Novel Hypomorphic Alleles of the Mouse Tyrosinase Gene Induced by CRISPR-Cas9 Nucleases Cause Non-Albino Pigmentation Phenotypes

<div><p>Tyrosinase is a key enzyme in melanin biosynthesis. Mutations in the gene encoding tyrosinase (<i>Tyr</i>) cause oculocutaneous albinism (OCA1) in humans. Alleles of the <i>Tyr</i> gene have been useful in studying pigment biology and coat color formation. Over 100 different <i>Tyr</i> alleles have been reported in mice, of which ≈24% are spontaneous mutations, ≈60% are radiation-induced, and the remaining alleles were obtained by chemical mutagenesis and gene targeting. Therefore, most mutations were random and could not be predicted <i>a priori</i>. Using the CRISPR-Cas9 system, we targeted two distinct regions of exon 1 to induce pigmentation changes and used an <i>in vivo</i> visual phenotype along with heteroduplex mobility assays (HMA) as readouts of CRISPR-Cas9 activity. Most of the mutant alleles result in complete loss of tyrosinase activity leading to an albino phenotype. In this study, we describe two novel in-frame deletion alleles of <i>Tyr</i>, <i>dhoosara</i> (Sanskrit for gray) and <i>chandana</i> (Sanskrit for sandalwood). These alleles are hypomorphic and show lighter pigmentation phenotypes of the body and eyes. This study demonstrates the utility of CRISPR-Cas9 system in generating domain-specific in-frame deletions and helps gain further insights into structure-function of <i>Tyr</i> gene.</p></div

Details of the F0 animals obtained from CRISPR-Cas9 injections.

<p>Details of the F0 animals obtained from CRISPR-Cas9 injections.</p

Comparison of <i>dhoosara</i> and <i>chandana</i> with the albino and black/wild type mice.

<p>(A) Dorsal view showing the coat color of albino, <i>chandana</i>, <i>dhoosara</i>, and black animals. Increasing levels of pigmentation can be seen in the hind limbs and tips of tails as well. (B) Frontal view of the face with increasing pigmentation in the nose region. Differences in the eye color can be noted. (C) Brightfield images of RPE wholemounts from Albino, <i>chandana</i>, <i>dhoosara</i> and Black mice. (D) Brightfield images of retinal cryosections from Albino, <i>chandana</i>, <i>dhoosara</i> and black mice. The RPE layer is the only layer within the eyeball that contains pigment. Scale bar = 50 μm. (E) Mean gray values (quantified in ImageJ) obtained from the RPE wholemounts reflecting relative intensity of RPE cell pigmentation. Results are presented in a bar chart with standard error of mean used for error bars. All groups are significantly different from each other (p<0.05, t-test). (F) Western Blot of tyrosinase protein isolated from skin of albino (alb), <i>chandana (cha)</i>, <i>dhoosara (dho)</i>, and black animals (arrow points to the 60 kDa tyrosinase band); 50 kDa tubulin protein (lower panel) is used as a control.</p

CRISPR targeting and mutation detection by heteroduplex mobility assay in the <i>Tyr</i> gene.

<p>(A) Schematic showing CRISPR targeting regions (blue bold arrows), PCR primer binding sites, and amplicon sizes. (B) Breeding scheme with genotype of the zygotes used for CRISPR-Cas9 injections, and the CRISPR target sequences on both chromosomes. (C, D, E) Images of ethidium bromide stained polyacrylamide gels (6%) showing separation of homoduplex and heteroduplex PCR amplicons from CRISPR-Cas9 RNA injected, single cultured blastocysts (C, arrowheads) and tail DNA of potential founder mice (D, E). Gels on the left correspond to the 5’CRISPR target site, and those on the right correspond to the 3’CRISPR target site. Small and large square brackets indicate homoduplex and heteroduplex bands, respectively. L = 100 bp ladder; C = uninjected wildtype control.</p

Schematic of possible sequence of events producing related <i>dhoosara</i> and <i>chandana</i> alleles.

<p>CRISPR-Cas9 nuclease activity in the zygote at the 5’ target site on the wildtype chromosome results in a 15 bp deletion. After the cell division, nuclease activity persists and creates a DSB at the 3’ target site on the previously modified chromosome. NHEJ repair in this daughter cell results in a second, 3 bp deletion.</p

Multiples mutant alleles resulting from NHEJ at 5’ and 3’ CRISPR target sites.

<p>Multiples mutant alleles resulting from NHEJ at 5’ and 3’ CRISPR target sites.</p

Body-composition changes in the Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE)-2 study: A 2-y randomized controlled trial of calorie restriction in nonobese humans

Background: Calorie restriction (CR) retards aging and increases longevity in many animal models. However, it is unclear whether CR can be implemented in humans without adverse effects on body composition.Objective: We evaluated the effect of a 2-y CR regimen on body composition including the influence of sex and body mass index (BMI; in kg/m2) among participants enrolled in CALERIE-2 (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy), a multicenter, randomized controlled trial.Design: Participants were 218 nonobese (BMI: 21.9-28.0) adults aged 21-51 y who were randomly assigned to 25% CR (CR, n = 143) or ad libitum control (AL, n = 75) in a 2:1 ratio. Measures at baseline and 12 and 24 mo included body weight, waist circumference, fat mass (FM), fat-free mass (FFM), and appendicular mass by dual-energy X-ray absorptiometry; activity-related energy expenditure (AREE) by doubly labeled water; and dietary protein intake by self-report. Values are expressed as means ± SDs.Results: The CR group achieved 11.9% ± 0.7% CR over 2-y and had significant decreases in weight (-7.6 ± 0.3 compared with 0.4 ± 0.5 kg), waist circumference (-6.2 ± 0.4 compared with 0.9 ± 0.5 cm), FM (-5.4 ± 0.3 compared with 0.5 ± 0.4 kg), and FFM (-2.0 ± 0.2 compared with -0.0 ± 0.2 kg) at 24 mo relative to the AL group (all between-group P < 0.001). Moreover, FFM as a percentage of body weight at 24 mo was higher, and percentage of FM was lower in the CR group than in the AL. AREE, but not protein intake, predicted preservation of FFM during CR (P < 0.01). Men in the CR group lost significantly more trunk fat (P = 0.03) and FFM expressed as a percentage of weight loss (P < 0.001) than women in the CR group.Conclusions: Two years of CR had broadly favorable effects on both whole-body and regional adiposity that could facilitate health span in humans. The decrements in FFM were commensurate with the reduced body mass; although men in the CR group lost more FFM than the women did, the percentage of FFM in the men in the CR group was higher than at baseline. CALERIE was registered at clinicaltrials.gov as NCT00427193