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Abstract Background The developmental transition between the late fetus and a newborn animal is associated with profound changes in skeletal muscle function as it adapts to the new physiological demands of locomotion and postural support against gravity. The mechanisms underpinning this adaption process are unclear but are likely to be initiated by changes in hormone levels. We tested the hypothesis that this developmental transition is associated with large coordinated changes in the transcription of skeletal muscle genes. Results Using an ovine model, transcriptional profiling was performed on Longissimus dorsi skeletal muscle taken at three fetal developmental time points (80, 100 and 120 d of fetal development) and two postnatal time points, one approximately 3 days postpartum and a second at 3 months of age. The developmental time course was dominated by large changes in expression of 2,471 genes during the interval between late fetal development (120 d fetal development) and 1-3 days postpartum. Analysis of the functions of genes that were uniquely up-regulated in this interval showed strong enrichment for oxidative metabolism and the tricarboxylic acid cycle indicating enhanced mitochondrial activity. Histological examination of tissues from these developmental time points directly confirmed a marked increase in mitochondrial activity between the late fetal and early postnatal samples. The promoters of genes that were up-regulated during this fetal to neonatal transition were enriched for estrogen receptor 1 and estrogen related receptor alpha cis-regulatory motifs. The genes down-regulated during this interval highlighted de-emphasis of an array of functions including Wnt signaling, cell adhesion and differentiation. There were also changes in gene expression prior to this late fetal - postnatal transition and between the two postnatal time points. The former genes were enriched for functions involving the extracellular matrix and immune response while the latter principally involved functions associated with transcriptional regulation of metabolic processes. Conclusions It is concluded that during late skeletal muscle development there are substantial and coordinated changes in the transcription of a large number of genes many of which are probably triggered by increased estrogen levels. These changes probably underpin the adaption of muscle to new physiological demands in the postnatal environment.

Background: In food animal agriculture, there is a need to identify the mechanisms that can improve the efficiency of muscle growth and protein accretion. Callipyge sheep provide excellent machinery since the up-regulation of DLK1 and RTL1 results in extreme postnatal muscle hypertrophy in distinct muscles. The aim of this study is to distinguish the genes that directly respond to DLK1 and RTL1 signaling from the genes that change as the result of muscle specific effects. Results: The quantitative PCR results indicated that DLK1 expression was significantly increased in hypertrophied muscles but not in non-hypertrophied muscles. However, RTL1 was up-regulated in both hypertrophied and non-hypertrophied muscles. Five genes, including PARK7, DNTTIP1, SLC22A3, METTL21E and PDE4D, were consistently co-expressed with DLK1, and therefore were possible transcriptional target genes responding to DLK1 signaling. Treatment of myoblast and myotubes with DLK1 protein induced an average of 1.6-fold and 1.4-fold increase in Dnttip1 and Pde4d expression respectively. Myh4 expression was significantly elevated in DLK1-treated myotubes, whereas the expression of Mettl21e was significantly increased in the DLK1-treated myoblasts but reduced in DLK1-treated myotubes. DLK1 treatment had no impact on Park7 expression. In addition, Park7 and Dnttip1 increased Myh4 and decreased Myh7 promoter activity, resemble to the effects of Dlk1. In contrast, expression of Mettl21e increased Myh7 and decreased Myh4 luciferase activity. Conclusion: The study provided additional supports that RTL1 alone was insufficient to induce muscle hypertrophy and concluded that DLK1 was likely the primary effector of the hypertrophy phenotype. The results also suggested that DNTTIP1 and PDE4D were secondary effector genes responding to DLK1 signaling resulting in muscle fiber switch and muscular hypertrophy in callipyge lamb. [ABSTRACT FROM AUTHOR]

The commercial beef cattle industry produces calves for replacement or slaughter. Female replacements are important to advance herd genetics, therefore, a tool to influence sex ratios may enhance reproductive efficiency. A commercial semen sexing kit, Heifer-Plus™, used in conjunction with artificial insemination, may alter the sex ratio of offspring by increasing motility of the X chromosome-bearing sperm. The aim of this research was to assess the methodology of Heifer-Plus™ through evaluation of motion patterns and kinematic parameters in conventional semen straws. Four bulls representing Angus, Wagyu, and Holstein breeds were utilized. Six straws of cryopreserved semen from each bull were thawed in a water bath (37.5°C for 35 sec). Three straws from each bull were pooled and treated with Heifer-Plus™ and 3 straws were pooled as the no-treatment control. Post treatment, all samples were aliquoted in microcentrifuge tubes and Computer Assisted Semen Analysis (CASA) measurements of motility and kinematic factors were assessed. Semen samples were held at 37.5°C for incubation for three 15-min periods (15-mins, 30-mins, and 45-mins) measuring thermoresistance and longevity of spermatozoa. After incubation, 80 μL of each semen sample were observed on CASA. Data were analyzed using ANOVA method in GraphPad Prism and P-values ≤ 0.05 were considered significant. No effect of treatment on motility parameters or rapid velocity were measured, however there was a decrease in total motility (P=0.0045), progressive motility (P=0.0115) and rapid velocity (P =0.0099) across time intervals. Heifer-Plus™ treated cells had higher incidence of static velocity compared to control (P = .0038). Semen samples were clustered into subpopulation thresholdbased on sperm average path velocity (VAP) and linearity (LIN) at each time point. Spermatozoa treated with Heifer-Plus™ consistently exhibited a high velocity and variable linearity therefore were categorized consistently into two categories at each time point. [ABSTRACT FROM AUTHOR]

Spermatozoon motility is an important factor in successful artificial reproductive technologies. Successful reproduction requires properly developed spermatozoa with adequate forward, progressive motility that allows for transport through the female reproductive tract. Motility is driven by production of ATP; however, cryopreservation is known to have damaging effects on spermatozoa. Mitochondria utilize oxidative phosphorylation to synthesize ATP through an electrochemical proton motive force that is composed primarily of mitochondrial membrane potential (Δψm). The mitochondrial membrane potential can be measured using a fluorescent, carbocyanine JC-1 dye (5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide). The objective of this study was to examine correlations between the mitochondrial membrane potential and motility score. Cryopreserved semen samples from three bulls were donated to Tarleton State University for research purposes. Samples were thawed, placed under a phase contrast microscope, and analyzed by three individuals with varying levels of training for rough motility. These samples were then prepared with JC-1 dye according to manufacturer's instructions. Two microliters of dye were added to a stock preparation of each sample. Samples were examined on a FACS Calibur flow cytometer at University of Texas Southwestern Core in Dallas, TX. Flow cytometry analysis was performed using FlowJo V10.7. Statistical analysis was performed using SAS v9.4. The Pearson correlation coefficient showed a strong, positive correlation (r = 0.90) between the mitochondrial membrane potential and motility (P = 0.28), thus indicating as the mitochondrial membrane potential increases, so does the rough motility score. These data represent a subset of a population that demonstrates the need of further research on the ability for spermatozoa to produce ATP and the correlation in forward, progressive motility. This research can provide a foundation in which future researchers may develop an assay that allows for testing of mitochondrial membrane potential by producers to select bulls with greater breeding potential. [ABSTRACT FROM AUTHOR]