Technical note: Droplet digital PCR precisely and accurately quantifies sex skew in bovine semen.

Quantifying the relative population of sperm cells bearing the X or Y chromosome in a sexed-semen sample has historically been limited to methods that are either low throughput and sensitive to user subjectivity (e.g., fluorescence in situ hybridization), conterminous (using the same technology to generate and confirm the sex skew), or relatively insensitive (including quantitative PCR with a change detection threshold of 2×). Customers pay a premium for sexed semen and should have access to reliable sex skew data, generated by an accurate, precise test that is orthogonal to the method used to generate sexed semen. Droplet digital PCR (ddPCR) has the capacity to provide an accurate and precise sex skew quantitation by subdividing a pool of template DNA into nanoliter-scale droplets containing either 1 or 0 copies of template DNA. Then PCR amplification is conducted in the droplets, and the number of copies of the amplicon of interest can be counted as the number of fluorescence-positive droplets based on classic quantitative PCR fluorescent reporters. We have optimized and validated a multiplexed ddPCR assay that uses this copy counting method to quantify the sex skew (ratio of X or Y chromosomes) in frozen-thawed bovine sexed semen. The assay interrogates at least 1,000 cells per sample well, quantifying X and Y chromosome copy numbers along with an autosomal gene, GAPDH, used as an internal assay control to confirm total cells counted. The ddPCR sex skew assay achieved a 0.5-percentage-point variance for %X or %Y with a broad linear detection range, from 10 to 95% X, and provided reproducible skew values across a range of 9 to 27 ng of genomic DNA input. This approach overcomes some limitations of other sex skew assays by quantifying absolute X and Y chromosome copy numbers, thus providing a rigorous, independent assessment of sex-skewed semen.

Effects of Dietary Resistant Starch on the Wnt Signaling Pathway and Preneoplastic Cells in the Colons of Azoxymethane-Treated Rats.

Dietary resistant starch (RS) has been suggested to reduce colonic neoplasia. To determine the effects of digestion-resistant cornstarch on colonic carcinogenesis and Wnt signaling in azoxymethane (AOM)-treated F344 rats, diets containing naturally occurring RS from corn lines derived partially from Guat209 (GUAT), AR16035 (AR), or a hybrid (ARxGUAT), containing 34.5 ± 2.0, 0.2 ± 0.1, and 1.9 ± 0.1% RS, respectively, were fed at 55% of the diet. GUAT-fed rats had increased cecal content and tissue weight and decreased cecal pH compared with AR- or ARxGUAT-fed rats. Numbers of aberrant crypt foci (ACF) were not different among diet groups. Increased numbers of crypts/focus were observed in AOM-injected rats fed GUAT compared with rats fed other diets. ß-catenin mRNA expression of the crypts was significantly increased in GUAT-fed rats injected with AOM relative to those injected with saline. These findings suggest that selected dietary RSs may at some level further enhance colonocyte proliferation and differentiation in an AOM-treated colon.

Effect of Dietary-Resistant Starch on Inhibition of Colonic Preneoplasia and Wnt Signaling in Azoxymethane-Induced Rodent Models.

Dietary fiber has been reported to prevent preneoplastic colon lesions. The aim of this study was to determine the effect of resistant starches, novel dietary fibers, on the development of colonic preneoplasia and Wnt signaling in azoxymethane (AOM)-treated rats and mice fed resistant starches at 55% of the diet after AOM treatment. Another objective was to determine the effect of resistant starches on the development of preneoplasia in rats treated with antibiotics (Ab), administered between AOM treatment and resistant starch feeding. Diets containing resistant starches, high-amylose (HA7), high-amylose-octenyl succinic anhydride (OS-HA7), or high-amylose-stearic acid (SA-HA7) were compared with control cornstarch (CS). The resistant starch content of the diets did not alter the yield of colonic lesions but animals treated with AOM and fed the diet with the highest resistant starch content, SA-HA7 developed the highest average aberrant crypt foci (ACF) per animal. Mice fed the OS-HA7 diet had decreased expression of some upstream Wnt genes in the colonic crypts. This study suggests that further research is needed to determine if resistant starch impacts colon carcinogenesis in rodents.

Identification of tissue-specific transcriptional markers of caloric restriction in the mouse and their use to evaluate caloric restriction mimetics.

Caloric restriction (CR) without malnutrition has been shown to retard several aspects of the aging process and to extend lifespan in different species. There is strong interest in the identification of CR mimetics (CRMs), compounds that mimic the beneficial effects of CR on lifespan and healthspan without restriction of energy intake. Identification of CRMs in mammals is currently inefficient due to the lack of screening tools. We have performed whole-genome transcriptional profiling of CR in seven mouse strains (C3H/HeJ, CBA/J, DBA/2J, B6C3F1/J, 129S1/SvImJ, C57BL/6J, and BALB/cJ) in white adipose tissue (WAT), gastrocnemius muscle, heart, and brain neocortex. This analysis has identified tissue-specific panels of genes that change in expression in multiple mouse strains with CR. We validated a subset of genes with qPCR and used these to evaluate the potential CRMs bezafibrate, pioglitazone, metformin, resveratrol, quercetin, 2,4-dinitrophenol, and L-carnitine when fed to C57BL/6J 2-month-old mice for 3 months. Compounds were also evaluated for their ability to modulate previously characterized biomarkers of CR, including mitochondrial enzymes citrate synthase and SIRT3, plasma inflammatory cytokines TNF-α and IFN-γ, glycated hemoglobin (HbA1c) levels and adipocyte size. Pioglitazone, a PPAR-γ agonist, and L-carnitine, an amino acid involved in lipid metabolism, displayed the strongest effects on both the novel transcriptional markers of CR and the additional CR biomarkers tested. Our findings provide panels of tissue-specific transcriptional markers of CR that can be used to identify novel CRMs, and also represent the first comparative molecular analysis of several potential CRMs in multiple tissues in mammals.