bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron microscopic and biochemical analyses of the organization of human sperm chromatin decondensed with Sarkosyl and dithiothreitol
Authors: Sobhon Prasert , Tanphaichitr Nongnuj , Chutatape Chutima , Vongpayabal Padung , Panuwatsuk Wannana
Published: June 2005

Human sperm chromatin was decondensed by treating the purified sperm heads with Sarkosyl for 60 minutes followed with dithiothreitol (DTT) for 20 minutes and overnight. Following Sarkosyl treatment all histones and nonhistones were removed; the remaining nucleoprotamines in the sperm heads exhibited two levels of higher‐order structure in the forms of 900–1200 Å thick and 380–520 Å thin knobby cords, which were randomly coiled. Subsequent treatment with DTT resulted in the dissociation of the 380–520 Å cords into subunits of 180–210 Å fibers, which were further decondensed into beads‐on‐a‐string structure with diameter of the beads about 120–150 Å.
Effects of advancing age on the ultrastructure of pinealocytes in the male white‐footed mouse (Peromyscus leucopus)
Authors: King Thomas S. , Karasek Michal , Petterborg Larry J. , Hansen John T. , Reiter Russel J.
Published: June 2005

Quantitative comparison of pinealocyte ultrastructure in 3‐month‐old and 28‐month‐old male white‐footed mice (Peromyscus leucopus) revealed decreases both in the area of the Golgi apparatus and in the number of dense‐core vesicles. In contrast, no differences between these two age groups were noted in the areas of granular endoplasmic reticulum, vacuoles with flocculent content, lysosome‐like bodies, or motochondra. Nor were any changes between groups of mice apparent in pinealocyte nuclear or cytoplasmic areas, nuclear: cytoplasmic ratios, or the number of pinealocyte nuclei per unit area. areas of unusual, annulate lamellae‐like structures were increased in the pinealocytes of a group of 28‐month‐old mice. These observations suggest a possible age‐associated decrease in the neurosecretory‐like (but not ependymal‐like) secretory process in the pinealocyte of white‐footed mice.
Effects of hormones on postimplantation mouse embryos in vitro. II. Progesterone and estrogen
Authors: Fisher D. L. , De Villarreal L. Martínez
Published: June 2005

Mouse embryos at day 9 of development were cultured for 24 to 42 h in 50% fetal calf serum and 50% Waymouth's medium containing 0.5 μg/ml insulin supplemented with various amounts of progesterone and estradiol‐17‐β. Unmodified medium contained approximately 0.2% of the normal maternal blood levels for that stage of pregnancy. The addition of 1 × 10−7M progesterone to the medium brought the level near that of the normal maternal circulating amount and appeared to be beneficial for in vitro development. After 24 h of cultivation there was a statistically significant increase in somite number, the number of embryos developing posterior limb buds, and protein accumulation over the control embryos. The addition of small amounts of estradiol‐17‐β (1 × 10−10M) increased the protein accumulation of the embryo over that of progesterone alone and seems to enhance the beneficial effects of progesterone addition.
Development of the spot pattern in the leopard frog
Authors: Bagnara Joseph T.
Published: June 2005

Expression of the spot pattern on the dorsal surface of metamorphosing froglets of Rana pipiens seems to be determined by the dorsal integument rather than by the neural crest. At the neurula stage, dorsal ectoderm appears to be loosely determined with respect to pigmentary pattern. Results of skin rotation experiments suggest that by early larval stages the prospective dorsal spot pattern is precisely fixed in the integument.
Studies on the water‐soluble lens proteins of the lizard, Calotes versicolor. II. Electrophoretic and immunological characterization
Authors: Pal J. K. , Nerurkar A. R. , Goel S. C.
Published: June 2005

The Sephadex G‐200 gel filtration fractions C1 to C6 of the water‐soluble lens proteins of Calotes versicolor have been characterized by polyacrylamide gel electrophoresis (PAGE), 7 M urea PAGE, SDS PAGE, and immunological tests. C1 fraction, an α‐crystallin which cross‐reacts with chick α, has very low amount of B chains. It shows two bands in SDS PAGE, one strong and another weak. C2 and C3 fractions, both of which partially cross‐react with chick β ‐crystallins, are largely similar but not identical. C2 in SDS PAGE produces a faint band with a molecular weight of 54,500, which suggests that C2 may either contain a small amount of δ‐crystallin in addition to βH crystallin or that Calotes βH has a high molecular weight subunit like human βH; however, in immunological tests no material cross‐reacting with chick δ was seen. C4 and C5 are low molecular weight, monomeric, and basic proteins which in all probability are not γ‐crystallins.
Role of daylength in the regulation of reproductive function in the male mongoose, Herpestes auropunctatus
Authors: Soares Michael J. , Hoffmann Joan C.
Published: June 2005

The male mongoose, Herpestes auropunctatus, displays a distinct seasonal reproductive rhythm in environments which show minimal changes in daylength. This investigation was designed to evaluate whether the reproductive system of the male mongoose was responsive to photoperiodic manipulations. Four experiments were conducted; two during the breeding season, one during the inactive season, and one during the recrudescence phase. Serum androgen levels and reproductive organ weights were similar in males exposed to either short (6L:18D) or control photoperiods (14L:10D) when the photoperiodic adjustment was initiated in April; however, serum androgen levels were significantly depressed after 60 days exposure to short photoperiods as were weights of prostate glands when the photoperiodic manipulation was initiated in May. An increase in the number of hours of light per day during the inactive season did not affect serum androgen levels or reproductive organ weights. Exposure to a very short photoperiod (2L:22D) during the recrudescence phase delayed, but did not prevent, the increase in serum androgen levels. Although the reproductive system of the male mongoose is responsive to daylength adjustments, the response is less pronounced when compared to the effects of photoperiod in other seasonal breeders.
Spontaneous activation of ovulated rat oocytes during in vitro culture
Authors: Keefer Carol L. , Schuetz Allen W.
Published: June 2005

Ovulated rat oocytes were observed to activate spontaneously during in vitro culture. The possible mechanisms involved in this activation were studied by culturing oocytes at various times (0–6 hr) after ovulation, in different media, and for different incubation periods (0–5 hr). Activated oocytes extruded the second polar body within 60 to 90 min of culture. Following 3 to 4 hr of culture chromosomes were scattered throughout the cytoplasm; however, no pronuclear formation was observed. Neither time after ovulation nor incubation in different media affected the rate of activation. The length of time the oviducts remained in the animal after cervical dislocation, however, significantly (P < 0.01) affected the rate of activation. Oocytes obtained as rapidly as possible had an activation rate of 21% during in vitro culture, whereas oocytes obtained from oviducts which remained in the animal for 5 min after cervical dislocation had an activation rate of 94%. Therefore, exposure to changing oviductal conditions following cervical dislocation appears to be the critical factor influencing spontaneous activation of metaphase II rat oocytes during in vitro culture. Our studies demonstrate that rat oocytes can spontaneously activate during in vitro culture, a factor which may affect the fertilizability of the oocyte.
Effect of antimetabolites on programming of inner cells of the mouse blastocyst
Authors: McCue Peter A. , Sherman Michael I.
Published: June 2005

When early blastocysts are subjected to immunosurgery, the resulting inner cell masses (ICMs) regenerate trophoblast cells. In contrast, ICMs from later blastocysts produce endoderm cells. We have found that if embryos are treated with cycloheximide during the transition from the early to late blastocyst stages, subsequently isolated ICMs give rise to trophoblast‐like giant cells. These cells do not, however, exhibit detectable levels of Δ5, 3β‐hydroxysteroid dehydrogenase, an enzyme normally found in primary trophoblast cells. Neither Colcemid nor α‐amanitin affects the conversion of the ICM program in the same way as cycloheximide, although α‐amanitin added at later stages interferes with the formation of a cohesive endoderm layer around the isolated ICM. We propose that the reprogramming of ICM cells involves at least two events: one terminates the giant cell program and the other, occurring later in development, promotes endoderm formation.
Trifluoperazine‐induced meiotic maturation in Xenopus laevis
Authors: Hollinger T. G. , Alvarez I. M.
Published: June 2005

Xenopus oocytes were exposed to trifluoperazine, a drug that binds to the calcium‐regulating protein, calmodulin. The drug induced meiotic maturation even in the absence of progesterone. When trifluoperazine was microinjected directly into oocytes the maturation of the cells was partially inhibited in that the white spot, indicative of germinal vesicle breakdown, did not appear even though the germinal itself was absent in dissected oocytes.
Shift of seasonal cycle in white‐tailed deer by oral administration of melatonin
Authors: Bubenik G. A.
Published: June 2005

A complete reversal of seasonally dependent events, like antler growth and change of pelage was achieved in white‐tailed bucks by oral application of melatonin. The drug was administered in a way that simulated the shortening of the natural photoperiod. Mineralization of antlers, shedding of velvet, complete change of summer pelage, and the onset of the rutting behavior was initiated aproximately 2 months ahead of time.
Visualization of the three‐dimensional distribution of collagen fibrils over preovulatory follicles in the hamster
Authors: Martin Gary G. , Miller‐Walker Cindy
Published: June 2005

Before an oocyte can escape from a preovulatory follicle, the apical wall must thin to the point of rupture. Although numerous layers of cells are present, it is the collagen fibrils in the theca externa that provide most of the strength to the developing follicle. The three‐dimensional distribution and integrity of these fibrils over a follicle cannot be appreciated with standard used methods such as examination of thin sections by transmission electron microscopy. In this paper we describe a technique that removes cells superficial to the collagen fibrils so that their distribution may be examined by scanning electron microscopy. On the third day of the hamster's 4‐day estrous cycle, bundles of fibrils pass from intrafollicular areas and ascend follicles. Approximately halfway up the follicle wall, the bundles fan out and form a meshwork of fibrils which covers the apex. As the time of ovulation approaches, the number of layers of fibrils decreases over the apex until a tear forms in the weakened matrix. Experimental results demonstrating that the meshwork is composed of collagen fibrils are presented. The usefulness of this technique in visualizing the collagen content in preovulatory follicles is discussed as well as factors that may aid in weakening this layer so that follicle rupture may occur.
Effect of selenium deficiency on liver and blood glutathione peroxidase activity in the black bullhead
Authors: Heisinger James F. , Dawson Steven M.
Published: June 2005

Male black bullheads, approximately 4 gm, were fed a selenium‐deficient torula yeast‐based diet for 18 weeks, and the activity of glutathione peroxidase was studied in liver and blood using H2O2 as a substrate. Controls were on the same diet, but received weekly intraperitoneal injections of Na2SeO3. At 12 and 18 weeks significant decreases in blood and liver glutathione peroxidase activity were observed in the experimental animals. Liver showed an even greater decrease than blood in glutathione peroxidase activity in the selenium‐deficient animals. Females (4 gm) kept on the diet for 15 weeks showed similar results. Liver activities were not decreased nearly as much when cumene hydroperoxide was used as the substrate instead of H2O2. This indicates that at least two glutathione peroxidase activities are present in fish liver. One is selenium dependent; its activity, as measured with H2O2 as substrate, becomes almost undetectable in selenium‐deficient fish. This situation is very similar to that found in mammalian species.
Protein pattern variability of the hemolymph of mantis shrimp, Squilla mantis L. (crustacea, stomatopoda)
Authors: Ferrero Enrico A. , Graziosi Giorgio , Marzari Roberto , Mosco Alessandro
Published: June 2005

The SDS‐PAGE of Squilla mantis hemolymph reveals 16 major protein bands. Three of them, showing a molecular weight (MW) around 125 kdal, are female specific proteins (FSP) to be considered as vitellogenins because their amount increases with ovarian maturity. The MW of the hemocyanin subunit is confirmed around 70 kdal. Low MW proteins appear or intensify at molt. Hemolymph incubation with 35S‐Methionine and subsequent autoradiography of SDS‐PAGE slabs show that hemocyanin and vitellogenins are not synthesized by the circulating hemocytes, while some proteins connected with molt are heavily labeled by the tracer.
Effects of successive generations of ether treatment on penetrance and expression of the bithorax phenocopy in Drosophila melanogaster
Authors: Ho M. W. , Tucker C. , Keeley D. , Saunders P. T.
Published: June 2005

Ether treatment of embryos in successive generations results in the progressive increase in penetrance of the bithorax phenocopy in both a massbred and an inbred line of Drosophila melanogaster without artificial selection for the phenocopy. The involvement of cumulative cytoplasmic modifications is suggested by the results of recipiocal crosses between the treated massbred line and its foundation stock, and by the lingering effects observed when ether treatment is withheld in later generations.

Regression analyses showed that the effect of successive generations of ether treatment on penetrance is cumulative and direct, and not mediated by possible effects on viability.

Ether treatment carried out on embryos at four consecutive age intervals in the 14th generation suggests that the effects of long‐term etherisation are as follows: an increased tendency to phenocopy at all ages tested; an extension of the critical period during which the phenocopy can be induced; and an increased resistance to the lethal effects of ether in older embryos.

The remarkable consistency in every aspect of the response in the two different lines—one containing at least 20 times as much genetic variation as the other—points to the existence of systematic organismic properties which do not depend on specific alleles in specific genes.

The possible evolutionary significance of our results is discussed.
Thyroid and skin‐shedding in the rat snake (Ptyas korros)
Authors: Chiu K. W. , Leung M. S. , Maderson P. F. A.
Published: June 2005

Epidermal‐thyroid relationships were studied in thyroidec‐tomized (;Tx) Ptyas korros kept at 23°C by observing changes in shedding frequency (;SF), body weight, oxygen consumption rate (;OCR), and postsurgical survival. Tx animals showed increased SFs but lost weight and eventually died, as did Tx animals receiving 3‐mono‐iodotyrosine injections. However, injections of 3, 5‐diiodothyronine inhibited shedding and the animals survived longer. OCRs were similar in all control and experimental groups. It is concluded that among thyroid secretions, only iodothyronines inhibit shedding. Snake shedding is concluded not to reflect general metabolic status as it does in lizards.
Mating‐type‐specific loss of conjugation competence by irritation in Euplotes vannus
Authors: Lueken W. , Gaertner M. , Breer H.
Published: June 2005

In order to characterize differences in mating types in Euplotes vannus, two cell populations of complementary mating types were mixed and exposed to a pattern of irritation (switching schedule of agitation and rest). Cells costimulate each other, as is seen from courtship behavior during still intervals, but do not pair. Prolonged periods of treatment cause distinctly reduced cell interactions. After 72 hr they have ceased completely: Overstimulated cells have lost their ability to conjugate. However, with fresh cells of mating types, which are different from both constituents of the mixture, overstimulated cells mate normally as judged by time course, cycloheximide‐sensitivity, and concanavalin A (ConA) binding. Conjugation competence thus is selectively lost only for that mating type which has been the partner in the perturbated mixture. The required classification of pairs with regard to mating‐type combinations were confirmed by several identification procedures using amicronucleates and doublets. The observed phenomena during the mating‐type‐specific loss of conjugation ability are consistent with the concept that this is due to a physiological disappearance of a specific mating substance, which might correspond to the receptor side of the extended gamone‐receptor hypothesis of Miyake ('81).
Preparation and cross‐reactivity of anti‐avian glutamine synthetase antibody
Authors: Smith Darwin D. , Vorhaben Jean E. , Campbell James W.
Published: June 2005

Rabbit antibody to chicken liver mitochondrial glutamine synthetase was purified by immunoaffinity chromatography for analysis of the immunological relatedness of vertebrate glutamine synthetases. The antibody cross‐reacted with enzymes from representitives of all five vertebrate classes, indicating a high degree of evolutionary conservatism in the structure of the enzymes. A unique aspect of the immunological similarity of these enzymes is that it exists between cytosolic and mitochondrial enzymes which are, in general, immunologically distinct. The antibody did not cross‐react with two insect glutamine synthetases. Compositional difference indices, calculated from the amino acid compositions of glutamine synthetases from several species, gave a mean estimate of over 80% sequence homology for the vertebrate enzymes. The avian mitochondrial enzyme gave a mean 78% homology with the mammalian cytosolic enzyme.
Sustained branchial apnea in the Australian short‐finned eel, Anguilla australis
Authors: Smith D. G. , Duiker W. , Cooke I. R. C.
Published: June 2005

Branchial and cutaneous O2 uptake as well as branchial ventilatory stroke volume and frequency were measured by twin‐chamber respirometry in conscious unoperated eels (Anguilla australis) at 20°C. The branchial ventilatory pattern comprised alternating periods of apnea and eupnea, together constituting a “Standard Breathing Cycle” (SBC = 1 apneic period plus the ensuing period of eupnea). SBC time in 17 eels averaged 15.5 min of which only 23% was devoted to eupnea. Reduction of the PO2 of inspired water from 155 to 80 torr significantly increased the proportion of time devoted to eupnea to 49% of SBC time without significantly changing SBC time. Absolute cutaneous O2 uptake (5.8 ml O2·h−1·kg−1) was largely independent of the frequency or occurrence of eupnea, with the relative contribution of the skin to total O2 uptake averaging 47%. The histological appearance of the skin in A. australis is very similar to that described in A. anguilla: eel skin is only poorly vascularized. It was concluded that the skin may contribute to O2 requirements other than its own, and that this adaptation is a consequence of the unusual intermittent pattern of gill ventilation.
Evidence for inherent morphogenetic properties of the myogenic regions of the embryonic chick wing
Authors: Searls Robert L.
Published: June 2005

The dorsal and ventral myogenic regions were isolated from the right and left wings of donor chick embryos. After removal of the ectoderm, the myogenic regions were grafted into the dorsal myogenic region of the right wing of host embryos in normal or reversed proximal‐distal orientation. All grafts were made so that the surface of the graft originally in contact with ectoderm was dorsal. It was expected that myogenic regions grafted into the myogenic region would participate in the normal formation of the host wing. However, after 7 days of further development many of the host wings had developed abnormal cartilages. To investigate the interactions between the tissue of the host and the tissue of the graft and the source of the tissue giving rise to ectopic cartilages, the donor embryos were labeled with tritiated thymidine. The location and shape of the graft were recorded at the time of the operation. The host wings and adjacent body wall were fixed 1, 3, and 4 days after the operation, sectioned, and prepared as autoradiographs. The location of the grafted cells in the host wing was determined by reconstructing the host wing and adjacent body wall. Serial sections and the reconstructions were examined to discover the correlates of abnormal cartilage formation. The following observations were made: 1) Grafts from the dorsal region of the right and left wing in normal orientation participated in the formation of the groove at the base of the wing ventral to the nineteenth somite that produces the extensor surface of the elbow. Grafts from the ventral region of the right and left wing in normal orientation, and all grafts in reversed orientation, did not participate in the formation of the groove. 2) Grafts in normal orientation increased in length on the axis of the humerus and did not increase in width. Grafts in reversed orientation increased in both length and width. Increase in width caused the graft to extend into the proximo‐caudal corner of the wing. 3) Wings with grafts from the dorsal regions of the right and left wings in normal orientation were not clearly abnormal 4 days after the operation. When the groove ventral to the nineteenth somite did not form normally, ectopic cartilage differentiated where the groove should have been from grafted cells of the myogenic region. Increase in width of the graft into the proximo‐caudal corner of the wing produced an increased mass of graft cells ventral to the nineteenth somite and an increased amount of ectopic cartilage.
Can differences in limb regeneration ability between individuals within certain amphibian species be explained by differences in the quantity of innervation?
Authors: Scadding Steven R.
Published: June 2005

In some species of amphibians, the regenerative response to limb amputation is not uniform. For example, regenerative ability varies from one individual to another within the species Xenopus laevis, Ambystoma maculatum, and Amphiuma tridactylum. In many species, limb regenerative ability declines with increasing age. The objective of this investigation was to determine if this variation in regenerative ability can be explained by variation in the quantity of innervation. In each of the above‐named species, limbs were amputated and allowed to regenerate. The quantity of innervation (percentage of cross‐sectional area of amputated surface occupied by nerves) was measured in the amputated part of the limb as close as possible to the amputation surface. The presence, rate, or extent of limb regeneration in that specific limb was then compared to the quantity of innervation at the amputation surface. The results indicated that there was no correlation between innervation and the rate or extent of regeneration in Xenopus laevis or Ambystoma maculatum. On the other hand, in Amphiuma tridactylum, those limbs that regenerated were the ones that had the highest levels of innervation. In Ambystoma maculatum, the quantity of innervation was measured at five different stages, from early larvae to mature adult. The results showed that the quantity of innervation was highest during the larval period, reaching a maximum at the late larval stage before declining greatly to the adult level. It appears that the decline in regenerative ability in the adult cannot be attributed solely to a reduction in innervation to below the threshold level.
The culture of chick embryo mesoderm cells in hydrated collagen gels
Authors: Sanders E. J. , Prasad S.
Published: June 2005

Chick embryo mesoderm cells at various stages of differentiation were cultured in three‐dimensional matrices of hydrated collagen. The tissues used were: stage 5 mesoderm from regions adjacent to the primitive streak; stage 12 mesoderm, comprising somitic, unsegmented (segmental plate) and lateral plate mesoderm; and stage 18 sclerotome. Explants were examined by phase contrast microscopy, including time‐lapse, and scanning and transmission electron microscopy. The cells showed an increased ability to adhere to, and move in, the collagen gel with advancing stage. Of the stage 12 tissues, the unsegmented mesoderm was initially the slowest to grow out of the explant. Sclerotome cells showed by far the greatest ability to move within the gel. Where the collagen fibrils were randomly oriented, the cell morphology was polypodial and advancing lamellipodia showed clear undulations at their leading edges. A distinction was drawn between these undulations and the classical major ruffles which are seen in two‐dimensional culture to uplift and pass back along the cell surface. The latter were not seen in the collagen matrix and were presumably suppressed by the three‐dimensional culture configuration while the leading edge undulations were not. Ultrastructural examination showed that the cells possessed patches of amorphous material on their surface, which was sometimes interposed between the plasma membrane and collagen fibrils. Addition of hyaluronie acid (2 mg/ml) had an effect only the segmented mesoderm, where outgrowth was enhanced. Although the addition of plasma fibronectin (50 μg/ml) to the cultures did not affect any of the tissues, the removal of this substance, by antifibronectin antiserum or by the use of fibronectin depleted serum, inhibited outgrowth in most cases. The only tissue not reproducibly inhibited in this way was sclerotome. Alignment of the collagen fibres by the explants was observed, accompanied by an elongation of the outgrowing cells which, in bipolar form, preferentially moved up and down the aligned tracts. Scanning electron microscopy suggested that cell processes attached to, and presumably exerted tension on, bundles of fibrils thereby pulling them into line. Cell‐to‐cell contact was not accompanied by contact paralysis as judged by time‐lapse micrography.
Endocrine regulation of spermatogenesis in Nereis diversicolor (Annelida Polychaeta): Experimental study of the control of meiotic differentiation
Authors: Bertout Marc
Published: June 2005

In Nereidae, spermatogenesis is regulated by a hormone secreted by the supraesophageal ganglion (brain hormone). The hormonal concentration decreases with worm age. Spermatogonial proliferation in young worms proceeds under a high hormonal level whereas differentiation of spermatozoa in aged worms occurs in the absence of brain hormone. Spermatogonia were removed from the endocrine influence of the brain in vitro by the organ culture method. Isolated parapodia produced spermatozoa after 13 days. Control cultures were obtained by associating a parapodium with the prostomium of a young worm. It seems that the brain hormone inhibits the spermatocyte differentiation since removal of the brain results in increased RNA synthesis, followed by DNA replication, meiosis, and spermiogenesis (Bertout, '83).

Modalities of the hormonal control of meiosis, especially at the level of the RNA syntheses related to meiotic differentiation, were investigated. Effects of reintroducing the hormonal influence during meiotic differentiation were studied through parapodium‐prostomium associations at various time after the brain inhibition has been lifted. Effects or RNA inhibitors (actinomycin D, α‐amanitin, cordycepin) were also tested. The results lead us to propose a hypothesis according to which brain hormone would interfere with molecular events related to the transition from the stage of spermatogonial proliferation (mitotic behavior) to the stage of meiotic differentiation (meiotic behavior).
Calcium‐binding phosphoprotein particles in the extrapallial fluid and innermost shell lamella of clams
Authors: Marsh M. E. , Sass R. L.
Published: June 2005

A calcium‐binding phosphoprotein has been isolated from the extrapallial fluid of clams where it occurs as discrete particles 30–40 nm in diameter at a concentration of 1.5–6.0 mM with respect to organic phosphate. The particles were isolated by nitration and differential centrifugation procedures. In particles obtained from Rangia cuneata, 90 mole % of the amino acid residues are aspartic acid (21.7%), serine (29.1%), histidine (34.6%), and lysine (4.6%). In Mercenaria mercenaria particles 95% of the residues are aspartic acid (20.1%), serine and threonine (26.9%), histidine (36.0%), and glycine (11.4%). The serine and threonine residues may be fully phosphorylated.

Particles from Rangia contain 1.45 moles of calcium plus magnesium and 0.24 moles of inorganic phosphate per mole of organic phosphate, and in Mercenaria particles these values are 1.29 and 0.164 respectively. Calcium and magnesium probably bind to organic phosphate and aspartic acid residues, and inorganic phosphate may bind secondarily through calcium and magnesium.

In Rangia, the innermost shell lamella (ISL) is a single continuous layer which forms the inner surface of the shell dorsal to the pallial attachment. It contains no crystalline mineral but is firmly attached to the mineral in the underlying calcined layer. The presence of phosphoprotein particles in the ISL was demonstrated by electron microscopy and amino acid analysis. Phosphoprotein particles are not present in the bulk shell; however, their occurrence in the extrapallial fluid and ISL coupled with their affinity for mineral ions suggests that the particles have an intermediary roll in shell deposition or dissolution.
Formation of a functional apical ectodermal ridge from nonridge ectoderm in limb buds of chick and quail embryos
Authors: Murphy Michael J. , Gasseling Mary T. , Saunders John W.
Published: June 2005

In an attempt to impede the inductive communications between the apical ectodermal ridge (AER) of the wing bud and its underlying mesoderm, we lined the apex of the trypsin‐isolated ectodermal hull of the chick limb bud with stage 23 or 25 quail back‐skin ectoderm or nonridge limb ectoderm. We then inserted a stage 21 chick wing‐bud mesodermal core into this hull with its apex against the putative barrier. Reciprocally, quail limb components were united with a barrier of chick nonridge limb ectoderm. Such composites, grafted to host chick embryos, usually formed wings comparable in perfection to those obtained when ectodermal and mesodermal elements are recombined and grafted without a lining ectodermal layer. The reestablishment of a normal vascular pattern in the composite limbs was delayed compared to controls, suggesting that the interposed layer of cells interferes, initially at least, with the communication between the AER and subjacent mesoderm, and that this interference delays the development of, particularly, the veinous channels draining the limb bud.

Histological study of Feulgen‐stained preparations showed that the interposed ectodermal cells begin moving into the overlying ectoderm as early as 6 h after grafting, populating the AER and adjoining ectoderm. By 48–50 h the ridge and adjacent ectoderm are composed entirely, or almost so, of cells of the interposed type. The original ridge cells are apparently displaced into the amniotic fluid, and the cells invading from below take over the functional attributes of the AER, inducing the growth of terminal limb parts.
In vitro estrogen modulation of pituitary and progesterone‐induced oocyte maturation in Rana pipiens
Authors: Lin Yu‐Wai P. , Schuetz Allen W.
Published: June 2005

The role of estrogen in the process of hormone‐induced meiotic maturation was investigated using in vitro culture of Rana pipiens ovarian follicles and isolated oocytes. Estrogen alone was ineffective in triggering maturation and did not act synergistically when combined with progesterone. Instead, slight inhibitory effects on oocyte maturation were observed when estrogen was added to the culture medium simultaneously with progesterone. Prolonged estrogen pretreatment (1–8 hr) was seen to be increasingly effective in inhibiting progesterone‐induced germinal vesicle breakdown (GVBD). Washing follicles after estrogen pretreatment diminished the inhibitory effects, suggesting continued presence of estrogen was necessary for maximal inhibition. Progesterone‐induced GVBD was inhibited by estrogen in denuded oocytes (follicle wall removed) indicating that estrogen acts directly on the oocyte. Incorporation of radioactive progesterone into ovarian follicles was not inhibited regardless of the estrogen concentration used. This suggests that estrogen inhibits oocyte maturation by raising intrafollicular threshold to progesterone rather than by suppressing hormone incorporation into ovarian follicles. Next, the action of estrogen on frog pituitary homogenate (FPH)‐induced GVBD was examined. Although both progesterone and FPH‐induced GVBD were inhibited by estrogen, the latter was remarkably more susceptible and did not require estrogen pretreatment. Furthermore, increased concentration of progesterone, but not FPH, overcame the inhibitory action of estrogen. The results suggest that estrogen may exert its inhibitory effects on gonadotropin action at more than one site. Estrogen can o modulate either the maturation‐inducing action of progesterone directly at the oocyte level or the suppression of progesterone production by the follicle cell. Hence, estrogen may play an important role as an endogenous regulator of oocyte meiotic maturation.
Parthenogenetic activation of mouse oocytes in vitro with ethanol and benzyl alcohol
Authors: Cuthbertson K. S. Roy
Published: June 2005

Treatment in vitro of ovulated mouse oocytes for 5–10 min with 4.5–8.6% ethanol or 0.24–0.4% benzyl alcohol was found to induce parthenogenetic activation. Suppression of the second polar body with cytochalasin D and subsequent culture in vitro gave a high yield of parthenogenetic morulae and blastocysts (up to 85% overall). Fifty percent of transferred diploid parthenogenones implanted, 14% developed into egg cylinders, and 8% formed somites and developed as far as the forelimb‐bud stage.
The organization of flexion‐evoking interneurons in the abdominal nerve cord of the crayfish, Procambarus clarkii
Authors: Larimer James L. , Jellies John
Published: June 2005

Intracellular recording and dye injection was used to investigate the flexion‐evoking interneurons in the isolated abdominal nerve cord of the crayfish, Procambarus clarkii. The interneurons described in this study have all of the characteristics of cells called flexion command fibers in earlier works. These interneurons show cell bodies in all of the abdominal ganglia, all are interganglionic, and those with posteriorly directed axons enter the terminal caudal ganglion. Some cells were found in as many as eight different preparations, supporting the idea that these interneurons are identified cells. In addition to presenting evidence for identities, evidence was obtained for serial homology in this premotor system. A summary of the general organization of the flexion premotor apparatus is offered. It consists primarily of parallel elements (command interneurons) that are either bipolar or monopolar whose axonal projections course to the terminal caudal ganglion or rostrally into the thoracic region, perhaps into the cerebral ganglion. When activated singly, these parallel elements do not recruit additional interneurons but there are data to suggest that several of these elements could act in concert and interact in a low‐gain fashion to produce coordinated positioning behavior.
Effects of abrasion and Na+ on dactyl‐mediated chemoreception in mature kelp crabs, Pugettia producta (Randall)
Authors: Hamilton K. A. , Case J. F.
Published: June 2005

Extracellular recordings from the mixed sensory nerves innervating the abraded dactylopodites of the kelp crab, Pugettia producta (Randall), indicate that at least some chemoreceptors and mechanoreceptors remain functional. The chemoreceptors of the abraded dactyls are sensitive to both the concentration and chemical nature of the stimulants. The responses of the chemoreceptors, but not of the mechanoreceptors, are reduced when choline is substituted for sodium in the stimulant solutions. Only chemoreception is blocked by the topical application of tetrodotoxin (TTX) to the dactyls; partial reversal of the blockage occurs with time. The differential blockage of receptor activity by low Na+ and TTX is consistent with the idea that spike initiation occurs more distally in the dendrites of the chemosensory neurons than in the mechanosensory neurons. The relevance of this to the ability of at least some abraded dactyl setae to remain functional in a long‐lived, nonmolting crab is considered.
Ectodermal control of the avascular zone of the peripheral mesoderm in the chick embryo
Authors: Feinberg Richard N. , Repo Mary A. , Saunders John W.
Published: June 2005

Prospective skin ectoderm is underlaid by a relatively thick (100 ± 20 μm) avascular zone of mesoderm in most regions of the early embryo. To determine whether or not the ectoderm exercises a role in the establishment and maintenance of the avascular zone, trypsin‐isolated pieces of backskin ectoderm from chick or quail embryos were implanted as a sheet into a slit cut deep into the capillary bed of the wing bud of host chick embryos of stages 19–23. In sham operations, slits were cut at various anteroposterior levels, and the wing was allowed to heal. At intervals of 3–48 hr after these operations, embryos were injected with India ink, fixed, and cleared. Implants formed flattened vesicles, usually in continuity with host ectoderm, but sometimes completely internalized. Periderm cells from each side of the vesicle faced each other, and the cells of the cuboidal layer faced an avascular mesodermal layer at least 100 μm thick at all points.

The implantation of prospective skin ectoderm resulted in the formation of an avascular zone in normally vascularized mesoderm of the wing bud. In contrast, the vascular bed of the limb bud abutted directly on implants of Millipore filters or of Silastic silicone (Dow Corning). Likewise, the capillary bed came in direct contact with implants of retinal pigment epithelium, an ectodermal derivative normally in close contact with the vascular choroid coat of the eye. These results, taken in conjunction with earlier experiments that show the necessity of the apical ectodermal ridge for the formation of the marginal veins of the limb bud, suggest that epithelial‐mesenchymal interactions are involved in important aspects of vasculogenesis in early embryos.
Heavy metal chelators prolong motility and viability of sea urchin sperm by inhibiting spontaneous acrosome reactions
Authors: Johnson Carl Hirschie , Epel David
Published: June 2005

A variety of heavy metal chelating agents is known to prolong the fertilizing capacity and motility of sea urchin sperm. We report here that these agents maintain fertilizing capacity by preventing acrosome reactions which occur spontaneously after dilution of sperm into seawater. These chelating agents also inhibit acrosome reactions induced by high pH or egg jelly. Since induction of the acrosome reaction leads to steps that abolish motility, specifically a massive Ca2 + uptake and concomitant acidification of the cytoplasm, motility is prolonged by these chelators. These observations also suggest that heavy metals play a role in controlling the acrosome reaction in sea urchin sperm.
Studies on the flagellar ATPase of bull spermatozoa: Extraction and characterization
Authors: Young Leona G. , Smithwick Eleanor B.
Published: June 2005

Adenosine triphosphatase (ATPase) activity of flagella isolated from ejaculated bull sperm was solubilized by 5 min exposure to 0.6 M KC1 at 4°C. ATPase activity in the flagellar extract was characterized with respect to enzyme, substrate, activator ion, salt, and hydrogen ion concentration. Flagellar extract required the presence of a divalent cation for activity: Mg2 +, Ca2 +, or Mn2+ could function as activator, but Zn2+ or Cd2+ could not. Magnesium‐activated ATPase was maximal in the presence of Mg2+ and ATP in equilimolar concentrations and at alkaline pH. Calcium activated ATPase was maximal over a wide range of Ca2 +:ATP ratios and at pH 8.0. The presence of increasing concentrations of Na+ and/or K+ ions in the assay medium (0.5–300 mM) had no effect on the ATPase activity of flagellar extract.
Inhibition of the acrosome reaction of sea urchin spermatozoa by a calmodulin antagonist, N‐(6‐aminohexyl)‐5‐chloro‐1‐naphthalenesulfonamide (W‐7)
Authors: Sano Kiyoshi
Published: June 2005

A calmodulin antagonist, W‐7 (N‐(6‐aminohexyl)‐5‐chloro‐l‐naphthalenesulfonamide), inhibited induction of the acrosome reaction of sea urchin spermatozoa by egg jelly at 20–50 μM, but W‐5 did not. The latter, a chlorine‐deficient derivative of W‐7, has a lower affinity for calmodulin than does W‐7. These results suggest that a Ca2+ ‐calmodulin‐dependent process plays an important role in the triggering process of the acrosome reaction of Sea urchin spermatozoa.
What makes Blepharida jump? A structural study of the metafemoral spring of a flea beetle
Authors: Furth David G. , Traub Wolfie , Harpaz Isaac
Published: June 2005

Blepharida sacra (Weise) is one of many species of flea beetles that have remarkable jumping abilities. The energy for its prodigious leaps is evidently stored in a central scroll‐shaped organ inside the hind femur of this insect—the metafemoral spring. X‐ray diffraction, scanning electron microscope, and analytical studies have established that this structure consists primarily of well‐oriented fibers of the polysaccharide α‐chitin, together with protein. The composition and orientation of these fibers appear to explain the role of this organ in the flea beetle jumping mechanism.
A histochemical and enzymatic study of the muscle fiber types in the water monitor, Varanus salvator
Authors: Gleeson Todd T.
Published: June 2005

Histochemical analysis of five muscles from the water monitor, Varanus salvator, identified three major classes of fibers based on histochemical activities of the enzymes myosin ATPase (mATPase), succinic dehydrogenase (SDH), and α‐glycerophosphate dehydrogenase αGPDH. Fast‐twitch, glycolytic (FG) fibers were the most abundant fiber type and exhibited the following reaction product intensities: mATPase, dark; SDH, light; αGPDH, moderate to dark. Fast‐twitch, oxidative, glycolytic (FOG) fibers were characteristically mATPase, dark; SDH, light; αGPDH, moderate to dark. The third class of fibers had the following histochemical characteristics: mATPase, light; SDH, moderate to dark; αGPDH, light. These fibers were considered to be either slow twitch, or tonic, and oxidative (S/O). Pyruvate kinase (PK), αGPDH, and citrate synthase (CS) activities were measured in homogenates of the same muscles studied histochemically. There was a positive relationship between both PK and αgpdh activities and the percentage of glycolytic fiber types within a muscle. Likewise, CS activities were greater in muscles high in FOG and S/O content. Based on CS activities, Varanus S/O fibers were eight‐fold more oxidative than FG fibers within the same muscle. PK/CS ratios suggested that FG fibers possess high anaerobic capacity, similar to the iguanid lizard Dipsosaurus. The fiber type composition of the gastrocnemius muscle, relative to that of other lizard species, suggests that varanid lizards may possess a greater proportion of FOG and S/O fibers than other lizards.
Cytokinesis: Effects of blocks between the mitotic apparatus and the surface on furrow establishment in flattened echinoderm eggs
Authors: Rappaport R. , Rappaport Barbara
Published: June 2005

The physical mechanism which accomplishes cytokinesis in animal cells develops as a consequence of interaction between the mitotic apparatus and the surface. The purpose of this investigation was to determine whether successful furrow establishment depends upon normal geometrical relations between the interactants in some areas but not in others. Blocks were positioned between different regions of the mitotic apparatus and the surface in flattened sea urchin (Tripneustes gratilla) and sand dollar (Echinarachnius parma) eggs. The blocking agents used were slit‐shaped perforations, needles, and oil drops. Results were consistent regardless of which block was used. Blocks located outside the equatorial plane did not affect furrowing. Perforations located in the equatorial plane resulted in furrow formation on the proximal surface of the perforation; no furrows formed distal to the perforation, either in the cell margin or the distal surface of the puncture. Oil drops and glass needles positioned in the equatorial plane affected furrowing. The magnitude of the effect was directly related to the size of the block. The results demonstrate that furrow establishment is not affected by drastic modifications of the geometrical relationship between the mitotic apparatus and the poles, but it is very susceptible to interference in the region between the mitotic apparatus and the equator.
Role of progesterone on oocyte maturation in the egg‐brooding hylid frog Gastrotheca riobambae (fowler)
Authors: de Albuja Carmen M. , Campos Margarita , del Pino Eugenia M.
Published: June 2005

In the egg‐brooding frog Gastrotheca riobambae (Fowler), oocyte maturation is comparable to the situation of other frog species. In isolated follicles, progesterone induces only germinal vesicle breakdown (GVBD), while human chorionic gonadotropin (hCG) induces GVBD and ovulation. In addition, defolliculated oocytes respond with GVBD to the treatment with progesterone, while hCG has no effect. As in other frogs, oocyte maturation in vitro depends on hormonal action and on the presence of divalent cations. In this frog, progesterone or a similar hormone conditions the brooding pouch for reproduction and induces pouch closure. Follicles from frogs with closed pouches showed GVBD after 15–17 hours of incubation with progesterone, while those from frogs with open pouches took 19–24 hours for GVBD. These findings suggest that follicles become stimulated for maturation when the pouch is closed and that this stimulated condition is maintained for several weeks in advance of the process of oocyte maturation. In G. riobambae, the external appearance of the pouch aperture indicates the reproductive condition of the ovary.