bluuebunny/crossref_metadata_2025_split huggingface dataset:
BDNF stimulates migration of cerebellar granule cells
Authors: Borghesani Paul R. , Peyrin Jean Michel , Klein Robyn , Rubin Joshua , Carter Alexandre R. , Schwartz Phillip M. , Luster Andrew , Corfas Gabriel , Segal Rosalind A. 
Published: April 2021

During development of the nervous system, neural progenitors arise in proliferative zones, then exit the cell cycle and migrate away from these zones. Here we show that migration of cerebellar granule cells out of their proliferative zone, the external granule cell layer (EGL), is impaired in Bdnf–/– mice. The reason for impaired migration is that BDNF directly and acutely stimulates granule cell migration. Purified Bdnf–/– granule cells show defects in initiation of migration along glial fibers and in Boyden chamber assays. This phenotype can be rescued by exogenous BDNF. Using time-lapse video microscopy we find that BDNF is acutely motogenic as it stimulates migration of individual granule cells immediately after addition. The stimulation of migration reflects both a chemokinetic and chemotactic effect of BDNF. Collectively, these data demonstrate that BDNF is directly motogenic for granule cells and provides a directional cue promoting migration from the EGL to the internal granule cell layer (IGL).Movies available on-line
A transcriptional profile of multicellular development inDictyostelium discoideum
Authors: Van Driessche Nancy , Shaw Chad , Katoh Mariko , Morio Takahiro , Sucgang Richard , Ibarra Miroslava , Kuwayama Hidekazu , Saito Tamao , Urushihara Hideko , Maeda Mineko , Takeuchi Ikuo , Ochiai Hiroshi , Eaton William , Tollett Jeffrey , Halter John , Kuspa Adam , Tanaka Yoshimasa , Shaulsky Gad 
Published: April 2021

A distinct feature of development in the simple eukaryote Dictyostelium discoideum is an aggregative transition from a unicellular to a multicellular phase. Using genome-wide transcriptional analysis we show that this transition is accompanied by a dramatic change in the expression of more than 25% of the genes in the genome. We also show that the transcription patterns of these genes are not sensitive to the strain or the nutritional history, indicating that Dictyostelium development is a robust physiological process that is accompanied by stereotypical transcriptional events. Analysis of the two differentiated cell types, spores and stalk cells, and their precursors revealed a large number of differentially expressed genes as well as unexpected patterns of gene expression, which shed new light on the timing and possible mechanisms of cell-type divergence. Our findings provide new perspectives on the complexity of the developmental program and the fraction of the genome that is regulated during development.Supplemental data available on-line
The elongation factors Pandora/Spt6 and Foggy/Spt5 promote transcription in the zebrafish embryo
Authors: Keegan Brian R. , Feldman Jessica L. , Lee Diana H. , Koos David S. , Ho Robert K. , Stainier Didier Y. R. , Yelon Deborah 
Published: April 2021

Precise temporal and spatial control of transcription is a fundamental component of embryonic development. Regulation of transcription elongation can act as a rate-limiting step during mRNA synthesis. The mechanisms of stimulation and repression of transcription elongation during development are not yet understood. We have identified a class of zebrafish mutations (pandora, sk8 and s30) that cause multiple developmental defects, including discrete problems with pigmentation, tail outgrowth, ear formation and cardiac differentiation. We demonstrate that the pandora gene encodes a protein similar to Spt6, a proposed transcription elongation factor. Additionally, the sk8 and s30 mutations are null alleles of the foggy/spt5 locus, which encodes another transcription elongation factor. Through real-time RT-PCR analysis, we demonstrate that Spt6 and Spt5 are both required for efficient kinetics of hsp70 transcription in vivo. Altogether, our results suggest that Spt6 and Spt5 play essential roles of comparable importance for promoting transcription during embryogenesis. This study provides the first genetic evidence for parallel functions of Spt6 and Spt5 in metazoans and establishes a system for the future analysis of transcription elongation during development.Supplemental figure available on-line
Etude du développement embryonnaire et recherches sur les cellules de régénération chez l’embryon de la Planaire Polycelis nigra (Turbellarié, Triclade)
Authors: Le Moigne A. 
Published: April 2021

ABSTRACT
Depuis les travaux de Dubois (1949) sur la régénération chez les Planaires, il est admis par la plupart des auteurs, que ce sont des cellules totipotentes du parenchyme, les néoblastes, qui participent à la formation du blastème de régénération. Une blessure déclenche leur migration vers la région lésée. On considère que les néoblastes ont conservé les caractères de cellules embryonnaires indifférenciées; ils se différencient dans le blastème pour reconstituer les organes manquants.
Anaerobiosis in the segmenting eggs of Bufo arenarum
Authors: Barbieri Francisco D. , de Legname Hortensia S. 
Published: April 2021

ABSTRACT
In the last few years our interest has been devoted to the energy metabolism of the eggs of the common toad Bufo arenarum Hensel which, like some other amphibian eggs, can cleave at a normal rate in the absence of oxygen or in the presence of cyanide (Barbieri & Legname, 1957). Under anaerobic conditions a rapid accumulation of lactic acid gives evidence of an intense glycolytic activity, which is inhibited when the eggs are returned to oxygen (Pasteur effect) (Barbieri & Salomón, 1963). Furthermore, an increase in oxygen uptake during the first 2 h of recovery has been observed (payment of the oxygen debt) (Legname, 1966). Taking into account the low value of the respiratory quotient (R.Q. = 0 ·5 –0 ·7) during this period it can be assumed that most of the oxygen is not involved in the oxidation of lactate (Legname, 1966). A similar respiratory response has already been described in Rana fusca (Brachet, 1934) and R.pipiens eggs (Cohen, 1955), and has served to support the idea of an ‘oxidative reserve’ in the eggs of these vertebrates (Brachet, 1934).
Teratogenic effects of calcium salts on chick embryos
Authors: Grabowski Casimer T. 
Published: April 2021

ABSTRACT
This investigation began as an attempt to protect chick embryos from the teratogenic effects of hypoxia by means of exogenously applied calcium pantothenate. The attempt was not only a failure, but it appeared that the compound alone was highly teratogenic. Since it was disturbing to consider that a vitamin, in low dosage, was teratogenic, the phenomenon was studied further by injecting equivalent concentrations of other calcium salts into the embryo. It quickly became apparent that very small quantities of calcium chloride solution injected into either the subgerminal area of the yolk sac or the allantois also produced pronounced abnormalities.
Studies on pattern regulation in hydra
Authors: Webster Gerald , Wolpert Lewis 
Published: April 2021

ABSTRACT
The regulation of hydra into hypostomal and non-hypostomal regions is considered as a model for the regulation of a linear pattern into two compartments. Regulation of such a system requires graded differences and a ‘principle of limited realization’. The hypostome is the dominant region in hydra and the time for its determination in isolated pieces depends upon the original position of the piece along the linear axis. The time increases in a disto-proximal direction from 4 h to more than 20 h. The determination of the hypostome is the first detectable event in distal regeneration and is probably the time-determining step in this process. Work on other hydroids is reinterpreted in these terms. The time for hypostome determination in proximal regions is significantly affected by the presence of more proximal regions, while in distal regions the time appears independent of the presence of more proximal regions.
Isolation and characterization of a low-molecular-weight substance activating head and bud formation in hydra
Authors: Schaller H. Chica 
Published: April 2021

ABSTRACT
From crude extracts of hydra, a substance activating head formation was isolated and enriched at least 100000-fold. The molecular weight was determined to be approximately 900. Sensitivity against proteases suggests that it is a peptide. The substance acts at a concentration equivalent to the extract of 1 hydra per ml or at a concentration of less than 10 * 10M. In its highly purified form the substance activates head and bud formation.
Histone synthesis during development ofTriturusembryos
Authors: Imoh Hiroshi , Kawakami Izumi 
Published: April 2021

ABSTRACTSynthesis of histone fractions and one basic protein fraction, which moved fast on gel electrophoresis and had been reported to increase in nuclei accompanying a decrease in cytoplasm during development, were studied with radioactive carbon dioxide as a tracer. Acid-extractable proteins of nuclei or cytoplasm, isolated from labelled embryos, were fractionated by polyacrylamide disc electrophoresis and the histone fractions and the fastmoving basic protein were identified. Radioactivities in these fractions and DNA were determined.Synthesis of the fast-moving basic protein was not detected throughout the period of development studied and this fraction was thought to move in from the cytoplasm to the nucleus during development. Syntheses of histone fractions were observed as early as the blastula stage. Rates of syntheses of four histone fractions (f3, f2b, f2a2 and f2al) per embryo increased thereafter, keeping pace with the increase in the rate of DNA synthesis with advancing development. The rate of the very lysine-rich f1 histone synthesis per embryo did not increase after the gastrula stage and the rate remained almost constant until the late tail-bud stage.Compositions of newly synthesized histones, calculated from the radioactivities incorporated into histone fractions, were almost the same during development and among different regions of neurula or tail-bud-stage embryos, with the exception of the f1 fraction, which varied depending on the stage and region of the embryos.The results are discussed in relation to the possible roles of the histone fractions in developing embryos.
Differentiation of the mammalian hepatic primordiumin vitro:I. Morphogenesis and the onset of haematopoiesis
Authors: Johnson G. R. , Jones R. O. 
Published: April 2021

ABSTRACTThis study was made to determine the nature of tissue contributions to murine hepatic morphogenesis, the developmental potential in vitro of various hepatic regions prior to and during definitive liver development, and to accurately determine the time of onset of hepatic haematopoiesis in vitro. Embryos were precisely staged by somite counts as well as time of original mating, and tissues were removed from the hepatic area at stages between anterior intestinal portal (9 days gestation) and definitive foetal liver (11·75–12 days gestation), and maintained in vitro for up to 4 weeks.Expiants of anterior intestinal portal origin gave rise only to sheets of epithelial cells, whereas tissues from embryos of 10 –11 days gestation, containing the hepatic sacculation of the ventral wall of the gut, gave rise to sheets of polygonal, frequently binucleate cells and granule containing cells, both suggestive of hepatic cytodifferentiation. Sinusoidal morphogenesis was also observed. Haematopoiesis was detected in vitro only in explants from 11·5-to 12-day embryos (28 to 30+ somites). The blood elements observed consisted of erythroblasts, granulocytes, megakaryocytes as well as macrophages and yolk sac derived erythroblasts. Duct systems, probably representative of the bile system, were also observed to develop.Current theories regarding hepatic morphogenesis are considered in the light of these observations. The inductive and cell seeding concepts of the origin of haematopoietic cells are discussed in view of the observed precise timing of the onset of hepatic haematopoiesis. Due to the substantial gestation time-gap between the detection of possible circulating haematopoietic stem cells (9 days gestation) and the actual onset of hepatic haematopoiesis (11·5 days gestation), it is suggested that either a suitable microenvironment must first develop within the hepatic area for haematopoiesis to occur, or that haematopoietic tissue arises in situ in the hepatic Anlage.
Genetic and physiologic control of fissioning and sexuality in planarians
Authors: Grasso Mario , Benazzi Mario 
Published: April 2021

ABSTRACTSeveral fissiparous strains of the planarian Dugesia gonocephala s.l. have been subjected for many months to continuous feeding on crushed tissues of sexually mature specimens of the planarians Polycelis nigra or (in a few cases) Dugesia lugubris. In a very high percentage of cases (especially after feeding on Polycelis nigra crushed tissues) the fissioning phenomena have been stopped and a sexual state has been induced. The sexualized specimens developed hyperplasie ovaries, testicular follicles and a more or less complete copulatory apparatus; some of them went so far as to lay sterile cocoons. As for the nature of sexualizing substances contained in crushed tissues of sexual planarians, further researches are required; we suggest they are neurosecretions stimulating sexuality and so inhibiting fissioning phenomena.
Measurements of cell adhesion:II Quantitative study of the effect of divalent ions on cell adhesion
Authors: Hornby Janet E. 
Published: April 2021

ABSTRACTThe forces of interaction found for 5-day chick limb-bud cells in media containing different divalent ions (magnesium, calcium, strontium or barium) show that the cells are most adhesive in the presence of magnesium ions, then calcium and strontium, then barium. When magnesium and calcium ions are present together at similar concentrations the calcium ions modify the action of the magnesium ions. The importance of magnesium ions in cell adhesion is discussed.
Dermo-epidermal interactions between birds and mammals: differentiation of cutaneous appendages
Authors: Dhouailly Danielle 
Published: April 2021

ABSTRACT
The capacity of skin constituents to participate in feather and hair morphogenesis has been analysed in chick and mouse embryos. Reconstituted homo- and heterospecific skin explants, consisting of epidermis and dermis from both species, were cultured for 8 days on the chorioallantoic membrane of the chick. Recombinants of dorsal 11·5- and 12·5-day mouse epidermis and dorsal 7-day or tarsometatarsal 12-day chick dermis gave rise to stage 2 abnormally elongated hair prepapillae. Associations of plantar 14·5-day mouse epidermis with dorsal 7-day chick dermis formed stage 3 hair papillae. The reverse combinations of dorsal 5- and 6-day chick epidermis and dorsal 11-5- to 14-5-day mouse dermis gave rise to arrested feather buds (with 11·5- and 12·5-day dermis) and to short and aberrant feather filaments (with 12·5-, 13·5- and 14·5-day dermis). These short filaments were characterized by the differentiation of easily recognizable but chaotically arranged barb-ridges. The same type of feather differentiation was obtained in recombinants of normally glabrous epidermis from the comb, midventral apterium, or tarsometatarsum from 10-day chick embryos and 13·5- and 14·5-day dorsal mouse dermis. Control homospecific recombinations formed typical well organized feather filaments or stage 4–5 hair cone follicles. Heterospecific associations of feather- or hair-forming epidermis with dermis from glabrous regions did not differentiate any kind of cutaneous appendages. When distribution of feather filaments was compared in recombinants of chick epidermis with either dorsal pelage hair dermis or upper-lip vibrissal dermis, it was found that the feather pattern conformed with the regional origin of the mouse dermis. It was concluded that, during feather and hair development, the dermis transmits two kinds of morphogenetic messages: one that is apparently non-specific and can therefore be understood and expressed by a foreign epidermis from another zoological class, leading to the formation of feather or hair buds, in conformity with the origin of the epidermis; the other message contains specific cues necessary for specific morphological organization of feather and hair.
Morphogenetic properties of the parts of the colony ofClytia johnstoni
Authors: Hale L. J. 
Published: April 2021

ABSTRACTThe morphogenetic potencies of the various parts of Clytia johnstoni have been ascertained by isolation and by grafting. The various parts of the colony behave on isolation in the following ways: Immediate development of a stolon (which in turn may grow hydranths, as in a normal colony). Shown by (i) all parts of the stolon except sometimes the growing tip, (ii) stalk primordia of length 0·5–1·4 mm, (iii) stalks of open hydranths (polarized, the stolon grows out of the cut basal end). Immediate differentiation of a polyp. Shown by (i) stalk primordia longer than 1·7 mm and some between 1·4 and 1·7 mm, (ii) bulbs greater than 0·28 mm diameter (i.e. had reached contractile stage), (iii) bulb primordia of all sizes having a ‘stalk’ longer than 0·35 mm; only the larger bulbs became polyps if the ‘stalk’ was shorter than 0·35 mm. Immediate incipient differentiation (of a polyp ?) was shown by some stalk primordia of length 1·4–1·7 mm long. Partial hydranth differentiation (stomach and buccal region, no tentacles) was shown by an occasional isolated bulb. Delayed stolon development. The time delay is variable but not random, with a marked tendency to start after 3–5 days and a less marked tendency after 9 days isolation. Shown by (i) all isolates which differentiated a polyp immediately on isolation, (ii) most bulb primordia less than 0·23 mm diameter and ‘stalks’ shorter than 0·35 mm, (iii) a few bulbs 0·23–0·27 mm in diameter. No development at any time. Shown by (i) Stalk primordia less than 0·5 mm long, (ii) bulbs of less than 0·23 mm diameter, (iii) some stolon tips, (iv) most isolated polyps (after regression). There is some evidence that a contractile growth region in an isolate gives it the power of immediate differentiation, in a stalk primordium to produce a stolon and in a bulb to a polyp. The time at which a stalk primordium passes to a bulb primordium appears to correspond to the time when, on isolation, it switches from being stolon producing to being hydranth producing. The peaks of regenerative activity (noted in 2(d) above) are the same as the most likely life-spans of hydranths but it is not known if there is any relation between the two sets of observations. The tips of growing stolons and hydranth stalk primordia have specific but weak inductive powers.
Size regulation in chimaeric mouse embryos
Authors: Buehr Mia , McLaren Anne 
Published: April 2021

ABSTRACT
The size of the inner cell mass and egg cylinder was estimated in mouse embryos derived from the aggregation of two 8-cell stages and in control ‘single’ embryos. The comparison suggests that growth regulation in the ‘double’ embryos takes place fairly rapidly, after the formation of the egg cylinder but before the appearance of the pro-amniotic cavity.
Analyse morphologique des chimères obtenues par greffes embryonnaires chez les Amphibiens Urodèles
Authors: Charlemagne Jacques , Houillon Charles 
Published: April 2021

ABSTRACT
Allogenic and heterospecific chimaeras have been made between four species of Amphibian Urodeles: Pleurodeles waltlii Michah., Triturus alpestris Laur. Trituras helveticas Raz. and Ambystoma mexicanum Shaw. These chimaeras are complementary (groups A, B, C) or not (groups D and E) and possess different morphologic types.
Allogenic chimaeras develop normally, are able to breed and easy to achieve. Their principal interest, especially for E group, is that each one possesses two pairs of gonads.
A number of certain types of heterogenic chimaeras have been obtained and have reached metamorphosis: 158 chimaeras between Pleurodeles waltlii and Triturus alpestris and 134 chimaeras between Pleurodeles waltlii and Triturus helveticas. Some live several years and raise interesting problems: immune reactions, growth regulation and sexual differentiation.
The development of Bithynia tentaculata (Prosobranchia, Gastropoda) after removal of the polar lobe
Authors: Gather James N. , Verdonk Nico H. 
Published: April 2021

ABSTRACT
The polar lobe of the egg of Bithynia, with a volume of less than 1 % of that of the egg, was surgically removed. Lobeless embryos form no mesentoblast cell nor mesoderm bands. They fail to establish bilateral symmetry and to form eyes, foot, operculum, shell, etc. They always differentiate larval head cells, ganglia, larval liver and mesenchyme and sometimes columnar epithelium, stomodeal entrance cells. endodermal tubes and muscles.
These results are discussed in relation to the structure of the lobe, the analysis of development of Bithynia and to similar experiments in other species.
Interaction between the proximo-distal and antero-posterior co-ordinates of positional value during the specification of positional information in the early development of the chick limb-bud
Authors: Summerbell Dennis 
Published: April 2021

ABSTRACT
The experiments examine the extent of reduplication of skeletal parts across the anteroposterior axis, following the transplantation of a zone of polarizing activity (ZPA) to the anterior margin of the limb-bud at successively later stages. Previous studies have suggested that the function of the apical ectodermal ridge (AER) is to maintain cells in a special region at the distal tip (the progress zone) labile, with respect to their positional value along the proximo-distal axis. Similarly, the results of these experiments demonstrate that cells in the progress zone are able to change their antero-posterior positional value under the influence of the grafted ZPA, while cells at more proximal levels remain unaffected. In turn, the ZPA may effect the activity of the AER and hence the progress zone.
Comparative remarks on the development of the tail cord among higher vertebrates
Authors: Hughes A. F. , Freeman R. B. 
Published: April 2021

ABSTRACT
The development of the caudal region of the neural tube is compared in tailed mammals with that of the chick and human. In rat, mouse, opossum and pig, the lumen of the cord extends caudally in an even manner, whereas in the chick and in man the addition of small cavities to the lumen results in a phase of irregular growth. In mammals with unreduced tails, the site of closure of the posterior neuropore is at the tip of the tail, whereas in pig, man and in the chick closure occurs before the formation of the tail-bud. The teratological implications of these findings are discussed.