SPATIAL PATTERNS OF THREADLIKE ELEMENTS IN THE AXOPLASM OF THE GIANT NERVE FIBER OF THE SQUID (LOLIGO PEALII L.) AS DISCLOSED BY DIFFERENTIAL INTERFERENCE MICROSCOPY AND BY ELECTRON MICROSCOPY

The giant nerve fiber of the squid (Loligo pealii L.) has been investigated in situ, and in fresh and fixed preparations, by differential interference microscopy and electron microscopy. A continuous, three-dimensional network, composed of threadlike elements, was disclosed in the axoplasm. The threadlike elements in the axoplasm are twisted as a whole into a steep, right-handed helix. In a peripheral ectoplasmic region, the elements are more parallel to one another and more densely packed than in a central endoplasmic core. The threadlike elements can be resolved into a hierarchy of decreasing order of size. Successive levels of the hierarchy are formed by the association of smaller elements into larger ones. The following levels in the hierarchy of network elements have been distinguished: 1–3-µ-wide threads, 0.1–0.35-µ-wide strands, and 70–250-A-wide unit-filament strands. The differential interference microscope selects, from the network, threads oriented at a specific angle to the long axis of the axon. The specific angle depends upon the orientation of the long axis of the axon relative to the direction of shear. It is postulated that the network configuration is expressed in the solid-state properties of the axoplasm essential for the normal functioning of the nerve fiber.     

THE FINE STRUCTURE OF BRUNNER''S GLANDS IN THE MOUSE

Examined with the electron microscope, the secretory cells of the submucosal glands of Brunner in the mouse present a curious combination of the fine-structural features of both serous and mucus-secreting cells. The cells have numerous mitochondria, abundant basal ergastoplasm, dense secretory granules that bear a superficial resemblance to pancreatic zymogen granules, and an unusually extensive Golgi apparatus. The prominence of the lamellar, vesicular, and vacuolar elements of the Golgi complex facilitates detailed observation of these components. More evident than in other glandular cells, aggregates of small vesicles appear to represent the transitional elements and are vehicles for transport of the product between the ergastoplasm and the Golgi complex. The numerous vesicular evaginations of smooth-surfaced regions on cisternae of the rough-surfaced endoplasmic reticulum and accumulations of innumerable vesicles of similar size in the area between the nearest profiles of the ergastoplasm and the Golgi complex support this contention. The cytological characteristics and physiologic properties of Brunner's glands in various species are discussed briefly. It is concluded that the submucosal glands of the mouse are excellent material for exploration of the ultrastructural correlates of both protein and carbohydrate secretion, and it is suggested that their secretion may have functions other than those generally attributed to them, namely, chemical and mechanical protection of the duodenal surface epithelium.     

THE EFFECT OF IRRADIATED PLASMA ON NORMAL HUMAN CHROMOSOMES AND ITS RELEVANCE TO THE LONG-LIVED LYMPHOCYTE HYPOTHESIS

The persistence of unstable chromosome-type aberrations in peripheral blood lymphocytes of irradiated individuals has led to the proposal that some lymphocytes survive for many years in vivo without undergoing mitosis (Fitzgerald, 1964). It has recently been shown, however, that plasma from irradiated individuals can induce chromosomal damage in cultures of normal blood lymphocytes (Hollowell & Littlefield, 1968) even when the plasma donors were irradiated 7 years earlier (Goh & Sumner, 1968). Goh (1968) has therefore suggested that ‘An alternate explanation to the “long-lived cell” theory proposed by others…would be that a substance is produced or activated by total body irradiation and remains capable of affecting the chromosomes for extensive lengths of time'. The present results show that a lymphocyte chromosome-breaking factor can be induced in the plasma of blood irradiated in vitro as well as in vivo. All of the aberrations induced by this ‘plasma factor’and those reported by other workers can be interpreted as being of the chromatid type. Before the long-lived lymphocyte hypothesis can be brought into serious disrepute, it must be shown that the plasma factor can induce aberrations of the same type as persist after in vivo irradiation (i.e. unequivocal chromosome-type aberrations, such as dicentrics and rings) and that these can be induced in vivo.     

CHROMOSOMAL LOCALIZATION OF REPETITIVE DNA IN THE NEWT, TRITURUS

The repetitive DNA sequences of the newt, Triturus viridescens, have been studied by nucleic acid hybridization procedures. Complementary RNA was synthesized enzymatically from unfractionated newt DNA. This RNA hybridized strongly to the centromeric regions of both somatic and lampbrush chromosomes It also bound to other loci scattered along the lengths of the chromosomes The amplified ribosomal DNA in the multiple oocyte nucleoli was demonstrated by in situ hybridization     

Theoretical structure of the polar regions of the tropocollagen molecule

The theoretical conformations of poly (Gly-Ala-Glu) have been studied. This peptide was chosen as a model for the glycine led triads of the polar regions in collagen. The most favorable conformations are found to be based on the extended and folded forms of the 2₇ helix (2_7a and 2_7b). It is suggested that triple-strand structures of folded 2₇ helices exist in the polar collagen regions, and a structural model is presented which is in accord with recent ultrastructural deformation studies. It is a necessary condition for this structure that glycine occur in the lead of the peptide triads. In regions of the collagen molecule where the primary sequence does not contain triads (e.g., in the telopeptide region), random structures based on energy minimization of peptide neighbors are considered briefly. It seems likely that such regions contain an admixture of left-hand α, polyproline II, and 2₇ helix structures.     

REPRODUCTIVE PHYSIOLOGY IN THE SEAGRASS,SYRINGODIUM FILIFORME,FROM THE GULF OF MEXICO AND THE CARIBBEAN

Reproductive physiology in Syringodium filiforme Kütz. is controlled primarily by temperature under day lengths ranging from 12 hr to continuous light. Texas plants can be induced to flower at temperatures ranging from 20 to 24 C, but southern Gulf of Mexico and Caribbean plants are most readily induced at 23–24 C. Texas plants proceed to anthesis at temperatures above 22 C, but St. Croix plants require higher temperatures, above 25 C, for emergence of flowers from the bracts. Flowers induced under continuous light proceed to anthesis under day lengths shortened to 11 hr, but further floral induction is inhibited even under inductive temperatures. In natural seagrass beds, flowering occurs primarily under lengthening day lengths and warming temperatures that follow winter minima, but inflorescences may occur at other times of the year if temperatures permit.     

EFFECTS OF CALCIUM-CONTAINING FIXATION SOLUTIONS ON CHOLINERGIC SYNAPTIC VESICLES

Calcium (Ca)-containing fixation solutions applied to slices of electric organ of the electric ray, Narcine brasiliensis, have been shown to have three distinct ultrastructural effects on cholinergic synaptic vesicles of the nerve terminals. (a) An electron-dense particle (EDS) is observed within the vesicle; the particle is seen in unosmicated, unstained tissues and can be removed from thin sections by Ca-chelating agents. It is concluded that the EDS represents Ca bound by the vesicle. It is suggested that the bound ATP of the vesicle provides anionic Ca binding sites. (b) The vesicle membrane tends to ‘crinkle’ or collapse depending on the concentration of the other components of the fixative solution. The ‘crinkling’ or collapse are largely reversed by a wash step in the absence of Ca. (c) The presence of Ca results in the appearance of a population of vesicles which form characteristic fusions or ‘tight’ junctions with the terminal membrane. This appears to be morphological evidence for the proposal, which has been frequently put forward, that Ca facilitates such a fusion before discharge of vesicle-bound transmitter. With the discovery that the use of Ca-containing fixatives leads to the demonstration of a subpopulation of synaptic vesicles fused to the terminal membrane, we are led to propose that this is the ultrastructural location of the newly synthesized acetylcholine which has been shown by others to be preferentially released by stimulation.     

AN EXPERIMENTAL ANALYSIS OF THE ROLE OF CYTOPLASMIC FOUNTAIN STREAMING IN FURROW ESTABLISHMENT

During furrow establishment the equatorial cell surface is altered so that it becomes capable of exerting the physical force required for cytokinesis. It has been suggested that the alteration results from deposition of a furrow-organizing substance at the equator by convergence of “fountain streaming” patterns of cytoplasmic flow. The purpose of this investigation was to determine whether a fountain streaming pattern is essential for furrow establishment. The shape of sand dollar eggs was altered before the time of furrow establishment in ways that would greatly disrupt fountain streaming. Shapes that should have abolished regions of convergence and shapes that should have created several such regions were created by notching and perforating cells. Furrow establishment took place under circumstances that would be highly unlikely if a fountain streaming pattern of cytoplasmic currents were necessary.     

A FINE STRUCTURAL ANALYSIS OF CLEAVAGE INDUCTION AND FURROWING IN THE EGGS OF ARBACIA PUNCTULATA

A fine structural study has been carried out on the various formed elements present before, during, and after the first cleavage division, not only in normally developing Arbacia eggs, but also in eggs which have been induced to cleave prematurely by high-pressure centrifugation. The aim has been to ascertain whether or not any of the morphologically identifiable components may be involved in initiating the furrowing process. Also, attention has been given to the fine structure of the cytoplasmic cortex, particulary in the walls of the furrow, in the hope of reaching a better understanding of the mechanics of cleavage. The annulate lamellae and the membranous envelope of the nucleus are the only formed elements which disappear shortly before cleavage, not only in eggs undergoing normal division, but also in eggs which have been induced to cleave ahead of schedule by high-pressure, high-force centrifugation. Therefore, it is suggested as a tentative hypothesis that materials liberated upon disintegration of the nuclear membrane and the annulate lamellae play an essential role in initiating and effecting the furrowing reaction, especially since the stratification of these elements in experimentally induced eggs corresponds to the position of the developing furrow. Another of the membranous elements in the egg, the Golgi complex, shows considerable modification as a result of high-pressure centrifugation, but these structures do not undergo disintegration. Rather, they become curled into rounded bodies. The vacuole population is not greatly affected by inducing treatments. During cleavage, both naturally occurring and experimentally induced, a considerable number of 50 A filaments appear in the denser cytoplasmic cortex, but only in the walls of the furrow. These filaments are similar to those which have been demonstrated in a number of contractile cells. Accordingly, it is suggested that this fibrillar system may be actively involved in the development of the cleavage force.     

Ultrastructure of infection-thread development during the infection of soybean by Rhizobium japonicum

The location and topography of infection sites in soybean (Glycine max (L.) Merr.) root hairs spot-inoculated with Rhizobium japonicum have been studied at the ultrastructural level. Infections commonly developed at sites created when the induced deformation of an emerging root hair caused a portion of the root-hair cell wall to press against an adjacent epidermal cell, entrapping rhizobia within the pocket between the two host cells. Infections were initiated by bacteria which became embedded in the mucigel in the enclosed groove. Infection-thread formation in soybean appears to involve degradation of mucigel material and localized disruption of the outer layer of the folded hair cell wall by one or more entrapped rhizobia. Rhizobia at the site of penetration are separated from the host cytoplasm by the host plasmalemma and by a layer of wall material that appears similar or identical to the normal inner layer of the hair cell wall. Proliferation of the bacteria results in an irregular, wall-bound sac near the site of penetration. Tubular infection threads, bounded by wall material of the same appearance as that surrounding the sac, emerge from the sac to carry rhizobia roughly single-file into the hair cell. Growing regions of the infection sac or thread are surrounded by host cytoplasm with high concentrations of organelles associated with synthesis and deposition of membrane and cell-wall material. The threads follow a highly irregular path toward the base of the hair cell. Threads commonly run along the base of the hair cell for some distance, and may branch and penetrate into subjacent cortical cells at several points in a manner analagous to the initial penetration of the root hair.     

MECHANICAL PROPERTIES OF MUSSEL BYSSUS THREADS

The byssus threads of the common mussel, Mytilus edulis L.,have been tested mechanically and the results from the testsrelated to the ecology of the animal. The threads are mechanicallysimilar to other crystalline polymers such as polyethylene havinga modulus of about 10⁸N m^–2 and a long relaxation time.Resilience of 60% is similar to tendon; ultimate strain is aboutfive times that of tendon at 0.44. The thread is laid down witha prestrain of 10% and so guys the mussel in position. Calculationshows that a mussel with 50 byssus threads would be able toresist all but severe winter storms (Received 1 December 1978;     

THE INCORPORATION OF GLUCOSE INTO BRAIN GLYCOGEN AND THE ACTIVITIES OF CEREBRAL GLYCOGEN PHOSPHORYLASE AND SYNTHETASE: SOME EFFECTS OF AMPHETAMINE

Abstract— The effects of amphetamine sulphate (5 mg/kg intraperitoneally) on the incorporation of radioactive carbon from [U-¹⁴C]glucose into the glycogen of mouse cerebral cortex, midbrain and hind-brain have been investigated. In all brain regions studied amphetamine induced a rapid decrease in glycogen followed by a slower return to control values. No significant alterations were observed in the steady state concentration of cerebral glucose. The initial fall in glycogen was associated with a fall in its specific radioactivity relative to that of cerebral glucose, whereas the resynthesis of the polysaccharide was associated with a marked increase in the relative specific radioactivity of glycogen. Other experiments demonstrated that amphetamine initially stimulates the breakdown of prelabelled glycogen and that the resulting molecule has fewer 1,4 linked glucose side chains.
Studies of the relative forms of the enzymes glycogen phosphorylase and glycogen synthetase suggested that rapid post mortem changes were less likely to occur if cerebral tissue was fixed by means of a freeze-blowing technique. Amphetamine administration resulted in a rapid though transient elevation of phosphorylase a activity in mouse forebrain. The level of glycogen synthetase I activity was unchanged initially but was markedly elevated during the period when there was a large increase in the rate of incorporation of glucose into glycogen. It is suggested that cerebral glycogen metabolism is controlled, at least in part, by the interconversion of the 'active' and 'inactive' forms of glycogen phosphorylase and synthetase.     

Somatic chromosomes of higher diptera

Summary The chromosome complements of eighty brain cells ofHylemya antiqua have been studied. The eighty cells were found in thirty-three larvae. Total complement length (TCL) is not randomly distributed among the larvae. Because there is an inverse correlation between chromosome length and width, it appears that in the cells studied the different chromosome lengths are partly expressions of different stages of metaphase contraction. It is suggested that synchronous division of cells still occurs in late larvae.The length of each chromosome arm is highly correlated with that of every other arm. It is possible that the correlations are complete but that inadequate technique causes the departures from completeness which are observed. The chromosome lengths are corrected slightly for distortions, but the corrections make very little difference in the correlation coefficients. There is a high value for the correlation between the correlation of two arm lengths and the sum of the two arm lengths. This is to be expected if the perfect correlation between all arm lengths is being obscured by errors of drawing and measurement.The autosomal arms have very similar coefficients of variation. The arm ratios (length of long arm divided by short arm) are not correlated with TCL or with each other, and arm ratio is randomly distributed among the larvae. The sex chromosomes have a smaller coefficient of variation than the autosomes, so that they are relatively large in small cells and relatively small in large cells.Twenty-two cells inHylemya fugax were measured. The autosomes also showed a high correlation between arm lengths. An entirely heterochromatic autosomal arm showed the same phenomenon of a low coefficient of variation which was shown by the heteropycnotic sex chromosomes inH. antiqua. The low variability of heterochromatic regions accompanied by an apparently non-random distribution of the TCL may produce an erroneous picture of the species complement when dealing with small numbers.It is suggested that for simplicity in using cytological observations of this sort for taxonomic purposes, the technique of measuring the percent TCL of a chromosome plus its arm ratio be replaced by the percent TCL of each arm plus the average length difference between the arms of each chromosome pair in units of percent TCL.     

THE INFLUENCE OF THE HOST ON THE DIMENSIONS OF THE PLANT PARASITIC NEMATODE, DITYLENCHUS DESTRUCTOR

Measurement data and body ratios from eleven populations of Ditylenchus destructor are presented. The data for lengths of males and females have been analysed for variance, and many differences between population means are shown to be significant. The essential importance of structural characters and the care with which sizes and dimensional ratios must be used, in the identification of a species, is emphasized.     

THE FLYING ABILITY OF ARCHAEOPTERYX

Estimates for the wing span, mass and wing area of Archaeopteryx lithographica are provided, and these are used to derive certain of the flight parameters. From the data available on the lengths of skeletal components, amplified by examination of casts of the specimens and full-size enlargements of photographs, the wing span is estimated at 58–59 cm and the wing area as 479 cm2. To judge from animals of similar size, the mass was probably about 200 g. These figures give an estimated minimum flying speed of 7-6 m/sec and a wing loading of 0–42 gf/cm2. These figures are, and must be from their method of derivation, comparable with those of similar sized modern birds, These data are used to reconsider the possibility of flapping flight in this bird. It is suggested that the primitive anatomy of the pectoral skeleton has been somewhat over-emphasized, and it is shown that the pectoral crest on the humerus was relatively very large compared with modern birds. The power required to fly would require muscular physiology outside the range of mammalian (at least, human) capability, but well within the modern avian range. It is felt that Archaeopteryx was capable of flapping flight, but that it was probably not long sustained.     

ELECTRON MICROSCOPY OF BASOPHILIC STRUCTURES OF SOME INVERTEBRATE OOCYTES : I. PERIODIC LAMELLAE AND THE NUCLEAR ENVELOPE

Highly basophilic plate-shaped regions from oocytes of the surf clam have been examined with the electron microscope. The regions are composed of flat, hollow vesicles perforated by pores arranged, in surface view, in a hexagonal pattern. Cross-sections of this structure show a periodicity consisting of loops (cross-sections of the continuous space within the vesicle) alternating with spaces partly filled with dense material (pores). These structures are shown to resemble closely, the nuclear envelope. Similarities to and differences from basophilic regions of other cells are discussed and it is suggested that the small granules of Palade (38) are represented by granules composing the walls of the annuli of the nuclear envelope and assumed to be present in the annuli of the vesicles. Because of differences in the structure of these regions from basophilic regions of other cells, the name periodic lamellae is suggested since the structures show periodically repeating substructures (annuli) in both cross-sections and surface views.     

STRUCTURAL BIOLOGY OF THE FIBRES OF THE COLLAGENOUS AND ELASTIC SYSTEMS

The different types of fibres of the collagenous and elastic systems can be demonstrated specifically in tissue sections by comparing the typical ultrastructural picture of each of the fibre types with studies using selective staining techniques for light microscopy. A practicalmodus operandi, which includes the recommended staining procedures and interpretation of the results, is presented. Micrographs and tables are provided to summarize the differential procedures. Reticulin fibres display a distinct argyrophilia when studied by means of silver impregnation techniques, and show up as a thin meshwork of weakly birefringent, greenish fibres when examined with the aid of the Picrosirius-polarization method. In addition, electron-microscopic studies showed that reticulin fibres are composed of a small number of thin collagen fibrils, contrasting with the very many thicker fibrils that could be localized ultrastructurally to the sites where non-argyrophilic, coarse collagen fibres had been characterized by the histochemical methods used. The three different fibre types of the elastic system belong to a continuous series: oxytalan—elaunin—elastic (all of the fibre types comprising collections of microfibrils with, in the given sequence, increasing amounts of elastin). The three distinct types of elastic system fibres have different staining characteristics and ultrastructural patterns. Ultrastructurally, a characteristic elastic fibre consists of two morphologically different components: a centrally located solid cylinder of amorphous and homogeneous elastin surrounded by tubular microfibrils. An oxytalan fibre is composed of a bundle of microfibrils, identical to the elastic fibre microfibrils, without amorphous material. In elaunin fibres, dispersed amorphous material (elastin) is intermingled among the microfibrils.     

ESTROGEN-INDUCED CYTODIFFERENTIATION OF THE OVALBUMIN-SECRETING GLANDS OF THE CHICK OVIDUCT

The histological, ultrastructural, and biochemical changes occurring during hormone-induced cytodifferentiation of the ovalbumin-secreting glands in the chick oviduct have been studied. Marked perivascular edema is an initial response of the immature oviduct stroma to diethylstilbestrol administration and is accompanied by an interstitial migration of mononuclear cells. Mitotic activity in the immature mucosal epithelium increases within 24 hr, and glands begin to develop on days 2–4 as budlike invaginations into the subepithelial stroma. An immediate intracellular effect of the hormone is aggregation of previously dispersed ribosomes. Ribosomal zones in the nucleolus gain prominence, and there is a progressive development of rough endoplasmic reticulum in the epithelial cells. Extensive profiles of endoplasmic reticulum are present in the gland cells by day 6. Fine apical progranules appear in the epithelial cells on day 2, and ovalbumin can be measured immunochemically by day 3 at about the same time that new species of nuclear RNA have been identified. Ovalbumin granules form within condensing vacuoles in the Golgi zone and begin to be released into the lumina of the gland acini at about day 6 of the treatment.     

RNA TRANSPORT FROM NUCLEUS TO CYTOPLASM IN CHIRONOMUS SALIVARY GLANDS

The fine structure and cytochemistry of the extremely large RNA puffs, or Balbiani rings, in salivary gland nuclei of midge, Chironomus thummi, larvae have been investigated. The Balbiani rings are composed of a diffuse mass of electron-opaque 400 to 500 A granules, short threads about 180 to 220 A in diameter and associated fine chromatin fibrils. These components appear to be organized into brushlike elements which form the ring. Electron microscope cytochemistry has shown that the granules and short threads contain RNA. After ribonuclease digestion, only 50 to 100 A chromatin fibrils were apparent in the Balbiani ring, and the granules were no longer demonstrable. Deoxyribonuclease digestion had no apparent effect on these structures. Observations indicate that the granules are formed from the short threads and released into the nucleoplasm in which they are evenly distributed. At the nuclear envelope, many granules have been observed partially or completely within the nuclear pores. These granules become elongated and are shown to penetrate the center of the pore in a rodlike form, about 200 A in diameter. The Balbiani ring granules are not normally visible within the cytoplasm adjacent to the nuclear envelope, but have been rarely found in this region. It is suggested that the granules represent the product of the Balbiani ring, possibly a messenger RNA bound to protein, and that they regularly pass into the cytoplasm through a narrow central channel in the pores of the nuclear envelope.     

革胡子鲇卵巢在第一次性周期内分化与发育的研究

用光镜和电镜研究了革胡子鲇（Ｃｌａｒｉａｓｌａｚｅｒａ）原生殖细胞的起源迁移,卵巢在第１次性周期内的分化与发育以及各发育时期卵母细胞的超微结构。原生殖细胞起源于内胚层,有固定的迁移路线,进入生殖嵴后,生殖嵴进一步分化,出现卵巢腔分化成卵巢,卵母细胞在第１次性周期内的发育可分成６个时相,描述了各时相卵母细胞的显微结构与超微结构。同时,叙述了卵母细胞中卵黄发生的形态形成。