig. 3d,e andFig. 4i); and without X, in which the chromosomal bridge lacked the MSL1 signal (3/140=2%; Supplementary Fig. 3f andFig. 4i). These results favour the idea that male X chromatids constitute chromosomal bridges. The chromosomal bridges were frequently associated with abnormally tangled DNA masses (95/140=68%; Fig. 4h and Supplementary Fig. 3c, arrows), suggesting compromised chromatin remodelling and/or condensation in male X chromatids. Notably, we observed that some X chromatids were asymmetrically segregated into two daughter cells (34/140=24%; Fig. 4h and Supplementary Fig. 3c,e, arrowheads), which presumably reflect the breakage of chromosomal bridges during cell division.


Male-killing symbiont damages host's dosage-compensated sex chromosome to induce embryonic apoptosis
Bridge and breakage of the male X chromosome during mitosis.(a) Epidermal cells of an uninfected male embryo at stage 11, in which pH2Av, MSL1 and DNA are visualized in green, magenta and blue as in Fig. 3a. (b,c) Magnified images of boxed regions in a, whose single-channelled images are shown in b′–b′′′ and c′–c′′′, respectively. Dotted circles highlight dividing cells in telophase. In b–b′′′, sister chromatids are normally segregating to daughter cells, whereas in c–c′′′, MSL1-labelled X chromatids seem to be segregating slightly slower than the other chromatids (arrows). (d) An image similar to a of a Spiroplasma-infected male embryo, exhibiting many pH2Av signals. (e,f) Magnified images of boxed regions in d, whose single-channelled images are shown in e′–e′′′ and f′–f′′′, respectively. Dotted circles highlight dividing cells in telophase, while arrows indicate inter-nuclear bridges overlapping with MSL1 and focal pH2Av signals, indicating that damaged male X chromatids constitute inter-nuclear bridges. (g,h) Two examples of anaphase chromatin bridges in infected male embryos at stage 9, wherein chromosomal DNA (green) and MSL1 representing X chromatids (magenta) are shown. Single-channelled images are shown in g′, g′′ and h′, h′′. Arrows and arrowheads in h–h′′ indicate an abnormally tangled DNA mass and asymmetrically segregated X chromatids, respectively. (i) Categorization of anaphase chromatin bridges in infected male embryos at stage 8–10. In total 140 anaphase bridges from 35 embryos were inspected. The categories ‘only X', ‘with X' and ‘without X' indicate complete, partial and no overlap between chromatin bridges and MSL1 signals. For more detail, see text. Scale bars, 20 μm (a,d) and 5 μm (b–c′′′, e–f′′′ and g–h′′).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036004&req=5

f4: Bridge and breakage of the male X chromosome during mitosis.(a) Epidermal cells of an uninfected male embryo at stage 11, in which pH2Av, MSL1 and DNA are visualized in green, magenta and blue as in Fig. 3a. (b,c) Magnified images of boxed regions in a, whose single-channelled images are shown in b′–b′′′ and c′–c′′′, respectively. Dotted circles highlight dividing cells in telophase. In b–b′′′, sister chromatids are normally segregating to daughter cells, whereas in c–c′′′, MSL1-labelled X chromatids seem to be segregating slightly slower than the other chromatids (arrows). (d) An image similar to a of a Spiroplasma-infected male embryo, exhibiting many pH2Av signals. (e,f) Magnified images of boxed regions in d, whose single-channelled images are shown in e′–e′′′ and f′–f′′′, respectively. Dotted circles highlight dividing cells in telophase, while arrows indicate inter-nuclear bridges overlapping with MSL1 and focal pH2Av signals, indicating that damaged male X chromatids constitute inter-nuclear bridges. (g,h) Two examples of anaphase chromatin bridges in infected male embryos at stage 9, wherein chromosomal DNA (green) and MSL1 representing X chromatids (magenta) are shown. Single-channelled images are shown in g′, g′′ and h′, h′′. Arrows and arrowheads in h–h′′ indicate an abnormally tangled DNA mass and asymmetrically segregated X chromatids, respectively. (i) Categorization of anaphase chromatin bridges in infected male embryos at stage 8–10. In total 140 anaphase bridges from 35 embryos were inspected. The categories ‘only X', ‘with X' and ‘without X' indicate complete, partial and no overlap between chromatin bridges and MSL1 signals. For more detail, see text. Scale bars, 20 μm (a,d) and 5 μm (b–c′′′, e–f′′′ and g–h′′).
Mentions: During the immunohistochemical experiments, we frequently observed inter-nuclear chromatin bridges in infected male embryos (Fig. 4d–f and Supplementary Fig. 3a). Notably, MSL1 signals frequently overlapped with chromatin bridges, suggesting that the male X chromosome may be involved in these abnormal structures (35/45 chromatin bridges observed in infected male embryos; Fig. 4e,f). To see more details, we analyzed 35 infected male embryos stained for both DNA and MSL1, and collected 140 mitotic cell images during anaphase, in which sister chromatids are about to separate and moving toward the opposite cell poles with a chromosomal bridge (Fig. 4g–i and Supplementary Fig. 3b–f). According to the extent of overlap between chromosomal bridges and MSL1 signals, we classified the images into three categories: only X, in which the chromosomal bridge and the MSL1 signal completely overlapped (116/140=83%; Fig. 4g–i and Supplementary Fig. 3c); with X, in which the chromosomal bridge and the MSL1 signal partially overlapped, or MSL1-labelled and unlabelled chromosomal bridges were observed simultaneously (21/140=15%; Supplementary Fig. 3d,e andFig. 4i); and without X, in which the chromosomal bridge lacked the MSL1 signal (3/140=2%; Supplementary Fig. 3f andFig. 4i). These results favour the idea that male X chromatids constitute chromosomal bridges. The chromosomal bridges were frequently associated with abnormally tangled DNA masses (95/140=68%; Fig. 4h and Supplementary Fig. 3c, arrows), suggesting compromised chromatin remodelling and/or condensation in male X chromatids. Notably, we observed that some X chromatids were asymmetrically segregated into two daughter cells (34/140=24%; Fig. 4h and Supplementary Fig. 3c,e, arrowheads), which presumably reflect the breakage of chromosomal bridges during cell division.

View Article: PubMed Central - PubMed

ABSTRACT

Some symbiotic bacteria are capable of interfering with host reproduction in selfish ways. How such bacteria can manipulate host's sex-related mechanisms is of fundamental interest encompassing cell, developmental and evolutionary biology. Here, we uncover the molecular and cellular mechanisms underlying Spiroplasma-induced embryonic male lethality in Drosophila melanogaster. Transcriptomic analysis reveals that many genes related to DNA damage and apoptosis are up-regulated specifically in infected male embryos. Detailed genetic and cytological analyses demonstrate that male-killing Spiroplasma causes DNA damage on the male X chromosome interacting with the male-specific lethal (MSL) complex. The damaged male X chromosome exhibits a chromatin bridge during mitosis, and bridge breakage triggers sex-specific abnormal apoptosis via p53-dependent pathways. Notably, the MSL complex is not only necessary but also sufficient for this cytotoxic process. These results highlight symbiont's sophisticated strategy to target host's sex chromosome and recruit host's molecular cascades toward massive apoptosis in a sex-specific manner.

No MeSH data available.