DAZL Knockout Pigs as Recipients for Spermatogonial Stem Cell Transplantation.

Spermatogonial stem cell (SSC) transplantation into the testis of a germ cell (GC)-depleted surrogate allows transmission of donor genotype via donor-derived sperm produced by the recipient. Transplantation of gene-edited SSCs provides an approach to propagate gene-edited large animal models. DAZL is a conserved RNA-binding protein important for GC development, and DAZL knockout (KO) causes defects in GC commitment and differentiation. We characterized DAZL-KO pigs as SSC transplantation recipients. While there were GCs in 1-week-old (wko) KO, complete GC depletion was observed by 10 wko. Donor GCs were transplanted into 18 DAZL-KO recipients at 10-13 wko. At sexual maturity, semen and testes were evaluated for transplantation efficiency and spermatogenesis. Approximately 22% of recipient seminiferous tubules contained GCs, including elongated spermatids and proliferating spermatogonia. The ejaculate of 89% of recipients contained sperm, exclusively from donor origin. However, sperm concentration was lower than the wild-type range. Testicular protein expression and serum hormonal levels were comparable between DAZL-KO and wild-type. Intratesticular testosterone and Leydig cell volume were increased, and Leydig cell number decreased in transplanted DAZL-KO testis compared to wild-type. In summary, DAZL-KO pigs support donor-derived spermatogenesis following SSC transplantation, but low spermatogenic efficiency currently limits their use for the production of offspring.

First gene-edited calf with reduced susceptibility to a major viral pathogen.

Bovine viral diarrhea virus (BVDV) is one of the most important viruses affecting the health and well-being of bovine species throughout the world. Here, we used CRISPR-mediated homology-directed repair and somatic cell nuclear transfer to produce a live calf with a six amino acid substitution in the BVDV binding domain of bovine CD46. The result was a gene-edited calf with dramatically reduced susceptibility to infection as measured by reduced clinical signs and the lack of viral infection in white blood cells. The edited calf has no off-target edits and appears normal and healthy at 20 months of age without obvious adverse effects from the on-target edit. This precision bred, proof-of-concept animal provides the first evidence that intentional genome alterations in the CD46 gene may reduce the burden of BVDV-associated diseases in cattle and is consistent with our stepwise, in vitro and ex vivo experiments with cell lines and matched fetal clones.

Targeted Gene Editing in Porcine Germ Cells.

As the genetic mutations driving human disease are identified, there is an increasing need for a biomedical model that can accurately represent the disease of interest and provide a platform for potential therapeutic testing. Pigs are a better model for human disease than rodents because of their genetic and physiological similarities to humans. However, current methods to generate porcine models are both technically challenging and expensive. Germline genetic modification through gene edited spermatogonia provides an effective alternative to how these models are developed. Here, we report an improved technique of gene editing in spermatogonia of pigs using CRISPR-Cas9 to generate different edits that reflect the genotypes of human diseases.

Evaluating Large Spontaneous Deletions in a Bovine Cell Line Selected for Bovine Viral Diarrhea Virus Resistance.

Bovine viral diarrhea virus's (BVDV) entry into bovine cells involves attachment of virions to cellular receptors, internalization, and pH-dependent fusion with endosomal membranes. The primary host receptor for BVDV is CD46; however, the complete set of host factors required for virus entry is unknown. The Madin-Darby bovine kidney (MDBK) cell line is susceptible to BVDV infection, while a derivative cell line (CRIB) is resistant at the level of virus entry. We performed complete genome sequencing of each to identify genomic variation underlying the resistant phenotype with the aim of identifying host factors essential for BVDV entry. Three large compound deletions in the BVDV-resistant CRIB cell line were identified and predicted to disrupt the function or expression of the genes PTPN12, GRID2, and RABGAP1L. However, CRISPR/Cas9 mediated knockout of these genes, individually or in combination, in the parental MDBK cell line did not impact virus entry or replication. Therefore, resistance to BVDV in the CRIB cell line is not due to the apparent spontaneous loss of PTPN12, GRID2, or RABGAP1L gene function. Identifying the functional cause of BVDV resistance in the CRIB cell line may require more detailed comparisons of the genomes and epigenomes.

Development of a porcine model of phenylketonuria with a humanized R408W mutation for gene editing.

Phenylketonuria (PKU) is a metabolic disorder whereby phenylalanine metabolism is deficient due to allelic variations in the gene for phenylalanine hydroxylase (PAH). There is no cure for PKU other than orthotopic liver transplantation, and the standard of care for patients is limited to dietary restrictions and key amino acid supplementation. Therefore, Pah was edited in pig fibroblasts for the generation of PKU clone piglets that harbor a common and severe human mutation, R408W. Additionally, the proximal region to the mutation was further humanized by introducing 5 single nucleotide polymorphisms (SNPs) to allow for development of gene editing machinery that could be translated directly from the pig model to human PKU patients that harbor at least one classic R408W allele. Resulting piglets were hypopigmented (a single Ossabaw piglet) and had low birthweight (all piglets). The piglets had similar levels of PAH expression, but no detectable enzymatic activity, consistent with the human phenotype. The piglets were fragile and required extensive neonatal care to prevent failure to thrive and early demise. Phenylalanine levels rose sharply when dietary Phe was unrestricted but could be rapidly reduced with a low Phe diet. Fibroblasts isolated from R408W piglets show susceptibility to correction using CRISPR or TALEN, with subsequent homology-directed recombination to correct Pah. This pig model of PKU provides a powerful new tool for development of all classes of therapeutic candidates to treat or cure PKU, as well as unique value for proof-of-concept studies for in vivo human gene editing platforms in the context of this humanized PKU allele.

Dysregulated ribonucleoprotein granules promote cardiomyopathy in RBM20 gene-edited pigs.

Ribonucleoprotein (RNP) granules are biomolecular condensates-liquid-liquid phase-separated droplets that organize and manage messenger RNA metabolism, cell signaling, biopolymer assembly, biochemical reactions and stress granule responses to cellular adversity. Dysregulated RNP granules drive neuromuscular degenerative disease but have not previously been linked to heart failure. By exploring the molecular basis of congenital dilated cardiomyopathy (DCM) in genome-edited pigs homozygous for an RBM20 allele encoding the pathogenic R636S variant of human RNA-binding motif protein-20 (RBM20), we discovered that RNP granules accumulated abnormally in the sarcoplasm, and we confirmed this finding in myocardium and reprogrammed cardiomyocytes from patients with DCM carrying the R636S allele. Dysregulated sarcoplasmic RBM20 RNP granules displayed liquid-like material properties, docked at precisely spaced intervals along cytoskeletal elements, promoted phase partitioning of cardiac biomolecules and fused with stress granules. Our results link dysregulated RNP granules to myocardial cellular pathobiology and heart failure in gene-edited pigs and patients with DCM caused by RBM20 mutation.

Efficient targeted integration directed by short homology in zebrafish and mammalian cells.

Efficient precision genome engineering requires high frequency and specificity of integration at the genomic target site. Here, we describe a set of resources to streamline reporter gene knock-ins in zebrafish and demonstrate the broader utility of the method in mammalian cells. Our approach uses short homology of 24-48 bp to drive targeted integration of DNA reporter cassettes by homology-mediated end joining (HMEJ) at high frequency at a double strand break in the targeted gene. Our vector series, pGTag (plasmids for Gene Tagging), contains reporters flanked by a universal CRISPR sgRNA sequence which enables in vivo liberation of the homology arms. We observed high rates of germline transmission (22-100%) for targeted knock-ins at eight zebrafish loci and efficient integration at safe harbor loci in porcine and human cells. Our system provides a straightforward and cost-effective approach for high efficiency gene targeting applications in CRISPR and TALEN compatible systems.

A reduction of primary cilia but not hedgehog signaling disrupts morphogenesis in testicular organoids.

Most mammalian cells possess a single, non-motile primary cilium that plays an important role in mediating cellular signaling pathways, such as Hedgehog (Hh) signaling. Primary cilia are present on testicular somatic cells and demonstrate a temporal expression during development; however, their role in testicular morphogenesis is not well characterized. To investigate the role of primary cilia and Hh signaling in Sertoli cells on morphogenesis, we inhibited assembly of primary cilia through CRISPR Cas9-mediated gene editing of ODF2, a structural component of primary cilia and siRNA-mediated gene silencing of IFT88, a functional component of the intraflagellar transport system. Knockdown of ODF2 and IFT88 resulted in a 50% reduction in the number of cells with primary cilia and significant shortening of the remaining cilia. The expression of GLI1, a downstream target of Hh signaling, was significantly reduced when IFT88 but not ODF2, was downregulated. When morphogenesis was examined using tubule formation in vitro and a novel testicular organoid system, loss of cilia after knockdown of both targets affected cellular assembly and organization. While the Hh pathway was found to be active during morphogenesis in vitro, addition of the Hh antagonist cyclopamine did not affect morphogenesis in either in vitro system. These results indicate that primary cilia are important for morphogenesis in vitro but Hh signaling is not the cilia-mediated pathway responsible for orchestrating morphogenic organization.

Targeted Gene Editing in Porcine Spermatogonia.

To study the pathophysiology of human diseases, develop innovative treatments, and refine approaches for regenerative medicine require appropriate preclinical models. Pigs share physiologic and anatomic characteristics with humans and are genetically more similar to humans than are mice. Genetically modified pigs are essential where rodent models do not mimic the human disease phenotype. The male germline stem cell or spermatogonial stem cell (SSC) is unique; it is the only cell type in an adult male that divides and contributes genes to future generations, making it an ideal target for genetic modification. Here we report that CRISPR/Cas9 ribonucleoprotein (RNP)-mediated gene editing in porcine spermatogonia that include SSCs is significantly more efficient than previously reported editing with TALENs and allows precise gene editing by homology directed repair (HDR). We also established homology-mediated end joining (HMEJ) as a second approach to targeted gene editing to enable introduction of larger transgenes and/or humanizing parts of the pig genome for disease modeling or regenerative medicine. In summary, the approaches established in the current study result in efficient targeted genome editing in porcine germ cells for precise replication of human disease alleles.

TALEN-mediated gene targeting in porcine spermatogonia.

Spermatogonia represent a diploid germ cell population that includes spermatogonial stem cells. In this report, we describe new methods for isolation of highly enriched porcine spermatogonia based on light scatter properties, and for targeted mutagenesis in porcine spermatogonia using nucleofection and TALENs. We optimized a nucleofection protocol to deliver TALENs specifically targeting the DMD locus in porcine spermatogonia. We also validated specific sorting of porcine spermatogonia based on light scatter properties. We were able to obtain a highly enriched germ cell population with over 90% of cells being UCH-L1 positive undifferentiated spermatogonia. After gene targeting in porcine spermatogonia, indel (insertion or deletion) mutations as a result of non-homologous end joining (NHEJ) were detected in up to 18% of transfected cells. Our report demonstrates for the first time an approach to obtain a live cell population highly enriched in undifferentiated spermatogonia from immature porcine testes, and that gene targeting can be achieved in porcine spermatogonia which will enable germ line modification.

Efficient nonmeiotic allele introgression in livestock using custom endonucleases.

We have expanded the livestock gene editing toolbox to include transcription activator-like (TAL) effector nuclease (TALEN)- and clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-stimulated homology-directed repair (HDR) using plasmid, rAAV, and oligonucleotide templates. Toward the genetic dehorning of dairy cattle, we introgressed a bovine POLLED allele into horned bull fibroblasts. Single nucleotide alterations or small indels were introduced into 14 additional genes in pig, goat, and cattle fibroblasts using TALEN mRNA and oligonucleotide transfection with efficiencies of 10-50% in populations. Several of the chosen edits mimic naturally occurring performance-enhancing or disease- resistance alleles, including alteration of single base pairs. Up to 70% of the fibroblast colonies propagated without selection harbored the intended edits, of which more than one-half were homozygous. Edited fibroblasts were used to generate pigs with knockout alleles in the DAZL and APC genes to model infertility and colon cancer. Our methods enable unprecedented meiosis-free intraspecific and interspecific introgression of select alleles in livestock for agricultural and biomedical applications.

Relationship of the International Prostate Symptom score with urinary flow studies, and catheterization rates following 125I prostate brachytherapy.

PURPOSE: Prostate cancer patients undergoing 125I brachytherapy were reviewed. A relationship between pretreatment risk factors including International Prostate Symptom (IPS) score, urinary flow studies, and posttreatment urinary morbidity was assessed. METHODS AND MATERIALS: Pretreatment IPS scores and urinary flow studies on 207 patients were reviewed. Relationship between scores and acute urinary morbidity was evaluated. RESULTS: Median age, 64 years; median baseline IPS score, 9; median prostate volume, 36 cc. Catheterization was required in 18% of patients. Baseline IPS score and peak flow rate (PFR) varied inversely, demonstrating that PFR for patients requiring a catheter was lower than that for those not requiring catheterization. Univariate regression showed that prostate volume, prior hormone therapy, and PFR were statistically predictive of postimplant urinary retention. For every one-unit increase in PFR, the odds of catheterization decreased by 6%. Multivariate analysis demonstrated that only PFR and prostate volume were predictive of postimplant urinary retention. CONCLUSIONS: Pretreatment IPS questionnaire and urinary flow studies assist in predicting risk of urinary morbidity and retention post-125I brachytherapy for prostate cancer.