Evaluation of carcass, live, and real-time ultrasound measures in feedlot cattle: I. Assessment of sex and breed effects.
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Carcass and live-animal measures from 1,029 cattle were collected at the Iowa State University Rhodes and McNay research farms over a 6-yr period. Data were from bull, heifer, and steer progeny of composite, Angus, and Simmental sires mated to three composite lines of dams. The objectives of this study were to estimate genetic parameters for carcass traits, to evaluate effects of sex and breed of sire on growth models (curves), and to suggest a strategy to adjust serially measured data to a constant age end point. Estimation of genetic parameters using a three-trait mixed model showed differences between bulls and steers in estimates of h2 and genetic correlations. Heritability for carcass weight, percentage of retail product, retail product weight, fat thickness, and longissimus muscle area from bull data were .43, .04, .46, .05, and .21, respectively. The corresponding values for steer data were in order of .32, .24, .40, .42, and .07, respectively. Analysis of serially measured fat thickness, longissimus muscle area, body weight, hip height, and ultrasound percentage of intramuscular fat using a repeated measures model showed a limitation in the use of growth models based on pooled data. In further evaluation of regression parameters using a linear mixed model analysis, sex and breed of sire showed an important (P < .05) effect on intercept and slope values. Regression of serially measured traits on age within animal showed a relatively larger R2 (62 to 98%) and a smaller root mean square error (RMSE, .09 to 8.85) as compared with R2 (0 to 58%) and RMSE (.31 to 67.9) values when the same model was used on pooled data. We concluded that regression parameters from a within-animal regression of a serially measured trait on age, averaged by sex and breed, are the best choice in describing growth and adjusting data to a constant age end point. (+info)
The relationship between DNA methylation and chromosome imprinting in the coccid Planococcus citri.
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The phenomenon of chromosome, or genomic, imprinting indicates the relevance of parental origin in determining functional differences between alleles, homologous chromosomes, or haploid sets. In mealybug males (Homoptera, Coccoidea), the haploid set of paternal origin undergoes heterochromatization at midcleavage and remains so in most of the tissues. This different behavior of the two haploid sets, which depends on their parental origin, represents one of the most striking examples of chromosome imprinting. In mammals, DNA methylation has been postulated as a possible molecular mechanism to differentially imprint DNA sequences during spermatogenesis or oogenesis. In the present article we addressed the role of DNA methylation in the imprinting of whole haploid sets as it occurs in Coccids. We investigated the DNA methylation patterns at both the molecular and chromosomal level in the mealybug Planococcus citri. We found that in both males and females the paternally derived haploid set is hypomethylated with respect to the maternally derived one. Therefore, in males, it is the paternally derived hypomethylated haploid set that is heterochromatized. Our data suggest that the two haploid sets are imprinted by parent-of-origin-specific DNA methylation with no correlation with the known gene-silencing properties of this base modification. (+info)
Genomic imprinting and position-effect variegation in Drosophila melanogaster.
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Genomic imprinting is a phenomenon in which the expression of a gene or chromosomal region depends on the sex of the individual transmitting it. The term imprinting was first coined to describe parent-specific chromosome behavior in the dipteran insect Sciara and has since been described in many organisms, including other insects, plants, fish, and mammals. In this article we describe a mini-X chromosome in Drosophila melanogaster that shows genomic imprinting of at least three closely linked genes. The imprinting of these genes is observed as mosaic silencing when the genes are transmitted by the male parent, in contrast to essentially wild-type expression when the same genes are maternally transmitted. We show that the imprint is due to the sex of the parent rather than to a conventional maternal effect, differential mitotic instability of the mini-X chromosome, or an allele-specific effect. Finally, we have examined the effects of classical modifiers of position-effect variegation on the maintenance and the establishment of the imprint. Factors that modify position-effect variegation alter the somatic expression but not the establishment of the imprint. This suggests that chromatin structure is important in maintenance of the imprint, but a separate mechanism may be responsible for its initiation. (+info)
Two structural variants of Nek2 kinase, termed Nek2A and Nek2B, are differentially expressed in Xenopus tissues and development.
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Nek2 kinase, a NIMA-related kinase, has been suggested to play both meiotic and mitotic roles in mammals, but its function(s) during development is poorly understood. We have isolated here cDNAs encoding a Xenopus homolog of mammalian Nek2 and have shown that Xenopus Nek2 has two structural variants, termed Nek2A and Nek2B. Nek2A, most likely a C-terminally spliced form, corresponds to the previously described human and mouse Nek2, while Nek2B is most probably a novel, C-terminally unspliced form of Nek2. As a consequence of this (probable) alternative splicing, Nek2B lacks the C-terminal 70-amino-acid sequence of Nek2A, which contains a PEST sequence (or a motif for rapid degradation). Western blot analysis reveals that Nek2A is expressed predominantly in the testis (presumably in spermatocytes) and very weakly in the stomach and, during development, only after the neurula stage. By contrast, Nek2B is expressed mainly in the ovary and in both primary and secondary oocytes and early embryos up to the neurula stage. These results suggest that Nek2A and Nek2B may play both meiotic and mitotic roles, but in a spatially and temporally complementary manner during Xenopus development, and that Nek2B, rather than Nek2A (or the conventional form of Nek2), may play an important role in early development. We discuss the possibility that a counterpart of Xenopus Nek2B might also exist and function in early mammalian development. (+info)
Tomographical description of tennis-loaded radius: reciprocal relation between bone size and volumetric BMD.
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Effects of long-term tennis loading on volumetric bone mineral density (vBMD) and geometric properties of playing-arm radius were examined. Paired forearms of 16 tennis players (10 women) and 12 healthy controls (7 women), aged 18-24 yr, were scanned at mid and distal site by using peripheral quantitative computerized tomography. Tomographic data at midradius showed that tennis playing led to a slight decrease in cortical vBMD (-0.8% vs. nonplaying arm, P < 0. 05) and increase both in periosteal and endocoritcal bone area (+15. 2% for periosteal bone, P < 0.001; and +18.8% for endocortical bone, P < 0.001). These data suggest that, together with an increase in cortical thickness (+6.4%, P < 0.01), cortical drift toward periosteal direction resulted in improvement of mechanical characteristics of the playing-arm midradius. Enlargement of periosteal bone area was also observed at distal radius (+6.8%, P < 0.01), and the relative side-to-side difference in periosteal bone area was inversely related to that in trabecular vBMD (r = -0.53, P < 0.05). We conclude that an improvement of mechanical properties of young adult bone in response to long-term exercise is related to geometric adaptation but less to changes in vBMD. (+info)
Hormonal regulation of apolipoprotein AI.
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Apolipoprotein AI (apo AI) is the major protein component of the serum high-density lipoprotein (HDL) particles. The antiatherogenic properties of apo AI alone or as part of HDL and their inverse correlation with the incidence of coronary heart disease underlie the clinical importance of the protein. A detailed understanding of the mechanisms by which apo AI is regulated will help us develop new and better ways to manipulate expression of the protein. Although there are many factors that influence apo AI expression, endogenous hormones are attractive because simple changes in abundance of these compounds will alter gene activity. Hormones belonging to the thyroid/steroid family that influence activity of the gene include thyroid hormone, glucocorticoids, gender-specific steroids and retinoic acid. Whereas thyroid, glucocorticoid and estradiol enhance activity of the gene, retinoic acid and androgens decrease it. The mechanisms that mediate the effects of the hormones include direct effects of the ligand and nuclear receptor complex on gene activity. However, indirect means involving the participation of transcription factors other than the hormone receptors are also possible. In summary, members of the same hormone family may have different mechanisms that mediate their activities on apo AI gene activity. (+info)
The obese gene is expressed in lean littermates of the genetically obese mouse (C57BL/6J ob/ob).
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Some individuals of the mixed group of "lean" littermates (+/ob and +/+) of (C57BL/6J ob/ob) often suggest phenotypic characteristics of ob/ob animals. Therefore, it was of interest to determine whether expression of the ob gene had physiological significance in +/ob animals. Body weight (BW), fasting blood glucose (FBG), and body core temperature (Tr) were monitored between 62 and 364 days of age in +/+ and +/ob mice. Among females but not males, +/ob mice were heavier (P = 0.003) and FBG levels were greater (P = 0.04) than in +/+ animals. Comparison of Tr indicated differences suggesting falling Tr in +/ob but rising Tr in +/+ mice with age in males but not females. Multivariate analysis of variance yielded genotype effects for both males (P = 0.002) and females (P = 0.02). BW, FBG, and Tr alone were sufficient at the 75% level for genotypic characterization and separation of +/? animals as +/ob or +/+; clearly, expression of the ob gene in heterozygotes of the +/ob animal may make the mixed +/? group inappropriate as lean controls. (+info)
Does gender influence the strength and mechanisms of the muscle metaboreflex during dynamic exercise in dogs?
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Ischemia of active skeletal muscle stimulates neuronal afferents within the muscle, which elicits a reflex increase in sympathetic nerve activity, systemic arterial pressure (SAP), and heart rate (HR), termed the muscle metaboreflex. We retrospectively investigated whether gender influences the activation of the muscle metaboreflex and the primary mechanisms used by this reflex, augmentation of cardiac output (CO) and peripheral vasoconstriction, using 15 female and 13 male chronically instrumented dogs exercising on a treadmill (3.2 km/h, 0% grade). Metaboreflex activation was achieved via progressive partial vascular occlusion of the terminal aorta during exercise. In both females and males, hindlimb ischemia elicited similar substantial increases in SAP (56.1 +/- 3.0 and 55.1 +/- 4.2 mmHg, respectively), HR (25.8 +/- 4.8 and 33.9 +/- 2.8 beats/min, respectively), and CO (1.39 +/- 0.3 and 1.64 +/- 0.2 liters, respectively) and a similar substantial decrease in renal vascular conductance (RVC; 42.7 +/- 4.9 and 42.9 +/- 5.3%, respectively). Both groups also demonstrated similar metaboreflex thresholds and sensitivities of SAP, HR, CO, and RVC. We conclude that the strength and mechanisms mediating the metaboreflex responses during dynamic exercise in dogs are not affected by gender. (+info)