The polar Ras-like GTPase MglA activates type IV pilus via SgmX to enable twitching motility in Myxococcus xanthus

International audienceType IV pili (Tfp) are highly conserved macromolecular structures that fulfill diverse cellular functions, such as adhesion to host cells, the import of extracellular DNA, kin recognition, and cell motility (twitching). Outstandingly, twitching motility enables a poorly understood process by which highly coordinated groups of hundreds of cells move in cooperative manner, providing a basis for multicellular behaviors, such as biofilm formation. In the social bacteria Myxococcus xanthus, we know that twitching motility is under the dependence of the small GTPase MglA, but the underlying molecular mechanisms remain elusive. Here we show that MglA complexed to GTP recruits a newly characterized Tfp regulator , termed SgmX, to activate Tfp machines at the bacterial cell pole. This mechanism also ensures spatial regulation of Tfp, explaining how MglA switching provokes directional reversals. This discovery paves the way to elucidate how polar Tfp machines are regulated to coordinate multicellular movements, a conserved feature in twitching bacteria. type IV pilus | cell motility | small GTPase | Myxococcus xanthu

p53-dependent programmed necrosis controls germ cell homeostasis during spermatogenesis

International audienceThe importance of regulated necrosis in pathologies such as cerebral stroke and myocardial infarction is now fully recognized. However, the physiological relevance of regulated necrosis remains unclear. Here, we report a conserved role for p53 in regulating necrosis in Drosophila and mammalian spermatogenesis. We found that Drosophila p53 is required for the programmed necrosis that occurs spontaneously in mitotic germ cells during spermatogenesis. This form of necrosis involved an atypical function of the initiator caspase Dronc/Caspase 9, independent of its catalytic activity. Prevention of p53-dependent necrosis resulted in testicular hyperplasia, which was reversed by restoring necrosis in spermatogonia. In mouse testes, p53 was required for heat-induced germ cell necrosis, indicating that regulation of necrosis is a primordial function of p53 conserved from invertebrates to vertebrates. Drosophila and mouse spermatogenesis will thus be useful models to identify inducers of necrosis to treat cancers that are refractory to apoptosis

Quel enseignement de l’écologie à l’école ?

Regard de la SFE

Quel enseignement de l’écologie à l’école ?

Regard de la SFE

Germ cells in the testes of <i>p53</i>-deficient mice are resistant to heat-induced necrosis.

<p>(<b>A</b>-<b>C”</b>) Sections of heat-shocked testes from 6–8-week-old wild-type (<i>wt</i>, <b>A</b>-<b>A”</b>), <i>p53</i>^<i>+/-</i> (<b>B</b>-<b>B”</b>), and <i>p53</i>^<i>-/-</i> (<b>C</b>-<b>C”</b>) mice, counterstained with HES (<b>A</b>, <b>B</b>, <b>C</b>) and stained with TUNEL (<b>A'</b>, <b>A” B'</b>, <b>B”</b>, <b>C'</b>, <b>C”</b>). Black and blue arrowheads indicate seminiferous tubules fully and partially filled with TUNEL⁺ cells, respectively. Scale bars, 200 μm (<b>A</b>, <b>A', B</b>, <b>B', C</b>, <b>C'</b>) and 50 μm (<b>A”</b>, <b>B”</b>, <b>C”</b>). (<b>D</b>) Quantification of the total fraction of seminiferous tubules containing TUNEL⁺ cells (left) and the fraction of seminiferous tubules partially filled with TUNEL⁺ cells (right) shown in <b>A</b>-<b>C”</b> (mean ± s.e.m. of N testes/genotype). <i>*p <</i> 0.05, *<i>*p <</i> 0.01 by Welch’s two-sample t-test.</p

p53-dependent necrotic cell death suppresses testicular hyperplasia in <i>Drosophila</i>.

<p>(<b>A</b>-<b>F</b>) Bright field images of testes from adult wild-type (<i>wt; w</i>^<i>1118</i>, <b>A</b>) flies and flies lacking genes required for germ cell death (<b>B-F</b>). The testis apical tip and hub region are indicated by the white dotted square and white asterisk, respectively. Scale bar, 100 μm. (<b>G</b>) Frequency of testes with apical tip hyperplasia (mean ± s.e.m. of three independent experiments, N testes/genotype). *<i>*p <</i> 0.01, **<i>*p <</i> 0.001 versus <i>wt</i> flies by Fisher’s exact test. (<b>H</b>-<b>K</b>) TUNEL staining (<b>H</b>, <b>I</b>) and p53 immunostaining (<b>J</b>, <b>K</b>) of spermatogonial cysts (white arrowheads in <b>H</b>, <b>I</b>) in adult testes from <i>p53</i> mutant flies expressing <i>Dp53</i> (<b>H</b>, <b>J</b>) and <i>DΔNp53</i> (<b>I</b>, <b>K</b>) under the control of the <i>nanos [nos]-gal4</i> driver. Nuclei are stained with DAPI and the hub region is indicated by the white asterisk. Scale bar, 40 μm. (<b>L</b>-<b>M'</b>) Propidium iodide (PI) staining (<b>L</b>, <b>M</b>) and cleaved Dcp-1 immunostaining (<b>L’</b>-<b>M’</b>) of <i>p53</i> mutant fly testes expressing <i>Dp53</i> (<b>L</b>-<b>L’</b>) and <i>DΔNp53</i> (<b>M</b>-<b>M'</b>) under the control of the <i>nanos [nos]-gal4</i> driver. PI⁺ and cleaved Dcp-1⁺ spermatogonial cysts are indicated by magenta and green arrowheads, respectively. Nuclei are stained with DAPI and the hub region is indicated by a white (<b>L</b>, <b>M</b>) or black (<b>L'</b>-<b>M'</b>) asterisk. Scale bar, 20 μm. (<b>N</b>) Quantification of TUNEL⁺ spermatogonial cysts expressed as % of <i>wt</i> (mean ± s.e.m. of three independent experiments, N testes/genotype). <i>*p <</i> 0.05 by two-tailed unpaired Student’s t-test. (<b>O</b>) Frequency of adult testes with apical tip hyperplasia in flies of the indicated genotypes (mean ± s.e.m. of three independent experiments, N testes/genotype). <i>*p <</i> 0.05, **<i>*p <</i> 0.001 by Fisher’s exact test.</p

Mild hyperthermia induces germ cell necrosis during mouse spermatogenesis.

<p>(<b>A</b>-<b>D</b>) Electron micrographs of non-treated (<b>A</b>) or heat-shocked mice testes at 6 (<b>B</b>-<b>C'</b>) and 24 hours (<b>D</b>) after heat shock, showing cellular morphological hallmarks of necrosis (<b>B</b>-<b>C'</b>) or apoptosis (<b>D</b>, red arrowheads). White asterisks indicate extranuclear densities observed in the cytoplasm that may reflect an unrelated acid phosphatase activity previously observed in GCs (<b>D</b> [<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1007024#pgen.1007024.ref067" target="_blank">67</a>]). Insets (red squares in <b>A</b>-<b>C'</b>) show ruptured nuclear membranes (yellow arrowheads in <b>B'</b> and <b>C'</b>). N and CP indicate nucleus and cytoplasm, respectively. SC indicates Sertoli cells. (<b>E</b>-<b>I</b>) Sections of non-treated (NT, <b>E</b>) or heat-shocked testes from 6–8-week-old wild-type mice stained with anti-cleaved caspase-3 antibody (<b>E</b>-<b>I</b>) at the indicated time after heat-shock. Blue arrowheads (<b>H</b>) indicate cleaved caspase-3⁺ cells. Scale bar, 100 μm. (<b>J</b>-<b>N</b>) Sections of non-treated (NT, <b>J</b>) or heat-shocked testes from 6–8-week-old wild-type mice stained with TUNEL (<b>J</b>-<b>N</b>) at the indicated time after heat-shock. Black arrowheads (<b>K</b>-<b>M</b>) indicate TUNEL⁺ cells. Scale bar, 100 μm (<b>J-N)</b>. (<b>O</b>) Quantification of the total fraction of tubules containing TUNEL⁺ cells (blue curve) and the fraction of tubules partially filled with TUNEL⁺ cells (red curve) at the indicated time after heat shock. (<b>P</b>) Quantification of activated caspase-3⁺ cells per section (mean ± s.e.m) at the indicated times after heat shock.</p

Atypical Dronc function is required for necrotic cell death.

<p><b>(A)</b> Schematic of Dronc protein highlighting the N-terminal containing CARD domain and the Dronc^C>A mutation in the catalytic domain. (<b>B</b>) Quantification of TUNEL⁺ spermatogonial cysts of adult testes from <i>dronc</i>^{<i>I29/L32</i>} mutant flies expressing wild-type (<i>dronc</i>^<i>WT</i>) or catalytically inactive (<i>dronc</i>^<i>C>A</i>) <i>dronc</i> under the control of the endogenous promoter sequences. Quantification is expressed as % of <i>wt</i> (mean ± s.e.m. of three independent experiments, N testes/genotype). <i>*p <</i> 0.05 by two-tailed unpaired Student’s t-test. (<b>C</b>-<b>H</b>) TUNEL staining of spermatogonial cysts (white arrowheads in <b>D</b>-<b>G</b>) in adult testes from <i>dronc</i>^{<i>I29/L32</i>} mutant flies (<b>C</b>) expressing full-length <i>dronc</i>^<i>WT</i> (<b>D</b>), full-length <i>dronc</i>^<i>C>A</i> (<b>E</b>), CARD prodomain-deleted wild-type <i>dronc</i> (<i>ΔNdronc</i>^<i>WT</i>, <b>F</b>), CARD prodomain-deleted catalytically inactive <i>dronc</i> (<i>ΔNdronc</i>^<i>C>A</i>, <b>G</b>), or the CARD prodomain only (<i>dronc</i>^<i>CARD</i>, <b>H</b>) under the control of the <i>nos</i> driver. Nuclei are stained with DAPI and the hub region is indicated by the white asterisk. Scale bar, 40 μm. (<b>I</b>) Quantification of TUNEL⁺ spermatogonial cysts expressed as % of <i>wt</i> (mean ± s.e.m. of three independent experiments, N testes/genotype). *<i>*p <</i> 0.01, ***<i>p</i> < 0.001 versus <i>dronc</i>^{<i>I29/L32</i>} by two-tailed unpaired Student’s t-test. (<b>J</b>-<b>L</b>) Phalloidin staining of F-actin-rich investment cones (dotted rectangles, enlarged in insets) in adult testes from <i>dronc</i>^{<i>I29/L32</i>} mutant flies (<b>J</b>), expressing wild-type <i>dronc</i> (<i>dronc</i>^<i>WT</i>, <b>K</b>) or catalytically inactive <i>dronc</i> (<i>dronc</i>^<i>C>A</i>, <b>L</b>) under the control of endogenous promoter sequences. Scale bar, 40 μm.</p