Distribution Of Cell Division Research Articles

Observations on the embryonic development of the mud crab, Scylla paramamosain

To investigate the embryonic development of the mud crab Scylla paramamosain, we analyzed three critical parameters: egg color of, embryo morphology (through conventional and laser scanning confocal microscopy), and the distribution of cell divisions. During embryonic development, the egg color exhibited a progressive transition, shifting from orange to reddish-orange, then to brown, before ultimately darkening to black. Each embryo displayed a spherical shape, measuring approximately 280 μm in diameter, characterized by a smooth surface devoid of any depressions. The embryonic cell division was in the form of mixed oogenesis, comprised of complete division in the early stage, spiral oogenesis in the middle stage and surface division in the late stage. It is noteworthy that the blastopore appeared at the position where the transparent area and cell aggregation just appeared under the microscope, and the blastomere was a characteristic of the embryo entering the gastrulation stage. After entering the gastrulation stage, the cells aggregated towards the blastopore and formed two symmetrical cell clusters, which formed a V-shape with the void of the classic blastopore. When the transparent region occupied approximately 1/5 of the embryo’s volume, the embryo entered the nauplius stage, and the thoracic and abdominal armor, as well as the optic lobe and abdominal limb primordia, could be clearly distinguished. The appearance of the compound eye pigment band indicated the stage of compound eye pigment formation. At this time, the transparent area accounted for 1/4 of the embryo and a large number of ganglia appeared. The change of the compound eye pigment band from red to black was also one of the reasons for the blackening of the egg color of the crabs. The data obtained through this study have potential applications in the determination of embryonic development status and obtaining of high-quality seeds for S. paramamosain culture.

Quantitative proliferation dynamics and random chromosome segregation of hair follicle stem cells

Regulation of stem cell (SC) proliferation is central to tissue homoeostasis, injury repair, and cancer development. Accumulation of replication errors in SCs is limited by either infrequent division and/or by chromosome sorting to retain preferentially the oldest 'immortal' DNA strand. The frequency of SC divisions and the chromosome-sorting phenomenon are difficult to examine accurately with existing methods. To address this question, we developed a strategy to count divisions of hair follicle (HF) SCs over time, and provide the first quantitative proliferation history of a tissue SC during its normal homoeostasis. We uncovered an unexpectedly high cellular turnover in the SC compartment in one round of activation. Our study provides quantitative data in support of the long-standing infrequent SC division model, and shows that HF SCs do not retain the older DNA strands or sort their chromosome. This new ability to count divisions in vivo has relevance for obtaining basic knowledge of tissue kinetics.

Cellular basis of developmental plasticity observed in heterophyllous leaf formation of Ludwigia arcuata (Onagraceae)

When heterophyllous plants of Ludwigia arcuata Walt. (Onagraceae) were transferred from aerial condition to submergence, young developing leaves were matured into leaves with intermediate shape between aerial-type and submerged-type, showing spatulate shape (spoon-shaped). This change was also induced by the exposure of plants to ethylene. On the other hand, when the plants were transferred from submergence to aerial conditions, young developing leaves were matured into intermediate-type leaves with elliptic shape (spearhead shape). Anatomical analysis revealed that the formation of spatulate leaf was caused by the reduction of the number of epidermal cells aligned in the leaf transverse direction in the basal region of the leaf while the tip regions remained as before and did not respond to this treatment. During development, the ethylene-induced spatulate leaves showed that three types of alterations in epidermal cell division were involved in this process. Changes in the distribution of cell divisions in leaf lamina were detected by the first day of ethylene exposure, and changes in the orientation of cell division planes were detected by the second day. However, changes in the number of cells aligned in the leaf transverse direction were not detected by this time. Three days after ethylene exposure, frequency of cell divisions changed, and by the time changes of cell numbers aligned in the leaf transverse direction were observed. Thus, the formation of intermediate-type leaves in L. arcuata was ascribed to the alterations of cell division patterns which was induced by ethylene.

Histochemical analysis of root meristem activity in Arabidopsis thaliana using a cyclin:GUS (β-glucuronidase) marker line.

We used a transgenic Arabidopsis line expressing a translational fusion between a mitotic cyclin and the reporter gene β-glucuronidase (GUS) to investigate cell divisions in postembryonic root meristems. The fusion protein contains the cyclin destruction box (CDB) and this leads to a rapid degradation of the chimeric GUS-protein after mitosis. Hence, the staining pattern of the meristem marks dividing cells. We observed that upon germination the first cell divisions occur in epidermis cells at the junction with the hypocotyl. Moreover, the accelerated root growth on media supplemented with sucrose correlates with an increased number of dividing cells and an enlargement of the root meristematic zone. The conditional root expansion mutants pom pom1 and procuste1 (quill) suppress this sugar effect leading to a smaller meristematic zone. Simultaneous visualisation of the nucleus revealed that the CYCAT1:CDB:GUS expression is subcellularly localised around the nucleus. This particular staining starts at prophase and disappears after the completion of the new cell wall. In metaphase the staining invades the cytoplasm whereas in the telophase it concentrates again around the nucleus. This cell cycle-dependent distribution was used to characterise the two root specific cytokinesis mutants pleiade1 and hyade1. In both mutants, cells which fail to develop a complete cell wall during cytokinesis divide synchronously in further cell divisions leading to multinucleate cells. These experiments demonstrate the usefulness of the CYCAT1:CDB:GUS marker line for studying cell division of wild-type and mutants. Furthermore, this line can be used to analyse the influence of biotic and abiotic signals on the rate and spatial distribution of cell divisions.

Induction and development of somatic embryos from spinach (Spinacia oleracea) leaf segments

Somatic embryogenesis was induced in embryogenic calli of Spinacia oleracea L., on a Murashige and Skoog (1962) medium, containing 4.6 μM kinetin as the sole growth regulator. Abscisic acid, gibberellic acid, and indole-3-acetic acid were supplemented to kinetin-containing medium and their effects on the initiation of somatic embryos was studied. Abscisic acid at a particular concentration (4 μM) dramatically increased the number of embryos per g fresh weight of callus, while both gibberellic acid and indole-3-acetic acid suppressed the embryo initiation. It is suggested that the promoting effect of abscisic acid on the embryo initiation may be explained as a stress response of the tissue. The relative number of globular embryos vs. the embryos in heart/torpedo and cotyledonary stages was increased at 4 μM abscisic acid and at all gibberellic acid concentrations (0.3–10 μM). In contrast, the ratio of globular to polar embryos was lower than in controls at 1 μM abscisic acid and indole-3-acetic acid (1 and 10 μM). The effects of growth regulators on the ratio of globular to polar embryos indicate that they interfere with the normal distribution of cell division and cell expansion during early embryogenesis.

Temperature Affects Expansion Rate of Maize Leaves without Change in Spatial Distribution of Cell Length (Analysis of the Coordination between Cell Division and Cell Expansion).

We have analyzed the way in which temperature affects leaf elongation rate of maize (Zea mays L.) leaves, while spatial distributions (observed at a given time) of cell length and of proportion of cells in DNA replication are unaffected. We have evaluated, in six growth chamber experiments with constant temperatures (from 13 to 34[deg]C) and two field experiments with fluctuating temperatures, (a) the spatial distributions of cell length and of leaf elongation rate, and (b) the distribution of cell division, either by using the continuity equation or by flow cytometry. Leaf elongation rate was closely related to meristem temperature, with a common relationship in the field and in the growth chamber. Cell division and cell elongation occurred in the first 20 and 60 mm after the ligule, respectively, at all temperatures. Similar quantitative responses to temperature were observed for local cell division and local tissue expansion rates (common x intercept and normalized slope), and both responses were spatially uniform over the whole expanding zone (common time courses in thermal time). As a consequence, faster cell elongation matched faster cell division rate and faster elongation was compensated for by faster cell displacement, resulting in temperature-invariant profiles of cell length and of proportion of dividing cells. Cell-to-cell communication, therefore, was not necessary to account for coordination.

THE DEVELOPMENTAL BASIS OF ANISOPHYLLY IN SELAGINELLA MARTENSII. II. HISTOGENESIS

The anisophyllous shoots of Selaginella martensii are characterized by opposite pairs of dorsal and ventral leaves which differ in size and form. This paper documents the processes of histogenesis for each leaf type and shows that both leaf types show a strong basipetal gradient of tissue maturation as indicated by cell size, distribution of cell division, cell vacuolation, intercellular space formation and stomatal differentiation. These processes are complete at an earlier stage of development in dorsal leaves (P7–8) than for ventral leaves (P12, 13). Measurement of cell number in the uppermost dermal layer indicate that cell divisions occur at a greater rate during ventral leaf development and observations of mitotic figures indicate that cell division occurs over a slightly longer time period in ventral leaves (through P6) as compared with dorsal leaves (through P5). While the morphological and histological differences that occur between the mature ventral and dorsal leaves begin to appear at or shortly after leaf inception, the general pattern of histogenesis of both types of leaf is similar. Histologically the dorsal leaf is primarily distinguished by a precocious maturation of tissues.

Distribution of cell divisions in the optic vesicle and presumptive ectoderm of chick embryos

It has been shown that dividing cells are arranged in nests in the optic vesicle and the presumptive ectoderm in the period of contact between the two in a 48-hour-old chick embyro. The degree of this arrangement in the optic vesicle and ectoderm is variable: in the optic vesicle there are 29.4% of isolated mitoses and 25.9% of paired mitoses. The number of dividing cells per nest in the ocular rudiment is up to seven. In the ectoderm isolated mitoses account for 72.7%, paired ones −18.3%. The number of mitoses per nest does not exceed four. The number of isolated mitoses and various combinations of conjugate mitoses varies during a day.

CELL DEVELOPMENT DURING EARLY EMBRYOGENESIS IN CAPSELLA AND GOSSYPIUM

The early stages of embryo development in Gossypium hirsutum (cotton) and Capsella bursapastoris were examined with regard to patterns of cell development, embryo and cell size, and distribution of cell divisions. A striking reduction in the total size of the cotton embryo was observed following the first division of the embryo. This decrease in total embryo size continued for several more divisions, and it was not until the embryo contained approximately 75 cells that its total size was larger than the zygote. Distinctive patterns of cell divisions were found in both embryos and indicate that changes in groups of cells undergoing mitosis are of fundamental importance in understanding the development of form in the embryo. A greater degree of variation in development of cell lineages than is generally reported was observed in both embryos.

Cell Development During Early Embryogenesis in Capsella and Gossypium

The early stages of embryo development in Gossypium hirsutum (cotton) and Capsella bursapastoris were examined with regard to patterns of cell development, embryo and cell size, and distribution of cell divisions. A striking reduction in the total size of the cotton embryo was observed following the first division of the embryo. This decrease in total embryo size continued for several more divisions, and it was not until the embryo contained approximately 75 cells that its total size was larger than the zygote. Distinctive patterns of cell divisions were found in both embryos and indicate that changes in groups of cells undergoing mitosis are of fundamental importance in understanding the development of form in the embryo. A greater degree of variation in development of cell lineages than is generally reported was observed in both embryos.

Some morphological, anatomical, and physiological changes in the pear fruit (Pyrus communis var. Williams Bon Chrétien) during development and following harvest

Morphological, anatomical, and physiological changes occurring in the developing fruit of Pyrus communis var. Williams Bon Chretien were studied at frequent intervals, from blossom until after commercial maturity, in three successive seasons. Morphological changes were shown by increase in measurements of volume, long and short axis, and the width of the cortex (flesh), the morphology of the fruit being interpreted by the receptacular theory, Anatomical changes were given by the duration and distribution of cell division, differentiation of tissues, cell size, and cell number. Physiological changes were expressed as changes in fresh weight, dry weight, and moisture content for the whole fruit, and separately for the flesh, peel, and core in the second and third seasons. Total and reducing sugars, starch, titratable acidity, and total and protein nitrogen were estimated per gram of dried flesh at each sampling. Respiration rates for whole fruit were measured by the Pettenkofer method. Physiological changes could not be expressed on a per cell basis because of the complex structure of pear tissue. Data presented on the basis of the number of days from blossom showed two distinct stages in fruit growth. Stage I, the first 42-56 days of development, corresponded to the main cell division period and was characterized by more rapid morphological but slower physiological changes (except for increase in protein nitrogen) than Stage 11, the remainder of the time on the tree. Comparable trends were found in the three seasons, but drought reduced growth rate in the first season. Some ripening changes were followed on removal from the tree and after periods of cold storage at 0°C.

The distribution of mitoses and cells in the tissues bounded by the socket wall of the rabbit mandibular incisor

The distribution of cell division has been the subject of a study of the continuous production of dental pulp and of the special cell layers directly concerned with the formation of the hard dental tissues, which underlies the extrusion of the rodent incisor. From two young and two adult rabbits, five axial microscopic sections of each mandibular incisor were selected and stained with haematoxylin. Before death, the left incisor of each animal had been made to erupt rapidly by being cut out of occlusion with its opponents. In each section the outlines of the tooth and socket and the positions of mitoses were measured. Cell populations were estimated in the special cell layers, basal 3 mm of the pulp, and intermediate layer of the lingual periodontal tissues. Young animals differed mainly from older in showing more mitoses on or near the socket walls. Rapidly erupting incisors showed 1-4 times more mitoses than their norm ally erupting fellows, having erupted 1-9 times faster during the period of measurement. The proportion of prophase and metaphase to later stages of mitosis was greatest in the enamel organ, least in the periodontal tissues. Mitoses were found in the internal enamel epithelium , stratum intermedium and stellate reticulum of the enamel organ, none further coronally than 700 µ from the base. The greatest concentrations of pulpal mitoses were found opposite the regions of proliferation of the internal epithelia of the enamel and cement organs. Of all pulpal mitoses, 65 % were found in the basal millimetre—coronal to this the axial distribution showed a sharp decline, but individuals were found up to 10 mm from the base; 16 % were in the walls of blood vessels. In the basal millimetre of the pulp few cell divisions occurred in the centre, many at the periphery: such disparity did not appear coronal to this. The pulps of rapidly erupting incisors were depleted of cells at the base : the basal centre—poor in mitoses— apparently contributes cells to pulpal growth, its cell density being maintained, presumably, by migration from the periphery. An explanation of the distribution of mitoses has been sought, by comparison with connective tissue orientation, in the tensions produced by eruptive movement. Mitoses were found the length of the intermediate layer of the periodontal tissues, with a distribution across the lingual periodontal membrane showing a sharp peak at about 20 µ from the cement surface. This distribution may be related to the processes whereby the incisor is permitted to erupt and yet is anchored to its socket.