bluuebunny/crossref_metadata_2025 huggingface dataset:
Why molecular biology needs palaeontology
Authors: Morris S. Conway
Published: April 2021

Molecular biology has re-opened the debate on metazoan diversification, including the vexing question of the origin of the major body plans (phyla). In particular, sequence analyses of rRNA have reconfigured significantly metazoan phylogeny, while homeobox genes suggest there could be an underlying similarity of developmental instructions in nominally disparate phyla. Despite this dramatic progress I argue that this renaissance of activity is lop-sided, but can be redressed by palaeontological data, especially from the Cambrian and immediately preceding Vendían. The fossil record complements and amplifies the conclusions derived from molecular biology, notably in the early radiation of cnidarians (Ediacaran faunas) and key steps in the diversification of the protostomes.
Evolutionary developmental biology of the tetrapod limb
Authors: Hinchliffe J. Richard
Published: April 2021

New insights into the origin of the tetrapod limb, and its early development and patterning, are emerging from a variety of fields. A wide diversity of approaches was reported at the BSDB Spring Symposium on ‘The Evolution of Developmental Mechanisms’ (Edinburgh, 1994); here I review the contributions these various approaches have made to understanding the evolutionary developmental biology of the tetrapod limb. The fields covered included palaeontology, descriptive embryology, experimental embryological analysis of interactions within developing limbs plus description and manipulation of homeobox gene expression in early limb buds. Concepts are equally varied, sometimes conflicting, sometimes overlapping. Some concern the limb ‘archetype’ (can the palaeon tologists and morphologists still define this with precision? how far is there a limb developmental bauplan?); others are based on identification of epigenetic factors (eg secondary inductions), as generating pattern; while yet others assume a direct gene-morphology relationship. But all the contributors ask the same compelling question: can we explain both the similarity (homology) and variety of tetrapod limbs (and the fins of the Crossopterygians) in terms of developmental mechanisms?
The evolution of insect patterning mechanisms: a survey of progress and problems in comparative molecular embryology
Authors: Sander Klaus
Published: April 2021

This report surveys data and interpretations presented by speakers in the Arthropod Session of the 1994 BSDB Spring Symposium. After a short review of phylogenetical aspects in premolecular insect embryology, the following topics are discussed: the ancestral germ type of pterygote insects, correlations between oogenesis and embryonic pattern formation, the universality or otherwise of bicoid as the anterior morphogen, novel functions in the insect Hox complex, the formal asymmetry between evolution and decay of complex gene networks, novel regulatory interactions as the main cause of evolutive changes, the repeated activity of conserved gene networks in successive steps of ontogenesis and strategies for future research. Interspersed are some unpublished data on oogenesis and pattern formation in lower dipterans, and their possible evolutionary implications.
Protein families in the metazoan genome
Authors: Chothia Cyrus
Published: April 2021

The evolution of development involves the development of new proteins. Estimates based on the initial results of the genome projects, and on the data banks of protein sequences and structures, suggest that the large majority of proteins come from no more than one thousand families. Members of a family are descended from a common ancestor.

Protein families evolve by gene duplication and mutation. Mutations change the conformation of the peripheral regions of proteins; i.e. the regions that are involved, at least in part, in their function. If mutations proceed until only 20% of the residues in related proteins are identical, it is common for the conformational changes to affect half the structure.

Most of the proteins involved in the interactions of cells, and in their assembly to form multicellular organisms, are mosaic proteins. These are large and have a modular structure, in that they are built of sets of homologous domains that are drawn from a relatively small number of protein families. Patthy’s model for the evolution of mosaic proteins describes how they arose through the insertion of introns into genes, gene duplications and intronic recom- bination.

The rates of progress in the genome sequencing projects, and in protein structure analyses, means that in a few years we will have a fairly complete outline description of the molecules responsible for the structure and function of organisms at several different levels of developmental com- plexity. This should make a major contribution to our understanding of the evolution of development.
The evolutionary origin of development: cycles, patterning, Privilege and continuity
Authors: Wolpert L.
Published: April 2021

A scenario for the evolution of a simple spherical multicellular organism from a single eukaryotic cell is proposed. Its evolution is based on environmentally induced alterations in the cell cycle, which then, by the Baldwin effect, become autonomous. Further patterning of this primitive organism -a Blastaea, could again involve environmentally induced signals like contact with the substratum, which could then become autonomous, by, perhaps, cytoplasmic localization and asymmetric cell division. Generating differences between cells based on positional information is probably very primitive, and is well conserved; its relation to asymmetric cell division is still unclear. Differentiation of new cell types can arise from non equivalence and gene duplication. Periodicity also evolved very early on. The origin of gastrulation may be related to mechanisms of feeding.

The embryo may be evolutionarily privileged and this may facilitate the evolution of novel forms.

Larvae are secondarily derived and direct development is the primitive condition as required by the continuity principle.
[3H]Uridine incorporation during previtellogenesis and early vitellogenesis in the oocytes of the chick (Gallus gallus)
Authors: Callebaut Marc
Published: April 2021

During the weeks following hatching of poultry, oocyte differentiation is most advanced in the central part of the ovarian cortex. For instance, in the 5-day-old chicken, oocytes surrounded by a ring of cuboidal cells (constituting early follicles) are appearing in the central part of the cortex. At the extreme periphery of the same cortex one occasionally can find a few germ cells which are still in the late preleptotene, and often all the intermediate stages can be seen at inter-mediate localizations. D’Hollander (1904) has described the different types of oocytes that can be found during the days following hatching. His investigations indicate that during the so-called extrafollicular phase the nucleus probably passes out of pachytene and into a stage when the chromatin is found in heavy filaments split longitudinally in places. Later the cells go through a pseudo-reticular stage in which the nucleoli and the nuclear membrane have reappeared. Between the fifth and the twentieth day after hatching, the intrafollicular phase sets in and the chromatin may also be found in the form of chains (chiasmata), clearly indicating the diplotene stage. From this stage it passes through a granular stage and becomes progressively retracted from the nuclear wall, finally giving ‘barbed’ or lampbrush chromosomes. In the 20-day-old chick, numerous oocyte nuclei with a lampbrush configuration and a large nucleolus can be seen.
Changes in somatic cell nuclei inserted into growing and maturing amphibian oocytes
Authors: Gurdon J. B.
Published: April 2021

When somatic cell nuclei are injected into enucleated unfertilized eggs they very soon cease RNA synthesis (Gurdon & Brown, 1965; Gurdon. 1967a), and commence DNA synthesis (Graham, Arms & Gurdon, 1966). By means of such experiments it has been shown (i) that components of living egg cytoplasm can substantially change the nature of nuclear activity, (ii) that nuclear activity is altered in such a way as to conform to that of the host egg cell, and (iii) that these effects are obtained with the nuclei of adult as well as embryonic cells. The experiments to be reported here were designed to find out whether the same generalizations apply to nuclei inserted into cells other than eggs, and whether they are true of changes in nuclear activity other than the repression of RNA synthesis and the induction of DNA synthesis. For this purpose growing and maturing amphibian oocytes have been used. Growing oocytes are characterized by the very active synthesis of RNA (Brown & Littna, 1964), and by the absence of nuclear DNA synthesis whether [3H]thymidine is supplied intraperitoneally (Izawa, Allfrey & Mirsky, 1963a), or is injected directly into living oocytes (Gurdon, 1967b). Maturing oocytes are in the process of completing meiosis and contain condensed chromosomes inactive in both RNA and DNA synthesis. If cytoplasmic components are of general importance in controlling nuclear activity, it would be predicted that nuclei inactive in RNA synthesis, or unaccustomed to division, should display these activities following insertion, respectively, into growing or maturing oocytes. The results reported here show that this expectation is realized, and permit some general conclusions to be drawn on the widespread importance of the cytoplasmic control of nuclear activity during cell differentiation.
The effect of cold on hind-limb growth and lateral motor column development in Rana pipiens
Authors: Decker R. S. , Kollros J. J.
Published: April 2021

A quantitative correspondence between nerve centers and their peripheral area of innervation has long been inferred from comparative and pathological studies. Many investigations have shown that by varying the mass or number of peripheral structures (1) a hypoplasia or hyperplasia, or (2) a hypotrophy or hypertrophy of their corresponding nerve centers results, indicating that a developmental relationship exists between that periphery and its innervating center. These changes in nerve cell number and size have been demonstrated in a variety of sites, including the spinal cord and spinal ganglia of chicks and amphibians (Piatt, 1948; Hamburger, 1955, 1958; Weiss, 1955).
Differentiation of kidney antigens in the human foetus
Authors: Linder Ewert
Published: April 2021

The appearance of new antigens in the embryo during differentiation has been investigated by a number of authors. Among the proteins studied were myosin (Holtzer, 1961; Ebert, 1962), lens crystallin (Ten Cate & Van Doorenmaalen, 1950), chick embryo haemoglobin (Wilt, 1962), and keratin during feather formation in chick embryo (Ben-Or & Bell, 1965). The development of liver proteins in the chick embryo was studied by D’Amelio, Mutolo & Piazza (1963).
Contractile responses at the surface of an amphibian egg
Authors: Gingell D.
Published: April 2021

During the course of experiments involving the application of polyelectrolytes to amoebae (Gingell, 1967a) it became apparent that highly charged cations are capable of affecting cellular motility. In some circumstances localized applications apparently result in contraction of the cell surface. Korohoda, Forrester, Moreman & Ambrose (1968) subsequently described a reversible charge-dependent response at the surface of isolated amoeba nuclei, which they attributed to nuclear membrane contraction and expansion. Dr Korohoda suggested to me that the surface of Xenopus laevis eggs might be expected to provide a conveniently large experimental system since any contraction would be readily visible.
Quantitative estimation of the stage of embryonic development in the locust, Schistocerca gregaria
Authors: Tyrer N. M.
Published: April 2021

An understanding of the physiological and structural development of an embryo requires a knowledge of the precise state that development has reached. Without this knowledge it is not possible to compare findings from experiments performed on different embryos or to relate them to structural changes during development.
The lateral line system at metamorphosis in Xenopus laevis (Daudin)
Authors: Shelton Peter M. J.
Published: April 2021

Marked changes in the anatomy of the lateral line system occur during the metamorphosis of Xenopus. The distribution of rows differs in larva and adult and the orientation and number of organs are modified at metamorphosis.

Larval plaques are functional, as shown by recording from their nerves.

Two classes of cells with polarized cilia are present in the tadpole well before the orientation of individual organ plaques is rearranged at metamorphosis.

The topography of the skin surface around individual plaques changes at metamorphosis. This change may reduce the directional sensitivity of organs.

Myelinated inhibitory axons in the lateralis nerve are found only when the tadpole matures. This change takes place at a time when the adult method of locomotion is developed.
The glandular aspects of the tabby syndrome in the mouse
Authors: Grüneberg Hans
Published: April 2021

The tabby syndrome includes abnormalities of the coat and of the sinus hairs, of the teeth, of a multitude of exocrine glands and of some surface structures like tail rings, plicae digitales and the papilla vallata of the tongue. All structures known to be affected by the tabby gene arise by the downgrowth of a surface epithelium into the membrana propria. The involvement of some structures but not of others cannot be accounted for by common origin from one germ layer (as both ectodermal and endodermal derivatives are involved), nor by common function of the structures affected, nor by a time concept such that structures formed before a critical period escape unharmed. The fault may lie either with the surface epithelium, or with the stimuli from the membrana propria which elicit local downgrowth, or with the interaction between the two. It seems least likely that the fault lies with the membrana propria, but a decision cannot be made on the information so far available.

New facts concerning the manifestation of tabby in Ta/+ ♀♀ either lend no support to the ‘inactive X-chromosome’ hypothesis or are at variance with it.

The tabby syndrome is also found in the autosomal genes for crinkled and (presumably) downless.
Morphogenèse trochantérienne provoquée par une régénération fémorale chez le phasme Carausius morosus Br
Authors: Bart Par A.
Published: April 2021

Morphogenesis of the trochanter produced by femoral regeneration in the phasmid Carausius morosus Br.

When the femur of Carausius is cut, about a trochanter’s length from its base, the regenerating limb is made by outgrowths from both the femur and the trochanter.

These two morphogenetic processes may be partly autonomous. The femur can develop into femur, tibia and tarsus while, simultaneously, the trochanter forms femur and tibia. Sometimes the outgrowths form together a femoro-tibial chimera segment whose length is nearly that of a femur or a tibia.

However, in three-quarters of the cases a partial regulation takes place so that a large development of the femoral outgrowth corresponds to a weak development of the trochanteral one. Generally, the longer the initial piece of femur the greater the femoral outgrowth.

The onset of the trochanteral morphogenesis and the relative importance of the trochanteral and femoral outgrowths seem to be related to the degree of distalization of the femoral mass during regeneration.
Age factor in the induced metamorphosis of thyroidectomized tadpoles
Authors: Hsü C. Y. , Yü N. W. , Liang H. M.
Published: April 2021

Three age-groups of thyroidectomized tadpoles of Rana catesbeiana were treated with a series of the same graded increasing concentrations of thyroxin. Normal froglets were formed from the three groups at the end of the induced metamorphosis. Growth and metamorphosis were compared. It was found that while the growth rate was a function of ageing, the pattern and rate of metamorphosis were not affected by senile processes. Therefore a case of differentiation independent of age was presented.
Organ-culture studies of achondroplastic rabbit cartilage: evidence for a metabolic defect in glucose utilization
Authors: Shepard Thomas H. , Bass Glenda L.
Published: April 2021

Organ-culture studies were made using cartilage from achondroplastic (dwarf) rabbits (acfac) and their phenotypically normal litter-mates. A significantly higher incorporation of 14C from glucose and galactose was measured in the dwarf; incorporation of 35S from sulfate and 3H from thymidine was equal in the two types of explant. Also, 14CO2 and [14C]lactate production from glucose by the dwarf cartilage was increased. No difference in the ratio of 14CO2 evolution from [1 -14C]- and [6-14C]glucose was found between the two cartilage types. Explants of dwarf cartilage utilized more glucose from the medium than did the controls.

Radioautographs of tissue sections from the explants showed an increased number of grains from [14 C]glucose overlying the dwarf cartilage, and this difference was particularly great over the central portions of cartilage. The proportion of 14 C grains from glucose was greater over the dwarf nuclei, less over the dwarf matrix and equal over the cytoplasm of the two tissues. Grain counts of sulfate and of thymidine did not differ in the two types of cartilage.
The effects of actinomycin D on the early development of quail and chick embryos
Authors: Billett F. S. , Bowman Patricia , Pugh Doreen
Published: April 2021

In agreement with previous work it has been found that treatment of chick embryos at an early stage of development with small concentrations of actinomycin D (2·0–4·0 × 108 M) produces abnormalities of the brain, neural tube and somites but allows near normal development of heart and blood islands. Similar effects are produced on quail embryos by even smaller concentrations of actinomycin D (0·8–1·0 x 10−8 M).

In addition to the effect on the embryo, actinomycin D severely restricts the outgrowth of the explanted blastoderm; an effect which becomes obvious after about 8 h culture and coincides with the detachment of the blastoderm edge from the supporting vitelline membrane. Histological examination of the edge of the blastoderm shows that many cells have been killed by the actinomycin D. The pronounced effect of actinomycin D on the growth of the blastoderm cannot be ignored as a factor which causes the embryos to develop abnormally and it is suggested that it may even be the primary cause of the abnormalities. Under these circumstances any interpretation of the effects produced in the embryos in terms of the selective inhibition, or lack of inhibition, of specific messenger RNAs by actinomycin D seems to be unwarranted.

Using [3H]actinomycin D an estimate has been made of the concentration of the compound in the blastoderm tissues at the time when the embryonic abnormalities are produced. The total DNA content of the blastoderms has also been determined. These measurements indicate that the ratio between actinomycin D molecules and guanosine residues in the treated tissue is very low (of the order of 1:20000) and would probably not allow an effective inhibition of DNA-dependent RNA synthesis.
The components of regrowing nerves which support the regeneration of irradiated salamander limbs
Authors: Wallace H.
Published: April 2021

Forelimbs of juvenile axolotls do not regenerate when amputated in a previously irradiated region. They usually do regenerate, however, if they have also been denervated shortly after irradiation and well before amputation. Five series of experiments are reported which define the conditions permitting this paradoxical regeneration.

Crushing the nerves of the brachial plexus proved a satisfactory means of causing temporary denervation. Shielding any region of the arm or shoulder, during an irradiation that preceded such denervation, permits regeneration to occur at a region which was initially irradiated. Lengths of brachial nerve implanted into an irradiated arm also support its regeneration.

It is concluded that temporary denervation (including Wallerian degeneration and the regrowth of axons) mobilizes cells in a shielded region of the arm. These cells migrate both proximally and distally, so that some come to occupy the site of amputation. Schwann cells of the myelin sheath are identified as the cells most likely to behave in this way. It thus seems probable that those non-irradiated Schwann cells which occupy a generally irradiated limb-stump can form the exclusive source of a mesenchymal blastema and the various internal tissues of the regenerate.
Correlation between germinal vesicle and oocyte development in the adult Japanese quail (Coturnix coturnix japónica). A cytochemical and autoradiographic study
Authors: Callebaut Marc
Published: April 2021

Continuity in the various developmental stages of the oocytes in the adult laying Japanese quail may be demonstrated with a method of whole stock labelling of their nuclei by successive applications of [3H]thymidine during their premeiotic period.

Before they mature, the intraovarian oocytes of the adult Japanese quail go through three important successive stages. In each of these stages the chromosomes have a distinct morphology and cytochemical behaviour. During the first stage or prelampbrush chromosome stage, the chromosomes are Feulgen-positive or green after Unna, and on the autoradiographs show intense incorporation of [3H]uridine after injection of this RNA precursor into the animal. During the beginning of this period, which is of very variable duration, the oocyte seems to be in a state of structural stability. The most prominent feature found in the ooplasm of oocytes at this stage is the very large paranuclear Balbiani yolk-body complex, which can be found labelled after injection of [3H]thymidine into the animal. During the second stage or lampbrush chromosome stage, the Feulgen nuclear reaction in the chromosomes weakens or becomes negative and the paranuclear Balbiani yolk-body complex disappears. After Unna, the lampbrush chromosomes and their lateral loops are seen to be pyroninophilic.

On the autoradiographs after intraperitoneal injection of [3H]uridine rapid and intense RNase-sensitive incorporation of this precursor over the chromosomes and nucleoplasm may be noted. During this stage there is thus both cytochemical and autoradiographic evidence for RNA synthesis in the rapidly enlarging germinal vesicle. During the third or postlampbrush stage activity in the germinal vesicle sharply decreases; the volume of the germinal vesicle no longer increases, the very contracted chromosomes are present in the form of Feulgenpositive vacuolized central spherules, and, after intraperitoneal injection of [3H]uridine into the adult laying quail, incorporation cannot be demonstrated in the chromosomes. By contrast, the fundamental part of the ooplasm derived from the cortex, at that moment shows both cytochemical and autoradiographic evidence of the presence and/or synthesis of nucleic acids. The postlampbrush stage is a characteristic feature of non-mature oocytes with a germinal disc and can only be found in regularly laying Japanese quails exposed to full daytime or continuous illumination.
Morbidity of aging non-incubated chicken blastoderms: further cytological evidence and interpretation
Authors: Konishi T. , Kosin I. L.
Published: April 2021

Cytological analysis was carried out on the blastodermal cells of White Leghorn eggs subjected to several pre-incubation treatments. These treatments were storage, ranging from 0 days to 4 weeks, together with one or more of the following: (1) variation of ambient temperature (5 °C, 15·5 °C, 24 °C), (2) variation of carbon dioxide level (normal air, 1·5% CO2-enriched air), (3) increased humidity (wrapping in plastic bags). To facilitate analysis, the chromosomal configuration of metaphase cells was classified into four types, I–IV, according to their increasingly ‘abnormal’ appearance, which included condensation, dispersal and/or clumping of chromosomes. In interphase cells, the degree of ‘abnormality’ was rated on the staining capacity and shape of the nuclei.

The study yielded the following results.

Temperature of storage was the most important single factor determining the state of ‘normality’ of the nuclei. The CO2 level in the storage chamber or the use of plastic bags (to provide the eggs in storage with a special ‘ mini-environment ‘, believed largely due to increased humidity) had little effect on the cytological picture of the affected blastoderms. As the blastoderms of eggs stored at 15·5 °C aged, the proportion of Type IV chromosomal configurations steadily rose. At 24 °C the aging process frequently followed a different route: both metaphase and post-metaphase chromosomes often simply disintegrated; the progression from Type I to Type IV was not in evidence. Aging at 5 °C resulted in an early appearance of uniformly dark-stained, spherical or oval nuclei. These were similar to those observed in the terminal stages of retrogression seen in the interphase nuclei. During extended storage at 15·5 °C, mitosis was shown to be blocked at metaphase. No active mitoses were observed in the blastoderms of eggs stored at 5 °C. At 24 °C however, limited mitotic activity was present, up to and including anaphase. The presence or absence of a high level of mitotic activity during pre-incubation storage was not crucial to the survival of the blastoderm. However, an environment that permitted limited mitosis was important if the cells were to have the best possible chance for remaining alive during storage. The CO2 content of the air or the use of plastic bags played no role in this respect. Two explanations, at the nuclear level, are suggested for the observed chain of events in the blastoderm of a stored chicken egg.
The growth of rats and mice vibrissae under normal and some abnormal conditions
Authors: Ibrahim Lamees , Wright E. A.
Published: April 2021

The growth of hair from the mystacial vibrissal follicles of C3H mice and Wistar rats has been measured for up to seven cycles. Normally growth in length and thickness was regular and little affected by age or sex. Plucking vibrissae at any stage during the growing period was followed by the appearance of a new vibrissa 8—11 days later. Plucking when growth had ceased had no effect on the time of appearance of the subsequent cycle. New whiskers emerging after plucking grew at the normal rate. Withholding food slowed the growth of vibrissae within 1 day. Normal growth was re-established 3 days after return to full diet.
Mechanical stresses and morphological patterns in amphibian embryos
Authors: Beloussov L. V. , Dorfman J. G. , Cherdantzev V. G.
Published: April 2021

Embryos of Rana temporaria have been dissected and shape alterations of different parts of the embryo, taking place within 1 h of separation, have been studied. Two categories of deformation have been revealed. The first category comprises those deformations which take place immediately after separation. They are insensitive to cooling, cyanide and Cytochalasin B treatment. These deformations, which consist of a shortening of initially elongated cells, are considered to be the passive relaxations of previously established elastic tensile stresses. Deformations of the second category proceed more slowly. They are inhibited by cooling, cyanide and Cytochalasin B treatment, are accompanied by elongation and migration of cells and occasionally lead to rather complex morphodifferentiations of isolated fragments. These processes are considered to be the result of the active work of intracellular contractile systems, either pre-existing or induced de novo. By analysing the arrangement of the passive deformations we have constructed maps of mechanical stresses in embryos from late blastula up to the early tail-bud stage. At several embryonic stages drastic transformations of the stress pattern occur, these transformations being separated by periods during which the pattern of stress distribution remains topologically constant. A correlation between the arrangement of stress lines and the presumptive morphological pattern of the embryo is pointed out. Some possible relations between tensile tissue stresses and active mechanochemical processes are discussed.
Pattern formation in early developmental stages of amphibian embryos
Authors: Tiedemann H.
Published: April 2021

The causal morphological analysis of the determination and differentiation processes in early developmental stages has been successfully carried out, especially in insects, sea urchins, amphibians and mammals. In all these investigations the final outcome of isolation and transplantation experiments has been evaluated by histological analysis of the differentiated tissues. In such experiments the term determination, which has been used in several ways, can be defined as follows: A certain region of a cleaving egg or an embryo is said to be determined if after isolation it forms the same tissues as in the intact embryo.
Clonal development of the retinal epithelium in mouse chimaeras and X-inactivation mosaics
Authors: West J. D.
Published: April 2021

A comparative study of coherent clones in the retinal epithelium is presented for mouse aggregation chimaeras and X-inactivation mosaics. There is a basic similarity in the number of coherent clones and the pattern of clonal development between mosaics and chimaeras. While this similarity is compatible with the difference in mean patch size reported by other authors this is at variance with some interpretations of previous work and suggests that no conclusive evidence on the timing of X-inactivation is provided by comparisons of patch sizes between chimaeras and mosaics.

The present clonal analysis also suggests that at days post coitum the cells in the retinal epithelium are distributed almost randomly while, in the adult, the cells are grouped into small coherent clones, which comprise an average of five or six nuclei. However, these data could also be explained by larger, irregular coherent clones.
Etude chez les oiseaux de 1’influence du mésenchyme néphrogène sur le canal de Wolff à l’aide d’associations hétérospécifiques
Authors: Martin C.
Published: April 2021

A study of the influence of mesonephric mesenchyme on the Wolffian duct in birds using heterospecific associations

An in ovo experimental study of mesonephric mesenchyme-Wolffian duct relationships has been performed with special reference to the progression and the ramification of the Wolffian duct in quail-chick and quail-duck associations. Two methods are used to obtain chimaeric mesonephros in ovo. First, a piece of a quail blastoderm containing the tip of the Wolffian duct is grafted on to a chick blastoderm behind an obstacle. The obstacle is a small piece of shell membrane and it prevents the migration of the chick Wolffian duct. Second, chimaeric blastoderms are made by associating in ovo halves of quail blastoderm (anterior or posterior) with the complementary halves of chick or of duck blastoderms. The experiments are performed in such a way that the Wolffian ducts are in the anterior part and the nephrogenic blastemas in the posterior part. In those experiments in which a Wolffian duct of one species is associated with the mesonephric mesenchyme of another, the Wolffian duct grows backward above the intermediate cell mass without any participation of the heterospecific cells. In quail-duck associations, the Wolffian duct reaches the cloaca and buds off the ureteric diverticulum later than it does in quail-chick associations.

The mesonephric mesenchymal area induces the Wolffian duct to branch out into a collecing system. Quail Wolffian duct gives rise to more numerous collecting tubules than does the chick Wolffian duct. In quail mesenchyme-chick Wolffian duct mesonephros, the collecting tubules are not always present and often the tubules derived from the mesenchyme invade the wall of the Wolffian duct. In all cases only very short collecting tubules are derived from the Wolffian duct.
Immunological studies on the incorporation of radioactive leucine into sea urchin embryonic proteins: extractability and turn-over of newly synthesized proteins
Authors: Westin Monica
Published: April 2021

This study was undertaken in order to investigate the turn-over of newly synthesized sea urchin embryonic proteins, the distribution of these proteins in the cell and their changes in solubility with time. Refined immunological methods providing unique possibilities for studies of individual proteins were utilized. The proteins were obtained in two soluble fractions: a concentrate of proteins from the cytosol was obtained by homogenization in a hypotonic medium and another fraction constituting membrane-associated proteins was solubilized by detergent treatment of the residual pellet; 75 °/0 of the total protein content in early and 60 % in later developmental stages was thus solubilized. The proteins solubilized by these mild methods retained their antigenicity and could be analyzed by immunodiffusion methods.

The fate of newly synthesized embryonic proteins was studied by incorporation of a radioactive amino acid using two different incubation procedures. The results of these studies indicated that newly synthesized proteins changed their solubility properties with time. Proteins were thus transfered from the soluble to the insoluble fraction. The findings that more proteins became insoluble during development mentioned above also supports such an interpretation.

The synthesis of individual proteins was studied by immunodiffusion and autoradiography. Most of the antigens in the two soluble fractions were identical. Experiments with absorbed antisera revealed that only two to four antigens were present exclusively in one of the two soluble fractions. Three groups of antigens differing in regard to their metabolic activities were distinguished. Some antigens were labeled after both procedures without substantially increasing in concentration during development. Thus, their labeling was probably sustained by turn-over. Other antigens were labeled only after one of the two incubation procedures indicating large variations in regard to synthesizing rates of individual proteins.
Aspects quantitatifs du peuplement des gonades par les cellules germinales chez l’embryon de Caille (Coturnix coturnix japonica)
Authors: Didier Eliane , Fargeix Noël
Published: April 2021

Quantitative aspects of the colonization of the gonads by germ cells in the quail embryo (Coturnix coturnix japonica)

A quantitative analysis made on quail embryos coming from 13 isolated parent-couples reveals some significative variations of a genetic origin, between some of the offspring studied : the differences observed concern both the quantitative importance of the colonization of gonads by germ cells and the asymmetrical distribution of PGCs (primordial germ cells) between the two genital ridges.

The chronological study of the colonization in the quail shows, as in both the duck and the chick, two periods of rapid and regular increase of the number of gonadic PGC, at stages from 13 to 18 and from 24 to 30 of Hamburger & Hamilton.

The distribution of germ cells between the two genital ridges is, at the beginning of the colonization, not very asymmetrical. Between stages 18 and 24 the asymmetry increases and remains stable so that the mean value of D % (percentage of the number of PGC contained in the right gonad) from that moment on is equal to 29 ·34 %. This value is specific for the quail embryo.
The Distribution of Placental Scars of First and Second Pregnancies in the Rat
Authors: Momberg Harold , Conaway Clinton
Published: April 2021

In albino rats placental scars of a second pregnancy partially or completely overlapped 32 of 312 old placental scars from a previous pregnancy in 61 uterine horns. Gross recognition of the superposed scars was often impossible. Microscopic recognition of the superposed sites was possible under the conditions of the experiment. The major changes in the distribution pattern of second pregnancy scars as compared to those of the first pregnancy are (a) the intervals between second pregnancy scars are more variable; (b) the most posterior new scar tends to be further from the cervix than the last first pregnancy scar; (c) the most anterior new scar tends to be closer to the oviduct than the corresponding first pregnancy scar; and (d) although the oviducal scar-free segment is longer than the cervical scar-free segment in both pregnancies, the difference is less in the second pregnancy.
Cell division, cell elongation and the co-ordination of crystallin gene expression during lens morphogenesis in the rat
Authors: McAvoy J. W.
Published: April 2021

A quantitative analysis of cell division and cell elongation was carried out during lens morphogenesis in the rat. At 13 days of development elongating cells in the posterior part of the lens vesicle (presumptive fibre cells) have a lower mitotic activity than cells in the anterior vesicle. By 14 days these elongating cells do not divide. Thus at 14 days of development the lens can be separated into two compartments; a proliferation compartment in the anterior lens and an elongation compartment in the posterior lens.

The three main groups of lens-specific proteins, α- β- and γ-crystallins, were localized by immunofluorescence. Alpha-crystallin is the first crystallin to be detected and is localized in some lens pit cells at 12 days of development. By 14 days all lens cells contain α-crystallin. Beta- and γ-crystallins are detected later at days and are localized in some cells situated primarily in the posterior part of the lens vesicle. At later stages of development these crystallins are restricted to cells of the elongation compartment, i.e. presumptive fibre and fibre cells. Possible mechanisms that govern the temporal and spatial distribution of crystal-lins are discussed
On the Regulation of Bilateral Symmetry in Plutei with Exchanged Meridional Halves and in Giant Plutei
Authors: Hörstadius Sven
Published: April 2021

After exchange of meridional halves between two eggs typical plutei were obtained in nearly all pairs (Text-fig. 2).

Two 32-cell stages were split along a meridian, flattened, and fused (Text-fig. 3). There resulted typical giant plutei (Text-fig. 4); plutei with a supernumerary rod at the dorsal pole (Text-fig. 6); plutei with a supernumerary dorsal strip of ciliated band (Text-fig. 7D); plutei with both supernumerary rod and a ciliated band in the dorsal part (Text-figs. 7 A-C, 8A); joined twins (Text-fig. 9); and plutei with two ventral sides (Text-figs. 8B, 10).

The results are interpreted in the light of the hypothesis that there is a dominating presumptive ventral centre capable of subduing the tendencies toward formation of a ventral side which are located in other parts of the egg.
The Effect of Maternal Immunization against Organ Tissues on Embryonic Differentiation in the Mouse
Authors: Gluecksohn-Waelsch Salome
Published: April 2021

The response of embryonic differentiation to injection of organ-tissue-emulsion into female mice prior to conception was studied. The injection of brain-emulsion into females of the DBA/I strain was followed by abnormalities of the developing nervous system in 8–9 per cent, of subsequently conceived embryos. Such abnormalities consisted of suppression of nervous-tissue differentiation, microcephaly, and abnormalities of closure of neural folds. As controls, female sibs of brain-injected mothers were injected with a heart-emulsion. No nervous-system abnormalities were observed in the subsequently conceived embryos of these mothers. The possible mechanism of the effect described here is discussed. It seems most likely that maternal antibodies are responsible for the nervous-system abnormalities of the embryos. Problems of the transmission of these antibodies to the embryo and of the mechanism of their effect on embryonic differentiation are discussed.
‘Matted’, a New Hair-mutant in the House-mouse: Genetics and Morphology
Authors: Searle A. G. , Spearman R. I.
Published: April 2021

Three types of hereditary hairlessness are known in the house-mouse. With Naked (Fraser, 1946) and Alopecia (Dickie, 1955), baldness results from the breaking of hairs; with hairless and its allele rhino, from the shedding of entire hairs (Fraser, 1946). The crinkled (Falconer, Fraser, & King, 1951) and ragged (Carter & Phillips, 1954) genes, however, lead to a complete absence of certain hair-types, due to delayed or imperfect follicle development (agenesis). In rough (Falconer & Snell, 1952) the fur is greasy and looks unkempt but no baldness occurs.
The Pluripotency of the Pharyngeal Primordium in Urodelan Neurulæ
Authors: Okada Tokindo S.
Published: April 2021

Explantation experiments of pharyngeal endoderm, alone or together with various ecto- or endomesodermal materials, within epidermal envelopes were performed, using the neurulae of Trituras pyrrhogaster and Hynobius nebulosus as materials. The piece of endoderm, when explanted alone within the envelope, did not differentiate into any definable structure, persisting as an amorphous mass of undifferentiated endodermal cells, even after a prolonged cultivation as long as 30-40 days. Typically differentiated endodermal structures were found only in the explants in which the endodermal piece was combined with the ecto- or endomesodermal materials. When the pharyngeal primordium was explanted together with the material of either neural fold or archenteric roof, irrespective of the regions from which these materials were removed, the production of pharynx always occurred. When combined with lateral plate mesoderm, the pharyngeal primordium generally developed into an intestinal vesicle. Oesophagus, stomach, liver, or pancreas was occasionally found in these combination explants. Some xenoplastic explantations, in which the pharyngeal rudiment of Hynobius was combined with ecto- or endomesodermal material from the neurula of Rana japónica, were also carried out. Hynobius endoderm showed differentiation into pharynx when combined with anterior neural material of Rana, but it produced an intestinal vesicle when lateral plate of Rana was included. In all the available specimens of the present experiments it was a rule that pharyngeal differentiation occurred within free mesenchyme, while intestinal structures were found to be surrounded by endothelial tissue. On the basis of above data it is concluded that the pharyngeal primordium is still pluripotent in the early neurula stage, and its future fate may be varied, depending mainly upon the sort of connective tissue which is present around it.
Evidence of prostaglandin involvement in blastocyst implantation
Authors: Holmes P. V. , Gordashko B. J.
Published: April 2021

Delayed-implantation mice were used to test for local implantation induction effects of prostaglandins E2 and F2α. Evidence of implantation was gathered by microdissection of implantation sites and by scanning electron microscopy. Indomethacin was tested for the ability to interfere with the mechanisms of estrogen-induced, normal implantation. Both prostaglandins appear to have significant effect inducing implantation when applied locally in the uterine lumen, PGE2 being more effective than PGF2α. The indomethacin clearly has a blocking effect on normal implantation. However, indomethacin appears only partially able to prevent the morphological changes indicative of the trophoblast cell transformation.
Repair of Wounds of the Mucosa in the Rectum of the Cat
Authors: McMinn R. M. H. , Johnson F. R.
Published: April 2021

Wound healing in the rectum of the cat has been studied following the creation of artificial ulcers by removing small areas of mucosa. During the first few days of the repair process epithelial cells migrated from the wound margins over the floor of the ulcer, in which granulation tissue began to accumulate. Mitotic figures were occasionally found in migrating epithelium. The striated borders of normal epithelial cells gave a strong reaction for alkaline phosphatase and were PAS-positive. These reactions were not present during migration in the early stages of repair. Glycogen granules, not normally detectable histochemically in this epithelium, were found in migrating cells at the end of the first week. The pattern of healing at later stages showed considerable variation, according to the amount of granulation tissue formed. Where the amount of such tissue was relatively small, increasing epithelialization occurred, with evidence of new crypt formation; where granulation tissue was exuberant, the margins of the original lesion may have been drawn together by the contraction of maturing connective tissue. Alkaline phosphatase was absent from the developing and maturing connective tissue.
Cell surface properties of amphibian embryonic cells
Authors: Matsuda Motoko
Published: April 2021

Gastrula and neurula embryos of Cynopspyrrhogaster were dissociated into cell suspensions with ethylenediaminetetraacetic acid (EDTA), trypsin, and alkali solution. The cells were cultured in Niu-Twitty’s balanced salt solution and their aggregates were examined histologically. The results indicated that the capacity of amphibian embryonic cells for aggregate formation, sorting out, and notochord differentiation was not suppressed by EDTA and alkali treatments. Trypsin treatment, however, virtually suppressed the cell’s capacity for aggregate formation. When aggregate formation resulted from trypsin-dissociated cells, the aggregates showed the sorting out and no differentiation of notochord.
Differential localization of [35S]sulfate within ectodermal basement membrane in relation to initiation of chick limb buds
Authors: Lunt Dennis M. , Seegmiller Robert E.
Published: April 2021

This study examined the possible developmental relationship between differential amounts of glycosaminoglycans (GAG) within the ectodermal basement membrane and initiation of limb outgrowth. Chick embryos at stages 11-20 were labeled in ovo with 35SO4 and processed for autoradiography. After exposure to sulfate for 15 min, the label was localized within the surface ectoderm whereas after 3 h the label was localized within the subjacent basement membrane. The label was sensitive to chondroitinase ABC. These experiments suggest that the labeled material was ectodermally derived chondroitin sulfate. At all stages examined, intense labeling of the basement membrane was associated with relatively undifferentiated, mitotically active tissue, e.g. limb-bud mesoderm. The labeling was less intense in regions with decreased mitotic activity, e.g. the flank. Thus, the labeling pattern of the basement membrane correlated with differential mitotic rates presumed to be associated with limb outgrowth. These observations support the hypothesis that communication between tissues of different origin resulting in altered mitotic behavior of limb and flank mesenchymal cells is facilitated by the ectodermal basement membrane.
The time required for positional signalling in the chick wing bud
Authors: Smith J. C.
Published: April 2021

An estimate of the time required for positional signalling in the chick wing bud was obtained by grafting irradiated quail polarizing regions to host wing buds and removing them at various times. Such polarizing regions must be present for at least 15 h to induce additional structures in the host wings. This result is discussed in terms of a diffusible morphogen model.