bluuebunny/crossref_metadata_2025 huggingface dataset:
A light- and electron-microscopic study of primordial germ cells in the early mouse embryo
Authors: Spiegelman Martha , Bennett Dorothea
Published: April 2021

The primordial germ cells (PGC’s) of the early mouse embryo have been identified in semi-thin and ultra-thin plastic sections on the combined bases of location and a distinctive set of morphological features. These cells originate extra-gonadally and their path of migration during the stages investigated agrees with results of previous histological and experimental studies. At 8–9 days of development, PGC’s are observed among the endoderm cells of the mid- and hindgut and the yolk stalk; at 10–11 days, PGC’s are seen in the dorsal mesentery, the dorsal coelomic lining, and in the rudimentary genital ridge; by 13 days, the gonad is abundantly populated with germ cells. During the migratory period the PGC’s appear as small (10–12 pm diameter), oval, basophilic cells which have a large nucleo-cytoplasmic ratio. These cells possess numerous free ribosomes and polysomes, a filamentous ground cytoplasm, and few profiles of endoplasmic reticulum. Mitochondria display small oval and thread-like profiles. A Golgi complex is not prominent in the PGC’s. The densely granular and fibrillar nucleus is often oval in outline but sometimes shows irregular contours. A large nucleolus is present. Although located among groups of cells that exhibit extensive cell junctions, the PGC’s have not been found to share such junctions with neighboring cells. Furthermore, the PGC’s possess small cytoplasmic processes that contain numerous microfilaments. These observations are interpreted as morphological correlates to the migratory activity of these cells.

In the early PGC’s located in the gut, regions of the endoplasmic reticulum where membranes are closely apposed, perhaps fused, often present the appearance of annulate cisternae. In addition, compact aggregates of granulofibrillar material are found in the cytoplasm of these same cells. Neither of these structures is detected in the mesenteric PGC’s, the gonadal germ cells, or any other cell of the embryo at the stages studied. It is suggested that these two cytoplasmic elements may be related to further differentiation of the germ cells.

The germ cells of the developing gonad are large, oval cells which possess a nucleus of very round contour. Both the nucleus and the cytoplasm retain a densely granular appearance. The expanded cytoplasm contains a large Golgi complex but still few profiles of endoplasmic reticulum. Free ribosomes and polysomes are abundant. The germ cells share extensive gap junctions with one another and with adjacent stromal cells.
Origin of the ectoplacental cone and secondary giant cells in mouse blastocysts reconstituted from isolated trophoblast and inner cell mass
Authors: Gardner R. L. , Papaioannou V. E. , Barton S. C.
Published: April 2021

Inner cell mass (ICM) and trophoblast tissue were isolated from -day post-coitum mouse blastocysts that were homozygous for different electrophoretic variants of the enzyme glucose phosphate isomerase (GPI). Blastocysts were reconstituted from these tissues, transferred to pseudo-pregnant recipients and allowed to develop to the early somite stage. The embryo plus membranes and trophoblast were dissected and typed separately for GPI. Contamination of trophoblast with maternal decidual tissue was quantified. The trophoblast of the implanted embryos was almost exclusively of the trophoblastdonor GPI type. The embryos plus membranes were mainly of the ICM-donor type but most also showed a substantial proportion of trophoblast-donor type. It is argued that the ICM controls trophoblast proliferation by inhibiting giant cell transformation of adjacent trophoblast cells rather than through making a significant cellular contribution.
Interactions de l’œil et du lobe optique au cours de la croissance post-embryonnaire des Insectes odonates
Authors: Mouze Michel
Published: April 2021

Different types of experiments have been performed in order to disturb or to destroy the relations between the eye and the optic lobe and then to study these isolated organs. The results show that growth and differentiation of the eye is independent of the optic lobe. How-ever, the structure of ommatidia whose post-retinal fibres have been sectioned is markedly modified. The growth of the optic lobe is closely related to the presence of the eye and more precisely to the connexion with the post-retinal fibres. The volume of the optic lobe, especially the more external optic ganglia, is reduced after its relations with the eye are disturbed. More-over numerous abnormalities in its structure evince a disordered organization of new nerve fibres, which are attracted by the newly constituted zone of the lamina and exert a mitogenic action on the outer growing zone of the optic lobe. These fibres seem to exert a regulatory effect upon the differentiation and final position of the new ganglion cells.
Extent and properties of the regeneration field in the larval legs of cockroaches (Leucophaea maderae): I. Extirpation experiments
Authors: Bohn Horst
Published: April 2021

Extirpation experiments have been performed on the larvae of cockroaches (Leucophaea maderae) to determine the extent and properties of the regeneration field of the legs of these insects. The distal segments, including the coxa, may all be removed without loss of regenerative capability; but regenerative capability eventually disappears if more proximal parts are removed. There are two regions adjoining the coxa anteriorly and posteriorly which are both important for leg regeneration. The anterior region consists of the sclerotized basal parts of the leg mainly formed by the trochantin and the praecoxa. The posterior region is an unsclerotized membranous area extending from the posterior border of the coxa to the anterior border of the next segment. This membrane is called ‘leg-inducing membrane’. If only one of these two regions is present, no leg regeneration will occur. The interaction of both parts is necessary to allow the formation of a complete leg. An extra leg with reversed anterior-posterior polarity is formed when the Teg-inducing membrane’ of one segment is brought into contact with the sclerites of the following segment after extirpation of the membranous area which normally separates them. This membranous area, which represents the most anterior part of a segment, is called ‘sclerite-inducing membrane’, for if the basal sclerites or part of them are combined with this membrane only sclerites are formed, either in normal or reversed polarity depending on the experimental conditions.
Morphogenesis of the rudimentary hind-limb of the Glass Snake (Ophisaurus apodus Pallas)
Authors: Rahmanl Tahereh M.-Z.
Published: April 2021

In the legless lizard, Ophisaurus apodus, the hind-limb primordium appears on the caudal extremity of the Wolffian ridge at an early stage in the development of the embryo (4·2 mm long). Three somites each send an extension into this young bud and distribute cells in its mesenchymal mass of cells. An apical epiblastic ridge, appearing as a fold from the exterior, forms on the limb-bud, which at this time is flattened at the distal end. A large vessel and nerves penetrate into the bud which appears normal at this stage. Necrosis then begins, first in the ridge, then in the cells of somitic derivation and finally, when the ridge has almost disappeared, in the mesenchymal cells. The bud which has been growing up till now, starts to regress at this point. It does not, however, disappear completely as it does in the forelimb, but remains as a rod-like appendage on each side of the cloaca. Inside this structure a rudi-mentary skeleton takes shape. The phallic primordium which appears on the ventro-caudal aspect of the hind-limb bud is not involved in this degenerative phenomenon and continues to develop.

The arrest of development may be due to the degeneration of the apical ridge; possibly resulting from a failure of induction by the somites or to an insufficient somitic contribution to the hind-limb bud.
Investigation on the origin of the definitive endoderm in the rat embryo
Authors: Levak-Švajger B. , Švajger A.
Published: April 2021

Single germ layers (or combinations of two of them) were isolated from the primitive streak and the head-fold stage rat embryos and grown for 15 days under the kidney capsule of syngeneic adult animals. The resulting teratomas were examined histologically for the presence of mature tissues, with special emphasis on derivatives of the primitive gut.

Ectoderm isolated together with the initial mesodermal wings at the primitive streak stage gave rise to tissue derivatives of all three definitive germ layers. Derivatives of the primitive gut were regularly present in these grafts. At the head-fold stage, isolated ectoderm (including the region of the primitive streak) differentiated into ectodermal and mesodermal derivatives only.

Endoderm isolated at the primitive streak stage did not develop when grafted and was always completely resorbed. At the head-fold stage, however, definitive endoderm differentiated into derivatives of the primitive gut if grafted together with adjacent mesoderm.

These findings indirectly suggest the migration of prospective endodermal cells from the primitive ectoderm, and therefore a general analogy with the course of events during gastrulation in the chick blastoderm.
Compartmentalization and growth of the Drosophila abdomen
Authors: Lawrence Peter A. , Green Sheila M. , Johnston Paul
Published: April 2021

An analysis of the cell lineage of the adult Drosophila abdomen is reported. Genetically marked clones are produced in the tergites in the embryo and in the sternites and pleura during larval life. The spatial disposition of the segment primordia is also studied in a series of 250 gynandromorphs. We conclude that in the embryo the segments are all separate polyclones soon after blastoderm and these are probably adjacent to each other. Gynandromorph analysis suggests that segments 2-6 develop from similarly sized cell groups but that the first tergite develops from a primordium which is equal to that of two other segments. We suggest that presumptive adult and larval cells are not separated at blastoderm. Our estimate from clonal analysis of the number of larval cells (12) which construct the sternites and pleura is equal to the number observed directly in the ventral nest of histoblasts.
Autonomy of tendon development in the embryonic chick wing
Authors: Kieny Madeleine , Chevallier Alain
Published: April 2021

The aim of this study performed in the embryonic chick wing is to test the ability of the tendons to form and develop in the absence of the muscle bellies.

The experiments were performed on 2-day chick embryos by destroying a portion of the somitic mesoderm by local X-irradiation. The irradiated part included the wing somite level 15-20 and extended three somites (or presumptive somites) in front and two to six presumptive somites in the rear of the wing somite level. The wings of the operated side were examined histologically 3-8 days after the X-irradiation.

The radio-destruction of the somitic mesoderm totally inhibited or severely impaired the development of the forearm muscles. But, despite the absence of the flexor and extensor muscles the differentiation of the distal manus tendons could be observed. This differentiation occurred at the same time and in the same position as in controls. However, these tendons were transient structures. They disappeared within three days after their individuation. Two mechanisms that progressed in proximo-distal direction were involved in their resorption: cellular dislocation and cell death.

We conclude that tendons start to develop autonomously from the muscle bulks, but for their maintenance and further development they require connexion to a muscle belly.
The Effect of Steroid Hormones on the Brown Trout (Salmo trutta L.) during the Period of Gonadal Differentiation
Authors: Ashby K. R.
Published: April 2021

Steroid hormones were administered to trout alevins by adding them to the culture medium in alcoholic solution, the concentration of hormone in the cultures being within the range 50 y to 400 y/1., and that of alcohol, O O5%o to O-3%o. A control culture was maintained in O-5°/oo of alcohol. Oestradiol (50 y and 300 y/I.) and testosterone (60 y/1.) had closely similar effects, which included strong inhibition of the development of germinal tissue except in one male treated with the higher oestradiol concentration, where stimulation occurred posteriorly. There was no evidence of sexual inversion, and vasa deferentia appeared in a normal proportion of individuals. With the partial exception of some males, a large area of the somatopleure in the individuals treated became, as in female breeding trout, a ciliated columnar epithelium resembling the internal epithelium of the gonoducts of other teleosts. The connective tissue of the gonadal area was unusually vascular, and in the body-fluids there were large amounts of deeply chromophil material. The tubules of the pronephros were much enlarged. Those of the mesonephros were increased in diameter and reduced in number in the culture treated with the higher concentration of oestradiol. Both concentrations of oestradiol caused the collapse of the gall-bladder, this being the only obvious difference from the effect of testosterone. There are strong reasons for believing that oestradiol caused enlargement of the cells of the interrenal (‘anterior interrenal’) gland, and some reason to think that in some instances testosterone could also cause their hypertrophy. Progesterone and more particularly desoxycorticosterone acetate inhibited the development of germinal tissue, except in some males treated with the former hormone, where in addition vasa deferentia developed precociously and were much enlarged. Vasa deferentia of a normal size were present in most other individuals lacking oocytes. There was a significant excess of females over males after treatment with DOCA, but the possibility of this being due to a selective mortality cannot be ruled out. There was evidence of such a mortality having occurred in the culture treated with progesterone. Deeply chromophil material was usually present in the body-fluids. Slight sterol-mimetic effects were observed in the controls treated with alcohol. Possible causes are discussed. The results are compared with those obtained from similar experiments in other teleosts and in tetrapods.
Induction by Regions lateral to the Streak in the Chick Embryo
Authors: Mulherkar Leela
Published: April 2021

The discovery of the organization centre of Amphibia by Spemann (1918) opened a new field in the outlook of experimental embryology; but there were several technical difficulties to be overcome in the application of the concept of the organizer to avian embryology. In this connexion the tissue culture technique has several advantages over the earlier methods of in situ sectioning or chorio-allantoic techniques, and it has helped a great deal in the understanding of the processes of development in the chick.
In vitro Culture of the Eye and the Retina of the Mouse and Rat
Authors: Lucas D. R. , Trowell O. A.
Published: April 2021

By means of an organ culture technique previously described, whole eyes of 8-11-day-old mice have been successfully maintained in vitro for 8 days. Isolated retinae from both rats and mice aged 9-14 days have been similarly maintained for 10 days. Isolated retinae survived best in a gas phase of air; 60 per cent, oxygen was toxic. In the whole eye, on the other hand, the retina survived better when pure oxygen was used, doubtless because the outer coats of the eye both consume oxygen and hinder its diffusion to the retina. Isolated rat retinae survived well in an entirely synthetic medium, but mouse retinae did not. Differentiation of the visual cell nuclei proceeded normally in vitro.
Further Observations on the ‘Metaplasia’ of an Amoeba, Naegleria gruberi
Authors: Willmer E. N.
Published: April 2021

The development of flagella by Naegleria gruberi, which occurs when a culture of organisms in the amoeboid form is treated with distilled water, has been shown (Willmer, 1956) to be a phenomenon probably related more to the ionic balance between the organism and its external environment than to the simple movement of water in and out of the cell in response to total osmotic changes. From Text-fig. 1 it may be seen that with respect to the response of the amoeba to different concentrations of the various salts investigated there are for each salt two somewhat critical concentrations. In the case of NaCl solutions in distilled water these turning points occur at about 30 mM. and 1 mM., and in the case of KC1 solutions at about 50 mM. and 6 mM. Above the higher of these concentrations in each case the organisms always assume the amoeboid form, and below the lower they become flagellate at least as frequently as they do in distilled water.
Action of Triethanomelamine (TEM) on Early Stages of Chick Embryos
Authors: Jurand A.
Published: April 2021

Of many closely related compounds investigated recently from the point of view of cytotoxity and tumour-inhibiting properties 2,4,6-tri-(ethyleneimino)-1,3,5-triazine (called also triethanomelamine or TEM) proved to be the most effective substance against the Walker rat carcinoma. First descriptions of this fact were published in 1950 (Buckley et al. and Burchenal et al.). Also in 1950 appeared the publication of the first results of the clinical application of TEM at the First International Cancer Congress (Mueller & Miller). Later on Karnovsky et al. (1951) and Petersen et al. (1951) recommended procedures for parenteral and oral administration of this substance in clinical treatment. Very recently TEM has been introduced in a commercial form for oral and parenteral administration in cases of leukaemia, Hodgkin’s disease, polycythaemia vera, and other neoplastic conditions.
Effects of some Amino-acid and Purine Antagonists on Chick Embryos
Authors: Waddington C. H. , Perry Margaret
Published: April 2021

Several authors have studied the effects on developing embryos of substances which are analogues of naturally occurring amino-acids and purines, and known to act, in other systems, as metabolic inhibitors. It was emphasized by Waddington, Feldman, & Perry (1955) that any particular substance may exhibit very different effects in embryos of different types. They found, for instance, that the purine analogue 8-azaguanine has a very strong action in the chick and a much lesser one in the newt embryo. It is therefore necessary to consider the various classes of embryos separately. In this communication we shall be concerned only with chick embryos.
Experiments on the Diffusibility of the Amphibian Evocator
Authors: Brahma S. K.
Published: April 2021

Presumptive neural plate ectoderm of an early gastrula, when separated by a porous membrane (average pore diameters, 4 mμ) from the axial mesoderm, failed to differentiate into neural tube either in Axolotl or in Xenopus. In ectodermal sandwich experiments induction always occurred on the side containing the organizer in Triturus alpestris and was prevented by the interposition of a porous membrane, when the latter had an average pore diameter of 4 mμ or 1· 45 μ. No cytoplasmic connexion across the membrane could be observed. The lack of induction through the membranes might be due either to a total failure of diffusion of an active substance, or to a failure of a diffusing substance to attain a high enough concentration on the other side of the membrane, or the induction may essentially involve cell-to-cell contact. No decision between these alternatives is reached.
The Melanoblast Reservoir Available to a Feather Papilla
Authors: Cock A. G. , Cohen J.
Published: April 2021

In an adult black-red hen which, when a newly hatched chick, had received a homograft of skin from the back of a dominant white chick, active feather papillae have been exchanged between follicles of the neck and the homograft. The distinctive structure of feathers of the two tracts permits reliable identification of feathers growing from these transplanted papillae. Each of six successful transplants from the neck into the homograft has so far produced only black-red feathers (one to three feathers in each case). Five transplants from the homograft into the neck have so far produced from two to five feathers each, with the following sequences of pigmentation types: white— white—white—white—mosaic; black-red—black-red—mosaic—mosaic— mosaic; black-red—white—white—white—black-red; white—white—black—red; white—white. A follicle on the homograft, about 1 cm. in from the edge, and not subjected to any operative interference, has produced three mosaic feathers in succession, each partly pigmented by host-type (black-red) melanocytes. It is concluded (a) that the papilla of a feather follicle contains a reservoir of melanoblasts sufficient to provide the melanocytes of several future feathers; (b) that this reservoir is from time to time augmented by melanoblasts migrating in from the surrounding tissue; and (c) that some of the melanoblasts within a papilla may remain inactive during the growth of one or more feathers, but contribute melanocytes to subsequent feathers. In the vane of each of the seven feathers which are mosaic in respect of their melanocytes, there is a marginal band of intense black where the black-red area adjoins the white. This, it is suggested, may be due to the diffusion of some substance from the white area, and may depend on the fact that the dominant white melanocytes also carried the gene for extended black. Our findings are discussed in relation to previous work on the pigmentation of feathers and hairs.
Factors Affecting Vertebral Variation in Mice
Authors: McLaren Anne , Michie Donald
Published: April 2021

C3H/Bi and C57BL/How inbred strains of mice are known to differ from one another in number of lumbar vertebrae. Reciprocal F1 hybrids between the two strains tend to resemble the maternal strain in this respect. Since the difference between reciprocal hybrids is shown in females as well as in males, it cannot be attributed to sex linkage. Analysis by means of egg transfer has shown that this reciprocal difference in the number of lumbar vertebrae is due to an influence exerted by the mother through the uterine environment, rather than through the cytoplasm of the egg. The number of lumbar vertebrae is not affected by the operation of egg transfer in itself, but only by the specific influence of the host uterine environment. In our material vertebral type is not influenced by the genetic constitution of the other embryos in the uterus, nor by their number. There is no marked dependence of number of lumbar vertebrae upon birth-weight. We conclude that in this instance the uterine environment does not act through promotion or inhibition of overall embryonic growth, but exerts a specific morphogenetic influence upon the unborn young.
Rabbit α-globin messenger RNA translation by the mouse ovum
Authors: Ebert Karl M. , Brinster R. L.
Published: April 2021

Fertilized mouse ova were injected with messenger RNA for rabbit globin. The ova were labelled with [3H]leucine and the synthesized rabbit α-globin measured by immunoprecipitation. Injection of rabbit globin mRNA from 4-0 to 15-8pg/ovum resulted in the synthesis of ∼1200dpm/ovum of a-globin during an 18 h incubation. A concentration of mRNA that was translated below the maximum level of globin synthesis was used to determine translation efficiency. The efficiency of translation was 14·1 molecules of a-globin synthesized/cell/h for each molecule of α-globin mRNA injected. The radioactivity in a-globin was 1 % of the total incorporation in acid-precipitable material. Total incorporation of control and injected ova was not significantly different. This study shows that the fertilized mouse ovum can translate an injected foreign message with essentially the same efficiency as that reported for the Xenopus oocyte but substantially lower than the reticulocyte and that the translational capacity of the mouse fertilized ovum for injected mRNA is limited with little if any spare translational ability.
Stage specificity in the mesenchyme requirement of rodent lung epithelium in vitro : a matter of growth control?
Authors: Lawson Kirstie A.
Published: April 2021

Epithelia from lung rudiments in which secondary bronchial buds are already established (14th and 13th gestational day for rat and mouse respectively) are able to undergo branching morphogenesis and cytodifferentiation in submandibular mesenchyme in vitro, whereas lung epithelium from one day younger foetuses rarely gives a morphogenetic response to submandibular mesenchyme and usually differentiates into primary (non-budding) bronchial epithelium.

The failure of 13-day rat lung epithelium to respond to submandibular mesenchyme can be prevented by peeling off the submandibular mesenchyme from the lung epithelium after days culture and replacing the same mesenchyme, or renewing it with fresh salivary mesenchyme ex vivo. Changes in the epithelial contour are visible by 10 h and buds form within 24 h ; this is followed by branching morphogenesis in more than 66 % of the samples.

The number of cells in S-phase in the epithelium is doubled within 3 to 5 h after the operation and the number of mitotic cells (colchicine block) is increased during an 11 to 19 h period after the operation. Substituting stomach mesenchyme for submandibular mesenchyme after the operation failed to elicit morphogenesis or an increase in the number of S-phase cells in the epithelium.

The proportion of epithelial cells in S-phase in unoperated recombinates does not differ from the proportion in the primary bronchial epithelium (non-budding) of homotypic lung recombinates, whereas the proportion of S-phase cells in operated recombinates approaches that found in the buds of homotypic lung recombinates. The distribution of S-phase cells in visibly responding recombinates 15 to 17 h after operation shows the same heterogeneity as in homotypic lung recombinates, newly formed buds having twice as many cells labelled with [3H]thymidine as the non-budding area.

Cell cycle parameters of intact rat lung growing in vitro were estimated using the labelled mitoses method. Primary bronchial epithelium and bronchial buds both had a total cell cycle time of about 13 h and an S-phase of about 10 h. The growth fraction was 0·54 in the primary bronchus and 0·95 in the buds. It is suggested that, also in the recombinates, differences in the proportion of S-phase cells at any one time in morphogenetically active and inactive areas of the epithelium are due to differences in the growth fraction.

It is concluded that an early event in the morphogenetic response of lung epithelium to submandibular mesenchyme after removing and restoring the mesenchyme is an increase in the size of the population of dividing cells and it is suggested that a high proportion of dividing cells in an epithelial population is a prerequisite for further interaction of epithelium and mesenchyme leading to branching morphogenesis.
Developmental potential of teratocarcinoma stem cells in utero following aggregation with cleavage-stage mouse embryos
Authors: Fujii Joanne T. , Martin Gail R.
Published: April 2021

Embryonal carcinoma cells were aggregated with cleavage stage mouse embryos, cultured briefly, and transferred as morulae to the uteri of pseudopregnant females. When midgestation foetuses were examined, many were morphologically abnormal. The severity of this abnormal development was correlated with the extent of contribution by embryonal carcinoma cells to the foetuses as indicated by GPI (glucose phosphate isomerase) analysis. This was true for all three of the cell lines studied, NG-2, PSA-1, and LT1-2D.

The clear correlation between increasingly abnormal development and more extensive participation by the embryonal carcinoma cells was not observed in control experiments in which embryos of different stages of development were aggregated together. The data therefore suggest that the embryonal carcinoma cells studied here are unable to support normal development in the absence of a substantial number of host embryonic cells. It remains unclear whether this is a consequence of the karyotypic abnormalities of the cells tested, or whether it reflects a characteristic limitation in the ability of embryonal carcinoma cells to independently direct normal development.

When aggregates were allowed to develop to term and the extent of chimaerism was examined in the live-born animals, it was found to be sporadic and limited. This is consistent with the results indicating that large contributions by embryonal carcinoma cells are not compatible with normal development at midgestation. The chimaerism observed in the liveborn animals was comparable in both frequency and in tissue distribution to that generally obtained in other studies using either the aggregation or blastocyst injection techniques..
Vascular architecture of the developing spinal cord in the rat: a suggested model
Authors: Simón-marín R. , Vilanova J. R. , Aguinagalde A. , Barberá-Guillem E.
Published: April 2021

The vascular architecture of the developing Sprague-Dawley rat spinal cord from Ell through E16 is reported. The paraffin-embedded cord is serially sectioned in the sagittal, transversal and frontal planes and stained with PAS and methenamine silver. Serial semithin transverse sections are stained with toluidine blue. The results demonstrate two highly integrated vascular systems: one sagittally disposed in three concentric networks and the other radially oriented around the cord. The sagittal plexus is configurated by rhombohexagonal polygons. The lateral radial stem vessels anastomose with the sagittal systems at the polygonal vertex. A structural vascular model of the cord is proposed. The periodical sequence distribution of vessels in the three planes and their relationship to spinal ganglia is suggestive of a neural metamera vascularly determined.
Localization of a pigment-containing structure near the surface of Xenopus eggs which contracts in response to calcium
Authors: Merriam R. W. , Sauterer R. A.
Published: April 2021

Contractions in surface structures of Xenopus eggs have been induced by application of the calcium ionophore A23187 or calcium ion. Local applications have shown that the contractile structure is present in both animal and vegetal hemispheres. It is, however, much stronger in the animal hemisphere and pigment embedded in it there defines the animal half.

The injection of cytochalasin B (CB) into whole cells or the application of the antibiotic to half cells cannot prevent the induced contractions. By experimental means, the contraction of a deeper, pigment-containing structure can be uncoupled from a thin, more superficial and relatively pigment-free layer on the egg surface. By this means it has been possible to establish that the CB-resistant contraction is due, at least partially, to a structurally distinguishable layer subjacent to the outer egg cortex. Scanning and transmission electron microscopy demonstrate a dense grainy matrix near the egg surface in which pigment granules but little yolk are embedded. This structure is much thicker in the pigmented hemisphere.

The presence of calcium ions in an isolation medium are shown to cause a loosening or dissolution of the structural connections between the dense, contractile structure near the surface and the cytoskeleton of the endoplasm.
Occlusion of the neural lumen in early mouse embryos analysed by light and electron microscopy
Authors: Kaufman M. H.
Published: April 2021

A histological account of neural tube occlusion during early mouse embryogenesis is presented here from an analysis of sections taken from plastic-embedded material. Because the overall pattern of neuroepithelial apposition and the duration of luminal occlusion appears to vary slightly from one embryo to another at otherwise similar stages of development, only a general guide to the events occurring in the mouse embryo between about midday on the 9th to late on the 10th day of gestation can be given. The earliest evidence of complete luminal occlusion was seen when the cephalic and caudal extremities of the neural tube were still widely open.

An ultrastructural analysis of the morphological appearance of the closely apposed luminal cells in zones of partial and complete occlusion has demonstrated that occlusion is brought about initially by the interdigitation of processes from closely apposed neuroepithelial cells. This initial event is followed by direct contact over a much more extensive area between the surfaces of apposed cells with a characteristically flattened luminal border. Apposition and luminal occlusion is probably facilitated by the presence of viscous extracellular material. Finally, complete occlusion involving an extensive region of the lumen occurs. The latter phenomenon is a transient event lasting 1 or at most 2 days in the mouse. At no stage were junctional complexes observed between closely apposed neuroepithelial cells in regions in which the neural lumen appeared to be completely occluded, though they were apparent between adjacent neuroepithelial cells.

Observations on the underlying mechanism(s) of cellular fusion are considered in the light of the ultrastructural findings. These results are compared with findings from analyses of various other sites of cellular fusion during embryogenesis. Attention is also drawn to the similarities and differences observed in the timing and overall pattern of events occurring during the early development of the neural tube in mouse and human embryos.
The effect of local application of retinoic acid to the anterior margin of the developing chick limb
Authors: Summerbell Dennis
Published: April 2021

Local application of retinoic acid to the chick limb bud produces effects that are dose and/or stage dependent. Low doses and/or old stages tend to give normal limbs or perhaps one or two supernumerary digits of a more anterior character. Medium doses and/or intermediate stages tend to give full mirror-image supernumeraries with two or even three extra digits including particularly digits of a posterior character. High doses and/or early stages give limbs in which supernumerary digits fail to form or are lost, and in which even host skeletal elements are missing or reduced. The effects are graded over the full dose and/or stage range.

Various explanations are discussed in the context of the current hypotheses of limb development. We conclude that one should not necessarily interpret the results as evidence that retinoids normally play a part in the control of development or regeneration.
The relationship between cleavage, DNA replication, and gene expression in the mouse 2-cell embryo
Authors: Bolton V. N. , Oades P. J. , Johnson M. H.
Published: April 2021

The 2-cell stage of mouse embryogenesis is characterized by two phases of α-amanitin-sensitive polypeptide synthetic activity, which appear to mark the first major expression of the embryonic genome, as assessed by examination of in vitro translates of mRNA. Using populations of embryos synchronized to the first cleavage division, we have established that DNA replication takes place over the period 1 to 5 ·5 h after the first cleavage division; the two bursts of putative transcription take place before and immediately after DNA replication, and the translation products are detectable in each case within 3 –4 h. In addition, we have shown that suppression of cytokinesis and the second round of DNA replication does not affect synthesis of the α-amanitin-sensitive polypeptides, and that neither DNA replication nor the loss of maternal mRNA that take place during the 2-cell stage are dependent upon synthesis of the α-amanitin-sensitive polypeptides.
Sur l’induction et la compétence dans les relations entre l’épiblaste et le mésenchyme de la patte de Poulet
Authors: Hampé par Armand
Published: April 2021

Dans une série d’expériences sur le rôle de l’épiblaste du bourgeon alaire, Saunders (1948) en découpe le bord épaissi et constate un arrêt de la croissance. Les seules ébauches de l’aile qui se développent sont celles qui sont déjà pré-sentes dans le mésenchyme. Les déficiences terminales sont d’autant plus accusées que l’excision est plus précoce, ce qui fait penser que l’épiblaste est responsable, d’une part de la croissance du membre et d’autre part de la déter-mination successive des divers segments: stylopode (article basal du membre), zeugopode (article intermédiaire) et autopode (article terminal, main ou pied). Mais il était cependant possible d’admettre que le mésenchyme du bourgeon décide par lui-même du segment à produire. Dans cette dernière éventualité, le rôle de l’épiblaste se bornerait à appeler le matériel cellulaire de la base.
Adenosine Triphosphatase Activity in Early Somite Tissue of the Chick Embryo
Authors: Deuchar E. M.
Published: April 2021

Segmented somite tissue of 40 to 45-hour chick embryos (stage 11, Hamburger & Hamilton, 1951) shows a higher calcium-activated ATP-ase activity than the somite tissue that has not yet segmented at this stage. The enzyme activity is not extracted by prior treatment of the tissues with 50 per cent, glycerol, and is not localized in the mitochondrial fraction. There is no difference in magnesium-activated (mitochondrial) ATP-ase activity between segmented and non-segmented mesoderm at this stage. It is postulated that the apparent increase in calcium-activated ATP-ase at the time of segmentation may represent a synthesis of myosin or of some myosin precursor.
The Sexual Development of Salpa fusiformis (Cuvier)
Authors: Sutton Muriel F.
Published: April 2021

The early sexual development of S. fusiformis Cuvier is described.

The fertilized egg begins to develop in the single ovarian follicle, dorsolaterally, close to the atrial epithelium. At the eight-cell stage the follicle cells (calymmocytes) proliferate rapidly and insinuate themselves between the blastomeres. Each blastomere at this point buds endogenously and the resultant seven daughter cells rapidly degenerate; a large residual cell persists. The calymmocytes continue to increase in number but their degeneration also is initiated. The follicle perforates the atrial epithelium, and is now known as the blastophore. A normal blastomere division occurs and is followed by a second phase of budding and daughter-cell degeneration. A structure, the placental knob, develops ventrally; one of its functions is to proliferate calymmocytes. The blastomeres begin to move around regularly and irregularly occurring spaces produced by calymmocyte degeneration, and, on gaining contact with each other, normal division is resumed. A medio-dorsal, neuro-chordal cell massif becomes recognizable and subsequently it moves antero-dorsally. Three regularly occurring cavities begin to develop during the neuro-chordal cell movement. They are centrally and laterally placed and will ultimately fuse and form, in part, the oozooid pharynx. The remaining blastomeres aggregate in groups which will give rise to the cloacal epithelium, remaining ectoderm, and endoderm. Mesodermal cells are not yet to be discerned with certainty. During the early stages of development of the three cavities an incubation fold develops from the adjacent atrial epithelium. It grows up around the blastophore. The aggregation of the cloacal, ectodermal, and endodermal blastomeres and the fusion of the central and lateral cavities occur after the closure of the fold.

The significance of certain phenomena, in particular of endogenous budding, are discussed. The conclusion favoured at present is that the budding process is an abnormal phase of division induced by a loss of blastomere contact.
L’Inhibition spécifique de la différenciation du cerveau des Planaires d’eau douce en régénération
Authors: Lender par Th.
Published: April 2021

La régénération des Planaires d’eau douce est caractérisée par la formation d’un blastème dû à l’accumulation de néoblastes. Ces cellules, à caractère embryonnaire, migrent vers la blessure puis se différencient pour reconstituer les tissus excisés (Wolff & Dubois, 1947; Dubois, 1949). Les tissus de la Planaire peuvent intervenir dans les processus de différenciation en favorisant l’apparition d’un organe. Ainsi le cerveau induit la régénération des yeux de la Planaire Polycelis nigra par l’intermédiaire de substances chimiques diffusibles (Wolff & Lender, 1950; Lender, 1952, 1956a). Mais d’autre part certains auteurs ont mis en évidence des phénomènes d’inhibition dans la régénération des Planaires. Morgan (1902) etRand & Ellis (1926) constatent qu’une tête inhibe la régénération d’une autre tête chez les Planaires bicéphales. Rand & Browne (1926) et Miller (1938) empêchent la régénération de la tête en greffant une région céphalique dans la région antérieure de la Planaire opérée. Chevtchenko (1937) constate que la tête de l’hôte inhibe le développement d’une région céphalique dans un greffon de tête implanté dans la région antérieure de la Planaire. L’inhibition ne se manifeste pas si le greffon est implanté dans la région caudale. Il semble donc que la tête des Planaires d’eau douce soit capable, dans certaines conditions, d’inhiber la différenciation d’une autre tête.
The Inhibitory Action of Antimycin A in the Early Chick Embryo
Authors: McKenzie J. , Ebert J. D.
Published: April 2021

Antimycin A, an antibiotic obtained from an undetermined species of strepto-myces, was isolated, crystallized, and described by Dunshee, Leben, Keitt, & Strong (1949), and its biological action has been studied by many workers since then. Ahmad, Schneider, & Strong (1950) demonstrated its effects on the growth and metabolism of yeast, on enzyme activities in the succinoxidase system, and on rats given the drug orally. Potter & Reif (1952) confirmed the inhibitory effect of antimycin A on the succinoxidase system in liver, suggested the presence of an ‘antimycin A-blocked factor’, identical, probably, with the ‘Slater factor’ and showed that, in certain tissues, there is an antimycin A-insensitive pathway for DPN oxidation. The same workers, Reif & Potter (1954), used the drug to characterize the pathways of DPN oxidation in different tissues. Green, Mii, & Kahout (1955) and Thorn (1956) argue from their experiments that the BAL-sensitive (Slater) factor and the antimycin A-sensitive factor are not identical.
The Skin Abnormality of ‘Ichthyosis’, a Mutant of the House Mouse
Authors: Spearman R. I.
Published: April 2021

The skin defect ‘ichthyosis’ of the house mouse is caused by a simple recessive gene (symbol zc) which arose as a spontaneous mutation. It was first described by Carter & Phillips (1950). ‘Ichthyotic’ mice have a thin coat of very short wavy hairs together with a scaly skin. There is, however, considerable individual variation in the severity of the defect. In badly affected animals the stratum corneum of the back is shed as large flakes, and the mice may be almost bald; but in less affected mice the skin is not very scaly and there is a complete though abnormal hair cover. The tail skin has a hard smooth appearance and is less flexible than normal. In some older mice a number of depressed rings form along its length, and a portion of the tail undergoes necrosis and drops off distal to one of the constrictions.
The pattern of alkaline phosphatase activity in the developing mouse spinal cord
Authors: Kwong W. H. , Tam P. P. L.
Published: April 2021

The localization of alkaline phosphatase activity in the lumbosacral region of the developing spinal cord was studied in 9·5-to 17·5-day mouse embryos. The activity was uniformly distributed in the pseudostratified neuroepithelium of the 9·5-day cord. In the 11-5-day cord in which the lateral motor columns were being formed, the enzymatic activity was localized in the ventrolateral sector of the cord. The enzyme-positive ventricular cells tended to be located medially whereas radially oriented enzyme-positive processes extended into the marginal layer. The 13·5-day cord displayed a similar distribution pattern, but there were many more radial processes and the enzyme-positive cells had spread laterally. Close apposition between the processes and the ventricular cells was observed. By 15·5 and 17·5 days, when the intermediate layer was fully developed and the ventricular layer had regressed to a thin ependyma, the activity had become diffusely located in the ventral half of the cord. The enzyme-positive cells and processes became less conspicuous. The silver-stained processes in the cord were found to be organized in an entirely different pattern from that of the enzyme-positive processes, suggesting that the enzyme-positive processes were not neuronal processes. The enzymatic activity found in the developing spinal cord may be associated with the migration of neuroblasts along the radially aligned processes.
Interdigital tissue chondrogenesis induced by surgical removal of the ectoderm in the embryonic chick leg bud
Authors: Hurle J. M. , Gañan Y.
Published: April 2021

In the present work, we have analysed the possible involvement of ectodermal tissue in the control of interdigital mesenchymal cell death. Two types of experiments were performed in the stages previous to the onset of interdigital cell death: (i) removal of the AER of the interdigit; (ii) removal of the dorsal ectoderm of the interdigit. After the operation embryos were sacrificed at 10–12h intervals and the leg buds were studied by whole-mount cartilage staining, vital staining with neutral red and scanning electron microscopy.

Between stages 27 and 30, ridge removal caused a local inhibition of the growth of the interdigit. In a high percentage of the cases, ridge removal at these stages was followed 30–40 h later by the formation of ectopic nodules of cartilage in the interdigit. The incidence of ectopic cartilage formation was maximum at stage 29 (60%). In all cases, cell death took place on schedule although the intensity and extent of necrosis appeared diminished in relation to the intensity of inhibition of interdigital growth and to the presence of interdigital cartilages. Ridge removal at stage 31 did not cause inhibition of the growth of the interdigit and ectopic chondrogenesis was only detected in 3 out of 35 operated embryos.

Dorsal ectoderm removal from the proximal zone of the interdigit at stage 29 caused the chondrogenesis of the proximal interdigital mesenchyme in 6 out of 18 operated embryos. The pattern of neutral red vital staining was consistent with these results revealing a partial inhibition of interdigital cell death in the proximal zone of the interdigit.

It is proposed that under the present experimental conditions the mesenchymal cells are diverted from the death programme by a primary transformation into cartilage.
Electric fields, contact guidance and the direction of nerve growth
Authors: McCaig Colin D.
Published: April 2021

Nerve orientation in response to electrical guidance cues in one direction and contact guidance cues in an orthogonal direction has been studied. Where neurites had a free choice between following contact guidance cues or electrical cues, the direction of nerve growth was determined predominantly by the vector of the applied electric field.