bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Influence of Hydrocortisone on the Metaplastic Action of Vitamin A on the Epidermis of Embryonic Chicken Skin in Organ Culture
Authors: Fell Honor B. 
Published: April 2021

ABSTRACTThe effects of hydrocortisone, vitamin A, and both agents together were compared in explants of skin from 9-day chick embryos grown in organ culture. In normal medium the periderm degenerated and was shed in the usual way. The epidermis differentiated and keratinized more rapidly than in the embryo; the feather germs differentiated into sheath and barb rudiments and keratinized, after which development ceased. Hydrocortisone alone caused extreme dilation of the peridermal cells which later were sloughed. The differentiation of the epidermis was much accelerated as compared with that of controls in normal medium. The feather germs aborted at an early stage, probably owing to precocious histological differentiation. With vitamin A alone the peridermal cells actively secreted mucus and many formed cilia-like processes; the periderm formed an integral part of the epithelium. In the epidermis keratinization was suppressed and mucous cells differentiated. The feathers remained almost unchanged; the epithelium failed to keratinize and often became secretory. In explants exposed to both agents together, during the first 2 days the periderm secreted copiously a dense, viscid substance the nature of which was unknown, but which appeared to contain both keratinous and mucous material; a similar secretion was sometimes produced by the epidermis at a later stage when the concentration of added vitamin A was low (5 i.u./ml.). The hormone and the vitamin were mutually antagonistic in their action on the epidermis. At first the hydrocortisone prevailed, and large areas of the epithelium often became squamous and keratinized; later the vitamin predominated, the keratin was sloughed, and mucous cells were formed. In two days, feather germs exposed to both agents at once, swelled to several times their original size. Changes like those produced by the hormone and vitamin together appeared in explants grown for 8 days in the presence of vitamin A and then transferred to medium containing hydrocortisone, but not in skin pretreated with the vitamin and then placed in normal medium. These effects were not seen in skin transplanted from medium with hydrocortisone to one containing vitamin A; the epidermis showed the usual changes produced by vitamin A alone.
Different contributions of pannier and wingless to the patterning of the dorsal mesothorax of Drosophila
Authors: García-García María J. , Ramain Philippe , Simpson Pat , Modolell Juan 
Published: April 2021

Abstract
In Drosophila, the GATA family transcription factor Pannier and the Wnt secreted protein Wingless are known to be important for the patterning of the notum, a part of the dorsal mesothorax of the fly. Thus, both proteins are necessary for the development of the dorsocentral mechanosensory bristles, although their roles in this process have not been clarified. Here, we show that Pannier directly activates the proneural genes achaete and scute by binding to the enhancer responsible for the expression of these genes in the dorsocentral proneural cluster. Moreover, the boundary of the expression domain of Pannier appears to delimit the proneural cluster laterally, while antagonism of Pannier function by the Zn-finger protein U-shaped sets its limit dorsally. So, Pannier and U-shaped provide positional information for the patterning of the dorsocentral cluster. In contrast and contrary to previous suggestions, Wingless does not play a similar role, since the levels and vectorial orientation of its concentration gradient in the dorsocentral area can be greatly modified without affecting the position of the dorsocentral cluster. Thus, Wingless has only a permissive role on dorsocentral achaete-scute expression. We also provide evidence indicating that Pannier and U-shaped are main effectors of the regulation of wingless expression in the presumptive notum.
Initiation of shoot apical meristem in rice: characterization of four SHOOTLESS genes
Authors: Satoh Namiko , Hong Soon-Kwan , Nishimura Asuka , Matsuoka Makoto , Kitano Hidemi , Nagato Yasuo 
Published: April 2021

Abstract
The regulatory mechanism of shoot apical meristem (SAM) initiation is an important subject in developmental plant biology. We characterized nine recessive mutations derived from four independent loci (SHL1-SHL4) causing the deletion of the SAM. Radicles were produced in these mutant embryos. Concomitant with the loss of SAM, two embryo-specific organs, coleoptile and epiblast, were lost, but the scutellum was formed normally. Therefore, differentiation of radicle and scutellum is regulated independently of SAM, but that of coleoptile and epiblast may depend on SAM. Regeneration experiments using adventitious shoots from the scutellum-derived calli showed that no adventitious shoots were regenerated in any shl mutant. However, small adventitious leaves were observed in both mutant and wild-type calli, but they soon became necrotic and showed no extensive growth. Thus, leaf primordia can initiate in the absence of SAM, but their extensive growth requires the SAM. An in situ hybridization experiment using a rice homeobox gene, OSH1, as a probe revealed that shl1 and shl2 modified the expression domain of OSH1, but normal expression of OSH1 was observed in shl3 and shl4 embryos. Accordingly, SHL1 and SHL2 function upstream of OSH1, and SHL3 and SHL4 downstream or independently of OSH1. These shl mutants are useful for elucidating the genetic program driving SAM initiation and for unraveling the interrelationships among various organs in grass embryos.
Rescuing the N-cadherin knockout by cardiac-specific expression of N- or E-cadherin
Authors: Luo Yang , Ferreira-Cornwell M. Celeste , Baldwin H. Scott , Kostetskii Igor , Lenox Jennifer M. , Lieberman Melanie , Radice Glenn L. 
Published: April 2021

ABSTRACT
Cell-cell adhesion mediated by some members of the cadherin family is essential for embryonic survival. The N-cadherin-null embryo dies during mid-gestation, with multiple developmental defects. We show that N-cadherin-null embryos expressing cadherins using muscle-specific promoters, α- or β-myosin heavy chain, are partially rescued. Somewhat surprisingly, either N-cadherin or E-cadherin was effective in rescuing the embryos. The rescued embryos exhibited an increased number of somites, branchial arches and the presence of forelimb buds; however, in contrast, brain development was severely impaired. In rescued animals, the aberrant yolk sac morphology seen in N-cadherin-null embryos was corrected, demonstrating that this phenotype was secondary to the cardiac defect. Dye injection studies and analysis of chimeric animals that have both wild-type and N-cadherin-null cells support the conclusion that obstruction of the cardiac outflow tract represents a major defect that is likely to be the primary cause of pericardial swelling seen in null embryos. Although rescued embryos were more developed than null embryos, they were smaller than wild-type embryos, even though the integrity of the cardiovascular system appeared normal. The smaller size of rescued embryos may be due, at least in part, to increased apoptosis observed in tissues not rescued by transgene expression, indicating that N-cadherin-mediated cell adhesion provides an essential survival signal for embryonic cells. Our data provide in vivo evidence that cadherin adhesion is essential for cell survival and for normal heart development. Our data also show that E-cadherin can functionally substitute for N-cadherin during cardiogenesis, suggesting a critical role for cadherin-mediated cell-cell adhesion, but not cadherin family member-specific signaling, at the looping stage of heart development.
MEIS-WNT5A axis regulates development of fourth ventricle choroid plexus
Authors: Kaiser Karol , Jang Ahram , Kompanikova Petra , Lun Melody P. , Prochazka Jan , Machon Ondrej , Dani Neil , Prochazkova Michaela , Laurent Benoit , Gyllborg Daniel , van Amerongen Renee , Fame Ryann M. , Gupta Suhasini , Wu Feizhen , Barker Roger A. , Bukova Ivana , Sedlacek Radislav , Kozmik Zbynek , Arenas Ernest , Lehtinen Maria K. , Bryja Vitezslav 
Published: April 2021

ABSTRACT
The choroid plexus (ChP) produces cerebrospinal fluid and forms an essential brain barrier. ChP tissues form in each brain ventricle, each one adopting a distinct shape, but remarkably little is known about the mechanisms underlying ChP development. Here, we show that epithelial WNT5A is crucial for determining fourth ventricle (4V) ChP morphogenesis and size in mouse. Systemic Wnt5a knockout, or forced Wnt5a overexpression beginning at embryonic day 10.5, profoundly reduced ChP size and development. However, Wnt5a expression was enriched in Foxj1-positive epithelial cells of 4V ChP plexus, and its conditional deletion in these cells affected the branched, villous morphology of the 4V ChP. We found that WNT5A was enriched in epithelial cells localized to the distal tips of 4V ChP villi, where WNT5A acted locally to activate non-canonical WNT signaling via ROR1 and ROR2 receptors. During 4V ChP development, MEIS1 bound to the proximal Wnt5a promoter, and gain- and loss-of-function approaches demonstrated that MEIS1 regulated Wnt5a expression. Collectively, our findings demonstrate a dual function of WNT5A in ChP development and identify MEIS transcription factors as upstream regulators of Wnt5a in the 4V ChP epithelium.
Metabolically active and polyploid renal tissues rely on graded cytoprotection to drive developmental and homeostatic stress resilience
Authors: Burbridge Katie , Holcombe Jack , Weavers Helen 
Published: April 2021

ABSTRACT
Body tissues are frequently exposed to stress, from toxic byproducts generated during cellular metabolism through to infection or wounding. Although it is well-established that tissues respond to exogenous injury by rapidly upregulating cytoprotective machinery, how energetically demanding tissues – vulnerable to persistent endogenous insult – withstand stress is poorly understood. Here, we show that the cytoprotective factors Nrf2 and Gadd45 act within a specific renal cell subtype, the energetically and biosynthetically active ‘principal’ cells, to drive stress resilience during Drosophila renal development and homeostasis. Renal tubules lacking Gadd45 exhibit striking morphogenetic defects (with cell death, inflammatory infiltration and reduced ploidy) and accumulate significant DNA damage in post-embryonic life. In parallel, the transcription factor Nrf2 is active during periods of intense renal physiological activity, where it protects metabolically active renal cells from oxidative damage. Despite its constitutive nature, renal cytoprotective activity must be precisely balanced and sustained at modest sub-injury levels; indeed, further experimental elevation dramatically perturbs renal development and function. We suggest that tissues requiring long-term protection must employ restrained cytoprotective activity, whereas higher levels might only be beneficial if activated transiently pre-emptive to exogenous insult.
The Effects in Chick Blastoderms of replacing the Primitive Node by a Graft of Posterior Primitive Streak
Authors: Abercrombie M. , Bellairs Ruth 
Published: April 2021

ABSTRACT
In chick embryos with a full-length primitive streak the primitive node has been replaced by a graft from the posterior end of the primitive streak, and the blastoderm subsequently cultivated by Waddington’s technique for 24 hours. More than half of those embryos which developed at all showed a doubling of the anterior part of the axis, variable in extent but considerably exceeding the original extent of the graft, with convergence to a single posterior part. Prechordal head, parachordal mesoderm, and neural plate were affected by the doubling. Most specimens had two notochords fusing posteriorly into a single one, or occasionally terminating independently at a common primitive streak. Other specimens had a notochord in only one of the two axes, or in neither. Marking experiments with phosphorus32 on a few specimens showed that the graft, which had become greatly elongated, contributed the mesoderm between the notochords, but did not form any notochordal tissue. The doubled axes were often asymmetrical, and in the head region probably incomplete. The total amount of neural and notochordal tissue in a doubled embryo was not significantly different in volume from that in a single embryo. In a few specimens in which the axis remained single the place of the notochord was taken by side-plate mesoderm, probably graft-derived. Posteriorly this midline mesoderm became somitic. The neural plate in such specimens was little if at all reduced. Other specimens failed to heal and developed a split axis. They were usually devoid of notochord, but occasionally had a notochord along one side of the split, or along both sides. Finally, a few specimens formed an almost normal single axis.
Limpet haemocytes: II. The role of spikes in locomotion and spreading
Authors: Partridge T. , Davies P. S. 
Published: April 2021

ABSTRACTA new preparation for the study of cell spreading and locomotion was investigated, using time-lapse cinemicrography and photomicrography. The preparation of limpet haemocytes has the advantage of being a natural one, not derived by tissue dissociation, and is functional at normal laboratory temperatures.The commonest cell type, the amoebocytes, have numerous spikes, up to 15 μm in length, which project from their surface, carry lamellar extensions between them, and run deep into the cytoplasm. In the spread cell this spike-supported lamella constitutes the margin of the cell, resulting in a crenate appearance. The extensions have the properties of lamellipodia, and spreading and locomotion both occur by extension, first of spikes then lamella. It is suggested that the direction of movement may be regulated by the spikes. Contact inhibition of movement is accompanied by disappearance of the spikes in the region of contact between cells and production of spikes in other regions which lead the cells away from the contact.Spreading of cells from large aggregates of amoebocytes entails rapid centrifugal locomotion of the peripheral cells which is thought to be a consequence of contact inhibition. However, there also appears to be an opposing influence which largely prevents complete loss of contact between cells, resulting in an epithelioid morphology in a spread culture.Amoebocytes are not adhesive to the substrate in Ca1+ and Mg2+-free (CMF) conditions but rapidly regain adhesiveness and spread normally on addition of either divalent cation to the concentration normally found in seawater. Spikes and lamellae are produced in CMF conditions but do not spread on to the substrate and do not show their normal reactions to contact with other cells.Macrophages spread as disks of gradually increasing diameter without the aid of spikes but with the formation of conspicuous ruffle-like thickenings. Once fully spread they become quiescent and show little or no further ruffling and undergo no significant locomotion. The attachment and spreading of these cells was found to be independent of the presence in the medium of divalent cations.
The accessibility of a developing lepidopteran nervous system to lanthanum and peroxidase
Authors: McLaughlin Barbara J. 
Published: April 2021

ABSTRACT
The accessibility of the nervous system of Manduca sexta to horseradish peroxidase and lanthanum during metamorphosis has been studied. In the fifth instar larva, peroxidase penetrates the thick neural lamella but does not reach the perineurium. In the first week after larval-pupal ecdysis, when the intercellular channels between hypertrophied perineurial I cells are the least tortuous, the enzymic tracer bypasses the perineurial I tight and gap junctions and penetrates as far as the perineurial II bracelet layer. During this time, there is active uptake of peroxidase by the perineurial I cells but no reaction product is found in the underlying perineurial II cell bracelet. In the second week after larval-pupal ecdysis, when the perineurium is a flattened interdigitating cell layer, peroxidase does not penetrate as far as the perineurial I and II interspace and there is little or no uptake of the protein by the perineurial I cells. Lanthanum, in contrast, passes the perineurial I tight and gap junctions, which are presumed to be macular, and travels within the entire perineurial I and II interspace throughout metamorphosis. As it travels within this interspace, it gains access to the perineurial II bracelet connexions, which differ in their ability to restrict lanthanum. Lanthanum is able to penetrate the entire overlapping connexion with its predominant gap junctions before being stopped, but penetrates the more complex interdigitating connexion with its extensive tight, gap and septate junctions for only a short distance. The relevance of the perineurial II bracelet layer and its intercellular connexions to the maintenance of a blood-brain barrier in this developing nervous system is discussed.
Effect of near ultraviolet and visible light on amoeba
Authors: Chatterjee S. , Bhattacharjee S. K. 
Published: April 2021

ABSTRACT
The near ultraviolet and visible light (VL) impinging at an intensity of 2·5 × 102 J s−1 m−s for 2·5 h kills the mitotic and the early 5-phase (0- to 15-min-old) amoebae. At the mid- and late S-period only a fraction of cells are killed by VL and the G2 phase cells are quite resistant. Amoebae of all cell cycle stages show a delay in the first mitotic division. DNA synthesis, as measured by [3H]thymidine incorporation, is depressed in the VL-exposed early-S amoebae. A concurrent but temporary inhibition in [3H]leucine incorporation also occurs in these cells. However, no significant change in [3H]uridine incorporation has been found.
To localize the site of lethal damage, nuclear transplantation studies were undertaken between the control amoebae and the amoebae treated with VL. The nucleus of a VL-exposed early S-phase cell recovers when transplanted immediately after VL exposure into an enucleate G2 cytoplasm but dies if grafted into an enucleate S-phase cytoplasm. The therapeutic effect of the G2 cytoplasm, although at a lower level, is also evident even when the treated early S-phase nucleus is implanted 20 h later, but not after 48 h, into the G2 cytoplasm. The amoeba cytoplasm shows resistance to VL-irradiation, can accept a control nucleus from any cell cycle stage, and function normally. The G, nucleus also remains apparently unaffected to VL exposure and can survive when it is transferred to the control cytoplasm of any cell-cycle phase. All these findings are discussed in the light of the possible existence of a repair system against VL-induced damage in the G2-phase amoeba.
Cell density dependence of the aggregation characteristics of the cellular slime mould Dictyostelium discoideum
Authors: Hashimoto Y. , Cohen M. H. , Robertson A. 
Published: April 2021

ABSTRACT
We have measured fruiting body density and spore formation efficiency in Dictyostelium discoideum as functions of initial cell density. Experiments were performed on agar made up with distilled water and on buffered agar. Minor differences are seen; these are discussed. The functions show 4 regions of density dependence which can be accounted for by changes in aggregation characteristics with density and changes in the efficiency of spore differentiation. The results are discussed in terms of the relaying mechanism for signal propagation controlling cell aggregation. They extend earlier measurements by Bonner & Dodd and by Hohl & Raper, supply data for a quantitative model of the aggregation process, allow estimates of signal range, and show the importance of entrainment between neighbouring centres in defining aggregation territories.
Selective In vivo damage by ‘visible’ light of brdu-containing mitochondrial dna in a thymidine kinase-deficient mouse cell line with persistent mitochondrial enzyme activity
Authors: Croizat B. , Attardi G. 
Published: April 2021

ABSTRACT
The selective incorporation of 5-bromodeoxyuridine (BrdU) into mitochondrial DNA (mit-DNA) in the LM(TK−) Cl1D cell line, a thymidine kinase-deficient derivative of L fibroblasts with persistent mitochondrial enzyme activity, has been utilized to specifically damage mit-DNA by ‘visible’ light irradiation. (‘Visible light’ indicates the source of light used, although the components most active photochemically on BrdU-substituted DNA are in the near-visible range, 300–340 nm.) (Szybalski & Opara-Kubinski, 1965).
LM(TK−) Cl 1D cells, which had been grown in the presence of 30 μg/ml BrdU, were irradiated with ‘visible’ light. Analysis of the pre-existing mit-DNA in these cells, which had been long-term labelled with [5-3H]deoxycytidine, showed a progressive decrease, with increasing duration of irradiation, in the proportion of the closed-circular form and an increase in that of the open-circular form of mit-DNA, with the subsequent appearance of fragments of this DNA. Furthermore, there was a decrease during irradiation in the total amount of mit-DNA, which became about 35 % of the non-irradiated control after 65 h irradiation. On the other hand, irradiation with ‘visible’ light failed to cause any quantitative or qualitative change, with respect to the non-irradiated control, in mit-DNA from cells grown in the absence of BrdU and long-term labelled with [Me-3H]thymidine.
An analysis of the incorporation of [5-3H]deoxycytidine into mit-DNA of BrdU-grown cells, during a 3-h exposure of the cells to the precursor following irradiation, showed a fairly rapid decline of mit-DNA labelling; this became about 50% of the non-irradiated control after 12 h irradiation, decreasing to about 25% in the next 48 h. By contrast, no effect of irradiation was observed on the subsequent pulse-labelling of mit-DNA with [Me-3H]thymidine in cells grown in the absence of BrdU. Furthermore, no change in the size of the extracted nuclear DNA was found in irradiated BrdU-grown cells.
The progressive and selective damage and destruction of mit-DNA during irradiation with ‘visible’ light of Cl 1D cells correlate fairly well with the kinetics of loss of cell viability occurring under the same conditions, as described in the accompanying paper, strongly suggesting a link between the two phenomena.
Studies on the function and composition of the 10-nm(100- å) filaments of vertebrate smooth muscle
Authors: Small J. V. , Sobieszek A. 
Published: April 2021

ABSTRACT
The extraction of isolated vertebrate smooth muscle cells at high and low ionic strength yields cell ghosts which are seen in the electron microscope to be composed of a complex network of 10-nm filaments, together with residual actin. After SDS-gel electrophoresis of the cell ghosts only 2 bands may be recognized, one corresponding to actin and the other migrating at about 55000 mol. wt that arises from the 10-nm filaments. The 10-nm filaments are extremely sensitive to proteolysis and are absent from cells exposed to crude collagenase in the presence of Triton X-100. Such cells, lacking 10-nm filaments, still contract in response to ATP. The data indicate that the 10-nm filaments are not essential for contraction, but rather form a specialized intracellular cytoskeleton.
While completely insoluble in concentrated salt solutions the 55000 mol. wt protein is readily extracted with acetic acid from homogenized and salt-extracted smooth muscle residue. The extracted protein reassembles, on dialysis, into filaments of about 10-nm diameter and has an amino acid composition almost identical to that deduced for vertebrate neurofilaments. From the cytoskeletal role that the 10-nm filaments play in smooth muscle and, as appears likely, in other cell types the filament protein has been tentatively termed ‘skeletin’. Results relating to the proportion of skeletin in smooth muscle and the structure of the 10-nm filaments are described and discussed.