Freeze-fracture replication of organized tissue without cryoprotection.
(1/576)
Fresh pieces of rat liver and pancreas were rapidly frozen without prior chemical fixation or cryoprotection, and replicated folloing freeze-fracture. Replicas revealed small peripheral areas free of ice crystals or damage and, within such areas, general ultrastructural morphology was essentially similar to that seen in conventionally processed material. On fracture faces of plasma and nuclear membranes a population of less prominent particles in addition to conventional membrane-associated particles was seen, and smooth areas devoid of particles of any type were seen on some nuclear membranes. These smooth areas did not appear to be similar to smooth areas allegedly arising as artifacts of conventional processing. Tight junctions and gap junctions appeared as they do in cryoprotected specimens. The results provide a base-line for assessing the possible effects of processing steps or agents on the ultrastructure of organized tissues as revealed in freeze-fracture replicas. (+info)
Vitrification of mouse germinal vesicle oocytes: effect of treatment temperature and egg yolk on chromatin and spindle normality and cumulus integrity.
(2/576)
The success rates for cryopreservation of immature oocytes from several species including human remain low, in contrast to major improvements with mature oocytes. In this study, a new approach has been developed using a short exposure ultra-rapid freezing protocol, examining the effect of temperature and egg yolk (two factors which may be expected to influence membrane flexibility) on the cryostability of immature mouse oocytes and cumulus complexes. These two factors were tested in various patterns for their cryoprotective effect using ethylene glycol as the principal cryoprotectant. The results showed that 37 degrees C pre- and post-freeze exposure significantly improved both survival and normal spindle configuration after in-vitro maturation. Egg yolk was found to produce further beneficial effects on both the oocyte and cumulus cell integrity, with the best effects being obtained at 37 degrees C with inclusion of egg yolk both before and after the freezing. This protocol produced > 80% normal survival post-thaw with intact and attached cumulus complex, 84% maturation rate and 45% normal metaphase configuration. In summary, a unique combination of high survival and meiotic normality together with good preservation of the attached cumulus cell mass has been achieved using a simple new vitrification procedure. (+info)
Effects of commonly used cryoprotectants on glycogen phosphorylase activity and structure.
(3/576)
The effects of a number of cryoprotectants on the kinetic and structural properties of glycogen phosphorylase b have been investigated. Kinetic studies showed that glycerol, one of the most commonly used cryoprotectants in X-ray crystallographic studies, is a competitive inhibitor with respect to substrate glucose-1-P with an apparent Ki value of 3.8% (v/v). Cryogenic experiments, with the enzyme, have shown that glycerol binds at the catalytic site and competes with glucose analogues that bind at the catalytic site, thus preventing the formation of complexes. This necessitated a change in the conditions for cryoprotection in crystallographic binding experiments with glycogen phosphorylase. It was found that 2-methyl-2,4-pentanediol (MPD), polyethylene glycols (PEGs) of various molecular weights, and dimethyl sulfoxide (DMSO) activated glycogen phosphorylase b to different extents, by stabilizing its most active conformation, while sucrose acted as a noncompetitive inhibitor and ethylene glycol as an uncompetitive inhibitor with respect to glucose-1-P. A parallel experimental investigation by X-ray crystallography showed that, at 100 K, both MPD and DMSO do not bind at the catalytic site, do not induce any significant conformational change on the enzyme molecule, and hence, are more suitable cryoprotectants than glycerol for binding studies with glycogen phosphorylase. (+info)
The cryopreservation protocol optimal for progenitor recovery is not optimal for preservation of marrow repopulating ability.
(4/576)
The efficiency of five different cryopreservation protocols (our original controlled-rate and noncontrolled-rate protocols) was evaluated on the basis of the recovery after thawing of very primitive pluripotent hemopoietic stem cells (MRA(CFU-GM), pluripotent progenitors (CFU-Sd12) and committed granulocyte-monocyte progenitors (CFU-GM) in mouse bone marrow. Although the nucleated cell recovery and viability determined immediately after the thawing and washing of the cells were found to be similar, whether controlled-rate or noncontrolled-rate cryopreservation protocols were used, the recovery of MRA(CFU-GM), CFU-Sd12 and CFU-GM varied depending on the type of protocol and the cryoprotector (DMSO) concentrations used. It was shown that the controlled-rate protocol was more efficient, enabling better MRA(CFU-GM), CFU-Sd12 and CFU-GM recovery from frozen samples. The most efficient was the controlled-rate protocol of cryopreservation designed to compensate for the release of fusion heat, which enabled a better survival of CFU-Sd12 and CFU-GM when combined with a lower (5%) DMSO concentration. On the contrary, a satisfactory survival rate of very primitive stem cells (MRA(CFU-GM)) was achieved only when 10% DMSO was included with a five-step protocol of cryopreservation. These results point to adequately used controlled-rate freezing as essential for a highly efficient cryopreservation of some of the categories of hematopoietic stem and progenitor cells. At the same time, it was obvious that a higher DMSO concentration was necessary for the cryopreservation of very primitive stem cells, but not, however, for more mature progenitor cells (CFU-S, CFU-GM). These results imply the existence of a mechanism that decreases the intracellular concentration of DMSO in primitive MRA cells, which is not the case for less primitive progenitors. (+info)
Differences in the width of the intercellular spaces in the epithelial basal infolding and the renal glomerular filtration site between freeze-substitution and conventional fixation.
(5/576)
After aldehyde prefixation, pretreatment with cryoprotectant and subsequent freeze-substitution with OsO4 in acetone (AC-FS), extensive gap junction-like close membrane appositions are frequently found in the basal infolding of the salivary gland epithelium, although the desmosomal intercellular space had the same width as with conventional electron microscopy. The intercellular space between podocyte pedicles and endothelial cells at the renal glomerular filtration site was narrower by the total width of 2 laminae lucidae following AC-FS than with conventional electron microscopy and was occupied by a homogeneous lamina densa without a lamina lucida, although no marked difference was discernable in the thickness of the lamina densa itself between the 2 preparative procedures. In addition, a decrease in the thickness of the glycocalyx was evident in the intestinal epithelial microvilli following AC-FS. It is thus likely that osmication in acetone at freezing temperatures remove the glycocalyx and related structures to a variable extent, and that this loss is responsible for reducing the intercellular spaces at some of the simple appositions narrower to the dimensions of the gap junction. It is also responsible for disappearance of the lamina lucida of the basement membrane. (+info)
Ooplasmic injections of rabbit round spermatid nuclei or intact round spermatids from fresh, cryopreserved and cryostored samples.
(6/576)
We compared the outcome of ooplasmic round spermatid nuclear injections (ROSNI) versus intact round spermatid injections (ROSI). Rabbit round spermatid nuclei and intact round spermatids were recovered and injected into rabbit oocytes (groups A and B, respectively). Fertilization, cleavage and embryonic development rates were compared. In additional studies, five protocols for cryopreservation of round spermatids and two protocols for cryostorage of round spermatids were applied. The outcome of ROSNI techniques using frozen-thawed or cryostored-warmed round spermatids was evaluated. The cleavage rate and the overall morula plus blastocyst development rate were significantly larger in group A than group B. ROSNI procedures are superior to ROSI techniques in the rabbit. The largest fertilization, cleavage and embryonic development rates after ROSNI techniques using cryopreserved or cryostored round spermatids were demonstrated in groups of round spermatids in which a mixture of seminal plasma plus test yolk buffer was employed as an extender, and dimethyl sulphoxide plus a high concentration of glycerol served as cryoprotectants. It appears that the seminal plasma contains factors protecting round spermatids during cryopreservation or cryostorage, and/or the employment of two cryoprotectants has a beneficial role in the maintenance of round spermatid reproductive capacity. (+info)
Effects of cryoprotectants and ice-seeding temperature on intracellular freezing and survival of human oocytes.
(7/576)
The accurate determination of the freezing conditions that promote intracellular ice formation (IIF) is crucial for designing cryopreservation protocols for cells. In this paper, the range of temperatures at which IIF occurs in human oocytes was determined. Fresh oocytes with a germinal vesicle, failed-to-fertilize (metaphase I and metaphase II stages) and polyspermic eggs were used for this study. The occurrence of IIF was first visualized at a cooling rate of 120 degrees C/min using a programmable thermal microscope stage connected to a videomicroscope. Then, with a cooling rate of 0.2 degrees C/min, the seeding temperature of the extracellular ice was modified to decrease the incidence of IIF and increase the survival rate of frozen-thawed human oocytes. After adding different cryoprotectants, the median temperature of IIF (TMED) was decreased by approximately 23 degrees C in mouse and only by approximately 6.5 degrees C in human oocytes. Using 1.5 M propylene glycol and seeding temperatures of -8.0, -6.0 and -4.5 degrees C, the incidence of IIF was 22/28 (78%), 8/24 (33%) and 0/33 (0%) and the 24 h post-thaw survival rate was 10/31(32%), 19/34 (56%) and 52/56 (93%) respectively. The results show that IIF occurs more readily in human oocytes, and that ice seeding between -6 degrees C and -8 degrees C triggers IIF in a large number of human oocytes. Undesirable IIF can be prevented and survival rates maximized by raising the seeding temperature as close as possible to the melting point of the solution, which in our instrument was -4.5 degrees C. (+info)
Subzero water permeability parameters of mouse spermatozoa in the presence of extracellular ice and cryoprotective agents.
(8/576)
Optimization of techniques for cryopreservation of mammalian sperm is limited by a lack of knowledge regarding water permeability characteristics during freezing in the presence of extracellular ice and cryoprotective agents (CPAs). Cryomicroscopy cannot be used to measure dehydration during freezing in mammalian sperm because they are highly nonspherical and their small dimensions are at the limits of light microscopic resolution. Using a new shape-independent differential scanning calorimeter (DSC) technique, volumetric shrinkage during freezing of ICR mouse epididymal sperm cell suspensions was obtained at cooling rates of 5 and 20 degrees C/min in the presence of extracellular ice and CPAs. Using previously published data, the mouse sperm cell was modeled as a cylinder (122-microm long, radius 0.46 microm) with an osmotically inactive cell volume (V(b)) of 0.61V(o), where V(o) is the isotonic cell volume. By fitting a model of water transport to the experimentally obtained volumetric shrinkage data, the best-fit membrane permeability parameters (L(pg) and E(Lp)) were determined. The "combined best-fit" membrane permeability parameters at 5 and 20 degrees C/min for mouse sperm cells in solution are as follows: in D-PBS: L(pg) = 1.7 x 10(-15) m(3)/Ns (0.01 microm/min-atm) and E(Lp) = 94.1 kJ/mole (22.5 kcal/mole) (R(2) = 0.94); in "low" CPA media (consisting of 1% glycerol, 6% raffinose, and 15% egg yolk in D-PBS): L(pg)[cpa] = 1.7 x 10(-15) m(3)/Ns (0.01 microm/min-atm) and E(Lp)[cpa] = 122.2 kJ/mole (29.2 kcal/mole) (R(2) = 0.98); and in "high" CPA media (consisting of 4% glycerol, 16% raffinose, and 15% egg yolk in D-PBS): L(pg)[cpa] = 0.68 x 10(-15) m(3)/Ns (0.004 microm/min-atm) and E(Lp)[cpa] = 63.6 kJ/mole (15.2 kcal/mole) (R(2) = 0.99). These parameters are significantly different than previously published parameters for mammalian sperm obtained at suprazero temperatures and at subzero temperatures in the absence of extracellular ice. The parameters obtained in this study also suggest that damaging intracellular ice formation (IIF) could occur in mouse sperm cells at cooling rates as low as 25-45 degrees C/min, depending on the concentrations of the CPAs. This may help to explain the discrepancy between the empirically determined optimal cryopreservation cooling rates, 10-40 degrees C/min, and the numerically predicted optimal cooling rates, greater than 5000 degrees C/min, obtained using suprazero mouse sperm permeability parameters that do not account for the presence of extracellular ice. As an independent test of this prediction, the percentages of viable and motile sperm cells were obtained after freezing at two different cooling rates ("slow" or 5 degrees C/min; "fast," or 20 degrees C/min) in both the low and high CPA media. The greatest sperm motility and viability was found with the low CPA media under fast (20 degrees C/min) cooling conditions. (+info)