bluuebunny/crossref_metadata_2025_split huggingface dataset:
The development of Xenopus tropicalis transgenic lines and their use in studying lens developmental timing in living embryos
Authors: Offield Martin F. , Hirsch Nicolas , Grainger Robert M. 
Published: April 2021

ABSTRACT
The generation of reporter lines for observing lens differentiation in vivo demonstrates a new strategy for embryological manipulation and allows us to address a long-standing question concerning the timing of the onset of differentiation. Xenopus tropicalis was used to make GFP reporter lines with γ1-crystallin promoter elements directing GFP expression within the early lens. X. tropicalis is a close relative of X. laevis that shares the same ease of tissue manipulation with the added benefits of a diploid genome and faster life cycle. The efficiency of the Xenopus transgenic technique was improved in order to generate greater numbers of normal, adult transgenic animals and to facilitate in vivo analysis of the crystallin promoter. This transgene is transmitted through the germline, providing an accurate and consistent way to monitor lens differentiation. This line permitted us to distinguish models for how the onset of differentiation is controlled: by a process intrinsic to differentiating tissue or one dependent on external cues. This experiment would not have been feasible without the sensitivity and accuracy provided by the in vivo reporter. We find that, in specified lens ectoderm transplanted from neural tube stage donors to younger neural-plate-stage hosts, the onset of differentiation, as measured by expression of the crystallin/GFP transgene, is delayed by an average of 4.4 hours. When specified lens ectoderm is explanted into culture, the delay was an average of 16.3 hours relative to control embryos. These data suggest that the onset of differentiation in specified ectoderm can be altered by the environment and imply that this onset is normally controlled by external cues rather than by an intrinsic mechanism.
Migration of cardiac neural crest cells in Splotch embryos
Authors: Epstein Jonathan A. , Li Jun , Lang Deborah , Chen Fabian , Brown Christopher B. , Jin Fuzi , Lu Min Min , Thomas Michael , Liu En-Chia J. , Wessels Andy , Lo Cecilia W. 
Published: April 2021

ABSTRACT
Pax3 encodes a transcription factor expressed during mid-gestation in the region of the dorsal neural tube that gives rise to migrating neural crest populations. In the absence of Pax3, both humans and mice develop with neural crest defects. Homozygous Splotch embryos that lack Pax3 die by embryonic day 13.5 with cardiac defects that resemble those induced by neural crest ablation in chick models. This has led to the hypothesis that Pax3 is required for cardiac neural crest migration. However, cardiac derivatives of Pax3-expressing precursor cells have not been previously defined, and Pax3-expressing cells within the heart have not been well demonstrated. Hence, the precise role of Pax3 during cardiac development remains unclear. Here, we use a Cre-lox method to fate map Pax3-expressing neural crest precursors to the cardiac outflow tract. We show that although Pax3 itself is extinguished prior to neural crest populating the heart, derivatives of these precursors contribute to the aorticopulmonary septum. We further show that neural crest cells are found in the outflow tract of Splotch embryos, albeit in reduced numbers. This indicates that contrary to prior reports, Pax3 is not required for cardiac neural crest migration. Using a neural tube explant culture assay, we demonstrate that neural crest cells from Splotch embryos show normal rates of proliferation but altered migratory characteristics. These studies suggest that Pax3 is required for fine tuning the migratory behavior of the cardiac neural crest cells while it is not essential for neural crest migration.
The putative Wnt receptor Xenopus frizzled-7 functions upstream of β-catenin in vertebrate dorsoventral mesoderm patterning
Authors: Sumanas Saulius , Strege Peter , Heasman Janet , Ekker Stephen C. 
Published: April 2021

ABSTRACT
We have isolated one member of the frizzled family of wnt receptors from Xenopus (Xfz7) to study the role of cell-cell communication in the establishment of the vertebrate axis. We demonstrate that this maternally encoded protein specifically synergizes with wnt proteins in ectopic axis induction. Embryos derived from oocytes depleted of maternal Xfz7 RNA by antisense oligonucleotide injection are deficient in dorsoanterior structures. Xfz7-depleted embryos are deficient in dorsal but not ventral mesoderm due to the reduced expression of the wnt target genes siamois, Xnr3 and goosecoid. These signaling defects can be restored by the addition of β-catenin but not Xwnt8b. Xfz7 thus functions upstream of the known GSK-3/axin/β-catenin intracellular signaling complex in vertebrate dorsoventral mesoderm specification.
Broad-complex, but not Ecdysone receptor, is required for progression of the morphogenetic furrow in the Drosophila eye
Authors: Brennan Catherine A. , Li Tong-Ruei , Bender Michael , Hsiung Frank , Moses Kevin 
Published: April 2021

ABSTRACT
The progression of the morphogenetic furrow in the developing Drosophila eye is an early metamorphic, ecdysteroid-dependent event. Although Ecdysone receptor-encoded nuclear receptor isoforms are the only known ecdysteroid receptors, we show that the Ecdysone receptor gene is not required for furrow function. DHR78, which encodes another candidate ecdysteroid receptor, is also not required. In contrast, zinc finger-containing isoforms encoded by the early ecdysone response gene Broad-complex regulate furrow progression and photoreceptor specification. br-encoded Broad-complex subfunctions are required for furrow progression and proper R8 specification, and are antagonized by other subfunctions of Broad-complex. There is a switch from Broad complex Z2 to Z1 zinc-finger isoform expression at the furrow which requires Z2 expression and responds to Hedgehog signals. These results suggest that a novel hormone transduction hierarchy involving an uncharacterized receptor operates in the eye disc.
Notch signalling acts in postmitotic avian myogenic cells to control MyoD activation
Authors: Hirsinger Estelle , Malapert Pascale , Dubrulle Julien , Delfini Marie-Claire , Duprez Delphine , Henrique Domingos , Ish-Horowicz David , Pourquié Olivier 
Published: April 2021

ABSTRACT
During Drosophila myogenesis, Notch signalling acts at multiple steps of the muscle differentiation process. In vertebrates, Notch activation has been shown to block MyoD activation and muscle differentiation in vitro, suggesting that this pathway may act to maintain the cells in an undifferentiated proliferative state. In this paper, we address the role of Notch signalling in vivo during chick myogenesis. We first demonstrate that the Notch1 receptor is expressed in postmitotic cells of the myotome and that the Notch ligands Delta1 and Serrate2 are detected in subsets of differentiating myogenic cells and are thus in position to signal to Notch1 during myogenic differentiation. We also reinvestigate the expression of MyoD and Myf5 during avian myogenesis, and observe that Myf5 is expressed earlier than MyoD, consistent with previous results in the mouse. We then show that forced expression of the Notch ligand, Delta1, during early myogenesis, using a retroviral system, has no effect on the expression of the early myogenic markers Pax3 and Myf5, but causes strong down-regulation of MyoD in infected somites. Although Delta1 overexpression results in the complete lack of differentiated muscles, detailed examination of the infected embryos shows that initial formation of a myotome is not prevented, indicating that exit from the cell cycle has not been blocked. These results suggest that Notch signalling acts in postmitotic myogenic cells to control a critical step of muscle differentiation.
mtv shapes the activity gradient of the Dpp morphogen through regulation of thickveins
Authors: Funakoshi Yoko , Minami Maki , Tabata Tetsuya 
Published: April 2021

ABSTRACT
Drosophila wings are patterned by a morphogen, Decapentaplegic (Dpp), a member of the TGFβ superfamily, which is expressed along the anterior and posterior compartment boundary. The distribution and activity of Dpp signaling is controlled in part by the level of expression of its major type I receptor, thickveins (tkv). The level of tkv is dynamically regulated by En and Hh. We have identified a novel gene, master of thickveins (mtv), which downregulates expression of tkv in response to Hh and En. mtv expression is controlled by En and Hh, and is complementary to tkv expression. In this report, we demonstrate that mtv integrates the activities of En and Hh that shape tkv expression pattern. Thus, mtv plays a key part of regulatory mechanism that makes the activity gradient of the Dpp morphogen.
Morphogenetic cell movements in the middle region of the dermomyotome dorsomedial lip associated with patterning and growth of the primary epaxial myotome
Authors: Denetclaw Wilfred F. , Berdougo Eli , Venters Sara J. , Ordahl Charles P. 
Published: April 2021

ABSTRACT
The morphogenetic cell movements responsible for growth and morphogenesis in vertebrate embryos are poorly understood. Myotome precursor cells undergo myotomal translocation; a key morphogenetic cell movement whereby myotomal precursor cells leave the dermomyotome epithelium and enter the subjacent myotome layer where myogenic differentiation ensues. The precursors to the embryonic epaxial myotome are concentrated in the dorsomedial lip (DML) of the somite dermomyotome (W. F. Denetclaw, B. Christ and C. P. Ordahl (1997) Development 124, 1601-1610), a finding recently substantiated through surgical transplantation studies (C. P. Ordahl, E. Berdougo, S. J. Venters and W. F. Denetclaw, Jr (2001) Development 128, 1731-1744). Confocal microscopy was used here to analyze the location and pattern of myotome cells whose precursors had earlier been labeled by fluorescent dye injection into the middle region of the DML, a site that maximizes the potential to discriminate among experimental outcomes. Double-dye injection experiments conducted at this site demonstrate that cells fated to form myotome do not involute around the recurved epithelium of the DML but rather are displaced laterally where they transiently intermingle with cells fated to enter the central epithelial sheet region of the dermomyotome. Time- and position-dependent labeling experiments demonstrated that myotome precursor cells translocate directly from the middle region of the DML without prior intra-epithelial ‘translational’ movements of precursor cells to either the cranial or caudal lips of the dermomyotome epithelium, nor were any such translational movements evident in these experiments. The morphogenetic cell movements demonstrated here to be involved in the directional growth and segmental patterning of the myotome and dermomyotome bear interesting similarities with those of other morphogenetic systems.
The homeoproteinXiro1is required for midbrain-hindbrain boundary formation
Authors: Glavic Alvaro , Gómez-Skarmeta José Luis , Mayor Roberto 
Published: April 2021

The isthmic organizer, which patterns the anterior hindbrain and midbrain, is one of the most studied secondary organizers. In recent years, new insights have been reported on the molecular nature of its morphogenetic activity. Studies in chick, mouse and zebrafish have converged to show that mutually repressive interactions between the homeoproteins encoded by Otx and Gbx genes position this organizer in the neural primordia.We present evidence that equivalent, in addition to novel, interactions between these and other genes operate in Xenopus embryos to position the isthmic organizer. We made use of fusion proteins in which we combined Otx2 or Gbx2 homeodomains with the E1A activation domain or the EnR repressor element which were then injected into embryos. Our results show that Otx2 and Gbx2 are likely to be transcriptional repressors, and that these two proteins repress each other transcription. Our experiments show that the interaction between these two proteins is required for the positioning of the isthmic organizer genes Fgf8, Pax2 and En2. In this study we also developed a novel in vitro assay for the study of the formation of this organizer. We show that conjugating animal caps previously injected with Otx2 and Gbx2 mRNAs recreate the interactions required for the induction of the isthmic organizer. We have used this assay to determine which cells produce and which cells receive the Fgf signal.Finally, we have added a novel genetic element to this process, Xiro1, which encode another homeoprotein. We show that the Xiro1 expression domain overlaps with territories expressing Otx2, Gbx2 and Fgf8. By expressing wild-type or dominant negative forms of Xiro1, we show that this gene activates the expression of Gbx2 in the hindbrain. In addition, Xiro1 is required in the Otx2 territory to allow cells within this region to respond to the signals produced by adjacent Gbx2 cells. Moreover, Xiro1 is absolutely required for Fgf8 expression at the isthmic organizer. We discuss a model where Xiro1 plays different roles in regulating the genetic cascade of interactions between Otx2 and Gbx2 that are necessary for the specification of the isthmic organizer.
Emx2regulates the proliferation of stem cells of the adult mammalian central nervous system
Authors: Galli Rossella , Fiocco Roberta , De Filippis Lidia , Muzio Luca , Gritti Angela , Mercurio Sara , Broccoli Vania , Pellegrini Massimo , Mallamaci Antonello , Vescovi Angelo L. 
Published: April 2021

The appropriate control of proliferation of neural precursors has fundamental implications for the development of the central nervous system and for cell homeostasis/replacement within specific brain regions throughout adulthood. The role of genetic determinants in this process is largely unknown.We report the expression of the homeobox transcription factor Emx2 within the periventricular region of the adult telencephalon. This neurogenetic area displays a large number of multipotent stem cells. Adult neural stem cells isolated from this region do express Emx2 and down-regulate it significantly upon differentiation into neurons and glia. Abolishing or, increasing Emx2 expression in adult neural stem cells greatly enhances or reduces their rate of proliferation, respectively. We determined that altering the expression of Emx2 affects neither the cell cycle length of adult neural stem cells nor their ability to generate neurons and glia. Rather, when Emx2 expression is abolished, the frequency of symmetric divisions that generate two stem cells increases, whereas it decreases when Emx2 expression is enhanced.
A simple technique for the preservation of vital dyes in fixed and sectioned embryos
Authors: Pertusa J. 
Published: April 2021

ABSTRACT
In embryological work using vital dyes it is highly desirable to be able to study the distribution of the dyes in fixed material, whether examined in toto or after embedding in paraffin and serial sectioning. However, both fixation and dehydration present problems for the preservation of colour in vitally stained cells. Some fixatives preserve some dyes but, so far as I am aware, none will preserve all the vital dyes in common use. On the other hand, ethyl alcohol destroys or dissolves all vital dyes and its use in dehydration is thus undesirable. Among the fixatives that have been proposed are those of Golowin (1902), Mitamura (1923), Parat & Painlevé (1925), and Tchéou Tai Chuin (1930) for neutral red; that of Izquierdo (1955) for toluidine blue; that of Gérard (1925) for Trypan blue; that of Turchini (1919) for methylene blue; that of Lehmann (1929) for Nile blue.
The influence of aminopterin on limb regeneration in Ambystoma mexicanum
Authors: Gebhardt D. O. E. , Faber J. 
Published: April 2021

ABSTRACT
During the last twenty-five years a number of authors have studied the influence of chemical substances on limb regeneration in amphibians. Examples of compounds which have been tested so far are: (1) the antimitotic agent, colchicine (Thornton, 1943); (2) the salt, beryllium nitrate (Thornton, 1949, 1950, 1951); (3) the carcinogens, dibenzanthracene and methylcholanthrene (Karczmar & Berg, 1952; Ruben & Balls, 1964); (4) the lathyrus factor, β-aminopropionitrile (Chang, Witschi & Ponseti, 1955); (5) the hormone, thyroxine (Hay, 1956); (6) atropine and other neuropharmacological drugs (Singer, Davis & Scheuing, 1960); (7) the metachromatic dye, toluidine blue (Csaba, Bierbauer & Tôrô, 1961); and (8) semicarbazide, an inhibitor of histamine formation (Deck & Shapiro, 1963). Most of these substances caused growth retardation as well as malformations of the limb regenerates.
The inhibitory effects of calf thymus-histone fractions on the development of the chick embryo
Authors: Sherbet Gajanan V. 
Published: April 2021

ABSTRACT
The genetic potentialities of an egg are transcribed, translated and built up into a temporal-spatial organization by epigenetic processes. How are these potentialities realized? Efforts to answer this question have naturally turned towards a study of the activity of the genetic material, which according to modern ideas is entirely composed of DNA. Stedmann & Stedmann (1950) originally suggested that certain basic proteins (histones) present in the nucleus were gene inhibitors. Since then various biochemical aspects of histone metabolism have been studied (see review by Phillips, 1962). A number of distinct histones have been isolated (Butler, 1964). But tissues from different species of animals or different tissues from the same species have been found to possess very similar complements of histones (Hnilica, Johns & Butler, 1962). No specificity of interaction between histones and different parts of the DNA molecule has been observed (Johns & Butler, 1964). However, histones have been found to inhibit the synthesis of DNA-dependent RNA (Huang & Bonner, 1962; Barr & Butler, 1963; Allfrey, Littau & Mirsky, 1963; Bonner & Huang, 1964).
Onset of the acquired potentiality for fusion in the palatal shelves of rats
Authors: Pourtois M. 
Published: April 2021

ABSTRACT
This paper is concerned with that phase of palate development in rats leading to fusion of the shelves in the midline. Previous experimentation in palate development in mammals has encompassed both the earlier phase of assumption of the horizontal position of the palatal shelves, and the subsequent approximation and fusion of the shelves. Since the two processes do not occur simultaneously and can theoretically be studied separately, it was possible and feasible to confine the experiment to the later fusion phase. The present research was designed to eliminate the possible confounding effects of palate rotation in vitro on the fusion of the shelves by approximation of the explanted palatal shelves in the same horizontal plane, irrespective of their original positions in the oral cavity.
Effects of ionizing radiation on meiotic maturation of frog oocytes: II. In vitro studies
Authors: Masui Yoshio 
Published: April 2021

ABSTRACT
To investigate genomic activities in ovarian follicle cells and oocytes during meiotic maturation, ovarian pieces isolated from adult frogs (Rana pipiens) were irradiated with doses of X-ray ranging from 12000 to 96000 R and then treated with a pituitary extract and/or progesterone. When the ovarian tissue was treated with the pituitary extract alone or the pituitary extract plus a low dose of progesterone, irradiation with 12000 or 24000 R brought about an enhancement of ovulation, while irradiation with X-ray doses higher than 36000 R suppressed ovulation. On the contary, when the tissue was treated with high doses of progesterone, X-irradiation always suppressed ovulation. X-Irradiation at high dosages suppressed pituitary-induced maturation of oocytes with follicles, but not progesterone-induced maturation.
When oocytes irradiated with 48000 R or less were transferred into unirradiated female frogs, they proved to be fertilizable, but those irradiated with 72000 R or more were un-fertilizable. Nuclear transplantation experiments revealed that X-irradiation did not deprive the oocytes of their capability to cleave, although it did retard the emergence of this capability in maturing oocytes. The embryos from oocytes irradiated with 48000 R or less developed into tadpoles, but no embryos developed beyond the gastrula stage if the oocytes were irradiated with 72000 R or more.
The effects of isonicotinic acid hydrazide on the early chick embryo
Authors: Castellano M. A. , Tórtora J. L. , Germino N. I. , Rama F. , Ohanian C. 
Published: April 2021

ABSTRACT
Unincubated White Leghorn fertile eggs were injected with isonicotinic acid hydrazide (INH) through a hole in the shell. A control group was injected with normal saline, a second group with INH plus vitamin B6, and a third group was left unopened. INH, in the doses we used, proved to be lethal for more than 50% of the early chick embryos, and also produced important developmental alterations. Alterations produced by INH were primarily observed at the level of the neural epithe-lium, particularly at its cephalic portion. The most important ones were a degenerative and necrotic process of the neural epithelium, and a distortion of the normal anatomical relations of the cephalic structures. The embryonic mortality and developmental alterations induced by INH were prevented to a considerable extent by the concurrent injection of pyridoxine hydrochloride and INH. The preventive action of vitamin B6 suggests that toxicity of INH in the chicken embryos is due to the antivitamin-B6 action of INH. Through this mechanism INH would block, specially, the amino acid metabolism. The developing nervous system was the embryonic area most sensitive to such metabolic alterations.
Effects of ionizing radiation on meiotic maturation of frog oocytes: I. In vivo studies
Authors: Masui Yoshio 
Published: April 2021

ABSTRACT
In an attempt to examine genomic function of the oocyte nucleus during meiotic maturation, the effects of X-irradiation on the oocyte of the frog (Rana pipiens) vitre studied. When oocytes were irradiated with 6000-36000 R before initiation of maturation, the ovulated eggs frequently failed to be fertilized and the jelly surrounding the unfertilizable eggs was always damaged. However, the egg itself proved to retain the capability of cleaving when a nucleus was transplanted from a blastula. Also, X-irradiated eggs when invested with the jelly from unirradiated frogs recovered their capacity for fertilization. The eggs thus fertilized developed and exhibited abnormalities characteristic of X-irradiation such as arrest of gastrulation and neurulation as well as production of haploidy. Irradiation of oocytes after completion of maturation brought about developmental abnormalities more frequently than irradiation before initiation of maturation. The Hertwig effect was found only when oocytes were irradiated after completion of maturation. However, no qualitative differences were found in the developmental abnormalities produced by irradiation before maturation and those produced by irradiation after maturation.
The influence of ‘hypophysectomy’ by means of surgical decapitation on skeletal growth in the developing chick embryo
Authors: Thommes Robert C. , Hajek Anthony S. , Mcwhinnie D. J. 
Published: April 2021

ABSTRACT
Wet, dry, and ash weights and calcium content were determined on demarrowed tibiae of normal and ‘hypophysectomized’ chick embryos from days 10·5 to 19·5 of incubation. All parameters noted above increased progressively through developmental time in normal embryos. ‘Hypophysectomy’ significantly affected bone wet and dry weights, and total mineral and calcium content. The data indicate that mineralization and matrix synthesis are retarded in the absence of the pituitary.