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Long-term maintenance of spermatogenesis in mammals is supported by GDNF, an essential growth factor required for spermatogonial stem cell (SSC) self-renewal. Exploiting a transgenic GDNF overexpression model, which expands and normalizes the pool of undifferentiated spermatogonia between Plzf +/+ and Plzf lu/lu mice, we used RNAseq to identify a rare subpopulation of cells that express EOMES, a T-box transcription factor. Lineage tracing and busulfan challenge show that these are SSCs that contribute to steady state spermatogenesis as well as regeneration following chemical injury. EOMES+ SSCs have a lower proliferation index in wild-type than in Plzf lu/lu mice, suggesting that PLZF regulates their proliferative activity and that EOMES+ SSCs are lost through proliferative exhaustion in Plzf lu/lu mice. Single cell RNA sequencing of EOMES+ cells from Plzf +/+ and Plzf lu/lu mice support the conclusion that SSCs are hierarchical yet heterogeneous.

Craniofacial abnormalities are among the most common features of human genetic syndromes and disorders. The etiology of these conditions is often complex, influenced by both genetic context and the environment. Frequently, craniofacial abnormalities present as part of a syndrome with clear comorbid phenotypes, providing additional insight into mechanisms of the causative gene or pathway. The mouse has been a key tool in our understanding of the genetic mechanisms of craniofacial development and disease, and can provide excellent models for human craniofacial abnormalities. While powerful genetic engineering tools in the mouse have contributed significantly our understanding of craniofacial development and dysmorphology, forward genetic approaches provide an unbiased means to identify new genes and pathways. Moreover, spontaneous mutations can occur on any number of genetic backgrounds, potentially revealing critical genes that require a specific genetic context. Here we report discovery and phenotyping of 43 craniofacial mouse models, derived primarily from a screen for spontaneous mutations in production colonies at the Jackson Laboratory. We identify the causative gene for 33 lines, including novel genes in pathways not previously connected to craniofacial development, and novel alleles of known genes that present with unique phenotypes. Together with our detailed characterization, this work provides a valuable gene discovery resource for the craniofacial community, and a rich source of mouse models for further investigation.

Long-term maintenance of spermatogenesis in mammals is supported by GDNF, an essential growth factor required for spermatogonial stem cell (SSC) self-renewal. Exploiting a transgenic GDNF overexpression model, which expands and normalizes the pool of undifferentiated spermatogonia between Plzf+/+ and Plzflu/lu mice, we used RNAseq to identify a rare subpopulation of cells that express EOMES, a T-box transcription factor. Lineage tracing and busulfan challenge show that these are long-term SSCs that contribute to steady state spermatogenesis as well as regeneration following chemical injury. EOMES+ SSCs have a lower proliferation index than EOMES− GFRA1+ spermatogonia in wild-type but not in Plzflu/lu mice. This comparison demonstrates that PLZF regulates their proliferative activity and suggests that EOMES+ SSCs are lost through proliferative exhaustion in Plzflu/lu mice. Single cell RNA sequencing of EOMES+ cells from Plzf+/+ and Plzflu/lu mice support a hierarchical model of both slow- and rapid-cycling SSCs.

Here, we describe an expansion of the typical DNA size limitations associated with CRISPR knock-in technology, more specifically, the physical extent to which mouse genomic DNA can be replaced with donor (in this case, human) DNA at an orthologous locus by zygotic injection. Driving our efforts was the desire to create a whole animal model that would replace 17 kilobase pairs (kbp) of the mouse Bcl2l11 gene with the corresponding 25-kbp segment of human BCL2L11, including a conditionally removable segment (2.9-kbp) of intron 2, a cryptic human exon immediately 3′ of this, and a native human exon some 20 kbp downstream. Using two methods, we first carried out the replacement by employing a combination of bacterial artificial chromosome recombineering, classic embryonic stem cell (ESC) targeting, dual selection, and recombinase-driven cassette removal (ESC/Blastocyst Approach). Using a unique second method, we employed the same vector (devoid of its selectable marker cassettes), microinjecting it along with redundant single guide RNAs (sgRNAs) and Cas9 mRNA into mouse zygotes (CRISPR/Zygote Approach). In both instances, we were able to achieve humanization of Bcl2l11 to the extent designed, remove all selection cassettes, and demonstrate the functionality of the conditionally removable, loxP-flanked, 2.9-kbp intronic segment.

Here, we describe an expansion of the DNA size limitations associated with CRISPR knock-in technology, more specifically, the physical extent to which mouse genomic DNA can be replaced with donor (in this case, human) DNA at an orthologous locus. Driving our efforts was the desire to create a whole animal model that would replace 17 kbp of the mouseBcl2l11gene with the corresponding 25-kbp segment of humanBCL2L11, including a conditionally removable segment (2.9-kbp) of intron 2, a cryptic human exon immediately 3′ of this, and a native human exon some 20 kbp downstream. Using two methods, we first carried out the replacement by employing a combination of bacterial artificial chromosome recombineering, classic ES cell targeting, dual selection, and recombinase-driven cassette removal (traditional approach). Using a unique second method, we employed the same vector (devoid of its selectable marker cassettes), microinjecting it along with CRISPR RNA guides andCas9into mouse zygotes (CRISPR approach). In both instances we were able to achieve humanization ofBcl2l11to the extent designed, remove all selection cassettes, and demonstrate the functionality of the conditionally removable,loxP-flanked, 2.9-kbp intronic segment.AUTHOR SUMMARYClustered regularly interspaced short palindromic repeat (CRISPR) technology can be used to place DNA sequences (designed in the laboratory) into the genomes of living organisms. Here, we describe a new method, whereby we have replaced an exceptionally large segment of the mouseBcl2l11gene with the corresponding segment of humanBCL2L11gene. The method represents an expansion of the DNA size limitations typically associated with the introduction of DNA sequences through traditional CRISPR methods.

The clinical significance of clonal hematopoiesis (CHIP or ARCH) remains a barrier to predicting the risk of hematologic malignancy. DNMT3A is a de novo DNA methyltransferase frequently mutated in clonal hematopoiesis, myelodysplastic syndrome and acute myeloid leukemia. Loss of or mutation in DNMT3A has been demonstrated to enhance self-renewal of hematopoietic stem cells (HSCs), suggesting that this is the predominant cell population driving clonal hematopoiesis. How DNMT3A-mutant cells become at risk for transformation is unclear, in part due to our limited understanding of how DNMT3A mutation confers a selective advantage and the cooperating mechanisms required for progression to MDS or AML. To address this gap in knowledge, we generated a cre-inducible Dnmt3a-LSL-R878H mouse model (representing the DNMT3A-R882H mutation commonly found in human AML), in which wild-type Dnmt3a expression is preserved prior to recombination. Heterozygous Dnmt3aR878H mice exhibit an expansion in both HSCs and multipotent progenitor (MPP) cell subsets with distinct kinetics. Transcriptional profiling of sorted HSC and MPP populations by RNA-seq revealed distinct transcriptional signatures indicating that different mechanisms underlie expansion of Dnmt3aR878H/+ HSCs and MPPs. Dnmt3a-mutant HSCs exhibit downregulation of genes important for differentiation, while Dnmt3a-mutant MPPs exhibit upregulation of genes associated with stem cell self-renewal, including Jam2 and Ryk. Functionally, we observe that Dnmt3a-mutant MPPs have enhanced serial replating capacity in in vitro colony assays. These data suggest that mutation in DNMT3A may cause clonal hematopoietic expansion through distinct mechanisms dependent on the cell-of-origin which incurs this mutation. To determine whether clonal hematopoiesis driven by Dnmt3aR878H/+ was sufficient to predispose to a hematologic malignancy, we generated an independent, Flp-inducible Npm1-FSF-cA mouse model (representing the NPM1cA mutation commonly found in human AML), in which wild-type Npm1 expression is preserved prior to recombination. Inducing Npm1cA mutation in hematopoietic stem and progenitor cells carrying Dnmt3aR878H caused development of a fully penetrant myeloproliferative disorder upon transplant into recipient mice. Transplantation of these cells into secondary recipient mice led to a fully penetrant AML with accelerated disease kinetics compared to primary transplant recipients. These data suggest that the combination of DNMT3A mutation followed by NPM1 mutation is sufficient to cause AML. In summary, this study reveals a novel cell context-specificity of how DNMT3A mutation confers a selective advantage and demonstrates that NPM1 mutation can cooperate with DNMT3A mutation to cause AML. This work has implications for predicting individuals at risk of progression from clonal hematopoiesis to AML. Disclosures No relevant conflicts of interest to declare.

Here we describe an expansion of the DNA size limitations associated with CRISPR knock-in technology, more specifically, the physical extent to which mouse genomic DNA can be replaced with donor (in this case, human) DNA at an orthologous locus. Driving our efforts was the desire to create a whole animal model inserting a 25-kbp segment of a human tumor-suppressor gene in place of 17 kbp of its corresponding mouse orthologue. Included within the human fragment is a conditionally removable (by Cre-loxP) segment of the gene's second intron, a cryptic exon immediately 3' of this, and a native exon some 20 kbp downstream. Using two methods, we first carried out the replacement by employing a combination of bacterial artificial chromosome recombineering, classic ES cell targeting, dual selection, and recombinase-driven cassette removal (traditional approach). Using a unique second method, we employed the same vector (devoid of its selectable marker cassettes), microinjecting it along with CRISPR RNA guides and Cas9 into mouse zygotes (CRISPR approach). In both instances, we were able to achieve humanization of the tumor suppressor to the extent designed, remove all selection cassettes, and demonstrate the functionality of the conditionally removable, loxP-flanked, intronic segment. Citation Format: Tiffany Leidy-Davis, Kai Cheng, Leslie Goodwin, Judith Morgan, Wen Chun Juan, Xavier Roca, Sin-Tiong Ong, David E. Bergstrom. Knock-in of a human tumor suppressor (25-kilobase pairs) by traditional and CRISPR/Cas9-stimulated homologous recombination [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5097.

Mutations of the otoferlin gene have been shown to underlie deafness disorders in humans and mice. Analyses of genetically engineered mice lacking otoferlin have demonstrated an essential role for this protein in vesicle exocytosis at the inner hair cell afferent synapse. Here, we report on the molecular and phenotypic characterization of a new ENU-induced missense mutation of the mouse otoferlin gene designated Otof deaf5Jcs . The mutation is a single T to A base substitution in exon 10 of Otof that causes a non-conservative amino acid change of isoleucine to asparagine in the C2B domain of the protein. Although strong immunoreactivity with an otoferlin-specific antibody was detected in cochlear hair cells of wildtype mice, no expression was detected in mutant mice, indicating that the missense mutation has a severe effect on the stability of the protein and potentially its localization. Auditory brainstem response (ABR) analysis demonstrated that mice homozygous for the missense mutation are profoundly deaf, consistent with an essential role for otoferlin in inner hair cell neurotransmission. Vestibular-evoked potentials (VsEPs) of mutant mice, however, were equivalent to those of wildtype mice, indicating that otoferlin is unnecessary for vestibular function even though it is highly expressed in both vestibular and cochlear hair cells.

Spontaneously arising mouse mutations have served as the foundation for understanding gene function for more than 100 years. We have used exome sequencing in an effort to identify the causative mutations for 172 distinct, spontaneously arising mouse models of Mendelian disorders, including a broad range of clinically relevant phenotypes. To analyze the resulting data, we developed an analytics pipeline that is optimized for mouse exome data and a variation database that allows for reproducible, user-defined data mining as well as nomination of mutation candidates through knowledge-based integration of sample and variant data. Using these new tools, putative pathogenic mutations were identified for 91 (53%) of the strains in our study. Despite the increased power offered by potentially unlimited pedigrees and controlled breeding, about half of our exome cases remained unsolved. Using a combination of manual analyses of exome alignments and whole-genome sequencing, we provide evidence that a large fraction of unsolved exome cases have underlying structural mutations. This result directly informs efforts to investigate the similar proportion of apparently Mendelian human phenotypes that are recalcitrant to exome sequencing.

Studies of spontaneous mutations in mice have provided valuable disease models and important insights into the mechanisms of human disease. Ruffled (rul) is a new autosomal recessive mutation causing abnormal hair coat in mice. The rul allele arose spontaneously in the RB156Bnr/EiJ inbred mouse strain. In addition to an abnormal coat texture, we found diffuse epidermal blistering, abnormal electrocardiograms (ECGs), and ventricular fibrosis in mutant animals. Using high-throughput sequencing (HTS) we found a frameshift mutation at 38,288,978bp of chromosome 13 in the desmoplakin gene (Dsp). The predicted mutant protein is truncated at the c-terminus and missing the majority of the plakin repeat domain. The phenotypes found in Dsp(rul) mice closely model a rare human disorder, Carvajal-Huerta syndrome. Carvajal-Huerta syndrome (CHS) is a rare cardiocutaneous disorder that presents in humans with wooly hair, palmoplantar keratoderma and ventricular cardiomyopathy. CHS results from an autosomal recessive mutation on the 3' end of desmoplakin (DSP) truncating the full length protein. The Dsp(rul) mouse provides a new model to investigate the pathogenesis of CHS, as well as the underlying basic biology of the adhesion molecules coded by the desmosomal genes.

Historically, spontaneous mutations in mice have served as valuable models of heritable human diseases, contributing substantially to our understanding of both disease mechanisms and basic biological pathways. While advances in molecular technologies have improved our ability to create mouse models of human disease through targeted mutagenesis and transgenesis, spontaneous mutations continue to provide valuable research tools for discovery of novel genes and functions. In addition, the genetic defects caused by spontaneous mutations are molecularly similar to mutations in the human genome and, therefore, often produce phenotypes that more closely resemble those characteristic of human disease than do genetically engineered mutations. Due to the rarity with which spontaneous mutations arise and the animal-intensive nature of their genetic analysis, large-scale spontaneous mutation analysis has traditionally been limited to large mammalian genetics institutes. More recently, ENU mutagenesis and new screening methods have increased the rate of mutant strain discovery, and high-throughput DNA sequencing has enabled rapid identification of the underlying genes and their causative mutations. Here we discuss the continued value of spontaneous mutations for biomedical research. Curr. Protoc. Mouse Biol. 2:103-118 © 2012 by John Wiley & Sons, Inc. Keywords: spontaneous mutations; mouse models; forward genetics; biomedical research

Sox genes encode proteins related to each other, and to the sex determining gene Sry, by the presence of a DNA binding motif known as the HMG domain. Although HMG domains can bind to related DNA sequences, Sox gene products may achieve target gene specificity by binding to preferred target sequences or by interacting with specific partner proteins. To assess their functional similarities, we replaced the HMG box of Sry with the HMG box of Sox3 or Sox9 and tested whether these constructs caused sex reversal in XX mice. Our results indicate that such chimeric transgenes can functionally replace Sry and elicit development of testis cords, male patterns of gene expression, and elaboration of male secondary sexual characteristics. This implies that chimeric SRY proteins with SOX HMG domains can bind to and regulate SRY target genes and that potential SRY partner factor interactions are not disrupted by HMG domain substitutions. genesis 28:111-124, 2000.

We report the development and optimization of reagents for in-solution, hybridization-based capture of the mouse exome. By validating this approach in a multiple inbred strains and in novel mutant strains, we show that whole exome sequencing is a robust approach for discovery of putative mutations, irrespective of strain background. We found strong candidate mutations for the majority of mutant exomes sequenced, including new models of orofacial clefting, urogenital dysmorphology, kyphosis and autoimmune hepatitis.

In humans, hereditary inactivation of either p22(phox) or gp91(phox) leads to chronic granulomatous disease (CGD), a severe immune disorder characterized by the inability of phagocytes to produce bacteria-destroying ROS. Heterodimers of p22(phox) and gp91(phox) proteins constitute the superoxide-producing cytochrome core of the phagocyte NADPH oxidase. In this study, we identified the nmf333 mouse strain as what we believe to be the first animal model of p22(phox) deficiency. Characterization of nmf333 mice revealed that deletion of p22(phox) inactivated not only the phagocyte NADPH oxidase, but also a second cytochrome in the inner ear epithelium. As a consequence, mice of the nmf333 strain exhibit a compound phenotype consisting of both a CGD-like immune defect and a balance disorder caused by the aberrant development of gravity-sensing organs. Thus, in addition to identifying a model of p22(phox)-dependent immune deficiency, our study indicates that a clinically identifiable patient population with an otherwise cryptic loss of gravity-sensor function may exist. Thus, p22(phox) represents a shared and essential component of at least 2 superoxide-producing cytochromes with entirely different biological functions. The site of p22(phox) expression in the inner ear leads us to propose what we believe to be a novel mechanism for the control of vestibular organogenesis.

If we are to understand the structure and function of the mammalian genome and its transmission to subsequent generations, we cannot neglect the Y Chromosome (Chr). However, certain properties of the Y have made it refractory to analysis. The bulk of the Y Chr does not recombine, and thus genetic maps based on standard Mendelian recombination are not feasible. For this reason, investigators have relied on physical approaches to map the human Y (Foote et al. 1992; Vollrath et al. 1992). We are using physical approaches to further our understanding of the mouse Y Chr by developing chromosome-specific DNA-based probes.

The vestibular system of the inner ear is responsible for the perception of motion and gravity. Key elements of this organ are otoconia, tiny biomineral particles in the utricle and the saccule. In response to gravity or linear acceleration, otoconia deflect the stereocilia of the hair cells, thus transducing kinetic movements into sensorineural action potentials. Here, we present an allelic series of mutations at the otoconia-deficient head tilt (het) locus, affecting the gene for NADPH oxidase 3 (Nox3). This series of mutations identifies for the first time a protein with a clear enzymatic function as indispensable for otoconia morphogenesis.

Chromosome deletion complexes in model organisms serve as valuable genetic tools for the functional and physical annotation of complex genomes. Among their many roles, deletions can serve as mapping tools for simple or quantitative trait loci (QTLs), genetic reagents for regional mutagenesis experiments, and, in the case of mice, models of human contiguous gene deletion syndromes. Deletions also are uniquely suited for identifying regions of the genome containing haploinsufficient or imprinted loci. Here we describe the creation of new deletions at the proximal end of mouse Chromosome (Chr) 17 by using the technique of ES cell irradiation and the extensive molecular characterization of these and previously isolated deletions that, in total, cover much of the mouse t complex. The deletions are arranged in five overlapping complexes that collectively span about 25 Mbp. Furthermore, we have integrated each of the deletion complexes with physical data from public and private mouse genome sequences, and our own genetic data, to resolve some discrepancies. These deletions will be useful for characterizing several phenomena related to the t complex and t haplotypes, including transmission ratio distortion, male infertility, and the collection of t haplotype embryonic lethal mutations. The deletions will also be useful for mapping other loci of interest on proximal Chr 17, including T-associated sex reversal ( Tas) and head-tilt ( het). The new deletions have thus far been used to localize the recently identified t haplolethal ( Thl1) locus to an approximately 1.3-Mbp interval.

Our interests lie in humanizing specific regions of the mouse genome using large segments of human DNA with extents of 10s to 100s of kilobase pairs. To that end, we have undertaken a series of projects to transfer large segments of human DNA, from human BAC clones, into the orthologous region of corresponding mouse BAC clones using— (1), traditional recombineering methods; (2), recombinase-mediated cassette exchange (RCME); and (3), a novel technology that we call trans- or trimolecular-recombineering. In each instance the goal is to place human DNA within the larger context of homologous BAC-derived mouse arms in E. coli. Completed constructs will be used to drive homologous recombination in mouse embryonic stem (ES) cells with positive selection imparted at each end of the transferred human segment using dual, recombinase recognition site-flanked, selectable marker cassettes. Properly targeted ES cells will be used to develop viable mouse strains carrying the humanized segments. Selection cassettes will be removed by crossing to mouse strains with germline expression of the appropriate recombinases. All experiments have been designed to maintain a fixed genetic background from community-standard C57BL/6 strains. Our poster presentation details the specifics of our projects and describes progress to date. This research is supported by National Cancer Institute Grant Number 5P30CA034196-28. Citation Format: Tiffany Leidy-Davis, David E. Bergstrom. Interspecific recombination between orthologous human and mouse BAC clones in E. coli: Exploring scalable humanization of cancer-relevant genes in the mouse genome. [abstract]. In: Proceedings of the AACR Special Conference: The Translational Impact of Model Organisms in Cancer; Nov 5-8, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(11 Suppl):Abstract nr A06.

In this report, we demonstrate the utility of interleukin-2 (IL-2) stimulation of spleen cell cultures and bivariate flow cytometry in the analysis and purification of the C57BL/6J mouse Y Chromosome. We determined that the DNA content of the C57BL/6J Y Chromosome is approximately 94.7 Mb, making it similar in size to human Chromosome 16 and significantly larger than previous estimates. In addition, we describe the bulk isolation of mouse Y Chromosomes and demonstrate enrichment of the isolated material using a fluorescencein situhybridization strategy. We detail the construction of two small insert Y Chromosome-specific libraries, ideal for sampling Y Chromosome sequences. From these libraries 1566 clones were analyzed. We provide a detailed characterization of 103 clones, generating nearly 50 kb of sequence. For 30 of these clones, we identify regions of homology to known Y chromosomal sequences, confirming the enrichment of the sorted DNA. From the remaining characterized clones, we describe the development of 15 male-specific PCR assays and 19 male–female PCR assays potentially originating from the pseudoautosomal region or other areas of X–Y or autosome–Y homology.