Germline mutagenesis of Nasonia vitripennis through ovarian delivery of CRISPR-Cas9 ribonucleoprotein

CRISPR/Cas9 gene editing is a powerful technology to study the genetics of rising model organisms, such as the jewel wasp Nasonia vitripennis. However, current methods involving embryonic microinjection of CRISPR reagents are challenging. Delivery of Cas9 ribonucleoprotein into female ovaries is an alternative that has only been explored in a small handful of insects, such as mosquitoes, whiteflies and beetles. Here, we developed a simple protocol for germline gene editing by injecting Cas9 ribonucleoprotein in adult N. vitripennis females using either ReMOT control (Receptor-Mediated Ovary Transduction of Cargo) or BAPC (Branched Amphiphilic Peptide Capsules) as ovary delivery methods. For ReMOT Control we used the Drosophila melanogaster-derived peptide 'P2C' fused to EGFP to visualize the ovary delivery, and fused to Cas9 protein for gene editing of the cinnabar gene using saponin as an endosomal escape reagent. For BAPC we optimized the concentrations of protein, sgRNA and the transfection reagent. We demonstrate delivery of protein cargo such as EGFP and Cas9 into developing oocytes via P2C peptide and BAPC. Additionally, somatic and germline gene editing were demonstrated. This approach will greatly facilitate CRISPR-applied genetic manipulation in this and other rising model organisms.

An unusually simple HP1 gene set in Hymenopteran insects

The heterochromatin protein 1 (HP1) gene family includes a set of paralogs in higher eukaryotes that serve fundamental roles in heterochromatin structure and maintenance, and other chromatin-related functions. At least 10 full and 16 partial HP1 genes exist among Drosophila species, with multiple gene gains, losses, and sub-functionalizations within this insect group. An important question is whether this diverse set of HP1 genes and their dynamic evolution represent the standard rule in eukaryotic groups. Here we have begun to address this question by bio-informatically identifying the HP1 family genes in representative species of the insect order Hymenoptera, which includes all ants, bees, wasps, and sawflies. Compared to Drosophila species, Hymenopterans have a much simpler set of HP1 genes, including one full and two partial HP1s. All 3 genes appear to have been present in the common ancestor of the Hymenopterans and they derive from a Drosophila HP1B-like gene. In ants, a partial HP1 gene containing only a chromoshadow domain harbors amino acid changes at highly conserved sites within the PxVxL recognition region, suggesting that this gene has undergone sub-functionalization. In the jewel wasp Nasonia vitripennis, the full HP1 and partial chromoshadow-only HP1 are expressed in both germ line and somatic tissues. However, the partial chromodomain-only HP1 is expressed exclusively in the ovary and testis, suggesting that it may have a specialized chromatin role during gametogenesis. Our findings demonstrate that the HP1 gene family is much simpler and evolutionarily less dynamic within the Hymenopterans compared to the much younger Drosophila group, a pattern that may reflect major differences in the range of chromatin-related functions present in these and perhaps other insect groups.

Identification of missense, nonsense, and deletion mutations in the GRHPR gene in patients with primary hyperoxaluria type II (PH2)

Primary hyperoxaluria type II (PH2) is a rare disease characterized by the absence of an enzyme with glyoxylate reductase, hydroxypyruvate reductase, and D-glycerate dehydrogenase activities. The gene encoding this enzyme (GRHPR) has been characterized, and a single mutation has been detected in four PH2 patients. In this report, we have identified five novel mutations. One nonsense mutation (C295T) results in a premature stop codon at codon 99. A 4-bp deletion mutation has been found in the 5' consensus splice site of intron D, resulting in a predicted splicing error. Three missense mutations have been detected, including a missense transversion (T965G) in exon 9 (Met322Arg), a missense transition (G494A) in the putative co-factor binding site in exon 6 (Gly165Asp), and a substitution of an adenosine for a guanine in the 3' splice site of intron G. The functional consequences of the missense transversion and transition mutations have been investigated by transfection of cDNA encoding the mutated protein into COS cells. Cells transfected with either mutant construct have no enzymatic activity, a finding that is not significantly different from the control (empty) vector (P<0.05). These results further confirm that mutations in the GRHPR gene form the genetic basis of PH2. Ten of the 11 patients that we have genotyped are homozygous for one of the six mutations identified to date. Because of this high proportion of homozygotes, we have used microsatellite markers in close linkage with the GRHPR gene to investigate the possibility that the patients are the offspring of related individuals. Our data suggest that two thirds of our patients are the offspring of either closely or distantly related persons. Furthermore, genotyping has revealed the possible presence of a founder effect for the two most common mutations and the location of the gene near the marker D9S1874.

The gene encoding hydroxypyruvate reductase (GRHPR) is mutated in patients with primary hyperoxaluria type II

Primary hyperoxaluria type II (PH2) is a rare monogenic disorder that is characterized by a lack of the enzyme that catalyzes the reduction of hydroxypyruvate to D-glycerate, the reduction of glyoxylate to glycolate and the oxidation of D-glycerate to hydroxypyruvate. The disease is characterized by an elevated urinary excretion of oxalate and L-glycerate. The increased oxalate excretion can cause nephrolithiasis and nephrocalci-nosis and can, in some cases, result in renal failure and systemic oxalate deposition. We identified a glyoxylate reductase/hydroxypyruvate reductase (GRHPR) cDNA clone from a human liver expressed sequence tag (EST) library. Nucleotide sequence analysis identified a 1198 nucleotide clone that encoded a 984 nucleotide open reading frame. The open reading frame encodes a predicted 328 amino acid protein with a mass of 35 563 Da. Transient transfection of the cDNA clone into COS cells verified that it encoded an enzyme with hydroxy-pyruvate reductase, glyoxylate reductase and D-glycerate dehydrogenase enzymatic activities. Database analysis of human ESTs reveals widespread tissue expression, indicating that the enzyme may have a previously unrecognized role in metabolism. The genomic structure of the human GRHPR gene was determined and contains nine exons and eight introns and spans approximately 9 kb pericentromeric on chromosome 9. Four PH2 patients representing two pairs of siblings from two unrelated families were analyzed for mutations in GRHPR by single strand conformation polymorphism analysis. All four patients were homozygous for a single nucleotide deletion at codon 35 in exon 2, resulting in a premature stop codon at codon 45. The cDNA that we have identified represents the first characterization of an animal GRHPR sequence. The data we present will facilitate future genetic testing to confirm the clinical diagnosis of PH2. These data will also facilitate heterozygote testing and prenatal testing in families affected with PH2 to aid in genetic counseling.