bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of chymotrypsin on the development of Dictyostelium discoideum
Authors: Kilpatrick David C. , Schmidt Jerzy A. , Stirling John L. , Pacy John , Jones Gareth E.
Published: April 2021

Development of the cellular slime mould Dictyostelium discoideum strain NC4, in the presence of α-chymotrypsin (3 mg/ml) is reversibly arrested at the tight aggregate stage (10/12 h). Pronase has a similar effect, but trypsin only retards normal development by about five hours. Normally developing cells are susceptible to α-chymotrypsin if they are transferred into its presence at any time up to the tight aggregate stage (10-12 h). Transfer after this stage does not affect the appearance of fruiting body structures in the normal time (24 h).

Electron microscopy showed the ultrastructure of α-chymotrypsin-blocked aggregates after starvation for 24 h to be consistent with a block at 10 –12 h of normal development. Poorly developed prespore vacuoles, having thin incomplete walls and a paucity of electrondense material, are present in some cells. No angular vacuolated cells characteristic of stalk cells are visible. Fruiting bodies formed in the presence of a α-chymotrypsin, either as minority structures when the enzyme is added before 10 –12 h of normal development, or as the majority structures on later enzyme addition, were found to be abnormal. Normal stalks were formed but the spores were immature. Prespore vacuoles were present, though disrupted, and the cells were not encapsulated by spore walls.

The electronegativity of intact slime mould amoebae was significantly reduced, and material containing L-[6-3H]-fucose and [l-14C]leucine was removed from the cell surface on α-chymotrypsin treatment. Few plasma membrane proteins were affected, however, and staining of polyacrylamide gels for glycopeptides using Con A-peroxide binding also showed little change.
Development of amphibian thymus I. Morphological differentiation, multiplication, migration and lysis of thymocytes in the urodelePleurodeles waltlii
Authors: Henry M. , Charlemagne J.
Published: April 2021

Different stages of thymus morphogenesis and thymocyte differentiation have been studied at the ultrastructural level in the urodele amphibian Pleurodeles waltlii Michah. From stage 38 to 42 the undifferentiated lymphoid stem-cells colonize the epithelial thymic buds. From stage 43 to 45 the lymphoid stem-cells differentiate into lymphoblasts and then transform into typical lymphocytes. A clasmatosis phenomenon seems to be involved in this transformation. From stage 46 to 52, a phase of intense proliferation occurs and relations between dense reticular epithelial cells and lymphocytes are described. At stage 53, numerous lymphocytes die in the thymic tissue and are phagocytosed by macrophages. At the same time, lymphocytes undergo migrations through the intra- and peri-thymic blood vessels. These lymphocytes should populate the peripheral lymphoid organs, according to the previous finding that stage 52 was the last developmental step for an efficient abrogation of cell-mediated immunity by thymectomy in Pleurodeles.
Evidence for tip control of the ‘slug/fruit’ switch in slugs ofDictyostelium discoideum
Authors: Smith Elizabeth , Williams Keith L.
Published: April 2021

Reciprocal transplants were performed between slugs of two strains of Dictyostelium discoideum. Slugs of one strain (NP84 ‘slugger’) showed prolonged migration, while slugs of the other strain (AX3 ‘fruiter’) migrated for a short period only. The transplant experiments showed that the ‘slug/fruit’ characteristic is tip dependent, since an NP84 tip induced an AX3 rear to migrate for a prolonged period, while an AX3 tip induced the rear of a NP84 slug to fruit without migration. These findings are not consistent with the hypothesis that tips of all stages release only one signal which is interpreted differently by the rest of the cells in the aggregate at different stages. Rather, we propose that the tip of a D. discoideum aggregate may release a number of signals, one of which is stage dependent, and triggers the ‘slug/fruit’ switch.
Changing muscle patterns in a segmental epidermal field
Authors: Williams G. J. A. , Caveney S.
Published: April 2021

The spatial rearrangements that take place during metamorphosis in the abdominal sternites and associated retractor muscles of the beetle Tenebrio molitor are described. This paper provides the descriptive background needed to consider whether a morphogenetic gradient is involved in specifying the position at which adult muscle attachments develop. (Experimental work in support of this gradient hypothesis is published in a companion paper.)

The ventral abdominal retractor muscles are extensively remodelled at metamorphosis so that the adult muscles differ considerably in appearance from the larval muscles from which they are derived. In particular, there is a change in both the absolute and relative positions of the sites of muscle attachment. Rearrangement of muscles takes place during both the pre- pupal period and the pupal stage. It is achieved by means of two separate and temporally distinct mechanisms. Epidermal remodelling in the pre-pupal period results in the movement of attached retractor muscles (epidermokinetic muscle movement). In the pupal stage, however, the muscles move over the basal surface of the epidermis (myokinetic muscle movement). Myokinetic movements may be brought about by extension of myoblast processes from the metamorphosing muscles. These findings are considered in terms of Poyarkoff’s theory that the pupa serves as an integumental mould, approximating the shape of the adult, within which certain adult muscles develop.
Cell behaviour and cleft palate in the mutant mouse, amputated
Authors: Flint O. P.
Published: April 2021

Cleft palate with a genetic origin normally arises because of a failure of the palatal shelves to elevate or fuse. Until now attention in studies of palatal development has been focused on two critical phases, those of elevation and fusion. In the mutant mouse, amputated, however, cleft palate arises because of a failure of the palatal shelves to make any significant outgrowth between the 12th day after conception when the palatal shelves are first observed and the 14th day when elevation and fusion normally occur. When cell proliferation (mitotic index) was measured in the palatal shelves on days 12, 13 and 14 no difference was found between mutant and normal. The failure of the mutant palate to grow cannot be accounted for on grounds of reduced cell proliferation. For this reason the palatal mesenchyme in 12·5-day and 14·5-day normal and amputated mice has been studied with the scanning electron microscope. This work shows that the mesenchymal cells in the mutant palate are clumped together and have much greater areas of cell contact than are observed in the normal palate. The abnormal cell behaviour described in mutant palatal mesenchyme is typical of amputated embryonic mesenchyme in general, and in other cases has been shown to cause abnormal morphogenesis. We propose that aberrant cell behaviour causing an aggregation through increased cell adhesion inhibits palatal outgrowth in the mutant, and for this reason the palatal shelves subsequently fail to elevate and fuse.
The retinotectal projections from surgically rounded-up half-eyes in Xenopus
Authors: Straznicky C. , Gaze R. M. , Keating M. J.
Published: April 2021

In Xenopus embryos of stage 32 half of one eye anlage was removed and the remaining half was surgically rounded-up. The visuotectal projections through such half-eyes, recorded after metamorphosis, showed in most cases a deformation of the map which corresponded to the deformation imposed on the half-eye at operation. Some eyes gave normal maps and some showed mirror-reduplication.
Effect of epidermal growth factor on secondary palatal epithelium in vitro: tissue isolation and recombination studies
Authors: Tyler Mary S. , Pratt Robert M.
Published: April 2021

Previous studies have shown that epidermal growth factor (EGF), a peptide of M.W. 6045, can specifically inhibit in organ culture the cessation of DNA synthesis and programmed cell death that normally occur in the presumptive fusion zone (PFZ) of the secondary palatal epithelium. The aim of this study was to determine if EGF acts directly on the epithelium to exert its effect and if there is a requirement for the underlying mesenchyme. Palatal processes from 13- and 14-day Swiss Webster embryonic mice were enzymatically separated into epithelium and mesenchyme which were then cultured alone or in transfilter recombination for up to 72 h. Tissues were examined by transmission- and scanning-electron microscopy and DNA synthesis was monitored autoradiographically using [3H]thymidine incorporation. In isolated epithelium cultured in control medium, cell death occurred in the PFZ and DNA synthesis did not occur in the oral and nasal epithelial regions. EGF (20– 50 ng/ml) did not prevent cell death in the PFZ and failed to stimulate DNA synthesis in the isolated epithelium; EGF, however, did have an effect on epithelial cell morphology. In the presence of mesenchyme and EGF, there was extensive proliferation in the entire epithelium and cell death within the PFZ was not evident. The results indicate that the stimulation of DNA synthesis in the palatal epithelium by EGF requires the presence of the underlying mesenchyme and that EFG alone is not sufficient to inhibit programmed cell death within the PFZ of the isolated palatal epithelium.
The migration of presumptive primordial germ cells through the endodermal cell mass in Xenopus laevis: A light and electron microscopic study
Authors: Kamimura Michiko , Kotani Minoru , Yamagata Kenzo
Published: April 2021

Presumptive primordial germ cells (pPGCs) were examined during migration from their deep endodermal position to the endodermal crest in Xenopus laevis, using light and electron microscopy with Epon sections, and several morphological characteristics of pPGCs, associated with their migration, were revealed. pPGCs displayed polymorphism, with smooth contours. The intercellular space around the pPGCs was large and variable in width and cytoplasmic processes from pPGCs were occasionally observed in it. It was shown quantitatively that pPGCs at the migratory stage had a tendency to move with the leading end, towards which the nucleus was localized, dragging the germinal plasm behind. These polarized pPGCs were frequently associated with large intercellular spaces, both at their leading and trailing ends. Cytoplasmic processes of polarizing pPGCs found in the large intercellular space at the leading end were conspicuous. Ultrastructurally, the nuclei of pPGCs were euchromatic, and the nucleolus was prominent. The germinal plasm at the light microscope level corresponded to the cytoplasmic area near the nucleus where a large number of mitochondria with well-developed cristae and most of the other organelles were aggregated. Centrioles and centriole-associated microtubules observed in the aggregate were thought to be important structures responsible for the cell polarization mentioned above. It was demonstrated quantitatively that the size of mitochondria in pPGCs was larger on average than that of mitochondria in neighbouring somatic endodermal cells. Numerous irregularly shaped small yolk platelets characterized pPGCs. These ultrastructural features suggested that pPGCs were in an activated metabolic state. It was concluded that the migration of pPGCs was attributable to active movement with high cell metabolism, causing the formation of cell processes and intracellular polarization.
Polyploidization of extraembryonic tissues during mouse embryogenesis
Authors: Ilgren E. B.
Published: April 2021

It has recently been shown that visceral yolk-sac endoderm is derived from the primitive endoderm of the 4-5-day mouse blastocyst (Gardner & Papaioannou, 1975; Gardner & Rossant, 1979). During development, primitive endodermal cells acquire nuclei with more than four times the haploid amount of DNA. The finding of metaphases with multiple sets of chromosomes suggests that the diploid precursors of such endodermal giant cells become truly polyploid. Amniotic cells also contain giant nuclei but the mechanism by which these arise is uncertain. The giant-cell transformation therefore appears to be a general feature of mouse extraembryonic development rather than a phenomenom restricted solely to trophoblast. The basis and significance of these findings are discussed in relation to the development of other extraembryonic membranes both of plant and animal origin.
Changes in protein synthesis during differentiation of embryonal carcinoma cells, and a comparison with embryo cells
Authors: Lovell-Badge R. H. , Evans M. J.
Published: April 2021

Two-dimensional electrophoresis was used to find changes in protein synthesis occurring as pluripotent embryonal carcinoma (EC) cells differentiate to give embryoid bodies in vitro. 2-D patterns from other embryonic cell lines, and from the inner cell mass (ICM) cells of mouse embryos, were also analysed for the expression of those proteins showing some change during embryoid body formation and for overall differences between these and the EC cells.

Most changes in protein synthesis occurred before 12 h but endoderm was not discerned morphologically on the outside of EC cell clumps until at least 18 h after their suspension. The number of changes occurring is small compared with the number of polypeptides resolved, but is in line with similar studies. Comparisons with nullipotent EC cells and an endodermal cell line have allowed these changes to be assigned, tentatively, to the different cell types within embryoid bodies, and may allow them to be used as markers of differentiation.

Comparisons between the 2-D patterns derived from ICMs and EC cells reveal substantial differences between the two that might not have been expected from their developmental homology. The importance of these differences to their pluripotentiality is discussed.
Analysis of the effects of encystment and excystment on incomplete doublets of Oxytricha fallax
Authors: Grimes Gary W. , Hammersmith Robert L.
Published: April 2021

Singlet cells of Oxytricha fallax possessing supernumerary rows of dorsally located marginal cirri were encysted, excysted, and observed for retention of the supernumerary rows. Without exception, cells lost the supernumerary rows as a result of cystment processes. (Encystment previously has been shown to result in the total resorption of ciliature.) In contrast, supernumerary dorsally located marginal cirral rows develop true-to-type during prefission morphogenesis and thus are inherited from cell to cell. These (and other) observations suggest that at least two levels of cytotactic control of cell patterning are operative on the ciliate cortex; one is dependent upon visible ciliature whereas the other is dependent upon an as yet ultrastructurally unidentifiable molecular architecture.
Alterations of chondroitin sulfate synthesized by chick embryo cartilage cultured in the presence of 6-aminonicotinamide
Authors: Seegmiller Robert E. , Horwitz Allen L. , Dorfman Albert
Published: April 2021

Treatment of day-4 chick embryos with 6-aminonicotinamide (6-AN) impairs limb chondrogenesis and produces micromelia. Interference with limb cartilage development may be related to decreased NAD-dependent synthesis of ATP due to the fact that chondrogenesis is dependent upon anaerobic metabolism. To better understand the effect of 6-AN on chondrogenesis, isolated cartilage epiphyses from day-11 chick embryos were treated in vitro. Sulfate incorporation into total glycosaminoglycans of treated epiphyses was 30 % of control. Incorporation of [3H]glucosamine was normal. Fractionation by gel chromatography showed that 40 % of the glycosaminoglycans synthesized by treated cells had a molecular weight of less than 15000 compared with 5 % of that of the control. A decrease in amount of chondroitin 6-sulfate, an increase of chondroitin 4-sulfate and no change in amount of unsulfated polysaccharide were observed. These results suggest that, upon exposure to 6-AN, chondrocytes produce shorter than normal chondroitin sulfate chains that are preferentially sulfated in the 4 position. Since endochondral bone formation plays an integral role in growth and development of the limb, a defect in production of chondroitin sulfate, a major constituent of cartilage matrix, appears to be involved in 6-AN-induced micromelia.
Impaired energy metabolism as an initial step in the mechanism for 6-aminonicotinamide-induced limb malformation
Authors: Sheffield Val C. , Seegmiller Robert E.
Published: April 2021

The analogue and antagonist of nicotinamide, 6-aminonicotinamide (6-AN), impairs cartilage formation and results in shortening of the limbs when administered to chick embryos. Studies have shown that 6-AN forms an abnormal NAD analogue which inhibits the activity of NAD-dependent enzymes associated with production of ATP. To determine if an effect on ATP synthesis might be associated with the mechanism of teratogenesis in the chick embryo, ATP levels of cartilage from day-8 chick embryos treated in vitro were assayed in relation to biosynthesis of protein, DNA and chondroitin sulfate. Incorporation of 35SO4= was inhibited by 6 h of treatment with 10μg/ml of 6-AN, whereas incorporation of [3H]thymidine and [3H]amino acid was not inhibited until 12 h. Incorporation of [3H]- glucosamine was increased at all treatment times. A decrease in the level of ATP preceded any detectable inhibition of precursor incorporation. These results are consistent with the hypothesis that 6-AN inhibits chondroitin sulfate synthesis through a reduction in the level of ATP in chondrocytes.
Coaggregation and formation of a joint myocardial tissue by embryonic mammalian and avian heart cells
Authors: Nag Asish C. , Cheng Mei , Healy Christopher J.
Published: April 2021

Intercellular adhesion and tissue reconstruction from homologous dissociated embryonic cells from two species were studied. Dissociated 12-day-old embryonic rat heart cells and 50-h-old embryonic chick heart cells were labeled with tritiated thymidine and allowed to aggregate in Erlenmeyer flasks during rotation culture on a gyratory water-bath shaker. The cultures were continued for 72 h. Cell aggregates were examined microscopically for evidence of contractility and subsequently processed at intervals between 1 and 72 h for transmission electron microscopic autoradiography. Rat and chick hearts used in this study appeared comparable in their stage of development and cellular composition. With the exception of mature blood cells and some fibroblastic non-muscle cells, all chick cardiac muscle cells were labeled with tritiated thymidine. As the cultures continued, aggregates increased in size by continuous accretion of cells and joining of small clusters. The cells within these mixed aggregates exhibited synchronous contractility from 1 h until the cultures were terminated. Most of the aggregation in both control and mixed aggregates was completed within 24 h. Control aggregates consisted of cells from a single species, either chick or rat. Approximately 18 % of labeled chick cardiac muscle cells established intercellular contacts and junctions with unlabeled rat cardiac muscle cells after 6 h of culture. This increased to 72 % after 72 h in culture. The junctions observed between chick and rat cardiac muscle cells were desmosomes and hemidesmosomes. Approximately 13 % of the cardiac muscle cells of one species either chick or rat were found scattered within clusters which contained .15 % of the cells from the other species after 72 h of culture. These scattered cells did not form junctions with monospecific cell groups. The implications of these intercellular adhesions between the same and different species are discussed, bearing two hypotheses in mind: (1) Moscona and collaborators, (2) Burdick and Steinberg. This study suggests that cellular as well as species identity plays an important role in the determination of intercellular adhesion among the embryonic cells from different species.
Sterility in mutant (t
Lx
/t
Ly
) male mice : I. A morphological study of spermiogenesis
Authors: Hillman Nina , Nadijcka Mary
Published: April 2021

The results from a comparative ultrastructural study of spermiogenesis in 6-, 10-, 14- and 17-month-old sterile t6/tw32, and fertile T/t6, T/tw32 and BALB/c, mice are reported. The studies show that all of the males contained the same types of defective spermatids and that defects were not limited to specific spermatid stages. Younger males had fewer abnormal spermatids than older males of the same genotype and at each age the BALB/c and t6/tw32 males appeared to contain more abnormal spermatids than the other males. No unique spermatid defect or increased frequency of a specific defect was found which can be correlated with infertility of the t6/tw32 males.
Vitamin A alters the internal viscosity of fragments of limb-bud mesenchyme
Authors: Kwasigroch T. E. , Kochhar D. M.
Published: April 2021

Two techniques were used to examine the effect of vitamin A compounds (vitamin A acid = retinoic acid and vitamin A acetate) upon the relative strengths of adhesion among mouse limb-bud mesenchymal cells. Treatment with retinoic acid in vivo and with vitamin A acetate in vitro reduced the rate at which the fragments of mesenchyme rounded-up when cultured on a non-adhesive substratum, but these compounds did not alter the behavior of tissues tested in fragment-fusion experiments. These conflicting results indicate that the two tests measure different activities of cells and suggest that treatment with vitamin A alters the property(ies) of cells which regulate the internal viscosity of tissues.
The Behaviourin vitroof Dissociated Embryonic Pituitary Tissue
Authors: Sobel H.
Published: April 2021

A method for the partial or complete disintegration of the pituitary tissue of the 8-day embryonic chick is described. The anterior lobe, after being partially disintegrated by incomplete dissolution of the intercellular substance, developed in vitro into typical glandular tissue. After dissociation of the anterior lobe into a suspension of discrete cells, the epithelial cells reaggregated under suitable conditions in vitro. The epithelial aggregate remained in a quiescent but apparently healthy state during further cultivation. The addition of perichondrial connective tissue to the aggregates caused them to resume growth and development and to differentiate into typical anterior lobe tissue. The mutual relationship of the connective and epithelial tissues in developing glands is discussed.
The behaviour of embryonic chick and quail tissues in culture
Authors: Bellairs Ruth , Ireland G. W. , Sanders E. J. , Stern C. D.
Published: April 2021

Pieces of tissue were dissected from early chick and quail embryos (Stages XTII and XIV of Eyal-Giladi & Kochav, 1976; and stages 3–5 of Hamburger & Hamilton, 1951).

These tissues were taken from three different regions of the early embryos, and from eight different regions of the older ones, and were derived mainly from the lower layer. Epiblast tissues were also used. The experiments were designed to test the ability of one tissue to penetrate another.

A single tissue was grown in culture in a Falcon dish for 18–24 h until it had formed a coherent sheet of cells (Explant I). A second tissue was then combined with it in one of two ways:

A small piece of tissue (Explant II) was explanted on top of Explant I. In most cases Explant II penetrated through Explant I and spread on the Falcon dish. Another small piece of tissue (Explant III) was explanted beside (in confrontation with) Explant I. Usually, Explant III penetrated into Explant 1 rather than vice versa.

The results were analysed to see if there were any variations in behaviour of the different tissues. The main result was that important differences were found to exist between certain types of chick and quail cells when grown in culture; the implications of this finding for the widely used technique of xenoplastic grafting are mentioned.

Another result was that Explant I was more likely to be penetrated when the second tissue was placed on top of it (Explant II) than when it was confronted with it (Explant III). The significance of these results is discussed.
Effects of L-phenylalanine on somite formation in the early chick embryo
Authors: Palén K. , Thörneby L.
Published: April 2021

Chick embryos were treated in ovo and in vitro with L-phenylalanine from the intermediate streak stage (Hamburger & Hamilton stage 3, 12–13 h of incubation) to the 7-somite stage (H&H stage 9, 29–33 h of incubation).

Treatment in ovo resulted in a large number of embryos developing somite blocks, i.e. imperfectly segmented somites. In embryos treated at an early developmental stage (12–21 h of incubation), the blocks of unsegmented somite mesoderm occurred mostly in the somite pairs 1–5, whereas treatment that began at a later stage (24–30 h of incubation) caused blocks in the somite pairs 5–10, i.e. the appearance of blocks of unsegmented somite mesoderm is correlated in time with the onset of the treatment. No difference regarding mitotic indices could be distinguished between normally segmented somites and blocks of unsegmented somite mesoderm. Autoradiography based on tritiated L-phenylalanine showed no regional differences in labelling of the chick embryo body. Electronmicroscopical observations indicate a slightly suppressed formation of microvilli in the cells of the unsegmented mesoderm blocks compared with cells in normally segmented somites. The observed disturbances are probably caused by a suppressed yolk granule decomposition in the developing somite cells.

The experiments in vitro support the findings in the in ovo material; at the same time, they reveal an unexpectedly slow diffusion of L-phenylalanine through the vitelline membrane.
The innervation of dorsoventrally reversed chick wings: evidence that motor axons do not actively seek out their appropriate targets
Authors: Summerbell Dennis , Stirling R. Victoria
Published: April 2021

In normal chick embryos the extensor (dorsal) muscles are innervated by motoneurones lying laterally in the motor horn, while flexor muscles are supplied by more medially placed motoneurones. After reversal of the dorsoventral axis of the forelimb prior to innervation in most cases the opposite pattern is found, the extensors innervated by medial and flexors by lateral motor neurones. In a minority of cases the normal innervation pattern is obtained.

Three hypotheses are discussed, two involving specific target affinity between motor axon and target and one involving passive deployment of axons to targets. We conclude that our results favour the latter hypothesis but that we cannot exclude a short-range specific signal.
Selective effect of gonadotrophins on cell coupling, nuclear maturation and protein synthesis in mammalian oocytes
Authors: Moor R. M. , Osborn J. C. , Cran D. G. , Walters D. E.
Published: April 2021

Individual gonadotrophic hormones were used to examine the degree to which changes in intercellular coupling between somatic and germ cells initiate meiotic maturation, regulate protein synthesis or alter the ultrastructure of the ovine oocyte. Follicle Stimulating Hormone (FSH; 50 ng ml−1) suppressed intercellular coupling to the same extent as that observed during oocyte maturation in vivo. At low concentrations FSH did not, however, initiate resumption of meiosis. By contrast, luteinising hormone (LH; 100-500 ng ml−1) invariably initiated meiosis in oocytes cultured within the follicle but did not disrupt intercellular coupling. We conclude that nuclear maturation is not dependent upon the disruption of cell contact between the oocyte and the surrounding follicle cells.

The profile of proteins synthesized by untreated oocytes differed greatly from that of oocytes matured for 18 h in follicles treated with a combination of FSH and LH. Pretreatment of follicles with either FSH or LH at low concentrations resulted in the synthesis of an intermediate and more variable pattern of proteins. No correlation was found between changes in protein synthesis and the extent of junctional communication between the cumulus cells and oocyte.

Membrane vesiculation and lysosomal change in the transzonal processes are early structural changes associated with the suppression of intercellular coupling in oocytes. These changes in coupling probably result in the relocation of intracellular organelles in the final stages of oocyte maturation.
The secretion of proteinsin vitrofromXenopusoocytes and their accessory cells: a biochemical and morphological study
Authors: Mohun T. J. , Lane C. D. , Colman A. , Wylie C. C.
Published: April 2021

Protein secretion by Xenopus laevis oocytes and their surrounding follicular cells in vitro has been investigated using two-dimensional gel electrophoresis. Viable oocytes, devoid of follicle layers, were prepared by treatment with collagenase; they retain in full their capacity to synthesize, sequester and export secretory proteins following microinjection with heterologous messenger RNA. Both RNA-injected and normal cells export a large number of endogenous oocyte proteins and, as with heterologous secretory translation products, these proteins are found within the oocyte in a vesicle fraction. Electron microscopy indicates that secretion involves exocytotic release of cortical vesicle contents. The follicular cells themselves also seem to contribute a number of proteins to the incubation medium surrounding isolated oocytes, but the presence of follicle layers is not required for the export of endogenous oocyte proteins.
Regeneration of subnormally innervated axolotl arms
Authors: Wallace H. , Watson A. , Egar M.
Published: April 2021

Forearms of juvenile axolotls contain about 5000 axons, of which only 25% are myelinated and visible by light microscopy. Virtually all the axons degenerate after transection of the brachial plexus, but repeated operations fail to keep the arm completely denervated. Regrown nerve fibres were detected by electron microscopy after 6 weeks of attempted denervation and related to the quantity usually considered necessary for limb regeneration. Such arms regenerated quite normally, provided their innervation had been depleted for several weeks before amputation. Among other ways of reconciling these observations to the neurotrophic theory of limb regeneration, it is suggested that tissues can adapt to deprivation of their nerve supply.
Differentiation of the yolk-sac endoderm under the influence of the digestive-tract mesenchyme
Authors: Masui Tohru
Published: April 2021

To reveal differentiation potency of yolk-sac endoderm, this tissue from quail embryos was cultured alone or in association with digestive-tract mesenchymes of chick embryos.

When yolk-sac endoderm was cultured alone in vitro, the endoderm of the area vitellina differentiated into the yolk-sac parenchyma, but the endoderm of the extraembryonic area pellucida (EEAP) failed to differentiate into yolk-sac parenchyma, and the endoderm of the area vasculosa became necrotic.

When endoderm of the area vitellina was cultured in association with digestive-tract mesenchymes, all the endodermal cells developed into yolk-sac parenchymal cells after two days. Later, basophilic cells appeared among them, and differentiated into both mesenchymespecific epithelia and intestinal-type epithelium with a striated border, and villi were also formed. Goblet cells appeared in all types of recombinations. The endoderm of the EEAP cultured with digestive-tract mesenchymes gave similar results to that of the area vitellina. In contrast, endoderm of the area vasculosa, when cultured with digestive-tract mesenchymes, became necrotic.

The present investigation demonstrated that the endoderms of the area vitellina and of the EEAP differ in self-differentiation potency, and that their developmental fates can be modified by the influence of digestive-tract mesenchymes. These endoderms can differentiate into the mesenchyme-specific epithelia, though they often differentiate also into the intestinal-type epithelium.
Influence of serum factors on the prevalence of “normal” and “foreign” differentiation pathways in cultures of chick embryo neuroretinal cells
Authors: Pomerai D. I. De , Gali M. A. H.
Published: April 2021

Embryonic (9-day) chick neuroretinal cells transdifferentiate extensively into lens and pigment cells during prolonged culture (4–5 weeks) in media containing foetal calf serum. Medium conditions which promote the attachment and differentiation of neural cells in other culture systems (e.g. horse serum, high glucose levels) both delay the onset and greatly reduce the extent of transdifferentiation in retinal cultures. In the presence of high glucose, horse serum (but not foetal calf serum) also favours cholinergic neuronal differentiation during the early phases of culture, as shown by the levels of choline acetyltransferase activity and accumulation of labelled choline. Substrate conditions have some effect on cholinergic differentiation (promoted by polylysine-coated dishes) but do not affect later transdifferentiation. These effects may be due in part to selective survival or growth of particular retinal cell types under the various medium conditions tested. Cultures stripped of neuronal cells contain negligible choline acetyltransferase activity, but still transdifferentiate into both lens and pigment cells, although more slowly than control cultures. Cell size distributions reveal a significant depletion of the larger cells in high glucose media with foetal calf serum, but not in those with horse serum.
Fetal murine hemopoiesis following in utero low-dose irradiation
Authors: Weinberg Sheila R. , McCarthy Emmeline G. , Macvittie Thomas J.
Published: April 2021

The influence of in utero low-dose ionizing radiation exposure on murine hemopoietic embryogenesis was investigated. In vitro assays such as micro plasma-clot cultures and double-layer soft agar cultures served as sensitive biodosimeters to determine erythropoietic and granulopoietic injuries. Day-10·5, HA/1CR, pregnant mice were irradiated with 0, 50, 100, 150,200, or 300 rads, and day-14·5 fetal livers were studied for colony-forming unit-erythroid (CFU-E), buist-forming unit-erythroid (BFU-E), granulocyte-macrophage colony-forming cell (GM-CFC), and macrophage-colony-forming cell (M-CFC) activity. Fetuses subjected to doses of 200 rads or higher on day 10-5 of gestation responded with a decrease in day-14·5 liver cellularity, reflecting injury to the developing organ and its inability to recover to the nonirradiated values. Difference in response between erythropoietin(EPO)-dependent and EPO-independent CFU-E strongly suggests existence of two populations of erythroid progenitor cells with different radiosensitivities. A dose of 200 rads markedly reduced CFU-E recovery, and a dose of 100 rads was sufficient to reduce BFU-E recovery to almost 10% of 0-rad values. Nonirradiated day-14·5 fetal liver had more GM-CFC compared to any of the irradiated fetuses, and a dramatically reduced M-CFC recovery occurred with each increase in dose following 150 rads. Our results showed that (1) fetal liver granulopoiesis is more sensitive to radiation injury compared to erythropoiesis, and (2) fetal liver has a greater potential for erythropoiesis recovery.
Hepatic induction in the avian embryo: Specificity of reactive endoderm and inductive mesoderm
Authors: Fukuda-Taira Sumiko
Published: April 2021

Mesoderm of precardiac and cardiac region (‘cardiac’ mesoderm) of chick, quail and mouse embryos could induce hepatic epithelium in the endoderm of the anterior half of young quail or chick embryos (anterior endoderm) in vitro as well as in vivo. No species specificity in the induction of hepatic epithelium by the ‘cardiac’ mesoderm could be observed.

The hepatic induction, was controlled strictly by tissue specificity of both endoderm and mesoderm. Replacement of the ‘cardiac’ mesoderm or the anterior endoderm by noncardiac mesoderms or endoderms other than the anterior endoderm resulted in failure of hepatic induction. Only the anterior endoderm was found to have competence for hepatic induction, indicating that it was committed, in unknown ways, to react with ‘cardiac’ mesoderm, and can properly be called pre-hepatic endoderm.

Comparison between the development of hepatic endoderm and the hepatic induction potency of ‘cardiac’ mesoderm, which was most intense during 1- to 1·5-incubation days and decreased gradually with the increase of the stage, suggests that in normal development the ‘cardiac’ mesoderm actually induces hepatic epithelium in the competent endoderm. Hepatic-induction potency remained up to 6 days, and was found in truncus arteriosus, ventricle and auricle areas and in endocardial and myocardial layers of the heart.
Effects of cystment on cells of Oxytricha fallax possessing supernumerary dorsal bristle rows
Authors: Hammersmith Robert L. , Grimes Gary W.
Published: April 2021

The patterning and organization of new structure in eukaryotic cells can, in certain cases, be controlled by existing structure. Sonneborn illustrated this in Paramecium two ways. (1) Cells with a doublet phenotype (individual cells with almost two complete sets of cortical structures) develop true to type and are inherited, sexually and asexually, independent of changes in nuclear genotype or fluid cytoplasm (Sonneborn, 1963). (2) Inverted rows of cilia and basal bodies maintain their inverted polarity during morphogenesis and cell division, again independent of changes in nuclear genotype or fluid cytoplasm (Beisson & Sonneborn, 1965). These observations led to formulation of the concept of ‘cytotaxis’ – the organization of new structure under the influence of preexisting structure (i.e. the molecular architecture of the cell which includes visible structure) (Sonneborn, 1964,1975). Cytotaxis thus represents an informational system for pattern development and regulation which is not under direct nuclear control. Several examples of cytotaxis have been demonstrated subsequently in other cell types (Grimes, 1973c, 1976; Grimes & Adler, 1978; Grimes & L’Hernault, 1979; Hammersmith, 1976b); Ng & Frankel, 1977).
Calcium and spreading behaviour of amphibian blastula and gastrula cells
Authors: Leblanc Jacqueline , Brick Irving
Published: April 2021

Cell locomotion involves several structural-functional activities: membrane extensibility, microfilament regulation and adhesive interactions. There is evidence for Ca21- requirement in all of these. Our data may clarify the role of Ca2+ in locomotion and adhesion. Morphologic and spreading responses of isolated blastula-late gastrula Rana pipiens germ layer cells to varying molar concentrations of Ca2+: 0-Ca2+, Standard Ca2+ (Barth’s Xsolution), 1·5 × and 2·0 × Std Ca2+ were viewed by S.E.M. after 1 h in culture. Ionic strength and pH were constant. All cells showed quantitative relationships between Ca2+ concentration and surface extensibility, projection formation and presumably adhesion, but with tissue- and stagespecific variations. Cells in Ca2+-free medium fail to adhere (50%), flatten or form surface projections. Cells in media with increasing Ca2+ generally formed more numerous and extensive surface projections, spread and adhered to a greater extent. In some cases there were no quantitative differences in response between 1·5 × and 2·0×standard Ca2+. Cells in suspension for 1 h in standard solution remained spherical, forming no projections. We infer from these results that both Ca2+ and contact with a physical substratum, cell-cell or cellglass are required for mobilization of the various systems involved in locomotion and adhesion. In addition, components of these systems are quantitatively activated by increased availability of Ca2+.
Somitogenesis in the amphibian Xenopus laevis: scanning electron microscopic analysis of intrasomitic cellular arrangements during somite rotation
Authors: Youn B. Woo , Malacinski George M.
Published: April 2021

The intrasomitic changes in cell arrangement which accompany somite rotation during somitogenesis in Xenopus laevis were analysed with the scanning electron microscope (SEM). Longitudinal, horizontal fractures of whole embryos were examined at various dorsoventral levels of stage-22 to -24 embryos. Observations of the gross morphological features of somitogenesis, and the cellular changes which accompany somite segmentation and somite rotation were made. Several of these observations lead to modifications of previous models for the cellular basis of somitogenesis in Xenopus. Individual cellular rearrangements, rather than simultaneous block rotation of a whole somite, appear to be responsible for the 90° rotation of myotomal cells within a single somite.

Cellular arrangments in fused somites were also examined. Some ultraviolet-irradiated embryos displayed a complete lack of a notochord. The somites in those embryos were fused across the midline beneath the neural tube. The dorsal and ventral arms of the somites are not fused. Normal rotation occurs only in the dorsal and ventral arms while, in the majority of cases, cells in the fused region fail to rotate normally. In some cases, individual cells in the fused region undergo partial rearrangement. Those observations support the notion that individual cellular rearrangements account for the rotation of the whole somite.
Location of pre-hepatic cells in the early developmental stages of quail embryos
Authors: Fukuda-Tatra Sumiko
Published: April 2021

The location of the pre-hepatic cells which can respond to the inductive influence of the cardiac mesoderm and differentiate to the hepatic epithelium was investigated in quail embryos between the unincubated and 8-somite stages.

These cells were found to exist in the whole area of the blastoderm of unincubated and prestreak stages. At the short-streak stage, just before the beginning of gastrulation, pre-hepatic cells are confined to the anterior part of the primitive streak. During gastrulation, pre-hepatic cells invaginate through this area of the primitive streak and enter the endoblastic layer. They are found in the anterior half of the endoblastic layer as well as in the lower half of the anterior part of the primitive streak at the medium- to definitive-streak stages. After gastrulation, they are consistently found only in the anterior half of the endoblastic layer. From the 1-somite stage, at least up to the 8-somite stage, the pre-hepatic cells are localized in the endoderm, anterior to the level of the 3rd somite.

Since the pre-hepatic cells or their progenitors were always found within the definitive endoblast which invaginates from the epiblast during gastrulation, it can be presumed that the pre-hepatic cells originate from the epiblast, invaginate through the anterior part of the primitive streak between the short- and the definitive-streak stage, and enter the definitive endoblast.
Probability aspects of supernumerary production in the regenerating limbs of the axolotl, Ambystoma mexicanum
Authors: Turner R. N.
Published: April 2021

The applicability of deterministic models, and in particular the polar co-ordinate model of French, Bryant & Bryant (1976), to the regenerative process has been investigated by performing ipsilateral blastemal rotations of varying angle on the fore and hind limbs of the axolotl. The results show that the frequency of supernumerary production rises with increasing angle to reach a peak at 180° and then falls off more rapidly, giving rise to an asymmetric distribution curve. The position of supernumerary outgrowth also suggests a probabilistic event, there being no consistent relationship between this parameter and the angle of rotation. The polar co-ordinate model is incapable of explaining these results and the work suggests that the determinism of current regeneration models may have to be abandoned in favour of a more stochastic theory.
Carbonic anhydrase activity in the chick embryo chorioallantois: regional distribution and vitamin D regulation*
Authors: Narbaitz Roberto , Kacew Sam , Sitwell Lucian
Published: April 2021

An electron microscopical and biochemical study of the chorionic epithelium from 16-and 17-day-old chick embryos was conducted. Using a combination of sections made either parallel or perpendicular to the chorionic surface, it was confirmed that the cell populations of the polar and equatorial regions of the membrane are different; the former contains a very reduced number of VC cells which are, contrariwise, widely distributed in the latter. This evidence was required for the interpretation of data on carbonic anhydrase activity. This enzymatic activity is known to increase in the chorioallantoic membrane at the time at which shell resorption begins but the enzyme is believed to be localized in other cell types in addition to VC cells. The results of the present experiments show that carbonic anhydrase activity is significantly higher in the region where VC cells are more frequent (equatorial) than in the region where they are rarely found (polar) and thus suggests that a substantial proportion of the activity measured in the whole membrane corresponds to VC cells.

Carbonic anhydrase activity in the equatorial region of the chorioallantoic membrane increased after 4 h and peaked 24 h after the administration of 1,25-DHCC. This time course is similar to the one on previous experiments in which serum calcium concentrations were determined after similar treatment. It is suggested that one of the effects of 1,25-DHCC on its target cells in the membrane (VC cells according to previous evidence) is to increase synthesis and/or activity of carbonic anhydrase.
Growth factors and pattern formation
Authors: Smith J. C.
Published: April 2021

Growth and pattern formation occur simultaneously in many epimorphic fields and it has been suggested that specification of positional information is somehow linked to cell division. It is possible, therefore, that boundary regions responsible for the specification of positional information produce cell growth factors. In this paper I review the properties of some known growth factors, describe their effects on the cell cycle and discuss how they might act. In developing a convenient in vitro assay for morphogenetic factors it will be much easier to measure incorporation of [3H]thymidine into responding cells than to estimate changes in positional value.
Autonomous development of parts isolated from primitive-streak-stage mouse embryos. Is development clonal?
Authors: Snow Michael H. L.
Published: April 2021

The relationship between growth rate and regionalization of amphibian, bird and mammalian embryos is briefly reviewed. In contrast to the others, mammals start gastrulation with few cells but accelerate cell proliferation coincidentally. Experiments are described which demonstrate (1) autonomous development of pieces isolated surgically from such mouse embryos, and (2) an absence of regeneration or regulation. Since such embryos regulate completely after chemically induced random cell death it is postulated that these results reflect developmental determination and a resulting mosaicism that suggests development may have a clonal basis. Maps are drawn, allocating positions to various tissues in the embryo.