bluuebunny/crossref_metadata_2025 huggingface dataset:
Anti-cancer & anti-metastasis properties of bioorganic-capped silver nanoparticles fabricated from Juniperus chinensis extract against lung cancer cells
Authors: Noorbazargan Hassan , Amintehrani Sobhan , Dolatabadi Aghigh , Mashayekhi Ainaz , Khayam Nazanin , Moulavi Pooria , Naghizadeh Mohammad , Mirzaie Amir , Mirzaei rad Fatmeh , Kavousi Mahsa
Published: April 2021

The current study evaluated the anti-cancer properties of bio-functionalized silver nanoparticles fabricated by Juniperus chinensis leaf extracts. The nanoparticles were characterized by scanning electron microscopy, transmission electron microscopy, UV–visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, dynamic light scattering, Zeta potential and X-ray spectroscopy. Further, this study elucidated the cellular and molecular mechanisms of nanoparticles for anti-proliferative and apoptotic effects on human lung cancer cells (A549) and compared them with commercial drug cisplatin. The size of the spherical nanoparticle was 12.96 nm with negative zeta potential. Up-regulation of caspase 3,9 and p53, Annexin V-FITC/PI, DAPI staining, and ROS production indicated the remarkable apoptotic effect of AgNPs compared to cisplatin. Moreover, down-regulation of MMP2/MMP9 scratch and matrigel assays revealed anti-metastatic properties of AgNPs. Cell cycle analysis and downregulation of cyclin D1 indicated cancer cell cessation in the G0/G1 phase. Overall, the results revealed that the green-synthetized AgNPs had anti-metastasis and anti-proliferation effects on lung cancer cells in comparison to cisplatin with lower side effects on the normal cell line.
Types of surgical patients enrolled in enhanced recovery after surgery (ERAS) programs in the USA
Authors: Singh Sunitha M. , Liverpool Asha , Romeiser Jamie L. , Thacker Julie , Gan Tong J. , Bennett-Guerrero Elliott
Published: April 2021

Background

Enhanced Recovery After Surgery (ERAS) programs have gained traction across US hospitals in the past two decades. Initially implemented for elective colorectal surgical procedures, ERAS has expanded to a variety of surgical service lines. There is little information regarding the extent to which various surgical service lines use ERAS.

Methods

A survey was performed to describe the prevalence of ERAS programs across surgical service lines in the USA. The survey had questions regarding the number of ERAS programs, operating rooms (ORs) and presence of anesthesia and/or surgery residency program at an institution. The survey was administered electronically to members of the American Society for Enhanced Recovery (ASER) and manually to participants at the 2018 Perioperative Quality and Enhanced Recovery Conference in San Francisco, CA.

Results

Responses were received from 88 unique institutions. The most commonly reported surgical service lines were colorectal (87%), gynecology (51%), orthopedic (49%), surgical oncology (39%), and urology (35%). A significant positive association was observed between the number of ORs and the number ERAS programs (Spearman’s Rho 0.5, p<0.0001). Furthermore, institutions that reported an anesthesia and/or surgery residency program had more ERAS programs (mean 5.0 ± 3.2) compared to those that did not (mean 2.0 ± 2.0) (Wilcoxon rank sum p< 0.001).

Conclusions

ERAS has expanded to a large extent outside of the colorectal surgery service line with increases notable in orthopedic surgery, obstetric/gynecology, surgical oncology, and urology procedures. Institutions with a higher number of ORs and the presence of an anesthesia and/or surgery residency program are associated with an increased number of ERAS programs.
Street-level workers, managers and institutional tensions: a comparative ethnography of healthcare practices of in/exclusion in three Italian public organisations
Authors: Perna Roberta
Published: April 2021

Public organisations are fundamental actors in migrant incorporation processes, as they are in charge of assessing migrants’ entitlement and providing access to welfare services. While a lot has been written on the individual determinants of street-level decisions, the role of organisational and institutional factors in shaping implementation practices has received little attention so far. By linking the street-level bureaucracy approach and the neo-institutionalist perspective in organisational analysis, this article investigates how public organisations mediate migrant incorporation processes in the field of healthcare. Drawing on a comparative ethnographic study of three public health organisations in an Italian region, the paper suggests that, in times of institutional tensions, managers’ priorities and framings of the issue, the ways they respond to decision-makers’ goals and allocate resources for implementing them, orient - and lead to variation in - street-level healthcare practices of in/exclusion for migrants with irregular status.
Development of a Certification Exam to Assess Undergraduate Students’ Proficiency in Biochemistry and Molecular Biology Core Concepts
Authors: Zeidan Quira , Loertscher Jennifer , Wolfson Adele J. , Tansey John T. , Offerdahl Erika G. , Kennelly Peter J. , Dries Daniel R. , Moore Victoria Del Gaizo , Dean Diane M. , Carastro L. Michael , Villafañe Sachel M. , Tyler Ludmila
Published: April 2021

Assessment of student learning aids in evidence-based decisions about educational efforts. This Essay describes the development of an annual certification exam offered by the American Society for Biochemistry and Molecular Biology and supported by a community of volunteers that assesses undergraduate students’ proficiency in core concept areas.
Management of Salivary Gland Malignancy: ASCO Guideline
Authors: Geiger Jessica L. , Ismaila Nofisat , Beadle Beth , Caudell Jimmy J. , Chau Nicole , Deschler Daniel , Glastonbury Christine , Kaufman Marnie , Lamarre Eric , Lau Harold Y. , Licitra Lisa , Moore Michael G. , Rodriguez Cristina , Roshal Anna , Seethala Raja , Swiecicki Paul , Ha Patrick
Published: April 2021

PURPOSE

To provide evidence-based recommendations for practicing physicians and other healthcare providers on the management of salivary gland malignancy.

METHODS

ASCO convened an Expert Panel of medical oncology, surgical oncology, radiation oncology, neuroradiology, pathology, and patient advocacy experts to conduct a literature search, which included systematic reviews, meta-analyses, randomized controlled trials, and prospective and retrospective comparative observational studies published from 2000 through 2020. Outcomes of interest included survival, diagnostic accuracy, disease recurrence, and quality of life. Expert Panel members used available evidence and informal consensus to develop evidence-based guideline recommendations.

RESULTS

The literature search identified 293 relevant studies to inform the evidence base for this guideline. Six main clinical questions were addressed, which included subquestions on preoperative evaluations, surgical diagnostic and therapeutic procedures, appropriate radiotherapy techniques, the role of systemic therapy, and follow-up evaluations.

RECOMMENDATIONS

When possible, evidence-based recommendations were developed to address the diagnosis and appropriate preoperative evaluations for patients with a salivary gland malignancy, therapeutic procedures, and appropriate treatment options in various salivary gland histologies. Additional information is available at www.asco.org/head-neck-cancer-guidelines .
Re/pro/ductions
Authors: Mercier Thomas Clément
Published: April 2021

This article examines Jacques Derrida’s work of self-reflection on his own teaching practice by using as a guiding thread the problematics of reproduction in the seminars of the 1970s. The first part of the article examines the sequence of seminars taught by Derrida at École normale supérieure from 1971 to 1977 to show how the concept of reproduction is deconstructed by Derrida across several seminars. Derrida systematically demonstrates, across several themes and fields (sociology and economy, biology and sexuality, art, technique, ontology, and so on), that the critical recourse to the concept of reproduction (for instance, in its Marxist form) risks being complicit in the reproductive system it criticizes. The deconstructive motif of débordement is introduced to problematize this onto-logic of re-production. The second part of the article analyzes more specifically the unpublished seminar GREPH, le concept de l’idéologie chez les idéologues français (1974–75), in which Derrida examines the seminar function, his role as a teacher, and his own situation within the French educational system. In particular, Derrida offers a deconstructive critique of the reproductive effects of teaching, and of the institution of philosophy inasmuch as it functions as a reproductive machine. This work of deconstruction is done in the seminar notably through readings of Marx, Engels, and Althusser, with special attention to the concepts of ideology, reproduction, and sexual difference.
The Seminar in Deconstruction
Authors: Rosenthal Adam R.
Published: April 2021

In this article the author explores how the problem of the seminar enters into the work of Jacques Derrida. He shows how it emerges not only within the context of the teaching institution but also as a conceptual thematic with a history far in excess of the educational institutions of France. As early as 1968 and as late as 2003, the word, concept, figure, and institution of “the seminar” was one that Derrida worked to define and problematize. The author thus asks how Derrida’s autobiographical relationship with the institution of the seminar both influenced and was influenced by what one might call the philosophical problem of the seminar. As Derrida points out on a number of occasions, the seminar is not a neutral space. Indeed, it is a particularly ambivalent one, as early discussions of it in “Plato’s Pharmacy” and Clang show. In appropriating the form, not only for his teaching but also as a problematic of the seminars that he gave, the author argues that Derrida precisely embraced the ambivalence of a space at once caught up in the politics of reproduction, hegemony, and tradition and, to that very extent, the site of a potential “event.”
Questions of the Foreigner in Of Hospitality
Authors: Haddad Samir
Published: April 2021

This article examines Derrida’s use of untranslatables as a tool for teaching in his seminars. Focusing specifically on two related clusters of terms that appear in the seminar sessions published in Of Hospitality—xenos/étranger/foreigner and hostis/hôte/host/guest—the author shows how Derrida uses untranslatable terms as a pedagogical device to enhance his students’ philosophical understanding, thus providing instructors with a model of a plurilingual pedagogical practice that can be followed in their own teaching of philosophy.
Über Zelldifferenzierung im Integument der Insekten und ihre Bedingungen
Authors: Henke Karl
Published: April 2021

Die besonderen Beiträge, die das Integument der Insekten zu den Fragen der Zelldifferenzierung bietet, beruhen wesentlich auf der Vielzahl verschieden-artiger Differenzierungen, die bei dieser hochentwickelten und dabei doch kleinwüchsigen Tiergruppe auf einzelne große Spezialzellen verteilt oft auf engem Raum nebeneinander vorkommen, oder auch, in der Metamorphose durch Häutungen die sonst meist verborgene Fähigkeit der Zelle zu wieder-holten Differenzierungsleistungen demonstrierend, nacheinander von denselben Zellen hervorgebracht werden. Ein weiterer charakteristischer Zug in der Entwicklung des Insektenintegumentes ist ihre Abhängigkeit von einer Serie hormonaler Anstöße, in deren Gefolge nach jeder Häutung zunächst eine Mitosenperiode, danach die Herstellung einer neuen Kutikula stattfindet und schließlich die Häutungsdrüsen in Tätigkeit treten, die beim Vollzug der nächsten Häutung mitwirken. Im Lauf der Entwicklung verändert sich nun die Zusammensetzung des jeweils wirksamen Hormonsystems, und damit, allein in Abhängigkeit von ihm, auch die Differenzierungsleistung des Integuments. So bringt das Grundepithel eines holometabolen Insekts unabhängig von seinem Alter und seiner Vorgeschichte je nach dem hormonalen Milieu, dem es aus-gesetzt wird, entweder eine larvale oder eine pupale oder schließlich eine imaginale Kutikula hervor (Piepho, 1950,1951). Im normalen Entwicklungsgang erfährtes also eine zweimalige Umdifferenzierung. Daneben können im Epithel regionale Unterschiede in der Höhe der Schwelle gegenüber bestimmten hormonalen Faktoren bestehen und ein Muster aus verschiedenen nebeneinander auftretenden Kutikularbildungen erzeugen (Piepho & Heims, 1952). Besonders empfindliche Anzeiger sowohl für die hormonalen wie auch für andere die Zelldifferenzierung bestimmende Einflüsse finden sich aber unter den für die Insekten charakteristischen, in das Grundepithel eingefügten Kleinorganen, die als Borsten, Schuppen, Drüsen oder Sinnesorgane aller Art jeweils aus wenigen, zum Teil einzeln unterschiedlich differenzierten und zu einer bestimmten Grofie heranwachsenden Zellen zusammengesetzt sind (Henke, 1947,1951).
Étude de quelques phénomènes de radioprotection sur un organe embryonnaire de Poulet cultivéin vitro
Authors: Kirrmann par J. M.
Published: April 2021

Au cours de travaux antérieurs, nous avons montré que certaines substances radioprotectrices étaient capables de prévenir plus ou moins complètement l’apparition d’une certaine malformation chez l’embryon de Poulet après irradiation aux rayons X (Wolff & Kirrmann, 1954; Kirrmann, 1955, 1957a). De même, certains gaz, substitués à l’atmosphère, sont capables de modifier l’action tératogène des rayons X (Kirrmann, 1957b, 1959). Ces différents corps conservent-ils leur action sur un organe embryonnaire isolé de l’organisme et cultivé à l’aide d’une technique de culture organotypique? Le présent travail se propose de répondre à cette question, intéressante du point de vue du mode d’action des rayonnements ionisants sur la matière vivante, et du développement des organes embryonnaires en culture.
Some New Data concerning the Formation of the Definitive Endoblast in the Chick Embryo
Authors: Vakaet L.
Published: April 2021

The origin of the primary deep layer in the chick blastoderm is a difficult problem, mainly because its formation commences during intra-uterine life. Yet this layer is not complete when the egg is laid. The process of completion is not yet uniformly interpreted. Some workers propose a concentric ingrowth from the germ-wall towards the centre of the blastoderm; Disse (1878) was the first to mention this. Others describe an anteriorly directed ingrowth exclusively from the posterior germ-wall—among them Duval (1888), Patterson (1909), and, more recently, Lutz (1955). Chen (1932) concludes from a study of the orientation of mitotic spindles that cell-proliferation, mainly taking place in the posterior germ-wall, is responsible for the completion of the endophyll. Isolated but multiple invagination of cells has been held partly responsible for the completion of the lower germ-layer. Nowack (1902) was the first to announce this opinion clearly; these cells were described as joining the endophyll, having descended from the ectophyll. Peter (1938), whose description of the stages of endophyll formation has become a classic, believes cell-proliferation to be the main factor in its completion. However, he admits addition of cells from the ectophyll. He moreover denies categorically that there is any relative movement of cells in the endophyll with respect to the ectophyll.
The Sex Ratio Before Uterine Implantation in the Golden Hamster
Authors: Sundell Gunhild
Published: April 2021

Blastocysts from the golden hamster have been sexed at 3·5 days after mating, i.e. before implantation, by analysing metaphase plates for the presence of XX or XY chromosomes. Out of 98 embryos sexed, 63 were males and 35 females, giving a sex ratio of 180:100; this significantly deviates from a ratio of 1:1 (X2 = 8·00, p < 0·01). The sex ratio among 167 young of the golden hamster was found to be 106:100. Some possibilities for the origin of this high sex ratio in early stages is discussed.
Axial Elongation in the Mouse and its Retardation in Homozygous Looptail Mice
Authors: Smith L. Jean , Stein Kathryn F.
Published: April 2021

Mice homozygous for the mutation Looptail have shorter bodies than normal homozygous or heterozygous littermates. Shortening is relatively greater in the posterior portion of the embryo. The regression or the shortening of the primitive streak is retarded but the separation of notochord from gut occurs prematurely in the abnormal embryos. Umbilical cords are shorter in Lp/Lp mice than in normal embryos or in heterozygotes. The possible significance of these facts in relation to the open neural folds in the homozygous Lp/Lp mice is discussed.
The Inhibitory Action of Insulin in the Early Chick Embryo
Authors: Barron Patricia , Mckenzie J.
Published: April 2021

Insulin, in varying concentrations, has been applied to the chick embryo explanted by New’s technique after 24 hours incubation at stages 3–8 and cultured for 22–24 hours in vitro. It has been demonstrated that, in whatever manner insulin is applied to the embryo, its effects are most frequently manifest in the brain and neural tube. Somites are inhibited to a much lesser extent and heart, except with the higher doses, is unaffected. Application of either sodium pyruvate or nicotinamide with the insulin has very little protective action and larger doses of both these substances potentiate the inhibitory action of insulin. Diphosphopyridine nucleotide in the oxidized form given with the insulin provides complete protection, but the reduced form of DPN has no such effect. Previous work by Spratt and others on the metabolic characteristics of the early chick embryo, by Landauer on the teratogeni caction of insulin, and recent investigations (e.g. by Randle & Smith) are considered in the light of our findings. Like Duffey & Ebert (1957) we hesitate to accept Spratt’s (1950) hypothesis for the dependence of brain on oxidative mechanisms and the heart on glycolysis. We suggest, instead, that the heart, in contrast to the brain, can if necessary survive for a period of time under anaerobic conditions but, where possible, it makes full use of aerobic metabolic pathways. The complete protection afforded by DPN but not by DPNH leads us to believe that the site of action of insulin lies in the reoxidation of the pyridine nucleotides, i.e. in a hydrogen transport system.
A Simplified Method for the Fusion of Two or More Amphibian Embryos
Authors: Hegenauer John C. , Nace George W.
Published: April 2021

The technique of fusing amphibian embryos in parabiotic or telobiotic union has been used extensively in the past 50 years for a variety of experimental and educational purposes (see citations in Burns, 1955; Hamburger, 1942, 1960; Rugh, 1948). Failures with current techniques, however, are too frequent. These are occasioned, most commonly, by improper juxtaposition of the embryos to facilitate wound healing, by separation of the embryos as a result of ciliary action, by freeing the embryos from the operating dish prior to completion of wound healing, by damage produced in freeing the conjoined embryos, or by infection. Many of these difficulties arise because the methods of constraining the embryos in paraffin-beeswax or permoplast operating dishes obstruct the operator’s view. It is a less obvious, but important, disadvantage that this method also prevents the free flow of medium just at the time when optimal conditions are necessary for maintenance and healing. This is especially true when anesthetized embryos are conjoined.
A Cytological Analysis of the Origin of Chromaffinoblasts in Some Mammals
Authors: Smitten N. A.
Published: April 2021

Two major facts have been established in cytological studies of cell differentia-tion in the rudiments of ganglia from the moment of their formation: In early embryogenesis there is a divergent differentiation of the originally uniform cells into neuroblastic and spongioblastic series.At later stages of embryogenesis there occurs a separation of chromaffino-blasts from the elements of the spongioblastic series.
Prolonged Life of AnucleolateXenopusTadpoles in Parabiosis
Authors: Wallace H.
Published: April 2021

Anucleolate Xenopus mutants have survived in parabiosis with normal individuals for four times their usual life-span. All tissues survive at least twice as long in parabiosis as they do in control anucleolate larvae. Lethality is thus concluded to be a secondary effect of the mutation, probably resulting from a defective blood-circulation. Several anucleolate tissues are lost despite parabiosis, but not in a manner suggesting a cell-lethal action. The mutation is better described as cell-sub vital. The anucleolate syndrome, of neural pycnosis and general retardation of differentiation and growth, is maintained in parabiosis. These symptoms may be direct results of the mutation in each cell. Some further cellular differentiation’ and growth in parabiosis show that the mutation does not completely arrest development. The anucleolate syndrome is found to be consistent with the theory that the nucleolus regulates some basic process of cellular metabolism.
Degeneration of the Remaining Pronephros ofRana temporariaafter Unilateral Pronephrectomy
Authors: fox H.
Published: April 2021

Hatched larvae of R. temporaria at stages approximately equivalent to stages 25-26 for R. dalmatina (Cambar & Marrot, 1954) were unilaterally pro-nephrectomized, and the fate of the single remaining pronephros system was compared with that of paired control systems throughout the phase of pronephric degeneration, which takes place in stages 49-54. In terms of comparable larval stages the remaining pronephros of operated specimens does not differ in its degeneration from control pronephroi, either qualitatively or quantitatively (expressed in terms of pronephric (or glomus) length), except that it includes some swollen tubules—a residue of the tubule compensatory hypertrophy resulting from unilateral pronephrectomy. After unilateral pronephrectomy unharmed glomeri in situ, which belonged to extirpated pronephroi, are likewise identical with contralateral glomeri of remaining pronephroi of the other side, and with the paired glomeri of controls. Hypo- or hyperfunction do not affect normal pronephric degeneration, and it is likely that the phenomenon is bound up with metamorphic processes independent of function.
The Effect of Chloroacetophenone on Chick Embryos Culturedin vitro
Authors: Lakshmi M. S.
Published: April 2021

The effect of chloroacetophenone (0·0005 M), which has been described as a powerful and irreversible —SH reactant, has been studied on chick embryos cultured in vitro at the primitive-streak and head-process stages. Abnormalities were produced predominantly in the brain region, and included improper differentiation, partial or complete non-closure, and defective lumen. Neural tubes were irregular and open. Shortening of the axis was also common. Embryos at the head-process stage were not affected by the substance at the concentration used. The effect of the chemical on the morphogenesis of the chick embryo is discussed.
A single cell approach to problems of cell lineage and commitment during embryogenesis ofDrosophila melanogaster
Authors: Technau Gerhard M.
Published: April 2021

The mechanisms leading to the commitment of a cell to a particular fate or to restrictions in its developmental potencies represent a problem of central importance in developmental biology. Both at the genetic and at the molecular level, studies addressing this topic using the fruitfly Drosophila melanogaster have advanced substantially, whereas, at the cellular level, experimental techniques have been most successfully applied to organisms composed of relatively large and accessible cells. The combined application of the different approaches to one system should improve our understanding of the process of commitment as a whole. Recently, a method has been devised to study cell lineage in Drosophila embryos at the single cell level. This method has been used to analyse the lineages, as well as the state of commitment of single cell progenitors from various ectodermal, mesodermal and endodermal anlagen and of the pole cells. The results obtained from a clonal analysis of wild-type larval structures are discussed in this review.
Thymocyte/stromal cell chimaerism in allothymus-graftedXenopus:developmental studies using theX. borealisfluorescence marker
Authors: Horton John D. , Russ Jane H. , Aitchison Pamela , Horton Trudy L.
Published: April 2021

These experiments employ the X. borealis (quina-crine-fluorescence) cell marker to illustrate that froglet (normal or in vivo-irradiated) thymuses, alloimplanted to 4- to 6-week-old, 7-day-thymec-tomized hosts, become filled with host lymphoid cells, while a range of thymic stromal cell types (e.g. epithelial derivatives and reticuloendothelial cells) remain donor derived. A time-course study of 4μm historesin-embedded sections reveals that for normal thymus implants, host cells begin to immigrate in good number only after metamorphosis. In contrast, 3000 rad-irradiated thymus implants begin to be repopulated with host lymphocytes within 2 weeks postimplantation, when hosts are still at a late larval stage of development. Despite rapid colonization by host lymphoid cells, irradiated thymuses remain small and often disappear in early adult life. Donor-derived lymphocytes frequent the blood and both the red pulp and perifollicular regions of the spleen following normal thymus implantation, whereas such thymic emigrants were not seen in the periphery of thymectomized hosts grafted with irradiated thymus glands.
The establishment of the embryonic-abembryonic axis in the mouse embryo
Authors: Garbutt C. Louise , Chisholm Julia C. , Johnson Martin H.
Published: April 2021

The influence of cell division order on the establishment of the embryonic–abembryonic axis (EA axis) of the mouse embryo was investigated. Aggregate embryos were constructed in which a labelled cell (or pair of cells) was combined with a group of unlabelled cells all of which were up to one cell cycle earlier or later in their progress through development to the blastocyst stage. The aggregates were cultured first to the nascent blastocyst stage and then to the expanded blastocyst stage. The positions of the progeny of the labelled cells in relation to the nascent blastocoel and to the orientation of the embryonic–abembryonic axis were recorded. It was concluded that cell division order does influence the establishment of the EA axis, early dividing cells tending to be associated with the nascent blastocoel and the site of the nascent blastocoel tending to mark the site of the abembryonic pole. However, the influence of division order was diminished by a requirement for intercellular cooperation during blastocoel formation and by a counteracting influence of division order arising from its effects on the allocation of cells to the inner cell mass.
The galactose-specific receptor system in rat liver during development
Authors: Dini Luciana , Conti-Devirgiliis Laura , Russo-Caia Salvatore
Published: April 2021

The number and distribution of galactose-specific binding sites were investigated in rat liver cells during perinatal development. Ligand binding to hepatocytes, macrophages and endothelial cells was followed with in vitro and in situ experiments by electron microscopy, using lactosylated bovine serum albumin adsorbed onto 5 nm colloidal gold particles as ligand.

Binding capacity, starting at a late stage of fetal development, is very low both on the hepatocyte and on the macrophage surface, which show single particles statistically distributed. By contrast, bound particles are absent from fetal endothelial cells, which also lack the typical coated regions. In vivo, experiments at 37 °C show that endocytosis occurs to some extent in prenatal life.

These results indicate that the expression of galactose-specific receptors’ activity on the different liver cell types follows different developmental patterns, which are independently modulated.
The assembly and positioning of cytoskeletal elements in Tetrahymena
Authors: Williams Norman E. , Honts Jerry E.
Published: April 2021

The oral skeleton of Tetrahymena is a precisely arranged assemblage of basal bodies, microtubule bundles and connecting filaments found associated with the feeding structure in this cell type. Tubulin and filament proteins have been isolated but no actin has been recovered. The conditional mutant NP1 of Tetrahymena thermophila forms a normal oral skeleton at the permissive temperature (28°C), but forms an abnormal one at the restrictive temperature (37°C). Antibodies against tubulin and oral filament protein OF1 were used to visualize the abnormal oral skeleton and stages in its development, and ultrastructural comparisons of abnormal and wild-type oral skeletons were made. It was found that the overall pattern of organization was altered in the mutant, whereas the substructure appeared every where to be normal. Studies of cells in which the mutant phenotype was coming to expression revealed that normal basal bodies in the oral skeleton failed to move from the disordered state characteristic of early stages of development into the correct pattern of four organized clusters characteristic of later stages. Together, these results suggest that the lesion in NP1 does not affect cytoskeleton assembly per se, but instead affects a discrete mechanism responsible for the positioning of cytoskeletal elements with respect to each other after they have been formed (metaassembly). Reasons for suspecting the involvement of the membrane skeleton are presented.
When and how does cell division order influence cell allocation to the inner cell mass of the mouse blastocyst?
Authors: Garbutt C. Louise , Johnson Martin H. , George Martin A.
Published: April 2021

Aggregate 8-cell embryos were constructed from four 2/8 pairs of blastomeres, one of which was marked with a short-term cell lineage marker and was also either 4 h older (derived from an early-dividing 4-cell) or 4h younger (derived from a late-dividing 4-cell) than the other three pairs. The aggregate embryos were cultured to the 16-cell stage, at which time a second marker was used to label the outside cell population. The embryos were then disaggregated and each cell was examined to determine its labelling pattern. From this analysis, we calculated the relative contributions to the inside cell population of the 16-cell embryo of older and younger cells. Older cells were found to contribute preferentially. However, if the construction of the aggregate 8-cell embryo was delayed until each of the contributing 2/8 cell pairs had undergone intercellular flattening and then had been exposed to medium low in calcium to reverse this flattening immediately prior to aggregation, the advantage possessed by the older cells was lost. These results support the suggestion that older cells derived from early-dividing 4-cell blastomeres contribute preferentially to the inner cell mass as a result of being early-flattening cells.
Neural determination of muscle fibre numbers in embryonic rat lumbrical muscles
Authors: Ross J. J. , Duxson M. J. , Harris A. J.
Published: April 2021

The generation and development of muscle cells in the IVth hindlimb lumbrical muscle of the rat was studied following total or partial denervation. Denervation was carried out by injection of β-bungarotoxin (j3-BTX), a neurotoxin which binds to and destroys peripheral nerves. Primary myotubes were generated in denervated muscles and reached their normal stable number on embryonic day 17 (E17). This number was not maintained and denervated muscles examined on E19 or E21 contained many degenerating primary myotubes. Embryos injected with β-bungarotoxin (β-BTX) on E12 or E13 suffered a partial loss of motoneurones, resulting in a reduced number of axons in the L4 ventral root (the IVth lumbrical muscle is supplied by axons in L4, L5 and L6 ventral roots) and reduced numbers of nerve terminals in the intrinsic muscles of the hindfoot. Twitch tension measurements showed that all myotubes in partly innervated muscles examined on E21 contracted in response to nerve stimulation. Primary myotubes were formed and maintained at normal numbers in muscles with innervation reduced throughout development, but a diminished number of secondary myotubes formed by E21. The latter was correlated with a reduction in number of mononucleate cells within the muscles. If β-BTX was injected on E18 to denervate muscles after primary myotube formation was complete, E21 embryo muscles contained degenerating primary myotubes. After injection to denervate muscles on E19, the day secondary myotubes begin to form, E21 muscles possessed normal numbers of primary myotubes. In both cases, secondary myotube formation had stopped about 1 day after the injection and the number of mononucleate cells was greatly reduced, indicating that cessation of secondary myotube generation was most probably due to exhaustion of the supply of competent myoblasts. We conclude that nerve terminals regulate the number of secondary myotubes by stimulating mitosis in a nerve-dependent population of myoblasts and that activation of these myoblasts requires the physical presence of nerve terminals as well as activation of contraction in primary myotubes.
Production of fertile salamanders by transfer of germ cell nuclei into eggs
Authors: Lesimple M. , Dournon C. , Labrousse M. , Houillon Ch.
Published: April 2021

In amphibians, the ability of somatic cell nuclei to give rise to embryos in nuclear transplantation experiments has been thoroughly investigated and shown to be limited, except in Xenopus laevis. Similar experiments have been performed with primordial germ cells from genital ridges and spermatogonia. In the present paper, we have studied the capacity of germ cell nuclei to promote development of complete and fertile adults in the urodele amphibian Pleurodeles waltl. Germ cell nuclei were taken from larvae at progressive stages of larval development up to meta-morphosis and transplanted into enucleated eggs. Two nonlethal chromosomal mutations were used as nuclear markers in two control series. Nuclei from all developmental stages tested were able to initiate larval development. Furthermore, nine individuals underwent metamorphosis (representing 3 % of normal blastulae) and six of these animals are now adults. When two of these six animals, a male and a female, were mated to each other, the offspring were normal. These results show conclusively, for the first time in amphibians, that germ cell nuclei remain totipotent at least during the larval period.
Clonal analysis of the developmental potential of 6th and 7th day visceral endoderm cells in the mouse
Authors: Cockroft D. L. , Gardner R. L.
Published: April 2021

Single visceral endoderm cells from the embryonic regions of 6th and 7th day conceptuses were cloned by blastocyst injection using the genetically determined presence or absence of cytoplasmic malic enzyme activity as an in situ cell marker. In the 6th day cell injection experiments wild-type donor cell clones were readily discernible in the extraembryonic membranes of more than half the midgestation null host conceptuses; a much lower cloning efficiency was encountered with 7th day cells. With one exception, the clones appeared to be confined to the extraembryonic endoderm, most occurring in the parietal endoderm only. By means of the in situ marker, the morphology and arrangement of donor cells in the parietal endoderm could be compared with that of host cells, thereby demonstrating that they had undergone an appropriate phenotypic change after colonizing this tissue. Control experiments indicated that the procedures used to dissociate and select donor cells for injection were likely to have ensured that a representative sample of visceral endoderm cells had been transplanted. Hence on the 6th day of development, a high proportion of cells in the visceral endoderm seem to retain primitive endodermal characteristics, but these appear to be lost by the 7th day, when markers of visceral endoderm differentiation have first been demonstrated.
An inducer protein may control the timing of fate switching in a bipotential glial progenitor cell in rat optic nerve
Authors: Hughes Simon M. , Raff Martin C.
Published: April 2021

In rat optic nerve, oligodendrocytes and type-2 astrocytes develop from a common (O-2A) progenitor cell. The first oligodendrocytes differentiate at birth, while the first type-2 astrocytes differentiate in the second postnatal week. We previously showed that the timing of oligodendrocyte differentiation depends on an intrinsic clock in the O-2A progenitor cell. Here we provide evidence that the timing of type-2 astrocyte differentiation, by contrast, may depend on an inducing protein that appears late in the developing nerve. We show that extracts of 3- to 4-week-old, but not 1-week-old, rat optic nerve contain a protein (apparent Mr ∼ 25 000) that induces O-2A progenitor cells in culture to express glial fibrillary acidic protein (GFAP), an astrocyte-specific marker in the rat central nervous system.
Molecular and cellular aspects of patterning sensory neurone connections in the vertebrate nervous system
Authors: Davies Alun M.
Published: April 2021

Sensory neurones display organizational features that are common to most populations of neurones in the vertebrate nervous system. First, their cell bodies are arranged in discrete groups (the sensory ganglia) each of which has characteristic receptive and projection fields (the peripheral and central target fields, respectively, to which the peripheral and central processes of the neurones grow in development). Second, nerve fibres make specific terminations within each target field; an important feature is that different kinds of sensory receptors in the periphery are connected to the appropriate kinds of second-order neurones in the central nervous system (CNS). Third, nerve fibre terminations in the peripheral and central target fields have a similar topographic order.
Primordial germ cells of the young chick blastoderm originate from the central zone of the area pellucida irrespective of the embryo-forming process
Authors: Ginsburg Malka , Eyal-Giladi Hefzibah
Published: April 2021

Early chick blastoderms (stages X–XII) were divided by a circular cut into two fragments. In one experimental group, the area opaca was separated from the marginal zone and the central disc of the area pellucida, while in another group the area opaca plus marginal zone were separated from the central disc. Other blastoderms of equivalent stages were each cut into three strips of equal size (either perpendicular or parallel to the axis of symmetry). The fragments were isolated and incubated for 43–48 h after which they were PAS-stained, whole-mounted and checked for the presence of primordial germ cells (PGCs). The results showed that most of the PGCs originated from the central disc and not from the periphery of the area pellucida and that they segregated from this zone even if no embryonic axis developed in the explant. In such cases, the PGCs were found to be dispersed throughout the entire explant, usually in association with forming blood islands. When an axis did develop in the explant, the PGCs were found to be concentrated around its anterior end, in a pattern resembling the germinal crescent. No indication of a quantitative regulation of PGCs was found in the expiants and the sum of PGCs, calculated for the complementary fragments of a blastoderm, matched the range of numbers in control blastoderms. Our results suggest that PGCs may already be determined as early as stage X and that their further differentiation is independent of the embryo-fonning process.
Cell behaviour during postembryonic pattern regulation in the insect abdomen (Oncopeltus fasciatus):I. Regeneration of segment borders
Authors: Campbell Gerard L. , Shelton Peter M. J.
Published: April 2021

The confrontation of cells from the anterior region of an abdominal segment of Oncopeltus with those from the posterior region of the same or the adjacent segment results in the generation of a segment border. The behaviour of epidermal cells during this regulation is described. It consists primarily of cell division and transverse elongation of cells at the site of confrontation. This behaviour can be separated from any associated purely with wound healing because a similar-sized wound to that used to ablate the segment border, performed within the segment, does not result in any cell division or elongation. The results are consistent with the view that there is a discontinuity in positional values at the segment border. The stability of such a discontinuity and the regeneration of segment borders are discussed in terms of there being a special population of cells at the segment border that have the property of isolating other cells with the maximum difference in positional values.
Cell behaviour during postembryonic pattern regulation in the insect abdomen (Oncopeltus fasciatus): II. Intrasegmental regulation
Authors: Campbell Gerard L.
Published: April 2021

Cells from different levels in the anteroposterior axis of an abdominal segment of Oncopeltus were confronted by scraping away the strip of epidermis that separated these levels. The cells migrate over the wound and meet in the centre. The subsequent behaviour of the epidermal cells was followed by preparing whole mounts of integument at various times after confrontation. These operations may lead to cell division and an alteration in cell shape at the confrontation site. The intensity of the induced cell behaviour pattern depends on which levels in the segment are confronted and the evidence suggests that it is directly related to the magnitude of the difference in positional values between confronted cells. The results can be explained by a nonlinear gradient of positional values within the segment with a crowding of values in the posterior region. It is also shown that segment border formation requires the confrontation of cells with a near maximum possible difference in positional values.
The neural tube origin of ventral root sheath cells in the chick embryo
Authors: Lunn E. R. , Scourfield J. , Keynes R. J. , Stern C. D.
Published: April 2021

The embryonic origin of peripheral nerve Schwann/ sheath cells is still uncertain. Although the neural crest is known to be an important source, it is not clear whether the ventral neural tube also contributes a progenitor population for motor axons. We have used the techniques of immunohistochemistry, electron microscopy and quail-chick grafting to examine this problem. Immunohistochemistry with monoclonal antibody HNK-1 identified a cluster of immunoreactive cells in the sclerotome, at the site of the future ventral root. With the electron microscope, nucleated cells could be seen breaching the basal lamina of the neural tube, exclusively in the region of the ventral root and preceding axon outgrowth. After grafting a length of crest-ablated quail neural tube in place of host chick neural tube, a population of quail cells was found localized to the ventral root exit zone, associated with the ventral root axons. Taken together, these observations support the possibility of a neural tube origin for ventral root sheath cells, although we found no evidence for a more extensive migration of these cells. The ventral root cells share certain phenotypic traits, such as HNK-1 immunoreactivity, with neural-crest-derived Schwann cells, but are not necessarily identical to them. We argue that while they may help motor axons to exit the neural tube at the correct position, they are unlikely to guide axons beyond the immediate vicinity of the neural tube.
Movement of the multicellular slug stage of Dictyostelium discoideum; an analytical approach
Authors: Breen Edmond J. , Vardy Phil. H. , Williams Keith L.
Published: April 2021

Time-lapse video recordings of migrating multicellular slugs of Dictyostelium discoideum were subjected to image analysis. A transient ‘collar-like’ structure was identified at the anterior end of the slug. This collar remains stationary in the wild-type strain WS380B; it is observed shortly after the advancing tip contacts the substratum. Stationary collars formed approximately every 12 min; they were matched with patterns revealed on the underside of slime trails with FITC-coupled monoclonal antibody MUD50. It is proposed that stationary collars are involved with the forward movement of the slug. The mutant strain HU2421 lacks the MUD50-epitope and forms collars which do not remain stationary but move backwards along the slug to collect at a ‘waist’ region. The slipping-collars observed in the mutant correlated with very slow migration rates. We propose thatHU2421 moves slowly because it lacks traction.
An amphibian cytoskeletal-type actin gene is expressed exclusively in muscle tissue
Authors: Mohun T. J. , Garrett N.
Published: April 2021

The complete nucleotide sequence of two Xenopus actin genes encoding cytoskeletal protein isoforms has been determined. Transcripts from these genes are remarkably similar in nucleotide sequence throughout their length and code for type-5 and type-8 cytoskeletal actins. Both share some sequence homology with human γ-actin mRNA within the 3′ untranslated region but none with the equivalent region of any vertebrate β-actin transcript. The promoter regions of the two Xenopus genes are virtually identical from the cap site to the CCAAT box and show extensive homology further upstream. Despite such similarity, the two genes are divergently expressed during embryonic development. The type-5 actin gene is expressed in all regions of the developing embryo whilst the type-8 gene is coregulated with the muscle-specific skeletal actin gene. In common with mammalian and avian cytoskeletal actin counterparts, the Xenopus genes possess a conserved sequence within their promoter that has previously been identified as a transcriptionfactor-binding site.
Ontogenic expression of a Cyl actin fusion gene injected into sea urchin eggs
Authors: Katula Karen S. , Hough-Evans Barbara R. , Britten Roy J. , Davidson Eric H.
Published: April 2021

The 5′ terminus of the Cyl actin gene transcription unit of Strongylocentrotus purpuratus was located by primer extension and other procedures, and the flanking upstream region was partially sequenced and mapped. A fusion gene was constructed containing about 2·5 kb of 5′ flanking sequence, the transcribed leader sequence, and the first few codons of the Cyl gene ligated to the bacterial gene coding for chloramphenicol acetyl transferase (CAT). This was microinjected into the cytoplasm of S. purpuratus eggs, and CAT enzyme activity was measured at various stages of embryonic development. CAT synthesis was activated between 10 and 14 h postfertilization, the same time at which newly synthesized transcripts of the endogenous Cyl gene first appear. The exogenous Cyl · CAT fusion DNA replicated actively during cleavage, as observed previously for other DNAs injected into sea urchin egg cytoplasm. Thus the absence of CAT activity prior to 10 h postfertilization could not be due to insufficient Cyl · CAT genes. The amounts of CAT enzyme produced by embryos bearing Cyl · CAT deletions that lack various regions of the Cyl sequence were measured. As little as 254 nucleotides of upstream Cyl sequence suffice for correct temporal activation of the fusion construct, although the level of CAT enzyme produced in embryos bearing any deletion retaining <850 nucleotides of upstream sequence was significantly lowered compared to controls bearing the complete Cyl · CAT fusion construct.