Multiple 9-1-1 complexes promote homolog synapsis, DSB repair, and ATR signaling during mammalian meiosis

The differential roles of rad9 alternatively spliced forms in double- strand DNA break repair during Drosophila meiosis

The 9-1-1 complex, comprising the Rad9, Hus1 and Rad1 proteins, is believed to operate as a component of a DNA damage checkpoint pathway. Our initial analysis of the Drosophila hus1 gene showed that Hus1 plays a dual role in meiosis, regulating both meiotic DNA damage checkpoint and homologous recombination repair. In this study, we further analyzed the meiotic roles of another protein in the complex, Rad9, which has two alternatively spliced forms, Rad9A and Rad9B. Using CRISPR/Cas9, we generated flies mutant for both rad9 isoforms. We found that, similarly to hus1, mutations in rad9 lead to female sterility. Also, double-strand DNA breaks (DSBs) that form during meiosis are not processed efficiently, and the DNA within the oocyte nucleus fails to form its characteristic shape in rad9 mutants. On the other hand, the hus1 mutation completely disrupts checkpoint activation in DSB repair enzyme mutants, whereas the rad9 mutation only partially impairs checkpoint activation in this context. Moreover, spatial rescue experiments revealed that Rad9B is efficient in repairing meiotic DSBs, while Rad9A is not. Furthermore, we found that female fertility in rad9 mutants depends on early efficient meiotic DSB repair but not on karyosome formation. In summary, our results demonstrate a differential role of Rad9 alternatively spliced forms during Drosophila meiosis in oogenesis, and while former studies showed that Hus1 is sufficient for the effective activation of the meiotic recombination checkpoint, our results revealed that this is not true for Rad9.

A TOPBP1 allele causing male infertility uncouples XY silencing dynamics from sex body formation

Meiotic sex chromosome inactivation (MSCI) is a critical feature of meiotic prophase I progression in males. While the ATR kinase and its activator TOPBP1 are key drivers of MSCI within the specialized sex body (SB) domain of the nucleus, how they promote silencing remains unclear given their multifaceted meiotic functions that also include DNA repair, chromosome synapsis, and SB formation. Here we report a novel mutant mouse harboring mutations in the TOPBP1-BRCT5 domain. Topbp1B5/B5 males are infertile, with impaired MSCI despite displaying grossly normal events of early prophase I, including synapsis and SB formation. Specific ATR-dependent events are disrupted, including phosphorylation and localization of the RNA:DNA helicase Senataxin. Topbp1B5/B5 spermatocytes initiate, but cannot maintain ongoing, MSCI. These findings reveal a non-canonical role for the ATR-TOPBP1 signaling axis in MSCI dynamics at advanced stages in pachynema and establish the first mouse mutant that separates ATR signaling and MSCI from SB formation.

Culture of the Intact Postnatal Naked Mole-Rat Ovary: From Meiotic Prophase to Single-Cell RNASeq

Recently, we reported that, in the naked mole-rat (Heterocephalus glaber) ovary, there is mitotic expansion of the primordial germ cells (PGCs), and the initiation of the meiotic program occurs postnatally. This is opposite to almost all other mammals, including humans and mice, whose reproductive cycle begins very early in development. In both mouse and human, the ovaries become populated with PGCs in utero; these PGCs will later generate the oogonia. After mitotic proliferation, these cells will trigger the meiotic program and initiate meiotic prophase I. Given that all these processes happen in utero, their analysis has been very challenging; so the ability to study them postnatally and to manipulate them with inhibitors or other substances, in the naked mole-rat, opens new possibilities in the field. In this chapter, we present a comprehensive collection of protocols that permit the culture of whole naked mole-rat ovaries, followed by analysis of germ cells, from PGCs to oocytes, in meiotic prophase I, as well the obtention of single-cell suspension or single-nuclei suspension for RNASeq.

The dynamic subcellular localisation of Rad1 is cell cycle dependent in Leishmania major

The subcellular localisation of Rad1, a subunit of the Leishmania major 9-1-1 complex, remains unexplored. Herein, we reveal that Rad1 localises predominantly to the nucleus. Upon hydroxyurea treatment, the diffuse nuclear localisation of Rad1 becomes more punctate, suggesting that Rad1 is responsive to replication stress. Moreover, Rad1 localisation correlates with cell cycle progression. In the majority of G1 to early S-phase cells, Rad1 localises predominantly to the nucleus. As cells progress from late-S phase to mitosis, Rad1 relocalizes to both the nucleus and the cytoplasm in ∼90 % of cells. This pattern of distribution is different from Rad9 and Hus1, which remain nuclear throughout the cell cycle, suggesting Leishmania Rad1 may regulate 9-1-1 activities and/or perform relevant functions outside the 9-1-1 complex.

A TOPBP1 Allele Causing Male Infertility Uncouples XY Silencing Dynamics From Sex Body Formation

Meiotic sex chromosome inactivation (MSCI) is a critical feature of meiotic prophase I progression in males. While the ATR kinase and its activator TOPBP1 are key drivers of MSCI within the specialized sex body (SB) domain of the nucleus, how they promote silencing remains unclear given their multifaceted meiotic functions that also include DNA repair, chromosome synapsis and SB formation. Here we report a novel mutant mouse harboring mutations in the TOPBP1-BRCT5 domain. Topbp1 B5/B5 males are infertile, with impaired MSCI despite displaying grossly normal events of early prophase I, including synapsis and SB formation. Specific ATR-dependent events are disrupted including phosphorylation and localization of the RNA:DNA helicase Senataxin. Topbp1 B5/B5 spermatocytes initiate, but cannot maintain ongoing, MSCI. These findings reveal a non-canonical role for the ATR-TOPBP1 signaling axis in MSCI dynamics at advanced stages in pachynema and establish the first mouse mutant that separates ATR signaling and MSCI from SB formation.

Expression of RAD9B in the mesostriatal system of rats and humans: Overexpression in a 6-OHDA rat model of Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disorder that affects primarily the dopaminergic (DAergic) neurons of the mesostriatal system, among other nuclei of the brain. Although it is considered an idiopathic disease, oxidative stress is believed to be involved in DAergic neuron death and therefore plays an important role in the onset and development of the disease. RAD9B is a paralog of the RAD9 checkpoint, sharing some similar functions related to DNA damage resistance and apoptosis, as well as the ability to form 9-1-1 heterotrimers with RAD1 and HUS1.

METHODS

In addition to immunohistochemistry, immunofluorescence and Western-blot analysis, we implemented Quantitative RT-PCR and in situ hybridization techniques.

RESULTS

We demonstrated RAD9B expression in rat and human mesencephalic DAergic cells using specific markers. Additionally, we observed significant overexpression of RAD9B mRNA (p<0.01) and protein (p<0.01) in the midbrain 48 h after inducing damage with 150 µg of 6-hydroxydopamine (6-OHDA) injected in a rat model of PD. Regarding protein expression, the increased levels were observed in neurons of the mesostriatal system and returned to normal 5 days post-injury.

CONCLUSIONS

This response to a neurotoxin, known to produce oxidative stress specifically on DAergic neurons indicates the potential importance of RAD9B in this highly vulnerable population to cell death. In this model, RAD9B function appears to provide neuroprotection, as the induced lesion resulted in only mild degeneration. This observation highlights the potential of RAD9B checkpoint protein as a valuable target for future therapeutic interventions aimed at promoting neuroprotection.

Characterization of the Postnatal Naked Mole-Rat Ovary: From Primordial Germ Cells to Meiotic Prophase I Oocytes

The mammalian reproductive cycle, including those of humans and mice, begins very early in development. In utero, the ovaries become populated with primordial germ cells (PGCs) that will generate the oogonia. First, these cells proliferate mitotically, and then they trigger the meiotic program and initiate meiotic prophase I. Since these processes happen during gestation, their study had been very limited and challenging. Recently, we reported that, in the naked mole-rat (Heterocephalus glaber) ovary, there is mitotic expansion of the PGCs, and the initiation of the meiotic program occurs postnatally. In this chapter, we present a comprehensive collection of protocols that permit the analysis of naked mole-rat germ cells, from PGCs to oocytes, in meiotic prophase I, using in vivo and in vitro approaches.