PATTERNS OF MITOSIS AND DIFFERENTIATION IN CELLS DERIVED FROM PEA ROOT PROTOPLASTS

Mitotic figures of diploid, tetraploid, octaploid and 16-ploid nuclei were observed in cultures of pea root protoplasts whose initial DNA content was apparently 2C and 4C. The distribution of these mitotic figures in the different ploidy levels paralleled the distribution of mitotic figures in the culture of intact root explants and may be related to the hormonal stimulation of mitoses in these cultures. The patterns of the time course of both DNA synthesis and cell division in the protoplast cultures were similar to such patterns observed in the culture of intact root explants, although longer lag periods were observed in the protoplast cultures. Mitotic abnormalities including both chromosome breakage and spindle disfunction were observed in protoplast cultures. A large portion of the cell pairs derived from mitoses (27 % in one experiment) contained Feulgen-positive micronuclei. An accumulation of an as yet unidentified differentiation product termed dense cytoplasmic protoplast derivative was observed. Some of the conditions influencing the development of these derivatives are reported.     

CELL DIVISION IN RELATION TO CYTODIFFERENTIATION IN CULTURED PEA ROOT SEGMENTS

One mm-thick segments cut 10–11 mm proximal to the root tip of germinating seeds of garden pea Pisum sativum were cultured in sterile nutrient medium containing auxin in the presence and absence of kinetin. In the absence of added cytokinin, pericyclic proliferation occurred, the cortical tissues showed no proliferation and were sloughed off, and a callus tissue of diploid cells was formed. In the presence of kinetin concentrations from 0.1–1.0 ppm cortical cells of the segments were induced to divide, beginning at the third day. From experiments with ³H-thymidine incorporation at different times of culture, from cytological squash preparations and from histological sections it was shown that the cortical cells stimulated to divide by cytokinin underwent DNA synthesis prior to division, were polyploid, and following cell division rapidly underwent cytodifferentiation at 5–7 days to form mature tracheary elements. At 10 days, when over 300,000 new cells had been formed per segment about 16% of these cells had formed tracheary elements. It was concluded that cytokinin, together with auxin, was essential for the initiation of DNA synthesis in the cortical cells, for their subsequent division, and finally for their specific cytodifferentiation.     

CELL POPULATION KINETICS IN CALLUS TISSUES OF CULTURED PEA ROOT SEGMENTS

Two callus tissues, one composed of diploid and the other of a mixture of diploid and polyploid cells, were derived by culturing 1-mm pea root segments; the mixed callus tissues were obtained by incorporation of kinetin in the culture medium. The callus tissues were used to determine (a) if cell proliferation was altered with the change in cell constituents of a callus; (b) the rate at which polyploid cells increased after kinetin stimulation; (c) the nature of the mitotic cycle in the diploid and mixed polyploid callus tissues; and (d) if the mitotic cycle changed as the tissue aged. Histological, cytological, radioisotope, and radioautographic analyses were made on callus tissue ranging from 1 to 4 days old. The results indicated that gross morphological changes were associated with the anatomical location of the proliferative cells. They showed that the percentage of polyploid division figures after stimulation by kinetin increased rapidly during the first 6 to 7 days in culture and then continued to increase at a much reduced rate. Cell counts revealed that cell proliferation in the mixed callus tissue was initially delayed when compared with the diploid tissue, but that after the delay was overcome cell number increased in each in similar manner. Analysis of the number of DNA-synthesizing cells showed that their percentage was highest during the first 2 days of culture and then leveled off at a value of about 10%. Mitotic cycle analysis indicated that it could be accurately measured only in the younger diploid callus tissues and that it increased in variability with increased age.     

THE DISTRIBUTION OF SPINDLE MICROTUBULES DURING MITOSIS IN CULTURED HUMAN CELLS

WI-38 and HeLa cells in mitosis have been selected from fixed monolayer cultures and serially sectioned for electron microscopy. Sections perpendicular to the spindle axis permit counting of the number of microtubules at each position on the spindle axis and hence the preparation of tubule distribution profiles. Errors intrinsic to this method are discussed. The changes in the tubule distributions from one mitotic stage to another provide evidence concerning the behavior of the spindle tubules during mitosis. The ratio of the number of tubules passing the chromosomes on the metaphase plate to the maximum number in each half spindle is about 1/2. This ratio changes little in early anaphase, and then decreases in late anaphase at about the same time that a zone of increased tubule number develops at the middle of the interzone. The region where the stem bodies form contains about 3/2 the number of tubules seen elsewhere in the interzone. This ratio is almost constant as the mid-body forms in telophase and then increases to 2/1 in early interphase before the final stages of cytokinesis occur.     

大脑皮质神经干细胞定向分化为神经元过程中Tau蛋白表达的研究

目的探讨Tau蛋白在新生大鼠大脑皮质神经干细胞定向分化为神经元过程中的表达及意义.方法采用细胞培养、免疫细胞化学方法(SABC法)观察及计算机图像分析技术测定Tau蛋白在神经干细胞定向分化为神经元过程中不同时段的表达情况.结果在神经干细胞定向分化为神经元的过程中,Tau蛋白由核周淡染分布渐至在胞体与突起中密集均匀分布,随着突起伸展而不断地延伸,并且Tau蛋白的表达量逐渐增加.结论新生大鼠大脑皮质神经干细胞定向分化为神经元过程中,Tau蛋白的时空表达与神经干细胞定向分化的神经元形态变化有一定的相关性并在此过程中发挥着重要的作用.     

PINOCYTOSIS IN ROOT CAP CELLS EXPOSED TO URANYL SALTS

In cap cells of intact plant roots exposed to 1mM uranyl for 30 min or less, uranyl crystals were found only in cell walls and in secretory products which had been extruded from the protoplast. In roots exposed for 10–20 hr to 0.1mm uranyl, packets of uranyl crystals bound to secretory products were found within the protoplasts of those exterior cells which contained accumulations of secretory products between the cell wall and protoplast. Although the evidence indicated that these packets of crystals entered the protoplast pinocytotically, results with these specialized exterior cells did not apply to the vast majority of root cap cells in which, after prolonged exposure to 0.1mm uranyl, crystals were concentrated in vacuoles. In roots exposed to 1 or 5mm uranyl for 1 hr, the plasmalemma of interior cap cells was much thicker (13.1 nm) than normal (8.2 nm), and many invaginations and vesicular structures were found near the protoplast surface. Crystals were confined to cell walls except for a few found in vesicles with thickened membranes. Serial sections indicated that most vesicular structures with thickened membranes were in contact with the cell wall, but a few, including some which contained uranyl crystals, were within the protoplast. These results provide evidence of pinocytotic activity in intact plant cells exposed to a toxic heavy metal.     

除草通对玉米幼苗根尖细胞有丝分裂的影响

本文研究了除草通对玉米幼苗初生不定根根尖细胞有丝分裂的影响。结果表明,除草通是一种影响细胞有丝分裂的除草剂,其作用方式在于阻止分生组织细胞从前期向中、后、末期的过渡,引起染色体凝集、短缩以及多核、多核仁等一系列畸形与异常变化。     

镉离子对蚕豆根尖细胞分裂的影响

蚕豆根尖经不同浓度(0.1—10.0ppm)的CdCl_2溶液处理24～48小时后,根的生长受到不同程度的抑制.对根尖细胞分裂的毒害则表现为低毒的C-有丝分裂和高毒的染色体断裂、粘连和液化.此外,对Cd~( )的毒害机理进行了简略讨论.     

胚胎大鼠背根神经节细胞的分离培养、纯化及生物学特性的研究

本实验取E15 SD胎鼠的背根神经节,用胰蛋白酶消化分离成单细胞,在NBl培养基中培养,并通过差速贴壁法进行背根神经节神经元(DRGn)的分离纯化,用神经元特异性的烯醇化酶(NSE)鉴定培养的神经元。结果发现DRGn在体外合适条件下可存活3-4周,DRGn纯化培养的纯度达91％左右。DRGn在体外能存活较长时间,可作为神经科学研究的细胞模型。     

DNA SYNTHESIS AND MITOSIS IN ERYTHROPOIETIC CELLS

Studies of newt (Triturus or Diemictylus viridescens) erythropoietic cells showed that DNA synthesis and mitosis normally occur throughout most of the developmental process. Mitotic divisions were found in all immature precursor stages from the proerythroblast to the highly hemoglobinized reticulocyte. Mitoses were absent in mature erythrocytes. Radioautographic examination of thymidine-³H incorporation into DNA revealed that all erythroid cells except the mature erythrocyte were labeled. Microphotometric measurements of Feulgen-stained smears showed that all immature stages were undergoing DNA synthesis whereas the mature erythrocyte was inactive. The results obtained from three independent methods clearly demonstrate that (a) no loss of DNA or of chromosomes occurs during erythrocytic development and (b) highly hemoglobinized and, therefore, well-differentiated cells normally do undergo DNA synthesis and mitosis.     

不同生长底物对培养背根神经节细胞的影响(简报)

发育期细胞和细胞外基质(extracellular matrix,ECM)之间的相互作用调节着细胞的功能,包括细胞的迁移、细胞骨架的构建、细胞的增值和分化。神经元“移居”体外后,失去了在体内所依托的组织学关系,必须黏附于一个固相表面才能生存,所以神经元只有在包被基质的培养器皿上才能存活,对于分离的神经元来说,能否尽快粘附到生长基质上是影响神经元体外存活的因素之一。许多研究证明     

CELL CYCLE KINETICS OF ENDOREDUPLICATION IN GAMMA-IRRADIATED ROOT MERISTEMS OF PISUM SATIVUM

Label and mitotic indices and microspectrophotometry of unlabeled interphase cells were used to measure the proportion of root meristem cells of Pisum sativum in each cell cycle stage after exposure to protracted gamma irradiation. Three seedling types were investigated: 1) intact seedlings, 2) seedlings with cotyledons detached and treated with lanolin paste applied to the area of cotyledon excision, and 3) seedlings with detached cotyledons and treated with a G2 Factor applied to the area of cotyledon excision in lanolin paste. In intact seedling meristems, predominant cell arrest occurred with a 4C amount of DNA while 0.30 of the cells underwent endoreduplication to arrest with an 8C amount of DNA. Only 0.07 cells arrested with a 2C amount of DNA. Polyploid cells were produced several days after the start of irradiation and were derived from a diploid cell population. In seedlings exposed to lanolin only, without cotyledons, most cells arrested with a 2C amount of DNA with no polyploid cells. In seedlings exposed to a G2 Factor in lanolin after cotyledon excision, most cells arrested with a 4C amount of DNA but no cells underwent endoreduplication. These experimental results suggest that the G2 Factor derived from cotyledons of Pisum sativum was necessary for predominant cell arrest in G2 but alone was not sufficient for the polyploidization step.     

离体培养小鼠神经细胞在有丝分裂过程中的膜电位变化(简报)

细胞分裂是个体生长和生命延续的基础,而且它还是理解肿瘤发生机制所不可缺少的理论基础,因此关于控制细胞有丝分裂基本机制的研究是很有意义的,受到广泛的重视。Grandin等证明了在胚胎细胞分裂时细胞内pH和钙离子都有相应的变化,虽然他们也同时记录了膜电位的变化,但未作详细的分析,而且上述研究都是在两栖类动物的卵母细胞上进行的,至今尚未见有关哺乳动物神经细胞在有丝分裂过程中膜电位变化的报道。     

鱼类培养细胞干扰素的诱导

对紫外线灭活的草鱼出血病病毒（ＧＣＨＶ）－Ｆ９株,在几种鲤科鱼类培养细胞中诱导产生干扰素的能力及影响干扰素产量的各因素进行了研究。纯化的ＧＣＨＶ在紫外线照射５分丧失感染性,但获得了在ＣＡＢ等５种鲤科鱼类培养细胞中高铲诱导产生干扰素的能力。干扰素的诱导需要病毒高复数感染细胞。干扰素主要在诱导后１４小时时内产生。培养上清中的新生牛血清对干扰素的产量有抑制作用。而在ＰＨ６．２－７．８范围内对干扰素产量无     

PERSISTENCE OF MESSENGER RNA THROUGH MITOSIS IN HELA CELLS

The decrease in protein synthesis which occurs in mammalian cells during cell division is associated with significant disaggregation of polyribosomes. For determining whether messenger RNA survives this disaggregation, the reformation of polyribosomes was investigated in synchronized HeLa cells as they progressed from metaphase into interphase in the presence of 2 µg/ml Actinomycin D. The persistence of messenger during cell division was evidenced by: (1) a progressive increase in the rate of protein synthesis in both treated and untreated cells for 45 min after metaphase; (2) reformation of polyribosomes, as determined by both sucrose gradients and electron microscopy, within 30 min after the addition of Actinomycin D to metaphase cells; (3) the persistence of approximately 50% of the rapidly labeled nonribosomal RNA which had associated with polyribosomes just before metaphase; (4) the resumption of synthesis, following cell division, of 6 selected peptides in Actinomycin-treated cells.