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11.
John Haddon 《BMJ (Clinical research ed.)》1911,1(2631):1349-1350
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An improved technique is described for the culture of explants from Helianthus tuberosus L. (Jerusalem artichoke). No xylem is formed when tuber discs are pre-cultured on a medium containing ßNAA, allowing uninfected discs to be selected for investigation of xylogenesis. Subsequent growth on a medium containing 0.45M 2,4-D and 9.3M kinetin stimulates a high proportion (up to 36%) of the cells to differentiate into xylem elements within a relatively short time (between 1 and 3 d after transfer). 相似文献
14.
The major regions of the inner ear begin to be distinguishable by their patterns of gene expression very early, before the otocyst has closed. Later, individual cells within a neurogenic or sensory patch become committed to specific pathways of differentiation. Insights gained from homologies with invertebrates and from studies of tissues other than the ear, combined with discoveries from screens for mutations affecting development in the zebrafish, are beginning to reveal the genes and signalling mechanisms that control these cell-fate choices in the developing inner ear. 相似文献
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Hyaluronan as a propellant for epithelial movement: the development of semicircular canals in the inner ear of Xenopus. 总被引:2,自引:0,他引:2
The membranous labyrinth of the inner ear, with its three semicircular canals, originates from a simple spheroidal otic vesicle. The process is easily observed in Xenopus. The vesicle develops three dorsal outpocketings; from the two opposite faces of each outpocketing pillars of tissue are protruded into the lumen; and these paired 'axial protrusions' eventually meet and fuse, to form a column of tissue spanning the lumen of the outpocketing like the hub of a wheel, with a tube of epithelium forming the semicircular canal around the periphery. Each axial protrusion consists of epithelium encasing a core of largely cell-free extracellular matrix that stains strongly with alcian blue. In sections, at least 60% of the stainable material is removed by treatment with Streptomyces hyaluronidase. When Streptomyces hyaluronidase is microinjected into the core of a protrusion in vivo, the protrusion collapses and the corresponding semicircular canal fails to form. Hyaluronan (hyaluronic acid) in the core of the protrusion therefore seems to be essential in driving the extension of the protrusion. Autoradiography with tritiated glucosamine indicates that the hyaluronan-rich matrix is synthesised by the epithelium covering the tip of the protrusion; the basal lamina here appears to be discontinuous. These findings indicate that the epithelium of the axial protrusion propels itself into the lumen of the otocyst by localised synthesis of hyaluronan. Hyaluronan may be used in a similar way in the development of other organs, such as the heart and the secondary palate. 相似文献
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Restriction-map variation associated with the G6PD polymorphism in natural populations of Drosophila melanogaster 总被引:10,自引:0,他引:10
Restriction-map variation was studied in 126 copies of the G6pd region in X
chromosome lines of Drosophila melanogaster from North America, Europe, and
Africa. Special attention was focused on the distribution of variation
relative to the geographically variable polymorphism for two
electrophoretic variants. Nucleotide heterozygosity as determined by eight
six-cutter restriction enzymes for the 13-kb region is estimated, on the
basis of the worldwide sample, to be 0.065%, which is the lowest value
reported for any comparable region in the D. melanogaster genome.
Significant linkage disequilibrium between electrophoretic alleles and
restriction-site variation is observed for several sites. In contrast to
published studies of other genetic regions, there are large insertions that
reach significant frequencies and are found across considerable geographic
distances. There is a clustering of this variation inside the first large
intervening sequence of the G6PD gene.
相似文献
19.
Nucleotide variation in the triosephosphate isomerase (Tpi) locus of Drosophila melanogaster and Drosophila simulans 总被引:3,自引:0,他引:3
Hasson E; Wang IN; Zeng LW; Kreitman M; Eanes WF 《Molecular biology and evolution》1998,15(6):756-769
DNA sequence variation in a 1.1-kb region including the coding portion of
the Tpi locus was examined in 25 homozygous third-chromosome lines of
Drosophila melanogaster, nine lines of Drosophila simulans, and one line of
Drosophila yakuba. Our data show that the widespread allozyme polymorphism
observed in cosmopolitan D. melanogaster is due to a glutamic acid
substitution occurring in a phylogenetically conserved lysine that has been
identified as part of the "hinged-lid" active site of the enzyme. This
observation suggests that the replacement polymorphism may have important
functional consequences. One replacement polymorphism was also observed in
D. simulans, although its functional relevance is more difficult to assess,
since it affects a site that is not strongly conserved. This amino acid
change in D. simulans is associated with a single lineage possessing seven
unique silent substitutions, which may be indicative of balancing selection
or population subdivision. The absence of fixed amino acid differences
between D. melanogaster and D. simulans and only a single difference with
D. yakuba suggests that triose phosphate isomerase is under strong
functional constraint. Silent variation is slightly higher for D.
melanogaster than for D. simulans. Finally, we outline the general lack of
evidence for old balanced polymorphisms at allozyme loci in D.
melanogaster.
相似文献
20.
Sander A Huisman Wendy Bijman-Lagcher Jan NM IJzermans Ron Smits Ron WF de Bruin 《Cell cycle (Georgetown, Tex.)》2015,14(14):2333-2339
Irinotecan is a widely used topoisomerase-I-inhibitor with a very narrow therapeutic window because of its severe toxicity. In the current study we have examined the effects of fasting prior to irinotecan treatment on toxicity and anti-tumor activity. FabplCre;Apc15lox/+ mice, which spontaneously develop intestinal tumors, of 27 weeks of age were randomized into 3-day fasted and ad libitum fed groups, followed by treatment with a flat-fixed high dose of irinotecan or vehicle. Side-effects were recorded until 11 days after the start of the experiment. Tumor size, and markers for cell-cycle activity, proliferation, angiogenesis, and senescence were measured. Fasted mice were protected against the side-effects of irinotecan treatment. Ad libitum fed mice developed visible signs of discomfort including weight loss, lower activity, ruffled coat, hunched-back posture, diarrhea, and leukopenia. Irinotecan reduced tumor size in fasted and ad libitum fed groups similarly compared to untreated controls (2.4 ± 0.67 mm and 2.4 ± 0.82 mm versus 3.0 ± 1.05 mm and 2.8 ± 1.08 mm respectively, P < 0.001). Immunohistochemical analysis showed reduced proliferation, a reduced number of vascular endothelial cells, and increased levels of senescence in tumors of both irinotecan treated groups. In conclusion, 3 days of fasting protects against the toxic side-effects of irinotecan in a clinically relevant mouse model of spontaneously developing colorectal cancer without affecting its anti-tumor activity. These results support fasting as a powerful way to improve treatment of colorectal carcinoma patients. 相似文献