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At least 73 records · Page 4Linked to original sources
PubMed2000

Nitinol stone retrieval-assisted ureteroscopic management of lower pole renal calculi.

OBJECTIVES: Current ureteroscopic intracorporeal lithotripsy devices and stone retrieval technology allow for the treatment of calculi located throughout the intrarenal collecting system. Difficulty accessing lower pole calculi, especially when the holmium laser fiber is used, is often encountered. We retrospectively reviewed our experience with cases in which lower pole renal calculi were ureteroscopically managed by holmium laser fragmentation, either in situ or by first displacing the stone into a less dependent position with the aid of a nitinol stone retrieval device. METHODS: Thirty-four patients (36 renal units) underwent ureteroscopic treatment of lower pole renal calculi between April 1998 and November 1999. Lower pole stones less than 20 mm were primarily treated by ureteroscopic means in patients who were obese, in patients who had a bleeding diathesis, in patients with stones resistant to shock wave lithotripsy, and in patients with complicated intrarenal anatomy, or as a salvage procedure after failed shock wave lithotripsy. Lower pole calculi were fragmented with a 200-micrometer holmium laser fiber by way of a 7.5F flexible ureteroscope. For those patients in whom the laser fiber reduced the ureteroscopic deflection, precluding re-entry into the lower pole calix, a 3.2F nitinol basket or a 2.6F nitinol grasper was used to displace the lower pole calculus into a more favorable position, allowing easier fragmentation. RESULTS: In 26 renal units, routine in situ holmium laser fragmentation was successfully performed. In the remaining 10 renal units, a nitinol device was passed into the lower pole, through the ureteroscope, for stone displacement. Only a minimal loss of deflection was seen. Irrigation was significantly reduced by the 3.2F nitinol basket, but improved with the use of the 2.6F nitinol grasper. This factor did not impede stone retrieval in any of the patients. At 3 months, 85% of patients were stone free by intravenous urography or computed tomography. CONCLUSIONS: Ureteroscopic management of lower pole calculi is a reasonable alternative to shock wave lithotripsy or percutaneous nephrolithotomy in patients with low-volume stone disease. If the stone cannot be fragmented in situ, nitinol basket or grasper retrieval, through a fully deflected ureteroscope, allows one to reposition the stone into a less dependent position, thus facilitating stone fragmentation.

Adult↗
PubMed2001

Performance of a shaking vessel with current pole.

To improve solid particle suspensions in liquids in a shaking vessel, a pole was installed at the axis of the shaking vessel, which was referred to as the "current pole". The performance of a shaking vessel with current pole at its central axis was examined experimentally with respect to particle dispersion, power consumption, mixing time and solid-liquid mass transfer coefficient. The current pole improved the particle suspension without an increase in power consumption and reduced the critical circulating frequency for complete suspension. The current pole was very effective in eliminating the stagnation point on the vessel bottom and to decrease the mixing time. The mass transfer coefficient with a current pole had the same value as that without a current pole above the critical circulating frequency for complete suspension. As the diameter of the current pole increased, the mixing time decreased. A pole diameter of 5% of the vessel diameter was effective for suspension.

Journal Article↗
PubMed2000

The pole-pressure test: an easy alternative in patients with ischemic legs and incompressible arteries.

BACKGROUND: Systolic ankle artery pressure measured classically by cuff-manometry and Doppler ultrasound in patients with severely ischemic legs may be falsely elevated because of impaired compressibility of the arteries. We evaluated a hydrostatic blood pressure or so-called pole pressure test by correlating the ankle artery pressure as well as tcpO2 with the pole pressure. PATIENTS AND METHODS: We enrolled 29 patients (18 male, 11 female, 10 diabetics) with critical leg ischaemia. The pole pressure was obtained by elevating the leg, and measuring the height at which the Doppler signal disappears by means of a calibrated pole (recalculating cm H2O for mmHg). We used an 8 MHz cw-Doppler device. Only pole pressure values up to 70 cm H2O were included. In addition tcpO2 at 45 degrees C was recorded at the forefoot of the same leg. RESULTS: When we included the values of the ten diabetic patients the pole pressure of 57.9 +/- 16.2 mmHg (mean +/- SD) was significantly lower by 40.7 mmHg than the ankle pressure of 98. +/- 38.4 mmHg, p < 0.0001 (paired t-test). Without the diabetics the difference was 33.7 mmHg. The correlation coefficient between pole pressure and ankle pressure was 0.546 including the patients with diabetes, and 0.609 excluding the diabetics. The correlation of tcpO2 with the pole pressure, however, was 0.624 regardless of the inclusion of diabetics, while that between tcpO2 and ankle pressure was only 0.250. CONCLUSIONS: The pole pressure test is an easy, inexpensive and fast method providing a meaningful, quantitative measure independent of the compressibility of the arteries.

Aged↗
PubMed1994

Ventilatory response pattern of Nordic skiers during simulated poling.

Cross-country ski poling is a distinctive exercise imposed by biomechanical motion which may influence the breathing pattern. To examine the ventilatory patterns of competitive cross-country skiers, the pulmonary function of nine male master level skiers was studied during simulated bilateral synchronous and asynchronous arm poling and upright leg cycling. Physiological and ventilatory responses during arm and leg exercise were compared on a Biokinetic arm ergometer and Monark bicycle. At similar levels of oxygen consumption, minute ventilation (VE) was lower for leg cycling than for the arm exercise modes. Heart rate was significantly higher (P < 0.05) during bilateral synchronous poling than for either bilateral asynchronous poling or leg cycling. Leg cycling elicited a higher tidal volume (VT) than either of the arm poling modes (1.8 vs 1.7 and 1.6 l). Breathing frequency (fR) was significantly higher (P < 0.05) for both arm exercise modes when compared to leg cycling (41 and 42 vs 27 breaths min-1). Frequency of strokes per breath (fS/fR) was significantly higher (P < 0.01) while cycling compared to synchronous arm work. The mean ratio of fS/fR per minute was 1.1:1 and 1.7:1 for arm exercise and leg cycling, respectively. Bilateral synchronous arm poling invoked a similar VE, lower VT and higher fR than bilateral asynchronous poling or leg cycling. These results demonstrate that ventilatory responses to arm poling are different from those to upright cycle exercise. There was a greater reliance during poling upon fR to maintain VE.

Arm↗
PubMed2005

Spindle pole organization in Drosophila S2 cells by dynein, abnormal spindle protein (Asp), and KLP10A.

Dynein is a critical mitotic motor whose inhibition causes defects in spindle pole organization and separation, chromosome congression or segregation, and anaphase spindle elongation, but results differ in different systems. We evaluated the functions of the dynein-dynactin complex by using RNA interference (RNAi)-mediated depletion of distinct subunits in Drosophila S2 cells. We observed a striking detachment of centrosomes from spindles, an increase in spindle length, and a loss of spindle pole focus. RNAi depletion of Ncd, another minus-end motor, produced disorganized spindles consisting of multiple disconnected mini-spindles, a different phenotype consistent with distinct pathways of spindle pole organization. Two candidate dynein-dependent spindle pole organizers also were investigated. RNAi depletion of the abnormal spindle protein, Asp, which localizes to focused poles of control spindles, produced a severe loss of spindle pole focus, whereas depletion of the pole-associated microtubule depolymerase KLP10A increased spindle microtubule density. Depletion of either protein produced long spindles. After RNAi depletion of dynein-dynactin, we observed subtle but significant mislocalization of KLP10A and Asp, suggesting that dynein-dynactin, Asp, and KLP10A have complex interdependent functions in spindle pole focusing and centrosome attachment. These results extend recent findings from Xenopus extracts to Drosophila cultured cells and suggest that common pathways contribute to spindle pole organization and length determination.

Animals↗
PubMed2002

Temporal pole hypometabolism may be linked to a reduction of grey matter in temporal lobe epilepsy.

In order to gain further insight into the pathophysiology of temporal pole hypometabolism, we decided to perform a voxel-based automated analysis of structural MRI in epileptic patients with or without temporal pole hypometabolism. After fully automated segmentation of cerebral grey matter from structural T1-weighted MRI scans, we applied the automated technique of statistical parametric mapping (SPM) to the analysis of grey matter of nine control subjects, and 18 patients with right medial temporal lobe epilepsy with (n = 13) or without (n = 5) significant temporal pole hypometabolism. Group comparisons between subject controls and epileptic patients with temporal pole hypometabolism showed a reduction of grey matter located into the superior part of the right temporal pole, the right hippocampus and the left parahippocampal gyrus. Epileptic patients without temporal pole hypometabolism did not exhibit temporal pole grey matter abnormalities. These findings suggest that a reduction of temporal pole neocortical grey matter might contribute to temporal pole hypometabolism in temporal lobe epilepsy.

Adult↗
PubMed1997

Evidence for cell cycle-specific, spindle pole body-mediated, nuclear positioning in the fission yeast Schizosaccharomyces pombe.

Specific changes in spatial order occur during cell cycle progression in fission yeast. Growth of the rod-shaped cells is highly regulated and undergoes a cell cycle and size-regulated switch from monopolar to bipolar tip extension. During both phases of growth, the interphase nucleus is maintained in a central location. Following the separation of the genome to the cell tips in mitosis, the two nuclei migrate back towards the cell equator before stopping in two new positions that will become the middle of the two new cells. Here we use simultaneous labeling of microtubules, chromatin and spindle pole bodies in wild-type and cdc mutants, to show that nuclear positioning is achieved by regulation of spindle pole body-mediated nuclear migration. We show that the number and location of nuclear positioning signals is regulated in a cell cycle-specific manner and that spindle pole body-mediated forces are likely to be responsible for maintaining correct nuclear position once the nuclei have reached the appropriate position in the cell. Accentuating the movement of the nuclei back towards the cell equator after mitosis by artificially increasing cell length shows that the spindle pole body leads the nucleus during this migration. When multiple spindle pole bodies are associated with the same or different nuclei they all go to the same point indicating that the different spindle pole bodies are responding to the same positional cue. In a septation-defective mutant cell, which contains four nuclei, the spindle pole bodies on the four different nuclei initially group as two pairs in regions that would become the middle of the new cells, were the cell able to divide. In the subsequent interphase, the nuclei aggregate as a group of four in the centre of the cell. The presence of two or three clusters of spindle pole bodies in larger cells with eight nuclei suggests that the mechanisms specifying the normally central location for multiple nuclei may be unable to operate properly as the cells get larger. Perturbation of microtubules with the microtubule poison thiabendazole prevents the spindle pole body clustering in septation mutants, demonstrating that nuclear positioning requires a functional microtubule cytoskeleton.

Anaphase↗
PubMed1983

Use of separate hand locations to calculate ground reaction force exerted on a vaulting pole.

A model was developed to permit calculation of the force exerted by the ground on a vaulting pole given the flexibility characteristics of the pole, the grip height of the upper hand, and the coordinates of each of the two hands relative to the base of the pole. The flexural rigidity of the pole was assumed constant throughout the length of the pole and not subject to hysteresis or dynamic loading effects. The model was based on the following rationale: knowing the initial angle of the base of the pole (beta 0) and the force vector (F1) exerted by the ground on the pole, it was possible to estimate the shape of the pole and the coordinates of the two hands following an iterative procedure. Conversely, it was possible to find a combination of beta 0 and F1 that made the pole fit two specified hand locations.

Biomechanical Phenomena↗
PubMed2001

Impact of lower pole renal anatomy on stone clearance after shock wave lithotripsy: fact or fiction?

PURPOSE: We determined whether there is a significant relationship between the spatial anatomy of the lower pole on preoperative excretory urography and stone fragment clearance after shock wave lithotripsy. MATERIALS AND METHODS: The anatomical factors affecting lower pole stone clearance after shock wave lithotripsy were evaluated retrospectively in 108 patients. Stone-free status was assessed by renal computerized tomography with or without renal ultrasound. The stone-free rate at 3 months was correlated with lower pole infundibular length and width in mm. as well as with the lower pole infundibulopelvic angle in degrees. The statistical significance of each lower pole anatomical factor as well as other stone, renal and treatment factors were correlated with the stone-free rate using the Mann-Whitney and chi-square tests. RESULTS: Three months after shock wave lithotripsy 79 patients (73.1%) were free of stones. Mean lower infundibular length plus or minus standard deviation was 20.9 +/- 6.56 mm., mean infundibular width was 5.65 +/- 2.34 mm. and the mean lower pole infundibulopelvic angle was 48.33 +/- 14.84 degrees. In 49 (45.4%) and 59 (54.6%) patients infundibular length was greater than 3 cm. and 3 cm. or less, respectively. Infundibular width was greater than 5 mm. and 5 mm. or less in 45 (41.7%) and 63 (58.3%) patients, respectively. No obtuse infundibulopelvic angles were noted. None of the 3 lower pole anatomical factors had any significant impact on the stone-free rate at 3 months. Renal morphology was the only factor significantly affecting the stone-free rate since stone clearance was significantly less in pyelonephritic kidneys (p = 0.0009). CONCLUSIONS: Differences in the intrarenal anatomy of the lower pole have no significant impact on stone clearance after shock wave lithotripsy. Further examination of the lower pole renal anatomy with a search for other contributing factors is still warranted.

Adolescent↗
PubMed1998

Tuft-to-capsule adhesions and their precursors: differences between the vascular and tubular poles of the human glomerulus.

Human glomerular capillary tufts were removed by microdissection and scanning electron microscopy was used to examine the surface of the capillary tuft and the interior of its Bowman's capsule in order to identify connections between the tuft and capsule. Glomeruli were examined in histologically normal renal cortex from 12 kidneys removed for tumour and 12 renal allografts removed for end-stage rejection. In normal kidney, the glomerular tuft was connected to Bowman's capsule by single podocytes and their processes. At the vascular pole, these were predominantly associated with parietal podocytes which lined Bowman's capsule. At the tubular pole, occasional podocytic processes derived from the capillary tuft bridged Bowman's space and connected to Bowman's capsule where there were no parietal podocytes. These podocytic connections were also found in all rejected transplants, but in addition adhesions were identified which consisted of thicker connections between the tuft and capsule. At the vascular pole, tuft-to-capsule adhesions were found in all 12 kidneys; these were always associated with parietal podocytes. Tubular pole adhesions were identified in ten of the 12 transplants. They were associated with abnormal squamous cells, but not with parietal podocytes. When the capillary tuft herniated into the proximal tubule, the tuft sometimes formed an adhesion with the origin of the proximal tubule. These observations suggest that podocyte connections between the glomerular tuft and Bowman's capsule may be precursors of glomerular adhesions at the vascular pole. Since tuft-to-capsule adhesions at the vascular pole differ morphologically from those at the tubular pole, this may reflect different pathogenetic mechanisms at the opposite poles of the glomerulus.

Chronic Disease↗
PubMed1994

Mitochondrially encoded 16S large ribosomal RNA is concentrated in the posterior polar plasm of early Drosophila embryos but is not required for pole cell formation.

In a molecular screen for polar-localized RNAs in Drosophila, we identified the mitochondrially encoded 16S large ribosomal RNA (16S RNA) as an RNA that is highly concentrated at the posterior pole of early embryos. This high posterior accumulation decreases sharply during the first hour of embryogenesis and reaches the uniform level found throughout the remainder of the embryo by the time pole cells form 1.5 hr after fertilization. At the cellular blastoderm stage the 16S RNA is uniformly distributed basal to the nuclei of all somatic cells and is present only at low levels in the pole cells and in the apical regions of the somatic cells. Transcripts produced by the 12S small rRNA gene are also concentrated in the posterior polar plasm and exhibit the same dynamic changes in distribution as the 16S RNA. In contrast, NADH dehydrogenase subunit 1 RNA, which is transcribed from the same strand of the mitochondrial genome just downstream of the 12S and 16S genes, does not exhibit a high posterior concentration but is uniformly distributed throughout early embryos. Posterior localization of 16S RNA is normal in embryos produced by mothers carrying mutations which affect posterior patterning without disrupting the polar plasm or polar granule integrity. However, posterior localization of 16S RNA is abolished in embryos produced by females carrying maternal-effect mutations that disrupt the posterior polar plasm and the polar granules. Ectopic localization of the oskar RNA to the anterior pole of the oocyte and early embryo results in anterior assembly of polar plasm and anterior budding of functional pole cells. We show that 16S and 12S RNAs are not concentrated at the anterior pole of such embryos. This leads to the conclusion that, although the 16S and 12S RNAs are concentrated in the posterior polar plasm during normal development, functional pole cells can form in the absence of high levels of these RNAs. These data argue against previous hypotheses that the 16S RNA serves an obligatory function in pole cell formation.

Animals↗
PubMed2006

Management of lower pole renal calculi: shock wave lithotripsy versus percutaneous nephrolithotomy versus flexible ureteroscopy.

Current ureteroscopic intracorporeal lithotripsy devices and stone retrieval technology allow for the treatment of calculi located throughout the intra-renal collecting system. Difficulty accessing lower pole calculi, especially when the holmium laser fiber is utilized, is often encountered. Herein we review our experience where lower pole renal calculi were ureteroscopically managed by holmium laser fragmentation, either in situ, or by first displacing the stone into a less dependent position with the aid of a nitinol stone retrieval device. Lower pole stones less than 20 mm can be primarily treated by ureteroscopic means in patients: that are obese; have a bleeding diathesis; with stones resistant to shockwave lithotripsy (SWL); with complicated intra-renal anatomy; or as a salvage procedure after failed SWL. Lower pole calculi are fragmented with a 200 microm holmium laser fiber via a 7.5 F flexible ureteroscope. For those patients where the laser fiber reduced ureteroscopic deflection, precluding re-entry into the lower pole calyx, a 1.9 F nitinol basket is used to displace the lower pole calculus into a more favorable position, thus allowing for easier fragmentation. A nitinol device passed into the lower pole, through the ureteroscope, for stone displacement cause only a minimal loss of deflection and no significant impact on irrigation. Eighty-five percent of patients were stone free by IVP or CT scan performed at 3 months. Ureteroscopic management of lower pole calculi is a reasonable alternative to SWL or percutaneous nephrolithotomy (PNL) in patients with low volume stone disease. If the stone cannot be fragmented in situ, nitinol basket or grasper retrieval, through a fully deflected ureteroscope, allows for repositioning of the stone into a less dependant position, thus facilitating stone fragmentation.

Adolescent↗
PubMed2004

"Tear-drop augmentation mastopexy": a technique to augment superior pole hollow.

Breast ptosis classification systems focus on the inferior descent of the nipple, as well as the descent and distribution of the breast parenchyma below the inframammary fold. Common problems, such as development of a superior pole hollow and an excessive width of the superior pole, extending into the axilla, are not addressed. Few procedures specifically address these deficiencies, and even less information is available in terms of preventative maneuvers when augmentation is desired as an adjunct. Round implants worsen the problem by creating a superior pole shelf, and anatomic implants are unreliable alternatives. Here, we present a technique-"tear-drop" augmentation mastopexy-that addresses superior pole hollow, excess superior pole width, as well as breast ptosis and hypomastia. Patients with moderate to severe breast ptosis (Regnault's classification), tubular breast deformity, and deformities secondary to previous breast surgery are included in the study. Skin is deepithelialized through a circumareolar incision, and a skin-fat flap is elevated completely encircling the breast. A 2-cm area of parenchyma is left attached to the skin in the lower half of the breast. Breast parenchyma in the superior half of the breast is then advanced and plicated in a superiomedial direction to move the nipple areolar complex to the desired new position. Care is taken to redefine the pectoralis major muscle at its axillary border. A 3-cm incision is then placed in the inferior part of the parenchyma at the 6 o'clock position to create a subpectoral pocket for placement of the implant. The tunnel is then closed to separate the implant pocket from the subcutaneous dissection. Residual dermal flap is used to define, and add durability to the parenchyma reshaping procedure. A 3-0 mersiline (Ethicon, Somerville, NJ) blocking suture is used for a uniform circumareolar skin closure. Patients (n:35), ages 17-48, underwent "tear-drop" augmentation mastopexy between January 1999 and September 2002 for correction of the breast ptosis, tubular breast deformity, and deformities secondary to previous aesthetic breast surgery. The average follow-up was 2 years. All patients displayed type 1 or 2 (Baker classification) capsules. One subcutaneous hematoma and one subcutaneous seroma were seen, which were both treated by percutaneous aspiration. No submuscular hematomas, infections, skin or nipple losses, or hypertrophic scars were noted. Patient satisfaction was high. A more natural "tear-drop" breast shape was created with an improvement in the superior pole hollow and narrowing of the superior breast. The smallest breasts did not benefit from this technique for elimination of the superior pole shelf, as correction was proportional to the amount of breast tissue available for superior advancement. The "tear-drop" augmentation mastopexy is a novel technique for correction of the breast ptosis with augmentation, avoiding problematic development of superior pole hollow and excess superior width. This technique is also well applied to tubular breast deformity as well as to secondary breast procedures. Long-term follow-up demonstrates a safe and reproducible result with high patient satisfaction. This technique may solve several problems associated with breast ptosis surgery, which before were not specifically addressed, and the technique warrants further investigation.

Adolescent↗
PubMed1989

Electron microscopic studies on primary mesenchyme cell ingression and gastrulation in relation to vegetal pole cell behavior in sea urchin embryos.

Early morphogenetic events of primary mesenchyme cell (PMC) ingression and gastrulation were examined by scanning and transmission electron microscopy, with special attention directed to changes in the shape of vegetal pole cells, the length of their microvilli, and interactions between microvilli and the hyaline layer (HL). Eight cells (vegetal pole cells) with elongated microvilli remained in the vegetal pole region while surrounding cells ingressed into the blastocoel to form the primary mesenchyme. These vegetal pole cells indented with the surrounding cells at the stage of gastrulation. The outer surface area with elongated microvilli of vegetal pole cells expanded at the stage of PMC ingression, but was considerably reduced at gastrulation. Microvilli on vegetal pole cells continued to adhere to the HL up to the stage of PMC ingression, but ceased to do so at the time of gastrulation. Thus, the area with separated HL, which is restricted to the region of the PMC released at the stage of PMC ingression, spreads almost entirely throughout the area of the indenting vegetal plate at gastrulation. The apical lamina, apparently consisting of fibrous material intertwinning the stalks of the microvilli, filled the space between the HL and ectodermal cells. The cells surrounding those of the vegetal pole and indenting with those at the stage of gastrulation appeared to behave in the same way as ingressing PMCs in both cell-shape and loss of adhesion of microvilli to HL. The role of vegetal pole cells in early morphogenetic events is discussed.

Animals↗
PubMed2006

The G-protein regulatory (GPR) motif-containing Leu-Gly-Asn-enriched protein (LGN) and Gialpha3 influence cortical positioning of the mitotic spindle poles at metaphase in symmetrically dividing mammalian cells.

We addressed the role of the G-protein regulatory (GPR) motif-containing Leu-Gly-Asn-enriched protein (LGN) and G-proteins (Gialpha3) in the positioning of the spindle pole during mammalian cell division. Immunocytochemistry indicated that both LGN and Gialpha3 co-localized at the spindle pole and at the midbody and the cell cortex during the different phases of mitosis. In marked contrast to the positioning of the spindle pole at metaphase midway between the cell cortex and the metaphase plate, the spindle pole was juxtaposed with the cell cortex at metaphase following increased expression of Gialpha3 and LGN. This repositioning of the spindle pole required the interaction of LGN with Gialpha. The influence of LGN and Gialpha3 on the cortical positioning of the spindle pole likely reflects either stronger pulling forces on the spindle pole exerted from the cell cortex or increased pushing forces exerted on the spindle pole from the mitotic spindle indicating that these events are regulated by GPR motif-containing proteins and G-proteins independent of asymmetry.

Amino Acid Motifs↗
PubMed1991

Effects of technique and pole grip on physiological demands of roller skiing on level terrain.

This study evaluated the physiological responses to roller skiing with three different techniques, and compared the physiological responses during roller skiing with a standard pole grip and an innovative "anatomical" pole grip. Data were collected on ten experienced cross-country ski racers while roller skiing with the double pole, V1 skate, and kick double pole techniques on a flat track at mean (+/- SD) velocities of 14.6 +/- 0.2, 16.4 +/- 0.3, and 18.0 +/- 0.4 km.h-1. The kick double pole technique induced the highest (p less than 0.05) oxygen uptakes, heart rates, and ventilations. The double pole technique elicited the lowest (p less than 0.05) oxygen uptakes, and the V1 skate technique elicited the lowest (p less than 0.05) perceived effort and respiratory exchange ratios. Comparison of the two pole grips showed no differences in the physiological responses and perceived effort. While the V1 skate technique is not the most economical roller skiing technique on flat ground, the lower associated perceived effort and respiratory exchange ratios may at least partially account for the general preference of cross-country ski racers to use the V1 skating technique rather than the double pole technique on flat terrain.

Adult↗
PubMed1981

Cooperation of kinetochores and pole in the establishment of monopolar mitotic apparatus.

Monopolar mitotic apparatus can be produced in sea urchin eggs by a manoeuvre that distributes the four poles of the second mitosis into four separate blastomeres. The pole of the monopolar mitotic apparatus generates a half-spindle that is similar in structural details to the half-spindle of a normal bipolar mitotic apparatus, although the chromosomes are not as well aligned as in a normal metaphase plate. The chromosomes are oriented; one kinetochore faces the pole while its sister kinetochore faces away from the pole. The poleward kinetochore is connected to the pole by bundles of microtubules. No microtubules are seen on the sister kinetochore that faces away from the pole. Therefore, a single pole can direct most of the events in the establishment of a mitotic apparatus. Our interpretation examines the cooperation of kinetochores and poles in the formation of microtubules between them, stressing the half-spindle as the medium of cooperation and leaving open the question whether the kinetochores are origins or terminations of microtubules.

Animals↗
PubMed1982

Induction of pole cells in sterilized Drosophila embryos by injection of subcellular fraction from eggs.

A subcellular fraction isolated from a homogenate of young Drosophila embryos was shown to be capable of inducing pole cells when injected into UV-sterilized Drosophila embryos. Most of the pole cell-inducing activity was recovered from the precipitate after centrifugation at 27,000 x g. The activity remained in this precipitate (called F-3 fraction hereafter) even after membranous structures were removed from it through centrifugation on a sucrose density gradient. Dialysis, lyophilization, and heating at 80 degrees C for 10 min did not inactivate the F-3 fraction. The pole cells, which were produced when the F-3 fraction was injected at the posterior pole of UV-sterilized embryos, did not develop into germ cells. Furthermore, the F-3 fraction was unable to induce pole cells when injected into the anterior region of the egg. These results can be explained by assuming that (i) pole cell formation and germ cell determination are controlled by different factors, (ii) pole cell formation requires at least two factors, which are normally localized in the posterior-pole cytoplasm, one of which is sensitive and one resistant to the UV dosage we used, and (iii) the subcellular fraction we obtained contains the UV-sensitive factor but not the UV-resistant factor.

Journal Article↗