Response to 13 generations of selection for increased 8-week body weight in lines of mice carrying a sheep growth hormone-based transgene

The purpose of this study was to evaluate selection in lines of transgenic mice. Two replicates of lines that either carried or did not carry the sheep metallothionein-1a sheep growth hormone transgene (oMt1a-oGH) were established. The host lines had been previously selected for rapid growth or selected randomly. Within-litter selection for increased 8-wk body weight was carried out for 13 generations. The frequency of oMt1a-oGH was monitored in all generations in the transgenic lines, but no genotypic information regarding the transgene was used as an aid to selection. The oMt1a-oGH was activated from weaning, at 3 wk, until 8 wk of age by adding ZnSO4 to the drinking water. Zinc stimulation of the transgene was not done during mating, gestation, or lactation. Data on body weights and weight gains were analyzed with a conventional mixed model and with an animal model. Genetic progress was achieved in all lines subjected to directional selection. In the control background, response to selection for 8-wk body weight was larger in the nontransgenic lines than in the transgenic lines, whereas no difference was found in the selected background. The frequency of the transgene was increased from the initial .5 to .62 in the randomly selected background but decreased to .04 in lines from a selected background. The REML estimates of variance components and genetic gain estimates varied greatly between the two methods. In general, there was better agreement between the realized heritability estimates and the heritability estimates obtained from the conventional mixed model analysis than between realized heritability estimates and results obtained using the animal model. Favorable correlated responses were obtained for 3- and 6-wk body weights and on 3- to 6- and 6- to 8-wk weight gains. Correlated responses to selection were larger in the selected than in the nonselected background but were not affected by the presence of the transgene. Results suggest that constructs similar to the oMt1a-oGH, which allow tight regulation, may be successfully incorporated into commercial livestock and should have larger effects in populations that have not been subject to selection.     

Components of heterosis for growth traits and litter size in line crosses of mice after long-term selection

Strains selected for 54 generations for large 8-week weight (N8, S8), for small weight (N6, S6), for high 3–5-week gain and low 8-week weight (N1) as well as unselected randomly mated control strains (N9, S9) were crossed, and F ₁, F ₂ and both back crosses created. N strains are derived from a NMRI base, S strains from a synthetic four-way cross among inbred lines. Heterosis for 8-week weight (8-ww) was some 6%, but 30% for 3–5-week gain and it was on average negative (22%) for 5–8-week gain. When epistatic effects were taken into account, it appeared that heterosis for 8-ww was largely due to beneficial effects of non-parental gene combinations, i.e. additive × additive epistatic effects were negative. These non-parental combinations neutralized the mostly negative dominance effects. The latter were mostly positive for early gain but in all 9 line crosses negative for late gain. The digenic effects of the non-parental origin were not large enough to balance the negative dominance effects for late gain, so that heterosis was negative. It appears therefore that early and late gain are affected by different sets of genes. Maternal additive effects on 8-ww and early gain are smaller than direct additive effects but mostly of similar sign. For late gain there appears to be no connection with direct additive effects. Direct litter heterosis was almost 50% but much of this was due to positively acting recombinational gene combinations, while direct litter dominance was mostly negative. Maternal additive effects on litter size differed depending on whether they were estimated from dams with crossbred or with purebred litter. Heterosis was small in crosses between control strains. Heterosis caused by recombinant gene pairs should be amenable to improvement by selection.     

Ontogeny of IGF-I responsiveness to bGH in young lambs

The ontogeny of hepatic growth hormone (GH) receptors (GHR), as measured by responses of both plasma insulin-like growth factor-I (IGF-I) and hepatic GHR to an exogenous bGH stimulus, was examined using sheep of different ages (Days 1-7, 14-21, 28-35, and 56-63 of life, and yearlings). The IGF-I response to bGH was first examined in yearling sheep using two doses of bGH (0.1 and 0.2 mg/kg LW/d). Based on these results, lambs in four groups up to Day 63 of life were treated for 5 d with bGH (n = 10) at a dose of 0.15 mg/kg LW/d or with saline (n = 10). Jugular blood samples were taken once daily on Days - 1, 4, and 5 of treatment. bGH treatment in lambs up to Day 63 of life had little effect on plasma concentrations of GH, insulin, glucose or urea, but significantly (P < 0.05) increased circulating concentrations of IGF-I at all ages and of NEFA at Day 62/63 of life. In contrast, bGH treatment at either dose in yearlings significantly increased these parameters, except for plasma urea concentrations which were decreased in bGH-treated yearlings. However, the responses of plasma IGF-I concentration to bGH stimulus in lambs up to Day 63 of life were small compared to those in yearling sheep. Consistent with this, bGH treatment failed to affect hepatic GH binding in young lambs, but up-regulated it in yearling sheep. Furthermore, basal (unstimulated) GH binding did not differ between sheep of 7 vs. 63 vs. 365 d of age, despite the greater IGF-I responses to bGH in the latter group. It is suggested that hepatic GHR in lambs up to Day 63 of life are not fully functional compared to the situation in yearlings.     

The impact of a transgene for ovine growth hormone on the performance of two breeds of sheep

The effect of a transgene encoding ovine growth hormone and regulated by a metallothionein promoter was examined in progeny of 69 Merino ewes and 49 Poll Dorset ewes that were inseminated by rams heterozygous for the gene construct. The presence of the transgene had no effect on the progeny from one of the three rams used, as evinced by a normal concentration and secretion pattern of growth hormone and normal growth rate and fatness. In progeny from the other two rams that bore an actively transcribed and translated copy of the transgene, the mean concentration of growth hormone in the plasma was twice that of controls, but the pulsatility of secretion was lost. These animals grew faster (P < 0.001) and were leaner (P < 0.001), but had a greater parasite fecal egg count (P < 0.001). The impact of the transgene differed between breeds with greater wool growth rate (P < 0.01) and live weight increase (P = 0.06) in Merino progeny compared with Poll Dorset cross. At 18 mo of age, the depth of the eyemuscle was decreased (P < 0.001), particularly in female sheep (P < 0.01). The results indicate that the production effects of genetic manipulation may depend on the age, the breed, and the sex of the animal. Furthermore, the transgene may fail to be expressed in some progeny so that its activity cannot be detected, even though the sheep bear the DNA construct.     

Effect of a major gene for growth on protein synthesis in mice

Rates of protein synthesis of mice with a major gene (hg) for rapid postweaning gain (line Ch) and their normal counterparts (line CH) were determined at 21, 31 and 42 d of age with an intraperitoneal injection of a flooding dose of 14C-leucine. A preliminary experiment demonstrated that the relationship between the specific activities of leucine in acid-soluble supernatants and carcass protein corresponded to the theoretical precursor-product relationship, indicating that the method is valid for estimating protein synthesis rates. Using this method at 21, 31 and 42 d of age, whole-body protein fractional synthesis rates (FSR) were 43.7, 32.7 and 29.1%/d and 41.9, 32.6 and 33.1%/d for lines CH and Ch, respectively. Although differences between lines were not significant, FSR decreased with age. Absolute synthesis rate (ASR), where ASR = (FSR) X (whole body protein), was greater (P less than .001) at 21, 31 and 42 d of age in line Ch as compared with CH, and increased (P less than .001) with age. The relative contributions of liver, gastrointestinal tract, heart-kidney-lung and remaining carcass to whole body protein ASR were not affected by line, but did change (P less than .05) with age. Whole body protein fractional breakdown rate (FBR), calculated as FSR minus whole body protein fractional growth, indicates that differences between lines CH and Ch whole-body FSR and(or) FBR exist only between 24 and 33 d of age, and that the maximum value of this difference probably does not exceed 10%.     

Composition of growth in mice with a major gene for rapid postweaning gain

Previous research from this laboratory identified the existence of a major gene for rapid growth in mice. This trait is expressed as rapid postweaning growth and is inherited as a single recessive gene, designated hg. The hg/hg males and females had greater (P less than .05) body weights at 49-d of age as compared with their Hg/-counterparts; 45.6 +/- .64 and 34.0 +/- .64 vs 33.2 +/- .23 and 27.3 +/- .15 g, respectively. Twenty-four male littermate pairs (hg/hg and Hg/-) were euthanized at 49 d of age for determination of carcass composition. Percentage body water was not affected by genotype (hg/hg, 66.7 +/- .5; Hg/-, 67.8 +/- .3). However, there was a decrease (P less than .05) in percentage body protein (20.2 +/- .1 vs 20.8 +/- .1) and body ash (3.4 +/- .01 vs 3.7 +/- .01) in hg/hg males as compared with Hg/- males, while percentage lipid was significantly increased in hg/hg males (8.7 +/- .5 vs 6.7 +/- .3). When carcass weights were adjusted for differences in dry weight, only body protein was significantly affected by genotype, being greater for hg/hg males (8.54 +/- .19 vs 7.70 +/- .19 g). All other components of body composition were not affected by genotype. The regression coefficient for the covariate of dry weight was significantly different from zero for all carcass components. However, there was no significant difference in the regression coefficient between Hg/- and hg/hg males for each component.(ABSTRACT TRUNCATED AT 250 WORDS)     

Efficiency of growth in mice with a major gene for rapid postweaning gain

Previous research in this laboratory demonstrated the existence of a major gene (hg), inherited as a homozygous recessive, which increases postweaning growth by 40 to 50% in C57Bl/6 mice (Ch) compared to the same genetic stock without the major gene (CH). Although its effect has not been previously evaluated, this single recessive allele is also in a line of mice selected for rapid postweaning gain for over 70 generations. Gh represents that line of mice with the major gene for growth (hg) in the growth-selected background and GH the growth-selected background without the major gene. Total body weight, daily weight gain, feed consumption and gain/feed, measured daily from 21 to 42 d of age, were all significantly greater (p less than .01) in the two lines with the hg/hg genotype (Ch and Gh) compared with their respective control lines (CH and GH). Differences in body composition at 42 d of age between CH compared with Ch and GH compared with Gh were accounted for by difference in body weight. Gross and net energetic efficiency, calculated assuming a similar maintenance energy requirement, were improved (P less than .01) in Ch and Gh compared to CH and GH, respectively. The results demonstrated that hg influences growth in growth-neutral and growth-selected backgrounds. The gene also alters energy metabolism by increasing energetic efficiency of growth and(or) decreasing maintenance energy requirement.     

Selection for increased adult body weight in mouse lines with and without the rat growth hormone transgene

SUMMARY: Four lines of mice with and without the rat growth hormone (rGH) transgene were developed to measure responses to selection for increased 42-day body weight and evaluate fitness of mice with and without the rGH transgene. Each line contained selected and unselected (control) sublines. At the last three generations of selection (Generations 12-14), selected sublines differed from unselected controls by 3.8 to 4.7 g (14.8 to 19.8%) in 42-day weight, -0.5 to -8.3% in fertility, and 0.5 to 1.6 in litter size at birth. The origin of the lines (W: previously selected for 42-day weight and C: unselected) affected 42-day weight, i. e. 42-day weight of mice originating from W was significantly (P < 0.01) heavier than that of mice originating from C. Responses to selection, as measured by the deviation of the selected subline from the control, continued to be positive over 14 generations. Realized heritability of 42-day weight ranged from 0.30 to 0.42. The rGH transgene that increased 63-day weight by 54% was not found at Generation 12. The unexpected loss of rGH transgene was due to poor fitness of mice with the rGH transgene. Mice with the transgene had lower fertility rate than those without the transgene (50.0 to 73.7% vs. 95.0%), smaller litter size (6.8 to 7.8 vs. 8.6) and poorer survival of the progeny (69.2 to 74.5% vs. 88.3%). Based on these data, selective advantage/disadvantage of the rGH transgene in the fitness traits was estimated quantitatively. The results from the study on growth and reproductive traits suggest that desirable effects of gene transfer on a specific trait (42- and 63-day weight in the present study) might be offset by undesirable effects on other traits (e. g., reproduction and survival) in some cases of transgenic animals. ZUSAMMENFASSUNG: Selektion auf hohes adultes Gewicht in M?uselinien mit und ohne Rattenwachstumshormon-Transgenen Vier M?uselinien mit und ohne das Rattenwachstumshormon (rGH) Transgen wurden zur Messung des Selektionserfolges auf gesteigertes 42-Tage-K?rpergewicht entwickelt, um auch Fitne? zu prüfen. Jede Linie bestand aus einer selektierten und aus einer unselektierten (Kontroll-)Unterlinie. In den drei letzten Selektionsgenerationen (Generationen 12-14) unterschieden sich die selektierten Unterlinien um 3,8 bis 4,7 g (14,8 bis 19,8%) im 42-Tage-Gewicht, -0,5 bis -8,3% in Fruchtbarkeit und 0,5 bis 1,6 in Wurfgr??e bei Geburt. Der Ursprung der Linien (W: früher auf 42-Tage-Gewicht selektiert, C: unselektiert) beeinflu?te das 42-Tage-Gewicht. M?use aus der ersten waren signifikant (p < 0,01) schwerer als jede aus C. Selektionserfolg gemessen als Abweichung von der Kontrolle war über 14 Generationen positiv, realisierte Heritabilit?t variierte von 0,3 bis 0,42. Das rGH-Transgen steigerte das 63-Tage-Gewicht um 54%, aber war in der Generation 12 nicht mehr vorhanden. Der unerwartete Verlust des RGH-Transgens war auf schlechte Fitne? der besitzenden M?use zurückzuführen. Transgene M?use hatten geringere Fruchtbarkeit als jene ohne das Transgen (50 bis 73,7% im Vergleich zu 95%), kleinere Wurfgr??e (6,8 bis 7,8 gegenüber 8,6) und schlechtere überlebensrate der Nachkommen (69,2 bis 74,5% im Vergleich zu 88,3%). Die Ergebnisse erlauben die quantitative Sch?tzung der selektiven Vorteile/Nachteile des rGH-Transgens im Bezug auf Fitne?. Erwünschte Wirkungen von Gentransfer auf spezifische Merkmale (41- und 63-Tage-Gewicht in dieser Untersuchung) k?nnen durch unerwünschte Wirkungen von Transgenen auf andere Merkmale (Reproduktion und überleben) neutralisiert werden.     

SV40增强子在bGH转基因鼠体内对真核基因转录效率的影响

把ＳＶ４０的增强子序列以紧邻（ｐＳＶＣＡＴＬＢＧＨ）和相距２．３ｋｂ的距离克隆到小鼠金属巯基组氨酸三甲内盐基因（ＭＴ－Ｉ）启动子的上游，用以研究了在体内（ｉｎｖｉｖｏ）环境下原核基因的增强于对真核基因转录调控的影响，以及增强子与启动子的距离对增强于增强转录效率的影响。在建立了ｐＳＶＣＡＴＬＢＧＨ和ｐＳＶ２ＬＢＧＨ两种转基因结构的不同种系的转基因鼠后，通过分析ＩＣＲ、ＫＢ（昆明白）和Ｃ５７ＢＬ３种种系的ｐＳＶＣＡＴＬＢＧＨ转基因鼠的６种主要器官中的ＣＡＴ活性，证明ＳＶ４０增强子可以增强真核基因──ＣＡＴ基因的转录效率而无种属及组织特异性；通过比较ＩＣＲ和昆明白（ＫＢ）两种种系的ｐＳＶＣＡＴＬＢＧＨ和ｐＳＶ２ＬＢＧＨ转基因鼠的心脏和肝脏中ｂＧＨｍＲＮＡ水平，证明在转基因鼠体内，在２．３ｋｂ距离内，ＳＶ４０增强子对由ＭＴ－Ｉ启动子启动的真核基因──ｂＧＨ基因的转录效率的增强效果无明显差异。     

Expression of nerve growth factor in itchy skins of atopic NC/NgaTnd mice

Although the possible involvement of neurotrophic factors in itchy skins of atopic dermatitis has been predicted, the exact mechanism by which itch is induced remains unclear. Since nerve growth factor (NGF) has crucial effects on development and functions of sensory nerves, we determined production of NGF and extension of nerve fibers in skins of NC/NgaTnd mice with or without atopic dermatitis. NC/NgaTnd mice spontaneously develop atopic dermatitis-like skin lesions when they are raised in air-unregulated conventional circumstances. We quantified scratching behavior of NC/NgaTnd mice during the development of dermatitis using a novel analytical system and compared to clinical skin severity scores. A significant correlation between the severity of dermatitis and the increase in the number of scratches was identified, indicating that scratching behavior may associate with clinical skin conditions. NGF contents in the skin lesions of conventional NC/NgaTnd mice were significantly higher than those in SPF mice. Positive reactions for NGF were observed in keratinocytes and fibroblasts in affected skins of conventional NC/NgaTnd mice. Immunohistochemical analysis showed the extension of protein gene product 9.5-positive nerve fibers from the dermis toward the epidermis at the skin lesions. These results suggest that sensory nerves induced by NGF may contribute to development of itch, and that NGF produced at the affected site may provide abnormal skin sensitivity in atopic dermatitis.     

Cytoplasmic effects on selection response for increased growth rate in mice

To determine if cytoplasmic effects have contributed to long-term selection response for increased growth rate in mice, reciprocal cross matings were made between an unselected control line (ICR) and a line (M16) derived from ICR by long-term selection for high postweaning weight gain from 3 to 6 wk of age. Embryos were recovered 2 to 4 d following mating and transferred to pseudopregnant F1 (DBA/2NCrlBR X C57BL/6NCrlBR) females. Thus, all embryos developed in similar uterine and postnatal maternal environments. A total of 122 M16 X ICR and 123 ICR X M16 mice was produced, representing 19 litters from each cross. Litters were standardized at birth to five to seven pups. Litter weights at birth and 1 wk were recorded. Body weights at 2, 3, 4, 5 and 6 wk and weight gain from 3 to 6 wk were obtained. Weights of liver, kidneys, and sc and epididymal fat pads of males were obtained at 6 wk. Females were mated at 8 wk, and litter size at birth was recorded. Least-squares procedures were used to test for differences between reciprocal crosses for all traits. Body weight at 4 wk was higher (P less than .05) for mice with ICR cytoplasm. No other significant differences were detected. There was no evidence that cytoplasmic effects influenced direct or correlated responses to long-term selection for increased postweaning weight gain.     

Correlated responses in growth hormone to selection for weight gain in mice

SUMMARY: Correlated responses in pituitary gland weight and growth hormone (GH) concentration in the serum and pituitary were studied in lines of mice selected for growth rate, and in controls. The selection criteria were weight gain between 28 and 38 days on an ad libitum feed intake (EPA line), or on intake restricted to 80% of the control mice (EPR line), and weight gain between 48 and 58 days under the above two feeding regimes (LPA and LPR lines). The control line was maintained by random breeding. In generation 13, pituitary weight and growth hormone levels were determined at 38 days in lines EPA, EPR and the control and at 58 days in lines LPA, LPR and the control. Pituitary weight, corrected for body weight gain, was smaller in the EPA line than in the control line at 38 days and was greater in the LPR line than in the control line at 58 days. There were large differences in serum GH concentrations between the selected lines and the control; the differences were statistically significant at 38 days, with the EPA and EPR lines having lower levels than the controls. ZUSAMMENFASSUNG: Ver?nderung von Wachstumshormonspiegel bei Selektion für Zuwachs bei M?usen Ver?nderungen im Hypophysengewicht und Wachstumshormon-(GH)-Konzentrationen im Serum und in der Hypophyse wurden bei Wachstumsselektionslinien und bei Kontrollm?usen untersucht. Selektionskriterien waren Zuwachs zwischen 28 und 38 Tagen bei ad libitum Futteraufnahme (EPA Linie) oder bei Linien, wo Futteraufnahme auf 80% derjenigen der Kontrollm?use (EPR Linie) begrenzt wurde und Zuwachs zwischen 48 und 58 Tagen unter beiden Futterweisen (LPA und LPR Linie). Die Kontrollinie wurde durch Zufallspaarung fortgepflanzt. In Generation 13 wurden Hypophysengewicht und Wachstumshormonspiegel im Alter von 38 Tagen in Linien EPA, EPR und in Kontrollen und bei 58 Tagen in Linien LPA und LPR und Kontrollen bestimmt. Hypophysengewicht, korrigiert für Zuwachs, war geringer in der LPA Linie als in der Kontrolle bei 38 Tagen Alter und gr??er in der LPR Linie als in der Kontrolle bei 58 Tagen. Zwischen GH Konzentrationen selektierter und Kontrollinien waren erhebliche Differenzen, die bei 38 Tagen signifikant waren, wobei EPA und EPR Linien geringere Werte als die Kontrollen aufwiesen.     

Identification of a virulence factor for Brucella abortus infection in BALB/c mice

Immunogenic or pathogenic factors of recombinant proteins (rBCSP20, rBCSP-31, and rBCSP45 of Brucella abortus strain 19) for mice were compared with factors of a proteinase K-treated lipopolysaccharide extracted from B abortus strain 2308. Mice were vaccinated with 4 products, using different inoculation schedules and were challenge exposed with a virulent culture of B abortus strain 2308. Blood samples were collected 2 weeks after vaccination and at necropsy and sera were obtained. Spleens were cultured for B abortus at necropsy (3 to 4 weeks after challenge exposure). Mice given proteinase K-treated lipopolysaccharide alone or in conjunction with rBCSP20 or rBCSP45 proteins were protected, but mice given rBCSP31 on the same day as challenge exposure were not. Vaccination with recombinant proteins alone neither provide protection nor significantly (P greater than 0.05) increase the pathogenic effect of the challenge-exposure culture. Seemingly, rBCSP31 might be a virulence factor of B abortus.     

混合稀土对小白鼠生长的影响

试验采用单因子设计,在相同基础日粮中分别添加0、25、50、75mg/kg的混合碳酸稀土组成4种日粮。20d的饲养试验结果表明,混合稀土能显著提高小白鼠的生长。与对照组相比,日粮中添加混合稀土能显著提高小白鼠的体增重(P<0.05)和采食量(P<0.05)。     

The effects of prior growth as a biofilm on the virulence of Salmonella typhimurium for mice

Relatively little is known about how growth as a biofilm affects the virulence of pathogenic bacteria. In this study, the virulence of Salmonella typhimurium grown as a biofilm, or as planktonic cells, was compared in mice. Increased numbers of colony forming units were recovered from the spleens of mice 5 days after i.p. injection with S. typhimurium grown as a biofilm, as compared with planktonic cells (P < 0.05). No significant difference in the CFU of S. typhimurium recovered from the liver was noted at the same time point, and no difference was noted in the CFU recovered from the spleen or liver at 5 days after i.v. or i.g. inoculation with 10(5) S. typhimurium. Nor were any differences noted at 7 days after i.p., i.v. or i.g. inoculation. Thus, any effect of growth as a biofilm has on the virulence of S. typhimurium seems to be limited to the first 5 days after i.p. inoculation.     

Studies on energy metabolism in lines of mice selected for different growth parameters

Growth is a very complex physiological process and is controlled by many genes and therefore easy to manipulate by selective breeding. Such manipulation of growth was realized by long-term selection of laboratory mice for different growth parameters (body weight, total protein amount in the carcass and an index combining body weight and endurance fitness) resulting in a high phenotypic and genetic differentiation compared to the nonselected control (Bünger et al. 1983, 1992, 1994; Renne et al. 1995). After 70 generations the 42-day body weights increased from 28 g at the start of selection to 58.3 g, 51.9 g and 47.4 g in these lines, respectively (Bünger et al. 1994). At the same time the carcass protein content increased from 2.92 to 5.23 g in the line selected for protein mass without an increase of fat percentage up to the age of 42 days (Renne et al. 1995). In comparison with that, selection for body weight was accompanied by a marked increase of fat percentage up to this age as reported in literature for many long-term selection experiments. Because of the different chemical composition of the body gain at relatively small differences in growth rate, these selected lines seemed to be suitable models for studying some aspects of energetic efficiency of growth. The results of a former experiment conducted in generations 32–42 suggested a higher efficiency of energy utilization in the line selected for body weight than in the other selected lines (Bünger et al. 1987). The objective of the present study was to characterize the energy metabolism of these different selected lines complementary to the studies on protein metabolism given by Schadereit et al. (1997, 1998).