Histological and Cytological Techniques to Study Perinatal Mouse Ovaries and Oocytes.

The regulation of female fertility in mammals depends on critical processes during oocyte development and maturation. Therefore, it is crucial to use specific approaches when studying mammalian female fertility to preserve ovary and oocyte structures effectively. The methods of collecting and culturing ovaries and oocytes play an essential role in the study of mammalian follicle development and oocyte quality.

Genetic control of meiosis surveillance mechanisms in mammals.

Meiosis is a specialized cell division that generates haploid gametes and is critical for successful sexual reproduction. During the extended meiotic prophase I, homologous chromosomes progressively pair, synapse and desynapse. These chromosomal dynamics are tightly integrated with meiotic recombination (MR), during which programmed DNA double-strand breaks (DSBs) are formed and subsequently repaired.

p53 Controls Meiotic Prophase Progression and Crossover Formation.

Meiosis initiates with the formation of double strand breaks (DSBs) throughout the genome. To avoid genomic instability, these DSBs need to be correctly repaired by homologous recombination. Surveillance mechanisms involving the DNA damage response (DDR) pathway ATM-CHK2-p53 can detect the persistence of unrepaired DBSs and activate the recombination-dependent arrest at the pachytene stage.

Massive genome inversion drives coexistence of divergent morphs in common quails.

The presence of population-specific phenotypes often reflects local adaptation or barriers to gene flow. The co-occurrence of phenotypic polymorphisms that are restricted within the range of a highly mobile species is more difficult to explain. An example of such polymorphisms is in the common quail Coturnix coturnix, a small migratory bird that moves widely during the breeding season in search of new mating opportunities, following ephemeral habitats, and whose females may lay successive clutches at different locations while migrating.

Adenoid cystic carcinoma and basaloid carcinoma of the breast: A clinicopathological study.

Adenoid cystic carcinoma of the breast (ACCB) is a rare triple negative tumor (TNT) with an excellent prognosis in most cases. Three different histologic types are recognized: classic ACCB, solid basaloid ACCB (SB-ACCB), and ACCB with high-grade transformation. A majority of these tumors show characteristic molecular and immunohistochemical (IHC) features, with fusion of MYB and NFIB genes and overexpression of MYB, respectively.

Cas9 in Human Embryos: On Target but No Repair.

In this issue of Cell, Zuccaro and colleagues show that on-target Cas9-mediated double-strand breaks cause chromosome loss or mis-repair of the disease allele in > 90% of human embryos. End joining repair pathways dominate, causing small insertions or deletions, which raises serious questions about using double-strand breaks for "gene surgery".

The DNA damage response is required for oocyte cyst breakdown and follicle formation in mice.

Mammalian oogonia proliferate without completing cytokinesis, forming cysts. Within these, oocytes differentiate and initiate meiosis, promoting double-strand break (DSBs) formation, which are repaired by homologous recombination (HR) causing the pairing and synapsis of the homologs. Errors in these processes activate checkpoint mechanisms, leading to apoptosis.

ATR function is indispensable to allow proper mammalian follicle development.

Mammalian female fertility relies on the proper development of follicles. Right after birth in the mouse, oocytes associate with somatic ovarian cells to form follicles. These follicles grow during the adult lifetime to produce viable gametes.

The PSMA8 subunit of the spermatoproteasome is essential for proper meiotic exit and mouse fertility.

The ubiquitin proteasome system regulates meiotic recombination in yeast through its association with the synaptonemal complex, a 'zipper'-like structure that holds homologous chromosome pairs in synapsis during meiotic prophase I. In mammals, the proteasome activator subunit PA200 targets acetylated histones for degradation during somatic DNA double strand break repair and during histone replacement during spermiogenesis. We investigated the role of the testis-specific proteasomal subunit α4s (PSMA8) during spermatogenesis, and found that PSMA8 was localized to and dependent on the central region of the synaptonemal complex.

Shu complex SWS1-SWSAP1 promotes early steps in mouse meiotic recombination.

The DNA-damage repair pathway homologous recombination (HR) requires factors that promote the activity of strand-exchange protein RAD51 and its meiosis-specific homolog DMC1. Here we show that the Shu complex SWS1-SWSAP1, a candidate for one such HR regulator, is dispensable for mouse viability but essential for male and female fertility, promoting the assembly of RAD51 and DMC1 on early meiotic HR intermediates. Only a fraction of mutant meiocytes progress to form crossovers, which are crucial for chromosome segregation, demonstrating crossover homeostasis.

ATR is required to complete meiotic recombination in mice.

Precise execution of recombination during meiosis is essential for forming chromosomally-balanced gametes. Meiotic recombination initiates with the formation and resection of DNA double-strand breaks (DSBs). Cellular responses to meiotic DSBs are critical for efficient repair and quality control, but molecular features of these remain poorly understood, particularly in mammals.

H2AFX and MDC1 promote maintenance of genomic integrity in male germ cells.

In somatic cells, and are close functional partners in DNA repair and damage response. However, it is not known whether they are also involved in the maintenance of genome integrity in meiosis. By analyzing chromosome dynamics in spermatocytes, we found that the synapsis of autosomes and X-Y chromosomes was impaired in a fraction of cells.

p53 and TAp63 participate in the recombination-dependent pachytene arrest in mouse spermatocytes.

To protect germ cells from genomic instability, surveillance mechanisms ensure meiosis occurs properly. In mammals, spermatocytes that display recombination defects experience a so-called recombination-dependent arrest at the pachytene stage, which relies on the MRE11 complex-ATM-CHK2 pathway responding to unrepaired DNA double-strand breaks (DSBs). Here, we asked if p53 family members-targets of ATM and CHK2-participate in this arrest.

CEP63 deficiency promotes p53-dependent microcephaly and reveals a role for the centrosome in meiotic recombination.

CEP63 is a centrosomal protein that facilitates centriole duplication and is regulated by the DNA damage response. Mutations in CEP63 cause Seckel syndrome, a human disease characterized by microcephaly and dwarfism. Here we demonstrate that Cep63-deficient mice recapitulate Seckel syndrome pathology.

The ATM signaling cascade promotes recombination-dependent pachytene arrest in mouse spermatocytes.

Most mutations that compromise meiotic recombination or synapsis in mouse spermatocytes result in arrest and apoptosis at the pachytene stage of the first meiotic prophase. Two main mechanisms are thought to trigger arrest: one independent of the double-strand breaks (DSBs) that initiate meiotic recombination, and another activated by persistent recombination intermediates. Mechanisms underlying the recombination-dependent arrest response are not well understood, so we sought to identify factors involved by examining mutants deficient for TRIP13, a conserved AAA+ ATPase required for the completion of meiotic DSB repair.

Strong artificial selection in domestic mammals did not result in an increased recombination rate.

Recombination rates vary in intensity and location at the species, individual, sex and chromosome levels. Despite the fundamental biological importance of this process, the selective forces that operate to shape recombination rate and patterns are unclear. Domestication offers a unique opportunity to study the interplay between recombination and selection.

The ATM signaling network in development and disease.

The DNA damage response (DDR) rapidly recognizes DNA lesions and initiates the appropriate cellular programs to maintain genome integrity. This includes the coordination of cell cycle checkpoints, transcription, translation, DNA repair, metabolism, and cell fate decisions, such as apoptosis or senescence (Jackson and Bartek, 2009). DNA double-strand breaks (DSBs) represent one of the most cytotoxic DNA lesions and defects in their metabolism underlie many human hereditary diseases characterized by genomic instability (Stracker and Petrini, 2011; McKinnon, 2012).

Homeostatic control of recombination is implemented progressively in mouse meiosis.

Humans suffer from high rates of fetal aneuploidy, often arising from the absence of meiotic crossover recombination between homologous chromosomes. Meiotic recombination is initiated by double-strand breaks (DSBs) generated by the SPO11 transesterase. In yeast and worms, at least one buffering mechanism, crossover homeostasis, maintains crossover numbers despite variation in DSB numbers.

Expression of arf tumor suppressor in spermatogonia facilitates meiotic progression in male germ cells.

The mammalian Cdkn2a (Ink4a-Arf) locus encodes two tumor suppressor proteins (p16(Ink4a) and p19(Arf)) that respectively enforce the anti-proliferative functions of the retinoblastoma protein (Rb) and the p53 transcription factor in response to oncogenic stress. Although p19(Arf) is not normally detected in tissues of young adult mice, a notable exception occurs in the male germ line, where Arf is expressed in spermatogonia, but not in meiotic spermatocytes arising from them. Unlike other contexts in which the induction of Arf potently inhibits cell proliferation, expression of p19(Arf) in spermatogonia does not interfere with mitotic cell division.

The E3 ubiquitin ligase Cullin 4A regulates meiotic progression in mouse spermatogenesis.

The Cullin-RING ubiquitin-ligase CRL4 controls cell cycle and DNA damage checkpoint response and ensures genomic integrity. Inactivation of the Cul4 component of the CRL4 E3 ligase complex in Caenorhabditis elegans by RNA interference results in massive mitotic DNA re-replication in the blast cells, largely due to failed degradation of the DNA licensing protein, CDT-1, and premature spermatogenesis. Here we show that inactivation of Cul4a by gene-targeting in mice only affected male but not female fertility.

Meiotic homologue alignment and its quality surveillance are controlled by mouse HORMAD1.

Meiotic crossover formation between homologous chromosomes (homologues) entails DNA double-strand break (DSB) formation, homology search using DSB ends, and synaptonemal-complex formation coupled with DSB repair. Meiotic progression must be prevented until DSB repair and homologue alignment are completed, to avoid the formation of aneuploid gametes. Here we show that mouse HORMAD1 ensures that sufficient numbers of processed DSBs are available for successful homology search.

Meiosis in a bottle: new approaches to overcome Mammalian meiocyte study limitations.

The study of meiosis is limited because of the intrinsic nature of gametogenesis in mammals. One way to overcome these limitations would be the use of culture systems that would allow meiotic progression in vitro. There have been some attempts to culture mammalian meiocytes in recent years.

Mouse TRIP13/PCH2 is required for recombination and normal higher-order chromosome structure during meiosis.

Accurate chromosome segregation during meiosis requires that homologous chromosomes pair and become physically connected so that they can orient properly on the meiosis I spindle. These connections are formed by homologous recombination closely integrated with the development of meiosis-specific, higher-order chromosome structures. The yeast Pch2 protein has emerged as an important factor with roles in both recombination and chromosome structure formation, but recent analysis suggested that TRIP13, the mouse Pch2 ortholog, is not required for the same processes.