Genetic ablation: targeted expression of a toxin gene causes microphthalmia in transgenic mice

Lineage-specific regulatory elements can be used to direct expression of a variety of genes to specific tissues in transgenic mice. If the hybrid constructs contain a gene encoding a cytotoxic gene product, then genetic ablation of a specific cell lineage can be achieved. We have generated six transgenic mice by introducing into fertilized eggs the mouse gamma 2-crystallin promoter fused to the coding region of the diphtheria toxin A-chain gene. Three of these mice and all the transgenic offspring analyzed were microphthalmic. The lenses of these mice displayed considerable heterogeneity: some were almost normal morphologically but reduced in size, whereas others were grossly aberrant and deficient in nuclear fiber cells. These studies indicate that programmed ablation of specific cell types can be stably transmitted through the germ line.     

Rise and fall of species occupancy in Cenozoic fossil mollusks

In the time between speciation and extinction, a species' ecological and biogeographic footprint-its occupancy-will vary in response to macroecological drivers and historical contingencies. Despite their importance for understanding macroecological processes, general patterns of long-term species occupancy remain largely unknown. We documented the occupancy histories of Cenozoic marine mollusks from New Zealand. For both genera and species, these show a distinct pattern of increase to relatively short-lived peak occupancy at mid-duration, followed by a decline toward extinction. Thus, species at greatest risk for extinction are those that have already been in decline for a substantial period of time. This pattern of protracted rise and fall stands in contrast to that of incumbency, insofar as species show no general tendency to stay near maximal occupancy once established.     

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 4. The effect of seasonal pattern of nitrogen fertilizer application and annual stocking rate

Greyface (Border Leicester × Scottish Blackface) ewes, mated in October, were housed in winter and turned out after lambing in late March to one of four treatments replicated three times on perennial ryegrass (Lolium perenne)-dominated pastures. On three of the treatments the stocking rate was 12·5 ewes plus lambs ha^?1 annum^?1 (SR_12·5), whereas on the fourth it was 15·0 ewes plus lambs ha^?1 annum^?1 (SR_15·0). There were two levels of applied fertilizer nitrogen (N), 152 kg N ha^?1 annum^?1 (N₁₅₂) and 205 kg N ha^?1 annum^?1 (N₂₀₅). Three patterns of nitrogen application were used: predominantly in spring (E), predominantly in autumn (L), and mainly in spring and autumn (E + L). Grazed sward surface height was controlled within the range 3·5–5·5 cm during spring and summer, and supplementary feed was offered when sward height was below 3·5 cm. The effects on animal performance, yield of silage and requirement for supplementary feed were measured over 3 years (1986–88). Management of the sward height within the specified limits resulted in similar levels of individual animal performance for all treatments, but treatment SR_15·0N₂₀₅E + L produced a significantly (P < 0·05) greater output of lamb per hectare. There was no evidence to suggest that, by increasing the amount of N fertilizer applied in the autumn, ewe reproductive performance was increased. Neither the treatment with the lower level of N applied in the spring (SR_12·5N₁₅₂L) nor the high stocking rate treatment (SR_15·0N₂₀₅E + L) was self-sufficient in winter feed (silage) production. SR_15·0N₂₀₅E + L also required more supplementary feed in both the lactation (38·1 kg ewe^?1) and the mating (9·1 kg ewe^?1) periods. SR_12·5N₁₅₂L required the second greatest amount of supplementary feed during lactation (36·1 kg ewe^?1), whereas SR_12·5N₂₀₅E + L required the least supplementary feed over both periods (27·8 kg and 4·8 kg ewe^?1). Taking all treatments together, there were significant (P < 0·05) differences between years in lamb weaning weight (kg), lamb output (kg ha^?1), yield of silage (kg ewe^?1) and supplementary feed required (kg ewe^?1), arising mainly from a lower level of herbage production in one year. Treatment SR_12·5N₁₅₂E generated the highest gross margin per hectare.     

Allometric basis of enrofloxacin scaling in green iguanas

When body size varies greatly, drug disposition can best be described as an allometric function of body weight. Therefore, the allometry of standard metabolic rate (SMR; 3/4 power) and body surface area (BSA; 2/3 power) have been advocated as surrogate markers for the prediction of key pharmacokinetic parameters. The goal of the present study was to examine the allometric basis of pharmacokinetic scaling within a species, green iguanas. Enrofloxacin was administered intravenously to 20 green iguanas (322-3824 g), and noncompartmental analysis was used to calculate standard pharmacokinetic parameters, which were log(10) transformed and regressed against log(10) body weight. The slopes of significant regressions were compared with the values of unity, 3/4, and 2/3. The slope of enrofloxacin total body clearance (Cl) was also compared with the slopes relating SMR and renal Cl of (99m)Tc-diethylenetriamine penta-acetic acid ((99m)DTPA) to body weight in iguanas. Enrofloxacin Cl depended allometrically on body weight with the power of 0.32. The slope of enrofloxacin Cl was significantly less than those of SMR, Cl of (99m)DTPA, and the 2/3 value. Therefore, the relationship between enrofloxacin Cl and body weight does not directly depend on the allometry of BSA, SMR, or renal Cl of (99m)DTPA in iguanas.     

Production and oxidation of wool grease after shearing

OBJECTIVE: To measure the production and amount of oxidation of wool grease secreted immediately after shearing. To identify components of wool grease that might act as a carrier to facilitate lateral diffusion of topically applied insecticides. DESIGN: Fine-wool Merino sheep were shorn and residual greasy wool was collected from the sheep's flank. The quantity of grease produced, and the amount of oxidation was measured during 18 days after shearing. Wool grease was fractionated into five component groups based on their polarity and the degree of oxidation in these fractions determined. RESULTS: There was a 24% increase in grease production within 2 days after shearing but secretions returned to pre-shearing amounts after 4 days. During this period wool grease oxidized rapidly. Of the grease fractions examined, sterol and wax esters remained essentially unoxidized whereas free sterols such as cholesterol and lanosterol, fatty acids and polar lipids, aldehydes and alcohols were extensively oxidized within 7 days after shearing. CONCLUSION: The transient increase in grease production after shearing may facilitate diffusion of topically applied synthetic pyrethroid insecticides. Oxidation of grease components may then contain the insecticide and limit further diffusion. Incorporating the insecticide in non-oxidising fractions of wool grease may make insecticide dispersion more efficient.     

Terraclor (PCNB) for control ofRhizoctonia solani. II. PCNB residues in tubers

Terraclor (PCNB) applied to soils by broadcast and row slightly reduced the incidence ofRhizoctonia solani but did not increase yield or per cent of U. S. No. 1 tubers either by weight or numbers. Residues of PCNB in tubers grown in treated soils increased as the rate per acre of PCNB increased. Almost all of the residues were in the tuber peel.     

Production of Lambs After the Transfer of Fresh and Cryopreserved in vitro Produced Embryos from Prepubertal Lamb Oocytes and Unsorted and Sex-sorted Frozen-thawed Spermatozoa

Cumulus-oocyte complexes from hormone-stimulated 3-4-week-old (n=43) and 6-7-week-old (n=12) prepubertal lambs were matured in vitro and incubated with unsorted, or X- or Y-spermatozoa separated with a high-speed cell sorter (SX MoFlo)frozen-thawed. Presumptive zygotes were then cultured to the blastocyst stage, and transferred to recipients fresh or after cryopreservation (frozen). Oocyte cleavage was higher (p <0.05) with unsorted (515/926, 55.6%) than X- or Y-spermatozoa (261/672, 38.8% and 229/651, 35.2%, respectively) and blastocyst formation (% zygotes) by Day 9 of in vitro culture was lower (p <0.05) for X- (102/261, 39.1%) than unsorted spermatozoa (249/515, 48.3%), but did not differ between Y-spermatozoa (103/229, 45.0%) and unsorted spermatozoa, or between X- and Y-spermatozoa (p >0.05). For fresh embryos, survival to term was 50.0% (3/6) for unsorted, 0.0% (0/6) for X- and 16.7% (1/6) for Y-spermatozoa-derived embryos (p >0.05), and for frozen embryos was 4.0% (2/50) for unsorted, 9.1% (2/22) for X- and 2.9% (1/34) Y-spermatozoa-derived embryos (p >0.05). Of the two lambs born from X-spermatozoa-derived embryos, one was female (50%), and from the two Y-spermatozoa-derived lambs, both were male (100%), demonstrating that lambs can be produced after the transfer of fresh and cryopreserved IVP embryos derived from prepubertal lamb oocytes and frozen-thawed sex-sorted sperm.     

Effect of body weight on the pharmacokinetics of flunixin meglumine in miniature horses and quarter horses

In most species, large variations in body size necessitate dose adjustments based on an allometric function of body weight. Despite the substantial disparity in body size between miniature horses and light‐breed horses, there are no studies investigating appropriate dosing of any veterinary drug in miniature horses. The purpose of this study was to determine whether miniature horses should receive a different dosage of flunixin meglumine than that used typically in light‐breed horses. A standard dose of flunixin meglumine was administered intravenously to eight horses of each breed, and three‐compartmental analysis was used to compare pharmacokinetic parameters between breed groups. The total body clearance of flunixin was 0.97 ± 0.30 mL/min/kg in miniature horses and 1.04 ± 0.27 mL/min/kg in quarter horses. There were no significant differences between miniature horses and quarter horses in total body clearance, the terminal elimination rate, area under the plasma concentration versus time curve, apparent volume of distribution at steady‐state or the volume of the central compartment for flunixin (P > 0.05). Therefore, flunixin meglumine may be administered to miniature horses at the same dosage as is used in light‐breed horses.