High-resolution HKG-banding in maize mitotic chromosomes

Root-tip maize chromosomes (2n=20) were prepared by high-resolution procedures after ethidium bromide/colchicine synchronization. Using HKG-banding (HCl−KOH-Giemsa), that shows both centromeric and intercalary heterochromatin, the banding pattern of the elongated-chromosomes showed one to nine well-resolved dark bands. Differences of HKG-banding pattern of elongated and compacted chromosomes were performed by image analysis.     

Microdissection of plant chromosomes by argon-ion laser beam

Summary Rice and barley chromosomal samples were prepared both on a polyester membrane and on an ordinary glass slide and subjected to microdissection by an argon-ion laser. The intensity and the position of the laser beam were controlled by a microcomputer. The most suitable intensity to obtain chromosomal fragments was determined experimentally. As a result, specific regions of the centromere, satellite, short arm, or long arm, of the barley and rice chromosomes were dissected out from the chromosomal spreads. Chromosomal fragments were also successfully transferred from the sample into an Eppendorf tube.     

两种鼠耳蝠的核型、G带和C带研究

使用肺、心脏等组织进行培养,用空气干燥法制作染色体标本,以胰酶法制作G带,BSG法制作c带,分析了贵州2种鼠耳蝠的核型、G带和c带.水鼠耳蝠Myotis daubentoni和小鼠耳蝠Myotis dividii的染色体数均为2n=44,拥有3对大型和1对中型中着丝粒染色体,染色体臂数(FN)=52;这2种鼠耳蝠的G带...     

Mapping of repeated DNA sequences in plant chromosomes by PRINS and C-PRINS

 The primed in situ DNA labelling (PRINS) procedure was optimised for the rapid physical mapping of several types of repetitive DNA sequences on the mitotic chromosomes of Vicia faba, Pisum sativum and Secale cereale. A localization of the highly repeated FokI sequence on V. faba chromosomes was achieved after a 7-min total reaction time. In addition, we report a procedure for direct cycling-PRINS (C-PRINS), a variation of PRINS which involves a sequence of thermal cycles analogous to the polymerase chain reaction. Compared to PRINS, C-PRINS was more sensitive. Further work is needed to improve the sensitivity of the reaction to allow for the reliable detection of low-copy DNA sequences. Received: 17 September 1996 / Accepted: 18 October 1996     

Elasticity measurements show the existence of thin rigid cores inside mitotic chromosomes

Chromosome condensation is one of the most critical steps during cell division. However, the structure of condensed mitotic chromosomes is poorly understood. In this paper we describe a new approach based on elasticity measurements for studying the structure of in vitro assembled mitotic chromosomes in Xenopus egg extract. The approach is based on a unique combination of measurements of both longitudinal deformability and bending rigidity of whole chromosomes. By using specially designed micropipettes, the chromosome force-extension curve was determined. Analysis of the curvature fluctuation spectrum allowed for the measurement of chromosome bending ridigity. The relationship between the values of these two parameters is very specific: the measured chromosome flexibility was found to be 2,000 times lower than the flexibility calculated from the experimentally determined Young modulus. This requires the chromosome structure to be formed of one or a few thin rigid elastic axes surrounded by a soft envelope. The properties of these axes are well-described by models developed for the elasticity of titin-like molecules. Additionally, the deformability of in vitro assembled chromosomes was found to be very similar to that of native somatic chromosomes, thus demonstrating the existence of an essentially identical structure.     

Why incongruous knee replacements do not fail early

Rapid failure of knee prostheses does not usually occur, despite the non-conforming nature of the articulation between femoral and tibial components and the associated large contact pressures. This theoretical study examines the likelihood of fatigue fracture of a layered elastic model loaded by a sliding cylindrical indenter. Cracks (line-defects) were assumed to have nucleated within the layer. The stress intensity factors (SIFs) associated with these cracks were calculated. The values obtained for the SIFs are quite low, with a corresponding low likelihood of crack-growth. When taken in conjunction with the experimentally derived fatigue laws of previous investigators, they suggest that short line-cracks should not grow. It seems that early failures have not simply been due to large shear stresses which occur beneath the prosthesis surface. Other factors, such as the degradation of material through heat-pressing, sterilisation or oxidation, or the deleterious effect of fusion defects, may be required to drive the cracks to delamination.     

Why acetylcholinesterase reactivators do not work in butyrylcholinesterase

The pyridinium oxime therapy for treatment of organophosphate poisoning is a well established, but not sufficient method. Recent trends also focus on prophylaxis as a way of preventing even the entrance of organophosphates into the nervous system. One of the possible prophylactic methods is increasing the concentration of butyrylcholinesterase in the blood with the simultaneous administration of butyrylcholinesterase reactivators, when the enzyme is continuously reactivated by oxime. This article summarizes and sets forth the structural differences between butyrylcholinesterase and acetylcholinesterase, essential for the future design of butyrylcholinesterase reactivators. Butyrylcholinesterase lacks the reactivator aromatic binding pocket found in acetylcholinesterase, which is itself a part of the acetylcholinesterase peripheral anionic site. This difference finally renders the current acetylcholinesterase reactivators, when used in butyrylcholinesterase, non-functional.     

Uptake of isolated plant chromosomes by plant protoplasts

For mass isolation of plant metaphase chromosomes, cultured cells of wheat (Triticum monococcum) and parsley (Petroselinum hortense) were synchronized by hydroxyurea and colchicine treatment. This synchronization procedure resulted in high mitotic synchrony, especially in suspension cultures of parsley in which 80% of the cells were found to be at the metaphase stage. Mitotic protoplasts isolated from these synchronized cell cultures served as a source for isolation of chromosomes. The described isolation and purification method yielded relatively pure chromosome suspension. The uptake of the isolated plant chromosomes into recipient wheat, parsley, and maize protoplasts was induced by polyethylene-glycol treatment. Cytological studies provided evidences for uptake of plant chromosomes into plant protoplasts.Abbreviations PEG polyethylene glycol - HU hydroxyruea - C colchicine - HUC hydroxyurea and colchicine - CIM chromosome isolation medium - TCM Tris chromosome medium     

C-banded wheat chromosomes in wheat and triticale

Summary The C-banding patterns of wheat chromosomes in 7 hexaploid triticale and 7 wheat genotypes are described and compared. All 14 wheat chromosome pairs were individually identified in the triticales and a tetraploid wheat, and all the B and two A genome chromosome pairs in the hexaploid wheat genotypes. Little variation was found between genotypes in the distribution of C-bands but considerable variation was found in their size, total number and total length.     

In situ fluorescent nick translation procedure for plant chromosomes

Pectinase and cellulase, which are used to macerate plant material, always show traces of DNase activities that result in DNA nicking. Moreover, the DNA polymerase I usually applied in the in situ nick translation techniques shows both 5' to 3' and 3' to 5' exonuclease activities. As a result, significant nonspecific labeling appears in control preparations that are not digested by a restriction endonuclease. Our procedure includes blocking nonspecific nick labeling before incubation with restriction enzymes (HpaII and HaeIII). This is achieved by incorporation of ddGTP into DNA by the Taq polymerase which lacks 3' to 5' exonuclease activity. This method gives satisfactory results because it eliminates nonspecific nick translation signals that are present after applying the methods described for animal material.     

Structural variation in the heterochromatin of rye chromosomes in triticales

Summary Although Giemsa C-banding techniques have been used extensively for assaying cereal heterochromatin, a more specific technique for analyzing cereal heterochromatin has been developed recently with the isolation of DNA sequences present in heterochromatin and their employment in in situ hybridization to cereal chromosomes. A number of triticales were examined for the occurrence of modified rye chromosomes using the in situ hybridization technique. With a heterogeneous sequence probe the amount of rye heterochromatin appears to be relatively constant in wheat backgrounds but when a specific sequence probe was employed variation was observed. Whether this variation reflects polymorphism in rye or whether it is a result of adaption of the rye genome to coexistence with the wheat genome in triticales is discussed. — The triticale Rosner was examined in detail and it was established that the rye chromosome 2R had been replaced by the wheat chromosome 2D.     

Why brown-headed cowbirds do not influence red-winged blackbird parent behaviour

Brown-headed cowbirds, Molothrus ater, frequently parasitize red-winged blackbirds,Agelaius phoeniceus . The presence of a brood parasite, unrelated to both host nestlings and parents, has provoked speculation regarding within-brood food allocation and parental provisioning. This study is the first to compare directly the effect of brood parasitism on host parent and offspring behaviour in younger and older broods. We videotaped 28 unparasitized red-winged blackbird broods and compared them to 22 parasitized broods. Red-winged blackbird nestling begging appears largely unaffected by cowbird parasitism. The presence of the cowbird in the nest affected neither the latency nor duration of host nestling begging, but stimulated more frequent begging by red-winged blackbird nestlings following food distribution. Begging by cowbirds was unique in two ways: (1) cowbirds maintained a consistent begging effort throughout the nestling period (but did not receive a consistent food share); and (2) cowbirds begged longer and more frequently following the allocation of food. Persistent begging by the cowbird following the allocation of food has implications for the division of parental care, if by doing so the brood parasite is able to provoke the foster parent to increase provisioning, at the expense of brooding. We found no evidence for the adjustment of parental care. Neither the foraging rates nor the lengths of the parental feeding visits differed markedly between parasitized and unparasitized broods. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.