Actin protects mammalian eggs against chromosome segregation errors

Aneuploidy is a cellular condition characterized by the gain or loss of specific chromosomes. This can arise from chromosome segregation problems during cell division in the germ line (a process called meiosis), and is the main cause of age-related female infertility, spontaneous miscarriage, and developmental disorders in humans. To segregate chromosomes, cells rely on a spindle-shaped structure made up of filaments called microtubules. On page 772 of this issue, Mogessie and Schuh (1) show that another cytoskeleton filament—actin—can be found in close association with microtubules in the spindle and promotes chromosome segregation fidelity during meiosis in mammalian oocytes

Assembly and Positioning of the Oocyte Meiotic Spindle

Fertilizable eggs develop from diploid precursor cells termed oocytes. Once every menstrual cycle, an oocyte matures into a fertilizable egg in the ovary. To this end, the oocyte eliminates half of its chromosomes into a small cell termed a polar body. The egg is then released into the Fallopian tube, where it can be fertilized. Upon fertilization, the egg completes the second meiotic division, and the mitotic division of the embryo starts. This review highlights recent work that has shed light on the cytoskeletal structures that drive the meiotic divisions of the oocyte in mammals. In particular, we focus on how mammalian oocytes assemble a microtubule spindle in the absence of centrosomes, how they position the spindle in preparation for polar body extrusion, and how the spindle segregates the chromosomes. We primarily focus on mouse oocytes as a model system but also highlight recent insights from human oocytes. Expected final online publication date for the Annual Review of Cell and Developmental Biology Volume 34 is October 6, 2018. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates

A Method for the Acute and Rapid Degradation of Endogenous Proteins.

Methods for the targeted disruption of protein function have revolutionized science and greatly expedited the systematic characterization of genes. Two main approaches are currently used to disrupt protein function: DNA knockout and RNA interference, which act at the genome and mRNA level, respectively. A method that directly alters endogenous protein levels is currently not available. Here, we present Trim-Away, a technique to degrade endogenous proteins acutely in mammalian cells without prior modification of the genome or mRNA. Trim-Away harnesses the cellular protein degradation machinery to remove unmodified native proteins within minutes of application. This rapidity minimizes the risk that phenotypes are compensated and that secondary, non-specific defects accumulate over time. Because Trim-Away utilizes antibodies, it can be applied to a wide range of target proteins using off-the-shelf reagents. Trim-Away allows the study of protein function in diverse cell types, including non-dividing primary cells where genome- and RNA-targeting methods are limited

Acute and rapid degradation of endogenous proteins by Trim-Away.

Protein depletion is a key approach to understanding the functions of a protein in a biological system. We recently developed the Trim-Away approach in order to rapidly degrade endogenous proteins without prior modification. Trim-Away is based on the ubiquitin ligase and Fc receptor TRIM21, which recognizes antibody-bound proteins and targets them for degradation by the proteasome. In a typical Trim-Away experiment, protein degradation is achieved in three steps: first, introduction of an antibody against the target protein; second, recruitment of endogenous or exogenous/overexpressed TRIM21 to the antibody-bound target protein; and third, proteasome-mediated degradation of the target protein, antibody and TRIM21 complex. Protein degradation by Trim-Away is acute and rapid, with half-lives of ~10-20 min. The major advantages of Trim-Away over other protein degradation methods are that it can be applied to any endogenous protein without prior modification; that it uses conventional antibodies that are widely available; and that it can be applied to a wide range of cell types, including nondividing primary human cells, for which other loss-of-function assays are challenging. In this protocol, we describe the detailed procedures for antibody preparation and delivery in mouse oocytes and cultured cells via microinjection and electroporation. In addition, we provide recommendations for antibody selection and validation, and for the generation of TRIM21-overexpressing cell lines for cases in which endogenous TRIM21 is limited. A typical Trim-Away experiment takes just a few hours.The research leading to these results received financial support from the Medical Research Council (MC_U105192711 and MC_U105181010), the Max Planck Society, the European Community’s Seventh Framework Programme (FP7/2007–2013) under grant agreement no. 241548, European Research Council (ERC) Starting Grant no. 337415 and a Wellcome Trust Investigator Award

Table of Contents

Chromosome errors, or aneuploidy, affect an exceptionally high number of human conceptions, causing pregnancy loss and congenital disorders. Here, we have followed chromosome segregation in human oocytes from females aged 9 to 43 years and report that aneuploidy follows a U-curve. Specific segregation error types show different age dependencies, providing a quantitative explanation for the U-curve. Whole-chromosome nondisjunction events are preferentially associated with increased aneuploidy in young girls, whereas centromeric and more extensive cohesion loss limit fertility as women age. Our findings suggest that chromosomal errors originating in oocytes determine the curve of natural fertility in humans. [Abstract copyright: Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Defining the causes of sporadic Parkinson's disease in the global Parkinson's genetics program (GP2)

The Global Parkinson’s Genetics Program (GP2) will genotype over 150,000 participants from around the world, and integrate genetic and clinical data for use in large-scale analyses to dramatically expand our understanding of the genetic architecture of PD. This report details the workflow for cohort integration into the complex arm of GP2, and together with our outline of the monogenic hub in a companion paper, provides a generalizable blueprint for establishing large scale collaborative research consortia

Multi-ancestry genome-wide association meta-analysis of Parkinson?s disease

Although over 90 independent risk variants have been identified for Parkinson’s disease using genome-wide association studies, most studies have been performed in just one population at a time. Here we performed a large-scale multi-ancestry meta-analysis of Parkinson’s disease with 49,049 cases, 18,785 proxy cases and 2,458,063 controls including individuals of European, East Asian, Latin American and African ancestry. In a meta-analysis, we identified 78 independent genome-wide significant loci, including 12 potentially novel loci (MTF2, PIK3CA, ADD1, SYBU, IRS2, USP8, PIGL, FASN, MYLK2, USP25, EP300 and PPP6R2) and fine-mapped 6 putative causal variants at 6 known PD loci. By combining our results with publicly available eQTL data, we identified 25 putative risk genes in these novel loci whose expression is associated with PD risk. This work lays the groundwork for future efforts aimed at identifying PD loci in non-European populations