Taf1 knockout is lethal in embryonic male mice and heterozygous females show weight and movement disorders.

The TATA box-binding protein-associated factor 1 (TAF1) is a ubiquitously expressed protein and the largest subunit of the basal transcription factor TFIID, which plays a key role in initiation of RNA polymerase II-dependent transcription. TAF1 missense variants in human males cause X-linked intellectual disability, a neurodevelopmental disorder, and TAF1 is dysregulated in X-linked dystonia-parkinsonism, a neurodegenerative disorder. However, this field has lacked a genetic mouse model of TAF1 disease to explore its mechanism in mammals and treatments. Here, we generated and validated a conditional cre-lox allele and the first ubiquitous Taf1 knockout mouse. We discovered that Taf1 deletion in male mice was embryonically lethal, which may explain why no null variants have been identified in humans. In the brains of Taf1 heterozygous female mice, no differences were found in gross structure, overall expression and protein localisation, suggesting extreme skewed X inactivation towards the non-mutant chromosome. Nevertheless, these female mice exhibited a significant increase in weight, weight with age, and reduced movement, suggesting that a small subset of neurons was negatively impacted by Taf1 loss. Finally, this new mouse model may be a future platform for the development of TAF1 disease therapeutics.

Endosomal structure and APP biology are not altered in a preclinical mouse cellular model of Down syndrome.

Individuals who have Down syndrome (trisomy 21) are at greatly increased risk of developing Alzheimer's disease, characterised by the accumulation in the brain of amyloid-ß plaques. Amyloid-ß is a product of the processing of the amyloid precursor protein, encoded by the APP gene on chromosome 21. In Down syndrome the first site of amyloid-ß accumulation is within endosomes, and changes to endosome biology occur early in Alzheimer's disease. Here, we determine if primary mouse embryonic fibroblasts isolated from a mouse model of Down syndrome can be used to study endosome and APP cell biology. We report that in this cellular model, endosome number, size and APP processing are not altered, likely because APP is not dosage sensitive in the model, despite three copies of App.

A novel knockout mouse for the small EDRK-rich factor 2 (Serf2) showing developmental and other deficits.

The small EDRK-rich factor 2 (SERF2) is a highly conserved protein that modifies amyloid fibre assembly in vitro and promotes protein misfolding. However, the role of SERF2 in regulating age-related proteotoxicity remains largely unexplored due to a lack of in vivo models. Here, we report the generation of Serf2 knockout mice using an ES cell targeting approach, with Serf2 knockout alleles being bred onto different defined genetic backgrounds. We highlight phenotyping data from heterozygous Serf2+/- mice, including unexpected male-specific phenotypes in startle response and pre-pulse inhibition. We report embryonic lethality in Serf2-/- null animals when bred onto a C57BL/6 N background. However, homozygous null animals were viable on a mixed genetic background and, remarkably, developed without obvious abnormalities. The Serf2 knockout mice provide a powerful tool to further investigate the role of SERF2 protein in previously unexplored pathophysiological pathways in the context of a whole organism.

Uses for humanised mouse models in precision medicine for neurodegenerative disease.

Neurodegenerative disease encompasses a wide range of disorders afflicting the central and peripheral nervous systems and is a major unmet biomedical need of our time. There are very limited treatments, and no cures, for most of these diseases, including Alzheimer's Disease, Parkinson's Disease, Huntington Disease, and Motor Neuron Diseases. Mouse and other animal models provide hope by analysing them to understand pathogenic mechanisms, to identify drug targets, and to develop gene therapies and stem cell therapies. However, despite many decades of research, virtually no new treatments have reached the clinic. Increasingly, it is apparent that human heterogeneity within clinically defined neurodegenerative disorders, and between patients with the same genetic mutations, significantly impacts disease presentation and, potentially, therapeutic efficacy. Therefore, stratifying patients according to genetics, lifestyle, disease presentation, ethnicity, and other parameters may hold the key to bringing effective therapies from the bench to the clinic. Here, we discuss genetic and cellular humanised mouse models, and how they help in defining the genetic and environmental parameters associated with neurodegenerative disease, and so help in developing effective precision medicine strategies for future healthcare.

Transgenic and physiological mouse models give insights into different aspects of amyotrophic lateral sclerosis.

A wide range of genetic mouse models is available to help researchers dissect human disease mechanisms. Each type of model has its own distinctive characteristics arising from the nature of the introduced mutation, as well as from the specific changes to the gene of interest. Here, we review the current range of mouse models with mutations in genes causative for the human neurodegenerative disease amyotrophic lateral sclerosis. We focus on the two main types of available mutants: transgenic mice and those that express mutant genes at physiological levels from gene targeting or from chemical mutagenesis. We compare the phenotypes for genes in which the two classes of model exist, to illustrate what they can teach us about different aspects of the disease, noting that informative models may not necessarily mimic the full trajectory of the human condition. Transgenic models can greatly overexpress mutant or wild-type proteins, giving us insight into protein deposition mechanisms, whereas models expressing mutant genes at physiological levels may develop slowly progressing phenotypes but illustrate early-stage disease processes. Although no mouse models fully recapitulate the human condition, almost all help researchers to understand normal and abnormal biological processes, providing that the individual characteristics of each model type, and how these may affect the interpretation of the data generated from each model, are considered and appreciated.

Characterization of Histone Modifications Associated with Inactive X-Chromosome in Trophoblast Stem Cells, eXtra-Embryonic Endoderm Cells and in In Vitro Derived Undifferentiated and Differentiated Epiblast Like Stem Cells.

In mouse, X-chromosome inactivation (XCI) can either be imprinted or random. Imprinted XCI (iXCI) is considered unstable and depending on continuous Xist expression, whereas random XCI (rXCI) is stably maintained even in the absence of Xist. Here we have systematically examined epigenetic modifications associated with the inactive X-chromosome (Xi) in Trophoblast Stem cells, eXtra-Embryonic Endoderm Cells, undifferentiated and differentiated Epiblast Like Stem Cells in order to understand intrinsic differences in epigenetic mechanisms involved in silencing of the inactive X-chromosome in lineages presenting iXCI and rXCI. Whereas euchromatic histone modifications are predominantly lost from the Xi territory in all cell types, the accumulation of heterochromatic modifications diverges in between the analysed cell lineages. Particularly, only the Xi of multipotent Trophoblast (iXCI) and Epiblast stem cells (rXCI) display a visible accumulation of Polycomb Repressive Complexes (PRCs), in contrast to the Xi in differentiated Epiblast Like Stem Cells and eXtra-embryonic Endoderm cells. Despite this, the histone modifications catalysed by PRCs, ubH2AK119 and H3K27me3, remain the best heterochromatic markers for the Xi in all assessed lineages. Heterochromatic chromatin modifications associated with the Xi are a reflection of the epigenetic landscape of the entire genome of the assessed cell regardless whether XCI is imprinted or random.

Xist and Tsix Transcription Dynamics Is Regulated by the X-to-Autosome Ratio and Semistable Transcriptional States.

In female mammals, X chromosome inactivation (XCI) is a key process in the control of gene dosage compensation between X-linked genes and autosomes. Xist and Tsix, two overlapping antisense-transcribed noncoding genes, are central elements of the X inactivation center (Xic) regulating XCI. Xist upregulation results in the coating of the entire X chromosome by Xist RNA in cis, whereas Tsix transcription acts as a negative regulator of Xist Here, we generated Xist and Tsix reporter mouse embryonic stem (ES) cell lines to study the genetic and dynamic regulation of these genes upon differentiation. Our results revealed mutually antagonistic roles for Tsix on Xist and vice versa and indicate the presence of semistable transcriptional states of the Xic locus predicting the outcome of XCI. These transcriptional states are instructed by the X-to-autosome ratio, directed by regulators of XCI, and can be modulated by tissue culture conditions.

Fitting the Puzzle Pieces: the Bigger Picture of XCI.

X chromosome inactivation (XCI) is a mammalian-specific process initiated in all female cells, leading to one inactivated X chromosome. The robust nature of XCI, and the complex mechanisms involved in directing this process, makes XCI an important model system to study all aspects of gene regulation. XCI is divided into distinct phases: initiation, establishment, and maintenance of the inactive X (Xi). Recent studies shed important new light on the mechanisms directing all three phases of XCI. These findings include new regulatory pathways in XCI initiation, and the identification of a plethora of new factors involved in establishing and maintaining the Xi. In this review, we will highlight and discuss these new findings in the bigger picture of XCI.