bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temporal colinearity and the phylotypic progression: a basis for the stability of a vertebrate Bauplan and the evolution of morphologies through heterochrony
Authors: Duboule Denis 
Published: April 2021

ABSTRACT
Vertebrate Hox genes are essential for the proper organiz ation of the body plan during development. Inactivation of these genes usually leads to important alterations, or transformations, in the identities of the affected develop ing structures. Hox genes are activated in a progressive temporal sequence which is colinear with the position of these genes on their respective complexes, so that ‘anterior’ genes are activated earlier than ‘posterior’ ones (temporal colinearity). Here, an hypothesis is considered in which the correct timing of activation of this gene family is necessary in order to properly establish the various expression domains. Slight modifications in the respective times of gene activation (heterochronies) may shift expression domains along the rostrocaudal axis and thus induce concurrent changes in morphologies. It is further argued that temporal colinearity only occurs in cells with high mitotic rates, which results in a strong linkale between patterning and growth control and makes the pat terning process unidirectional, from anterior, proximal and early, to posterior, distal and late, a model referred to as the ‘Einbahnstrasse’. While the nature of the mechanism(s) behind temporal and spatial colinearities is unknown, it is proposed that such a mechanism relies on meta-cis interactions, that is it may necessitate gene conti guity. Such a mechanism would be based on DNA-specific, rather than gene-specific, features such as chromatin con figurations or DNA replication. The existence of such a meta-cis mechanism would explain the extraordinary con servation of this genetic system during evolution as its basic properties would be linked to that of the genetic material itself. Consequently, it is hypothesized that, in vertebrates, the resistance of this mechanism to evolutionary variations may be the reason for the existence of a short develop mental window of morphological invariance (the phylo typic progression).
Collagen Formation and Wound Contraction during Repair of Small Excised Wounds in the Skin of Rats
Authors: Abercrombie M. , Flint M. H. , James D. W. 
Published: April 2021

ABSTRACT
Standard wounds of approximately 17 mm.2 area have been made in the dorsolumbar region of rats by cutting out a small square of skin within a standard tattoo-mark. By this technique, at 5, 10, 15, and 25 days after operation, the amount of wound contraction (disregarding epithelialization) has been measured, and the area of repair has been removed for collagen estimation by the hydroxyproline method of Neuman & Logan (1950). Contraction had occurred significantly 5 days after operation, was very active between 5 and 10 days, and did not proceed farther after 10 days. There was a decrease in wet weight of the wound content parallel to its contraction in area. During contraction the wound changed in shape from a square to a 4-pointed star. The rim of old tissue surrounding the wound diminished in length and in area. When contraction had ceased the surrounding skin was under abnormal tension, judged by the expansion when the wounded area,was excised. These observations can be accounted for by supposing that the content of the wounded area exerts a contractile force, and that the rim of original skin has some rigidity. Chemically measurable collagen formation had started 5 days after operation and it continued beyond 10 days, i.e. after contraction had ceased. The result was a progressive rise in both concentration and absolute amount of collagen in the wound. By 25 days the area under repair was, however, not nearly back to normal in collagen per unit area or per unit wet weight.
The inductors of differentiation of prefollicular tissue and the follicular epithelium in ovarioles of Pyrrhocoris apterus (Heteroptera)
Authors: Masner Petr 
Published: April 2021

ABSTRACT
Differentiation of the tissues of the telotrophic ovarioles from the embryonic primordium occurs gradually throughout larval development of bugs. All tissues are established already at the beginning of the last larval stage as ob-served by Wick & Bonhag (1955) in Oncopeltus fasciatus. During the last instar, when the corpora allata are morphogenetically inactive, the synthetic activity of the cells of first ovarian nutritive system, the trophocytes, takes place. The nutrients released by trophocytes at the final emergence activate the oocytes, starting previtellogenesis (Masner, 1966). The function of this nutritive system is known to be independent of any humoral control (Wigglesworth, 1936, and others). Food intake seems to be the only inductor of trophocyte growth. The developing oocyte grows into the prefollicular syncytium. The surrounding tissue starts to organize into a unilayered epithelium.
Fine structure of degenerating taste buds after denervation
Authors: Farbman Albert I. 
Published: April 2021

ABSTRACT
It is well known that taste buds are dependent on an intact nerve supply, and when experimentally denervated they degenerate and disappear (von Vintschgau & Honigschmied, 1877; von Vintschgau, 1880; Griffini, 1887; Meyer, 1897; Olmsted, 1920a, b, 1921, 1922; May, 1925; Whiteside, 1927; Torrey, 1934, 1936; Wagner, 1953; Guth, 1957, 1958, 1963; Beidler, 1962, 1963). Olmsted (1920 b) has suggested that the degenerating taste bud cells are cleared away by macrophages invading the epithelium; Guth (1957, 1958, 1963) has demon-strated sloughing of degenerating taste buds from the epithelial surface, and others believe that taste bud cells dedifferentiate to become lining epithelium (Meyer, 1897; Wagner, 1953). Because of this disagreement and because recent evidence for cell turnover in taste buds has indicated that cell death and replace-ment is a normal occurrence (Beidler, 1962, 1963; DeLorenzo, 1963; Beidler & Smallman, 1965), it is pertinent to study the fine structure of degenerating taste buds in the hope of elucidating the process by which taste bud cells and nerve terminals degenerate.
Is the presumptive notochord responsible for somite genesis in the chick?
Authors: Nicolet G. 
Published: April 2021

ABSTRACT
Fragments of Hensen’s node or head process were implanted into the primitive streak 0·8 mm behind the node. The posterior region was isolated from all influences emanating from the anterior part of the blastoderm, either by cutting off a large rectangular piece just in front of the implant or by explanting the region combined with the notochord implant into the area opaca. As controls, corresponding regions of the primitive streak were isolated or explanted.
In controls, somite formation never took place, while the implantation of presumptive notochord into this posterior region was followed by the formation of somites in most cases.
In these experiments, the action of the presumptive notochord in its new situation was similar to that of the chorda-factor in amphibians.
An ultrastructural study of primordial germ cells, oogonia and early oocytes in Xenopus laevis
Authors: Al-Mukhtar Kawakib A. K. , Webb Andrew C. 
Published: April 2021

ABSTRACT
Electron-microscope observations on the differentiation of germ cells in Xenopus laevis have revealed that the Balbiani body, cytoplasmic nucleolus-like bodies and groups of mitochondria associated with granular material previously reported only in older amphibian oocytes, are also present in the primordial germ cells, oogonia and early meiotic (pre-diplotene) oocytes of this species.
Although there is considerable morphological reorganization of the gonad as a whole at the time of sex determination, little visible change in the ultrastructure of the primordial germ cells appears to take place during their transition to oogonia. Both primordial germ cells and oogonia have highly lobed nuclei and their cytoplasm contains a conspicuous, juxtanuclear organelle aggregate (consisting for the most part of mitochondria), which is considered to represent the precursor of the Balbiani body.
In marked contrast, the transition from oogonium to oocyte in Xenopus is characterized by a distinctive change in nuclear shape (from lobed to round) associated with the onset of meiosis.
During leptotene the oocyte chromatin becomes visibly organized into electron-dense axial elements (representing the single unpaired chromosomes) which are surrounded by a fibrillar network. Towards the end of leptotene, these axial elements become attached to the inner surface of the nuclear membrane in a localized region adjacent to the juxtanuclear mitochondrial aggregate. Zygotene is marked by the initiation of axial element pairing over short regions, resulting in the typical synaptonemal complex configuration of paired homologous chromosomes. The polarization of these tripartite ribbons within the nucleus becomes more pronounced in late zygotene, producing the familiar Bouquet arrangement. The synaptonemal complexes are more extensive as synapsis reaches a climax during pachytene, whereas the polarization is to some extent lost. The fine structure of synaptonemal complexes in the Xenopus oocyte is essentially the same as that described in numerous other plant and animal meiocytes. It is not until the beginning of the extended diplotene phase that any appreciable increase in cell diameter takes place. During early diplotene (oocyte diameter approximately 50/μm), the compact Balbiani body characteristic of the pre-vitellogenic anuran oocyte is formed by condensation of the juxtanuclear mitochondrial aggregate.
Electron-dense, granular material appears to pass between nucleus and cytoplasm via nuclear pores in all stages of Xenopus germ cell differentiation studied. There is a distinct similarity in electron density and granular content between this ‘nuage material’ associated with the nuclear pores and the cytoplasmic aggregates of granular material in association with mitochondria or in the form of nucleolus-like bodies.
The growth of the retina in Xenopus laevis: an autoradiographic study
Authors: Feldman Joan D. , Gaze R. M. 
Published: April 2021

ABSTRACT
The retina of Xenopus laevis has previously been shown, using autoradiographic methods, to develop in the normal animal by the annular addition of cells at the ciliary margin.
The development of the retina in animals with surgically produced ‘compound eyes’ was subsequently studied. In these animals the eye cup was split along the dorsoventral axis and the resulting half-eyes were recombined so as to form animals with a double-nasal eye.
The retina in experimental animals was found to develop as in the normal animal. No labelling of cells with radioactive thymidine was seen along the cut edge of each half-eye; thus in terms of cell division each half of the compound eye remains a half.
Ultrastructural studies of the mouse blastocyst substages
Authors: Nadijcka Mary , Hillman Nina 
Published: April 2021

ABSTRACTThe mouse blastocyst stage covers approximately 2 days. During this period, embryonic development advances through four ultrastructurally distinct substages. Specific ultra-structural characteristics, such as changes in cell shape and/or the distribution of intracellular organelles, may be used to characterize the various cell types from each other at each sub-stage (e.g. trophoblast from inner cell mass cells), as well as to distinguish the same cells from each other at different substages (e.g. substage 1 abembryonic trophoblast cells from substage 2 abembryonic trophoblast cells). A distinguishing characteristic of these blastocyst substages are the membrane contacts (tight junctions, desmosomes, focal tight junctions) between cells. The apical surfaces of adjacent trophoblast cells, from the time of cavity formation until the initial stage of implantation, are connected by a tight junction and a desmosome. The basal region of the apposed trophoblast membranes, however, vary both in their spatial inter-relationship with each other and in their defined cellular contacts. Likewise, the cell contacts between the inner cell mass cells, and between these cells and the embryonic trophoblast cells, are distinctive for each blastocyst substage.
Zur Histogenese des Somiten beim Hühnchen
Authors: Mestres P. , Hinrichsen K. 
Published: April 2021

ABSTRACT

The histogenesis of somites in the chick
The somites of the thoracic region of chick embryos incubated for 2 (stages 13–15) and 3 days (stages 17–19) have been examined cytologically and ultrastructurally. Cell contacts and cell arrangement were studied first in spherical somites. The further development of the spherical somite is characterized by changes in the cell arrangement. According to these changes two somitic cell populations can be distinguished: a ventral one, which during the third day loses its epithelial arrangement and becomes disaggregated, and a dorsal one, the dermatome, which remains epithelial for a longer time. Some cells of the ventral group reaggregate on the apical surface of the dermatome cells, and constitute the myotome. The contacts between dermatome and myotome cells as well as between the myotome cells themselves are decribed. Although the myotome cells appear to be arranged in an epithelial-like order and develop a basement membrane at the sclerotome side, the characteristic contacts and cell polarity of epithelia were not observed. These observations are discussed in relation to the process of cell adhesion and cell communication during the morphogenesis of the secondary mesenchyme.
The role of Schwann cells in paradoxical regeneration in the axolotl
Authors: Maden M. 
Published: April 2021

ABSTRACT
The experiments described here examine further the conditions under which paradoxical regeneration occurs and provide support for the hypothesis that a proximal migration of Schwann cells is responsible for the phenomenon. When only the hand is shielded from irradition and the limb is denervated, amputation through the forearm or upper arm sometimes results in regeneration. The effects of variation in the time interval between denervation and amputation, the level of amputation and the method and number of denervations on the incidence of regeneration were investigated. The presence or absence of viable Schwann cells at the amputation plane was deduced from the remyelination of nerves under conditions which do or do not permit paradoxical regeneration. The nerves of totally irradiated and denervated limbs remain unmyelinated following regrowth of axons and such limbs do not regenerate after amputation. When only the hand was shielded from irradiation before the limbs were denervated, the new axons became completely remyelinated and some of these limbs regenerated when amputated. It is suggested that under these conditions Schwann cells can migrate proximally and can then proliferate further to form a blastema, since they would be the only unirradiated tissue present at the amputation plane.
Factors affecting the time of formation of the mouse blastocoele
Authors: Smith Rosita , McLaren Anne 
Published: April 2021

ABSTRACTIn normal mouse embryos developing in vivo, the first appearance of the blastocyst cavity was found to be associated more closely with developmental age, judged by cell number, than with chronological age, i.e. elapsed time since ovulation. When development was slowed by in vitro culture, formation of the blastocoele was delayed. However, cell number itself was not a critical factor, since the number of cells per embryo could be doubled or tripled or halved by experimental manipulation without substantially affecting the timing of blastocoele formation. Experiments in which one cell division was suppressed with cytochalasin-B, leading to tetraploidy, showed that the number of cell divisions since fertilization was also not critical. A possible role is suggested either for nucleocytoplasmic ratio, or for the number of nuclear or chromosomal divisions or DNA replications since fertilization, all of which increase during cleavage.
Participation of neural crest-derived cells in the genesis of the skull in birds
Authors: Lièvre Christiane S. Le 
Published: April 2021

ABSTRACT
The differentiation of cephalic neural crest cells into skeletal tissue in birds has been observed using the quail-chick nuclear marking system, which is based on specific differences in the distribution of the nuclear DNA. Chimaeras were formed by replacing a fragment of cephalic neural primordium of a 2- to 12-somite chicken embryo by the corresponding fragment isolated from an equivalent quail embryo. The participation of the graft-derived cells in the formation of the skull of these embryos was studied on histological sections after Feulgen and Rossenbeck staining.
Cells from the prosencephalic neural crest migrate into the frontal nasal process and mix with the mesencephalic neural crest cells in the lateral nasal processes, around the optic cupule and beneath the diencephalon. In addition, the mesencephalic neural crest cells form the bulk of the mesenchyme of the maxillary processes and mandibular arch, whereas the rhombencephalic neural crest cells become located in the branchial arches.
The origin of cartilages of the chondrocranium and bones of the neurocranium and viscerocranium has been shown in the chimaeric embryos: the basal plate cartilages, occipital bones, sphenoid bones and the cranial vault are mainly of mesodermal origin. However some parts have a dual origin: rhombo-mesencephalic neural crest cells are found in the otic capsule, and the frontal bone, the rostrum of parasphenoid and the orbital cartilages contain diverse amounts of prosencephalo-mesencephalic neural crest cells. The squamosals and the columella auris are formed from mesectodermic cells as are the nasal skeleton, the palatines and the maxillar bones. The mesectodermal origin of mandibular and hyoid bones and cartilages was already known.
From these results it appears that the cephalic neural crest is particularly important in the formation of the facial part of the skull, while the vault and dorsal part are mesodermal and cartilages and bones found in the intermediary region are of mixed origin. The presence of mixed structures implies that the mesoderm and the mesectoderm are equally competent towards the specific inducers of these bones and cartilages. This correlates with the equivalence in differentiation capacities already shown for cephalic mesodermal and mesectodermal mesenchymes.
Has collagen a role in muscle pattern formation in the developing chick wing? 1. An immunofluorescence study
Authors: Shellswell G. B. , Bailey A. J. , Duance V. C. , Restall D. J. 
Published: April 2021

ABSTRACT
We have used antibodies to three of the isomorphic forms of collagen, types I, III and V, in an immunofluorescence microscopy study of myogenesis in the embryonic chick wing, concentrating on the period between stages 27 and 30 (5 to 7·5 days incubation) which is when the dorsal and ventral muscle masses separate into discrete muscles.
We have demonstrated the presence of all three collagen types at the ectoderm-mesenchyme junction from stage 27 onwards. Type I collagen and then type III collagen are found in progressively deeper layers of the dermis at the later stages. Both types I and V collagen are initially present in the cartilage elements, but type 1 collagen becomes restricted to the periphery of these structures at later stages. The developing muscle areas show a lack of staining at all stages and it is only at the latest stages that types I and III collagen first appear in the surrounding epimysium.
We discuss possible mechanisms for the division of the muscle masses in the light of this information on the distribution of collagen types.
The eye margin and compound-eye development in the cockroach: evidence against recruitment
Authors: Nowel Mark S. , Shelton Peter M. J. 
Published: April 2021

ABSTRACT
The compound eye of the cockroach nymph grows from stadium to stadium by the addition of new ommatidia to the growing edge of the eye. By a series of transplant operations on Periplaneta americana and from SEM studies on Gromphadorhina portentosa it is shown that the proliferating region of the eye margin is a budding zone. There is no recruitment of larval head-capsule epidermis into the eye.
The haemoglobins of developing duck embryos
Authors: Cirotto C. , Arangi I. , Panara F. 
Published: April 2021

ABSTRACT
Three haemoglobins were isolated by ion-exchange chromatography from the haemolysates of embryonic duck erythrocytes up to 8 days of development. The component globins were characterized both by electrophoresis in dissociating conditions and by finger-printing analysis. The major haemoglobin fraction El appears to be an embryonic tetramer since its constituent globins are different from all the others synthesized during embryonic and adult life. The two minor fractions E2 and E3 show a-type subunits that are very similar to those of the two adult haemoglobins Al and A2 respectively. They are present all through embryonic life, as demonstrated by chromatographic analysis. For these reasons they have been considered foetal.
The two haemoglobins typical of the adult animal are found in the red cells of the embryo from 8 days of incubation. Their relative amounts change continuously during embryonic development and reach the adult value after hatching.
In vitro development of inner cell masses isolated from t0/t0 and tw5/tw5 mouse embryos
Authors: Hogan Brigid , Spiegelman Martha , Bennett Dorothea 
Published: April 2021

ABSTRACT
Inner cell masses (ICMs) isolated immunosurgically from mouse blastocysts segregating the homozygous lethal mutants t0/t0 and tw5 /tw5 were cultured in vitro. Presumed ICMs fail to grow after three days in culture (equivalent gestational day 7 · 5) when they consist of an outer layer of endoderm cells surrounding about 30 epiblast cells. Presumed homozygous tw5 / tw5 ICMs develop to a more advanced stage in culture and on the seventh day (equivalent gestational day 11 · 5) consist of an inner core of disorganized ectoderm cells with a small proamniotic cavity, surrounded by multiple layers of endoderm cells.
Essential role of the polyamines in early chick embryo development
Authors: Löwkvist B. , Heby O. , Emanuelsson H. 
Published: April 2021

ABSTRACT
The polyamines putrescine, spermidine and spermine were analyzed in chick embryos during the first 2 days of development. A rapid increase in the activity of ornithine de-carboxylase (ODC), the initial and rate-limiting enzyme in polyamine synthesis, was observed immediately after onset of incubation. Peak activities were found at 15 and 23 h of incubation. The first peak coincides with gastrulation and the second peak with early neurulation in the embryo. All three polyamines varied in a similar manner as did ODC, with putrescine and spermidine at about the same level and spermine at a lower level. The ODC activity was blocked by α-difluoromethylornithine, an enzyme-activated irreversible inhibitor. The inhibitor was administered to embryos in ovo at 5 h of incubation, i.e. prior to the first major increase in ODC activity. This block prevented the accumulation of the polyamines and inhibited development at gastrulation, suggesting a decisive role for polyamines in this developmental event.