bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ultrastructure of primary mesenchyme cell ingression in the sea urchin Lytechinus pictus
Authors: Katow Hideki , Solursh Michael 
Published: June 2005

AbstractThe ultrastructural changes associated with primary mesenchyme cell formation in the sea urchin Lytechinus pictus were studied by transmission (TEM) and scanning electron microscopy (SEM). Early during ingression, one can recognize about 30 presumptive primary mesenchyme cells, which form a ring around eight central cells, located at the apex of the vegetal pole. The first steps involve the loss of the basal lamina in the vegetal plate region and the loss of cilia from the 30 presumptive primary mesenchyme cells. These cells then elongate into bottle‐shaped cells which have a bulbous, appendage‐free basal end that protrudes into the blastocoel, and a thin neck region that forms numerous apical cell processes. Longitudinally oriented microtubules are observed in the peripheral cytoplasm in the neck region of the bottle‐shaped cells and in the adjacent cytoplasm of closely adherent neighboring non‐mesenchymal blastomeres. After the disappearance of apical junctions, the neck regions of the bottle‐shaped cells shorten, resulting in the transposition of the cells into the blastocoel as rounded primary mesenchyme. Mesenchyme cell displacement results in the temporary formation of fenestrae in the blastular wall, which are filled in by apical cell processes that extend from neighboring blastomeres. These morphological changes have several features in common with other examples of cells which exit from epithelia and are consistent with a morphological sequence involving the relaxation of the basal cytoplasm of the presumptive primary mesenchyme cells, followed by their active elongation and lateral compression by adjacent cells.
Regeneration in larvae and juveniles of the mud crab, Rhithropanopeus harrisii
Authors: McConaugha John R. , Costlow John D. 
Published: June 2005

AbstractBoth the megalopa and juvenile stages of the mud crab Rhithropanopeus harrisii were shown to have regenerative abilities following limb autotomy. The number of individual crabs initiating regeneration was directly dependent on the number of limbs autotomized and the stage of the molt cycle when autotomy occurred. The number of individuals undergoing regeneration and the proportion of the molt cycle when regeneration could be induced increased in later stages. Regeneration was associated with a significant delay in the molt cycle, while non‐regenerating individuals displayed a trend toward an accelerated molt cycle. The duration of the delay was independent of the number of limbs lost. It is hypothesized that this delay is due to an inhibition of ecdysone synthesis. This results in resetting the molt cycle to the intermolt or premolt stage.
The internal clock of reaggregating embryonic sea urchin cells
Authors: Spiegel Evelyn , Spiegel Melvin 
Published: June 2005

AbstractThe presence of micromere “a clock” during early cleavage in sea urchin embryos has been shown by several investigators. The suggestion that an internal clock may be operative in later developmental stages up to the pluteus is presented in this study.The development of reaggregating Arbacia cells was followed from dissociation at the 16‐cell stage to pluteus formation, using scanning electron microscopy. After 7 hr of development, the reaggregates were dissociated a second time and were again able to develop into plutei. The morphological development of both reaggregations appears to be identical. In addition, embryos of both reaggregations developed at the same rate as control embryos. Differences in the cells of the first and second dissociations as compared to controls are described, as is the ability of reaggregating cells to catch up to controls during early development. Possible reasons for their ability to make up for lost time are discussed, including non‐randomness of cell behavior, lack of dedifferentiation and the presence of an internal clock.
Regulation of expression of the ribosomal RNA cistrons in Ilyanassa embryos: Nucleolus‐like bodies and nucleologenesis
Authors: Naus Christian G. , Kidder Gerald M. 
Published: June 2005

AbstractIn embryos of the gastropod, Ilyanassa obsoleta, ribosomal RNA (rRNA) synthesis first becomes detectable using sucrose gradients at the end of cleavage (by 24 hours post trefoil at 19°C; the trefoil stage is characterized by maximal extension of the third polar lobe, in association with first cleavage). The nuclei of early embryos, however, contain several prominent nucleolus‐like bodies (NLBs) from the 2‐cell stage onward. Investigation of these NLBs ultra‐structurally and cytochemically has led to a model for nucleologenesis and the regulation of expression of the rRNA cistrons during cleavage. Throughout the cleavage period, NLBs consist of homogeneous, spherical accumulations of 5–8 nm diameter fibrils. By 18 hours post trefoil, they have become extensively associated with chromatin. By 22 hours post trefoil there are definitive, chromatin associated nucleoli which have a distinct, 15–25 nm granular component surrounding and intermingling with a matrix of 5–8 nm fibrils. This period marks the beginning of a reduction in the number of NLBs per nucleus, until most post‐gastrula nuclei contain only one or two definitive nucleoli. Both NLBs and nucleoli stained selectively with bismuth, which Locke and Huie ('77) consider to be specific for basic proteins within the nucleolus. In contrast, a silver staining technique (Bloom and Goodpasture, '76) selective for active nucleolus organizers stained nucleoli of post‐gastrula embryos but not NLBs of mid‐cleavage embryos. Electron microscope autoradiography showed the incorporation of 3H‐uridine into NLBs beginning in late cleavage, just prior to the appearance of a granular nucleolar component. The agranular NLBs present in cleavage nuclei appear, therefore, to be precursors of the fibrillar matrix of the nucleoli which eventually replace them. This transition is coincident with the activation of rRNA gene expression as NLBs associate with chromatin towards the end of cleavage.
The effect of the substrate on tadpole tailfin epidermal cells in vitro
Authors: Udoh Paul , Derby Albert 
Published: June 2005

AbstractThe behavior of epidermal cells was studied by employing two in vitro systems in which reepithelialization occurs: the single explant system and the fused system. Single explants (4–5 mm2) are prepared from the tailfins of R. catesbeiana tadpoles and cultured in Hank's balanced salt solution at 22°C. The fused system is prepared by placing single tailfin pieces on either side of a tailfin piece that was stripped of its epidermis. These tissues are placed onto a Millipore filter and cultured in Hank's at 22°C. In these experiments one can study the effect of the substrate, core vs a collagenous basement membrane, on the behavior of epidermal cells during reepithelialization.The results of these experiments demonstrate that there are differences in the behavior of epidermal cells in these two systems. In the fused system wound closure is associated with the occurrence of “contact inhibition,” the cessation of further cell migration, and the presence of an epidermal layer that exhibits a normal cytoarchitecture in the wound area. However, in the single explant system, wound closure occurs but an overaccumulation of epidermal cells in the wound area, “capping,” is observed.
Prevention of in vitro fertilization of canine oocytes by anti‐ovary antisera: A potential approach to fertility control in the bitch
Authors: Mahi Cherrie A. , Yanagimachi Ryuzo 
Published: June 2005

AbstractAntisera raised against canine ovaries were found to induce light scattering of the surface of the egg zona pellucida even when diluted 10,000 times, and to delay digestion of the zona by pronase.
The development of the posterior musculature of the embryonic chick wing
Authors: Searls Robert L. 
Published: June 2005

AbstractIt has been proposed that movements of cells at the base of the developing wing cause the wing to rotate (Yander and Searls, '80a,b). It was suggested that rotation of the wing caused the dorsal muscle mass of the wing bud to become the posterior musculature of the proximal part of the wing. Rotation of the wing was investigated by grafting dorsal myogenic tissue from a wing labeled with tritiated thymidine into the dorsal myogenic region of an unlabeled wing in its original orientation. Grafts were made both with and without their original ectoderm. The location and shape of the graft was recorded at the time of the operation. After a period of growth and morphogenesis, the host wing and adjacent body wall were fixed, sectioned, and prepared as autoradiographs. The location of the grafted cells was determined by reconstructing the host wing and adjacent body wall. It was found that the graft increased in length on the axis of the humerus and did not increase rapidly on any other axis. During stage 25, a deep groove began to form ventral to somite 19 because of ventral and cranial movement of the lateral body wall proximal to the base of the wing. The distal border of this groove was recognized as the posterior margin of the proximal wing. If the graft extended to the base of the wing, the graft participated in the formation of this groove. Grafted cells on the distal border of the groove were on the posterior surface of the wing at the level of the humerus.
In the absence of protein, estradiol suppresses meiosis of porcine oocytes in vitro
Authors: Racowsky Catherine , McGaughey Robert W. 
Published: June 2005

AbstractThe effect of estradiol on the spontaneous maturation of porcine oocytes was investigated. Cumulus‐enclosed (intact) and cumulus‐free (denuded) oocytes were cultured in the presence of estradiol‐17β (0 to 10μg/ml) in a chemically defined bicarbonate‐buffered medium that contained either dextran or BSA, or in a complex Hepes‐buffered medium that was supplemented with serum. After 24 hr, chromatin spreads were prepared and meiotic maturation was scored. The biochemical integrities of the cumulus cells were assessed by determination of the estradiol and progesterone content of spent media after culture of intact oocytes in the presence of 0.5 × 10−6 M testosterone and 10 μg/ml follicle‐stimulating hormone.Estradiol did not significantly affect the onset of maturation of either intact or denuded oocytes that were cultured in medium containing either BSA or serum. In serum‐supplemented medium, however, the progression of maturation beyond metaphase I was significantly affected by the steroid in a dose‐dependent manner. The steroid significantly inhibited the release from meiotic arrest of both types of oocyte cultured in medium supplemented with dextran. Supplementation of all media with testosterone and FSH significantly stimulated the synthesis of estradiol by the cumulus cells, compared with that of control groups. The synthesis of progesterone, however, was significantly stimulated by testosterone and FSH only in the BSA and serum‐supplemented media. It is concluded that exogenous estradiol has the capacity to arrest meiosis in vitro but that this capacity can only be expressed if no exogenous protein(s) is present. In the absence of exogenous protein, progesterone synthesis by the adherent cumulus cells is minimal.
Diurnal rhythms in developing ducts of the mouse mammary gland
Authors: Berger J. J. , Daniel C. W. 
Published: June 2005

AbstractDNA synthesis (LI) and mitotic activity (MI) were studied at different times of the day in the developing mammary gland end bud of the postnatal mouse. Both LI and MI displayed a clear diurnal variation. Animals studied at the middle of the 12‐hr dark cycle showed a LI 2.1–2.6 times that of the tissue from the middle of the 12‐hr light cycle. Intermediate values were obtained in tissue sampled midway between these extremes. Mitotic activity was studied 4 hr after the peak and trough of LI and exhibited a corresponding variation. These diurnal variations may be related to cyclic changes in secretion of pituitary hormones or other peptide growth factors, but variation between individual end buds in the same animal is more likely a result of morphogenetic interactions at the tissue level.
Actomyosin components of the asymmetric claw closer muscles of californian snapping shrimp
Authors: Leferovich John M. , Stephens Philip J. 
Published: June 2005

AbstractThe dimorphic claws of the Californian snapping shrimp, Alpheus californiensis, contain an opener and a closer muscle. The closer muscle in the smaller pincer claw is composed of fibers with short and intermediate sarcomere lengths, whereas the closer muscle in the larger snapper claw is composed of fibers with long sarcomeres. Electrophoretic analysis of actomyosin extracts from the closer muscle in each claw revealed some common components. However, the snapper contains two additional components with molecular weights of 25 and 100 daltons.
Polar plasm and pole cell formation in an insect egg developing with or without follicular epithelium: An ultrastructural study
Authors: Junquera Pablo 
Published: June 2005

AbstractAfter X‐ray irradiation, it is possible to obtain follicles and eggs of the gall midge Heteropeza pygmaea lacking the follicular epithelium. These “naked” eggs are able to develop up to the blastoderm stage but remain spherical instead of assuming an elongated shape. Polar plasm and pole cell formation have been studied at the ultrastructural level to investigate the role of the follicular epithelium and of the egg shape in the establishment of egg polarity and in the differentiation of germ line cells. It is shown that the normal egg shape and the follicular epithelium are not needed for the establishment of the anterior‐posterior polarity, as it is manifested by the polar plasm. Moreover, the polar plasm appears at that part of the naked eggs that is at the opposite side of the nurse chamber. Naked eggs are also able to form pole cells in a sequence of events, which strongly resembles that of pole cell formation in normal eggs. These events are described and discussed; they include the changes in the morphology of the polar granules and their association with other organelles during development, the shifting of the polar plasm towards an approaching cleavage nucleus, the cleavage of the first pole cell, and the appearance of pole cell‐specific nuclear lamellae.
Occurrence and function of prairie rattlesnake mouth gaping in a non‐feeding context
Authors: Graves Brent M. , Duvall David 
Published: June 2005

AbstractMouth gaping by rattlesnakes has been observed primarily during feeding sequences and interpreted as functioning to stretch the jaw in preparation for swallowing prey. However, exposure of prairie rattlesnakes to conspecific sociochemical signals elicited increased mouth‐gaping actions, and the latter were sequentially followed by tongue flicks at significant levels. Mouth gaping may function to facilitate vomeronasal olfaction independent of jaw‐stretching effects.
Monoclonal antibody against mouse sperm blocks a specific event in the fertilization process
Authors: Saling P. M. , Raines L. M. , O'rand M. G. 
Published: June 2005

AbstractHybridoma cell lines were produced by PEG (polyethylene glycol)‐induced fusion of myeloma cells (NS‐1/X63 Ag 8) with dispersed spleen cells from a Balb/c male mouse immunized syngeneically with homogenized Balb/c testis. Indirect immunefluorescence on mature (cauda epididymal) mouse sperm was employed as the primary screening assay. This procedure allowed the immediate identification of hybridomas which produce monoclonal antibodies of interest with respect to the fertilization process. One hybridoma cell line, M29, secretes an antibody of the IgM class that localizes to the equatorial segment of the mouse sperm head. This antibody is not species specific, but is restricted to the homologous functional area, the equatorial segment, in all other sperm examined (hamster, rabbit, human). When tested for a possible effect on the fertilization process, ascites fluid containing M29 antibody was very effective in blocking the fertilization of mouse gametes in vitro. The same inhibiting activity was observed regardless of whether the M29‐treated sperm first encountered the cumulus cell layer, the zona pellucida, or the egg plasma membrane. A large number of M29‐treated sperm were capable of penetrating zonae pellucidae when this layer was present. It appears, therefore, that M29 monoclonal antibody prevents fertilization specifically at the level of interaction between the sperm and egg plasma membranes; the other prefertilization events (hyperactivated motility, zona binding, acrosome reaction, zona penetration) seem little affected. Using the M29 antibody and related probes that are specific for particular biological events, it should be possible to map, in molecular terms, the functional domains of the sperm cell's membrane.
Comparison of the fertilizing ability of human spermatozoa preincubated in calcium‐ and strontium‐containing media
Authors: Mortimer D. 
Published: June 2005

AbstractHuman spermatozoa freed from seminal plasma using a discontinuous Percoll gradient procedure were incubated overnight in modified Tyrode's media containing either CaCl2 (CA medium) or with SrCl2 instead of CaCl2 (SR medium). The following morning these spermatozoa were washed by centrifugation, resuspended in fresh CA medium and incubated for either 2 or 3 h with zona‐free hamster eggs to test their fertilizing ability. Penetration rates were higher after 3 h of sperm‐egg contact than after 2 h, and the spermatozoa preincubated in SR medium penetrated significantly more hamster oocytes than those preincubated in CA medium.
The fine structure of germ plasm in eight‐cell embryos developing from normal and inverted eggs of Xenopus laevis
Authors: Jurand A. , Dixon K. E. 
Published: June 2005

AbstractWhen X. laevis eggs developed with their animal‐vegetal axis oriented normally, the mitochondria of the germ plasm in eight‐cell embryos were frequently found to adhere to each other forming branching chains, and also the aggregates of germinal granules were physically associated with adjacent mitochondria. In embryos of the same stage developing from eggs inverted by 180°, these two components were arranged more loosely, so that the whole region of the germ plasm was less compact in appearance. In these embryos, the average number of intermitochondrial adhesions was reduced to approximately one‐third of that in the controls, while the average distance from the edge of an aggregate of germinal granules to the nearest mitochondrion was almost three times the control value. The morphology of the aggregates of germinal granules was also altered: they were much less compact, often with a large central space, and the individual granular components appeared as rings organised into chains. Absence of these associations between the two main constituents of the germ plasm in inverted eggs may correlate with the reduced numbers of primordial germ cells that enter the genital ridges, i.e., the function of the germ plasm as a determinant of primordial germ cells may depend on these associations.
Stimulation of cellular proliferation and differentiation in the intact and regenerating planarian Dugesia(G) tigrina by the neuropeptide substance P
Authors: Saló Emili , Baguñà Jaume 
Published: June 2005

AbstractThe neuropeptide substance P (SP) is shown to be a potent mitogen for intact and regenerating planarians. At nanomolar concentrations, SP markedly enhances cellular proliferation causing an increase in the mitotic index and in the number of blastema cells. Moreover, albeit to a lower extent, SP enhances cellular differentiation as shown by the increases in eye and pharynx length in regenerating organisms. On the basis of these observations, we hypothesize that SP may be one of the postulated growth factors necessary for the stimulation of proliferation, and to a lesser extent differentiation of cells in intact and regenerating planarians.
Contractile responses to temperature in the locomotory musculature of striped bass Morone saxatilis
Authors: Moerland Timothy S. , Sidell Bruce D. 
Published: June 2005

AbstractThe effects of temperature on contractile function of isolated, chemically skinned red (slow oxidative) and white (fast glycolytic) fibers of skeletal muscle from thermally acclimated striped bass (Morone saxatilis) were determined. Acclimation to 10° or 25°C has no significant effect on maximum isometric tension (Po) or maximum unloaded contraction velocity (Vo) of fibers of either muscle type. Sensitivity to acute changes in temperature is markedly greater for slow‐twitch fibers than for white, fast‐twitch fibers. Q10 (15–5°C) of Vo is 1.58 and 2.27 and R10 (15–5°C; analogous to Q10, but for parameters that are not rate functions) of Po is 1.57 and 2.17 for fibers from white and red muscle, respectively. R10 of maximum attainable power output is 1.29 for white and 4.50 for red fibers. Power for low speed, sustained swimming is derived exclusively from red muscle in striped bass, permitting comparisons between swimming performance and contractile capacity to be drawn. For maximum sustainable swimming speed at 15°C, calculated contraction velocity of a red muscle fiber corresponds to the maximum power output of a single fiber of red muscle at 15°C. Thermal sensitivity of red muscle power output predicts that maximum sustained swimming speed of striped bass will be severely impaired at cold temperatures. However, cold acclimation induces a proliferation of the red muscle mass that may ameliorate the thermal sensitivity of red muscle contractile function.
Intrinsic control of regenerative loss in Xenopus laevis limbs
Authors: Muneoka Ken , Holler‐Dinsmore Gregory , Bryant Susan V. 
Published: June 2005

AbstractThe regenerative capability of Xenopus laevis hindlimbs was studied at different developmental stages. Three types of surgical deletion of the autopod were performed: simple amputations, 3‐digit wedge‐shaped deletions and 1‐digit wedge‐shaped deletions. The frequency of regenerative response and the digital patterns of the regenerates were analyzed. Regenerative capacity declines with developmental stage for all three types of deletions. For simple amputations this decline occurs in an orderly manner with the failure of anterior digits to regenerate at progressively later stages. A comparison between 1‐digit and 3‐digit deletions shows that for all stages of development, 3‐digit deletions regenerate better than one‐digit deletions. These data indicate that the amount of tissue removed is directly related to whether a regenerative response is observed. At any given stage, larger deletions are more likely to regenerate than smaller ones. These results are discussed with regard to the mechanisms by which growth during regeneration is controlled.
Effects of exogenous ecdysteroid titer on endogenous ecdysteroid production in vitro by testes of the tobacco budworm, Heliothis virescens
Authors: Loeb M. J. , Brandt E. P. , Woods C. W. 
Published: June 2005

AbstractTestes or the isolated sheaths of testes from late‐last‐instar larvae of the tobacco budworm, Heliothis virescens, spontaneously secreted ecdysteroids in vitro. Exogenous 20‐hydroxyecdysone, incubated with the testes or isolated testis sheaths, functioned in a local positive feedback system to increase production of the several ecdysteroids typical of H. virescens testes. The increase in ecdysteroid production by testis tissue was dependent on discrete ranges in exogenous ecdysteroid titer. Activation ratios of 2–5 resulted from exogenous 20‐hydroxyecdysone titers of 0.5 to 15 pg/μl, while activation ratios of 10–30 resulted from exogenous titers of 15–100 pg/μl of 20‐hydroxyecdysone. Activation ratios approached 200 with exogenous titers of 100–1,000 pg/μl of 20‐hydroxyecdysone.