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In 1980, 16 abortions or stillbirths occurred and 26 deformed calves were born in a beef herd of 115 Friesian cross Hereford cows mated to Charolais bulls. The deformities were principally arthrogryposes with contractures, particularly of the forelimbs, and various skull abnormalities. Following investigation it was considered highly unlikely that hereditary causes, infectious agents or a nutritional deficiency were responsible. The most likely cause was exposure to an unidentified teratogen early in pregnancy. 相似文献
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Söllner C Burghammer M Busch-Nentwich E Berger J Schwarz H Riekel C Nicolson T 《Science (New York, N.Y.)》2003,302(5643):282-286
The stone-like otoliths from the ears of teleost fishes are involved in balance and hearing and consist of calcium carbonate crystallites embedded in a protein framework. We report that a previously unknown gene, starmaker, is required in zebrafish for otolith morphogenesis. Reduction of starmaker activity by injection of modified antisense oligonucleotides causes a change in the crystal lattice structure and thus a change in otolith morphology. The expression pattern of starmaker, along with the presence of the protein on the growing otolith, suggest that the expression levels of starmaker control the shape of the otoliths. 相似文献
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Mobility and the restriction of mobility of plasma membrane lectin-binding components 总被引:13,自引:0,他引:13
Labeling by ferritin-conjugated agglutinins from Ricinus communis was used to demonstrate the relative mobilities of the agglutinin receptors located in specific regions on plasma membranes of rabbit spermatozoa. The relative mobility of lectin receptors was higher on postacrosomal regions of sperm than on acrosomal and tail regions. Lectin-induced clustering could not be demonstrated in the acrosomal and tail regions, an indication of the existence of localized restraints on the mobilities of lectin receptors. A system of transmembrane restraints may maintain the segregation of plasma membrane components into membrane domains on certain highly differentiated cells. 相似文献
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Ion leaching from a sugar maple forest in response to acidic deposition and nitrification 总被引:1,自引:0,他引:1
N. W. Foster P. W. Hazlett J. A. Nicolson I. K. Morrison 《Water, air, and soil pollution》1989,48(1-2):251-261
Year-to-year variation in acidic deposition within a mature sugar maple-dominated forest and in leaching of ions from the associated podzolic soil were examined at the Turkey Lakes Watershed between 1981 and 1986. Below-canopy inputs to the soil of SO4 2? and NO3 ? in throughfall averaged 640 and 295 eq. ha?1 yr?1; the corresponding ranges were 493–917 and 261–443 eq. ha?1 yr?1. The contribution of atmospheric deposition to SO4 2? NO3 ? and Ca2+ leaching decreased over the six years. During the study period, the mean annual volume-weighted NO3 ? concentration decreased in throughfall and forest-floor percolate and increased in the mineral-soil solution collected below the effective rooting zone. A substantial shift in the balance between SO4 2? and NO3 ?leaching from the mineral soil was observed; leaching of SO4 2?decreased and NO3 ? leaching increased with time. Leaching of Ca2+ and Mg2+ from the soil was increased as a result of excess NO3 ? production in the soil. The calculated output of NO3 ? from the soil, which averaged 1505 eq. ha?1 yr?1, considerably exceeded the atmospheric deposition of NO3 ?, whereas SO4 2? outputs were only moderately greater than inputs. 相似文献
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Barley stunt disorder in Scotland. 总被引:6,自引:5,他引:1
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