CRL2(LRR-1) E3-ligase regulates proliferation and progression through meiosis in the Caenorhabditis elegans germline.

The ubiquitin-proteolytic system controls the stability of proteins in space and time. In this study, using a temperature-sensitive mutant allele of the cul-2 gene, we show that CRL2(LRR-1) (CUL-2 RING E3 ubiquitin-ligase and the Leucine Rich Repeat 1 substrate recognition subunit) acts at multiple levels to control germline development. CRL2(LRR-1) promotes germ cell proliferation by counteracting the DNA replication ATL-1 checkpoint pathway. CRL2(LRR-1) also participates in the mitotic proliferation/meiotic entry decision, presumably controlling the stability of meiotic promoting factors in the mitotic zone of the germline. Finally, CRL2(LRR-1) inhibits the first steps of meiotic prophase by targeting in mitotic germ cells degradation of the HORMA domain-containing protein HTP-3, required for loading synaptonemal complex components onto meiotic chromosomes. Given its widespread evolutionary conservation, CUL-2 may similarly regulate germline development in other organisms as well.

The CRL2LRR-1 ubiquitin ligase regulates cell cycle progression during C. elegans development.

The molecular mechanisms that regulate cell cycle progression in a developmental context are poorly understood. Here, we show that the leucine-rich repeat protein LRR-1 promotes cell cycle progression during C. elegans development, both in the germ line and in the early embryo. Our results indicate that LRR-1 acts as a nuclear substrate-recognition subunit of a Cullin 2-RING E3 ligase complex (CRL2(LRR-1)), which ensures DNA replication integrity. LRR-1 contains a typical BC/Cul-2 box and binds CRL2 components in vitro and in vivo in a BC/Cul-2 box-dependent manner. Loss of lrr-1 function causes cell cycle arrest in the mitotic region of the germ line, resulting in sterility due to the depletion of germ cells. Inactivation of the DNA replication checkpoint signaling components ATL-1 and CHK-1 suppresses this cell cycle arrest and, remarkably, restores lrr-1 mutant fertility. Likewise, in the early embryo, loss of lrr-1 function induces CHK-1 phosphorylation and a severe cell cycle delay in P lineage division, causing embryonic lethality. Checkpoint activation is not constitutive in lrr-1 mutants but is induced by DNA damage, which may arise due to re-replication of some regions of the genome as evidenced by the accumulation of single-stranded DNA-replication protein A (ssDNA-RPA-1) nuclear foci and the increase in germ cell ploidy in lrr-1 and lrr-1; atl-1 double mutants, respectively. Collectively, these observations highlight a crucial function of the CRL2(LRR-1) complex in genome stability via maintenance of DNA replication integrity during C. elegans development.

Infection with Influenzavirus A in a murine model induces epithelial bronchial lesions and distinct waves of innate immune-cell recruitment.

Introduction: Inflammatory lesions after Influenza A viruses (IAV) are potential therapeutic target for which better understanding of post-infection immune mechanisms is required. Most studies to evaluate innate immune reactions induced by IAV are based on quantitative/functional methods and anatomical exploration is most often non-existent. We aimed to study pulmonary damage and macrophage recruitment using two-photon excitation microscopy (TPEM) after IAV infection. Methods: We infected C57BL/6 CD11c+YFP mice with A/Puerto Ricco/8/34 H1N1. We performed immune cell analysis, including flow cytometry, cytokine concentration assays, and TPEM observations after staining with anti-F4/80 antibody coupled to BV421. We adapted live lung slice (LLS) method for ex-vivo intravital microscopy to analyze cell motility. Results: TPEM provided complementary data to flow cytometry and cytokine assays by allowing observation of bronchial epithelium lesions and spreading of local infection. Addition of F4/80-BV421 staining allowed us to precisely determine timing of recruitment and pulmonary migration of macrophages. Ex-vivo LLS preserved cellular viability, allowing us to observe acceleration of macrophage motility. Conclusion: After IAV infection, we were able to explore structural consequences and successive waves of innate immune cell recruitment. By combining microscopy, flow cytometry and chemokine measurements, we describe novel and precise scenario of innate immune response against IAV.

Macrophages Characterization in an Injured Bone Tissue.

Biomaterial use is a promising approach to facilitate wound healing of the bone tissue. Biomaterials induce the formation of membrane capsules and the recruitment of different types of macrophages. Macrophages are immune cells that produce diverse combinations of cytokines playing an important role in bone healing and regeneration, but the exact mechanism remains to be studied. Our work aimed to identify in vivo macrophages in the Masquelet induced membrane in a rat model. Most of the macrophages in the damaged area were M2-like, with smaller numbers of M1-like macrophages. In addition, high expression of IL-1ß and IL-6 cytokines were detected in the membrane region by RT-qPCR. Using an innovative combination of two hybridization techniques (in situ hybridization and in situ hybridization chain reaction (in situ HCR)), M2b-like macrophages were identified for the first time in cryosections of non-decalcified bone. Our work has also demonstrated that microspectroscopical analysis is essential for macrophage characterization, as it allows the discrimination of fluorescence and autofluorescence. Finally, this work has revealed the limitations of immunolabelling and the potential of in situ HCR to provide valuable information for in vivo characterization of macrophages.