bluuebunny/crossref_metadata_2025 huggingface dataset:
Enteroendocrine APUD cells in the digestive tract of larval Barbus conchonius (Teleostei, Cyprinidae)
Authors: Rombout J. H. W. M. , Lamers C. H. J. , Hanstede J. G.
Published: April 2021

The development of Barbus conchonius is described with special attention to the differentiation of the gut.

Amine precursor uptake and decarboxylation (APUD)* are present in enteroendocrine cells during development, whereas these processes are lacking in adult specimens. The first APUD cells originate on the fourth day of development in the anterior part of the gut and on the fifth day in the caudal areas. The APUD facility of the cells disappears within 2 days, and after the 6th day APUD cells can no longer be distinguished in the intestinal epithelium.

The first APUD cells were observed when four types of enteroendocrine cells were recognized with the electron microscope. These enteroendocrine cells contain granules of different electron densities, and microtubules and cilia can be observed. Some enteroendocrine-like cells are found below the basement membrane of the intestinal epithelium, indicating a possible extra-endodermal origin.

APUD cells, except melanoblasts, have not been found migrating from the neural crest in ventral direction. The origin of the enteroendocrine cells of B. conchonius is discussed.

* Abbreviations: APUD, amine precursor uptake and decarboxylation; F1F, formalin-induced fluorescence; L-DOPA, L-dihydroxyphenylalanine; 5-HTP, 5-hydroxytryptophan.
Metabolic behaviour and cleavage capacity in the amphibian egg
Authors: Legname Arnaldo H. , Buhler Marta I.
Published: April 2021

During the winter season the full grown Bufo arenarum oocyte shows the metabolic behaviour characteristic of differentiated tissues of the same species. Due to seasonal variations, during the amplexus period, it acquires the metabolic behaviour of the segmenting egg.

Short-time-induced ovulations (5–6 h) determine germinal vesicle breakdown immediately before the expulsion of the oocyte, without modifying the ovarian metabolism of the same. The incidence of the operative type of metabolism upon their capacity to cleave after insemination and needle pricking, has been studied in coelomic oocytes, which have attained nuclear maturation and have not experienced oviducal secretion effects.

The results obtained indicate that the segmenting capacity of the egg is attained only when, through biochemical modifications, the oocyte acquires the metabolic behaviour characterizing embryonic cells.

It is postulated that the metabolic changes observed in the oocyte constitute a fundamental aspect of cytoplasmic maturation.
Allophenic mice in cleft-palate investigations
Authors: Sulik K. Miller , Ainip R. L.
Published: April 2021

TlWh (Rb (5; 19)lWh), an albino strain of mice not previously used in the investigation of cleft palate (CP), is homozygous for a (5; 19) Robertsonian translocation which provides conspicuous chromosomal markers. Preliminary studies in this laboratory revealed that CP is induced in all the offspring of TlWh females treated with 2 · 5 mg of cortisone acetate on days 11–14 of pregnancy and that palatal closure is accomplished at a later morphological and chronological age than in C57BL/6J strain mice. The latter strain had a CP frequency of 42 % under similar experimental conditions.

Eight- to 16-cell embryos were aggregated in the following combinations: TlWh ↔ TlWh, C57BL/6J ↔ C57BL/6J and TlWh ↔ C57BL/6J. The resulting allophenic blastocysts were transferred to pseudopregnant C57BL/6J recipients which were given the above cortisone treatment and killed on the 18th day of pregnancy. CP was found in all of the 48 TlWh ↔ TlWhfetuses, 4 (20 %) of 20 C57BL/6J ↔ C57BL/6J fetuses and in 17 (26-2 %) of 65 TlWh ↔ C57BL/6J fetuses. Analysis of chromosome preparations from the palates of the TlWh ↔ C57BL/6J fetuses demonstrated that there is a positive correlation between the presence of CP and the percentage of susceptible cells in the palate (P < 0·02). Other data suggest a possible growth advantage in favor of C57BL/6J cells in the palates of TlWh ↔ C57BL/6J allophenic mice.
Neurotrophic control of the cell cycle during amphibian limb regeneration
Authors: Maden M.
Published: April 2021

It is shown here that amputated and denervated limbs of larval axolotls dedifferentiate and a proportion of the cells released undergo DNA synthesis and mitosis. When the limb is denervated prior to amputation fewer cells go through the cell cycle, implying the existence of a pool of trophic factor in the limb. Recent work has demonstrated that denervated blastemal cells accumulate in the G1 phase of the cycle. These results strongly argue against the theory that the trophic factor controls the G2 phase. Rather, it is proposed that this factor regulates either the total number of cells cycling or the rate at which they cycle by varying the length of the G1 phase.
Acetylcholinesterase- and norepinephrine-containing nerves in developing rat lung
Authors: El-Bermani Al-Walid I. , Bloomquist Eunice I.
Published: April 2021

The lungs of rat fetuses at various stages of gestation and lungs of infant rats were examined histochemically for acetylcholinesterase (AChE) and norepinephrine (NE). No AChE is present in the fetal lungs until 15 days of gestation. At this stage a number of large round cells appear which stain heavily for AChE. These cells disappear by the 18th day of development and at 18 days no AChE-positive structures are demonstrable within the lung. The large AChE-positive cells are of similar size and distribution to fluorescent cells which become apparent after treatment of the mothers with L-DOPA. At 20 days, the day before delivery, a diffuse AChE reaction appears in the walls of large branches of intrapulmonary bronchi. At 20 days, also, sparse NE-containing nerves are present near the hilum and extend along bronchial arteries into the lung. Not until birth do AChE-containing nerves appear in intrathoracic structures. These are vagal preganglionic and postganglionic fibers near the trachea, bronchi, and esophagus. AChE-positive ganglion cells are present in the walls of extrapulmonary bronchi at birth, and perimuscular nerve plexuses containing AChE are also present in the bronchial walls. NE-containing nerves are visible in several divisions of the bronchial artery at birth. Three days postnatally, AChE-containing nerves have not yet invaded intrapulmonary structures, but at this stage the adult pattern of adrenergic innervation is present. By the fifth postnatal day, sparse AChE-positive nerves are associated with intrapulmonary bronchi, and rats 9 days old present the adult pattern of cholinesterase-containing nerves.
Scanning electron microscopy of cells isolated from amphibian early embryos
Authors: Stanisstreet Martin , Smith James L.
Published: April 2021

Cells have been dissociated from Xenopus and Ambystoma late blastulae, allowed to adhere to glass coverslips, and studied by scanning electron microscopy. Xenopus ectoderm cells initially show filopodia; later larger single pseudopodia are formed. Ambystoma ectoderm cells show fewer filopodia than Xenopus ectoderm, but later form pseudopodia. Ectoderm cells of both Xenopus and Ambystoma show links between adjacent cells. Xenopus endoderm cells do not show filopodia initially, but later show large pseudopodia.
The effect of retinoic acid on chondrogenesis in the fetal hamster tibia in vivo
Authors: Fraser B. A. , Travill A. A.
Published: April 2021

Chondrogenesis in the fetal hamster tibia was examined 24, 36 and 48 h after maternal administration of retinoic acid at a known teratogenic dose (80 mg/kg) on day 10 of gestation. Twenty-four hours after treatment the tibial chondroblasts were more closely packed with less intervening fibrillar or granular matrix than in the controls. By 36 h post treatment, an intercellular matrix containing wide clumped fibrils unassociated with matrix granules had begun to accumulate, while the chondroblasts had a relatively poorly developed Golgi apparatus and smooth, non-scalloped cell outlines. Cells frequently maintained contact through pseudopodial processes. Forty-eight hours after retinoic acid treatment, the chondroblasts appeared similar to controls of the same age. It is suggested that the paucity and abnormality of the extracellular matrix prevents the chondroblasts from assuming their normal spatial relations with each other, resulting in a small skeletal blastema.
Developmental studies of the lethal geneBldin the mouse
Authors: Vankin G. Lawrence , Caspari Ernst W.
Published: April 2021

In matings of Bld/ + × Bld/ + mice a characteristic type of abnormal embryo is found on days 6 and 7 after impregnation which dies at 8 days and accounts for about 25 % of all living embryos. These embryos are regarded as the lethal Bld/Bld homozygotes. Before 6 days the embryos appear slightly retarded. Entodermal cells invade the yolk sac and the trophectoderm does not fuse to the uterine decidua. Late on day 6 the yolk sac is filled with a cap of unorganized cells of entodermal origin, surrounded by both a thick membrane of non-living material, corresponding to Reichert’s membrane, and external to this a con-tinuous layer of trophectoderm; there is still almost no contact with uterine tissue. At 7 days 10 h amniotic folds are formed. Mesoderm appears occasionally but is not always present; when it appears it does not grow out from its place of origin. Entodermal cells, particularly in the proximal part of the extra-embryonic region, become polyploid. At the same time, the trophectoderm makes contact with the uterine decidua and gives rise to primary giant cells. Twelve hours later, the embryonic cells begin to degenerate, first in the region of the amniotic fold and the mesoderm. The embryo dies shortly afterwards.

It is suggested that the primary target tissues affected by the Bld/Bld constitution are trophectoderm and entoderm. Many but not all of the abnormal features appearing later can be ascribed to insufficient nutrition of the embryo, due to failure of attachment of the trophectoderm and the filling of the yolk sac with entodermal cells.
Acquisition of differentiative capacity in imaginal wing discs of Drosophila melanogaster
Authors: Bownes Mary , Roberts Sarah
Published: April 2021

The wing discs from larvae undergoing the moult from 1st to 2nd instar are able to differentiate some parts of the adult wing when forced to undergo a premature metamorphosis. The first structures which differentiate are parts of the wing hinge and the wing blade. As development proceeds and older discs are forced through metamorphosis, the capacity to differentiate moves out both proximally and distally until gradually all of the derivatives of a mature wing disc are formed. Individual structures often differentiate from young discs in an incomplete form and pattern elements, such as bristles or sensilla, are added as older discs are tested.
Development of the segmental innervation of the chick forelimb
Authors: Pettigrew A. G. , Lindeman R. , Bennett M. R.
Published: April 2021

A number of recent studies have shown that during embryonic development the initial innervation of a target structure may be made up, in part, by axons which do not form part of the mature innervation of that structure. In the present study we have examined the motor innervation of the major muscles of the chick forelimb at different stages of development using HR.P-uptake-labelling of motoneurons, electrophysiological recording and measurement of muscle contraction.

In the mature White Leghorn chick the major contribution to the motor innervation of the forelimb is from spinal segments 14, 15 and 16. Using the HRP-labelling technique we have shown that at stages 26-29 of development motoneurons in segments 12—17 have axon terminals in the presumptive biceps muscle. Between stages 30 and 35, however, the axon terminals arising from segments 12, 13, 16 and 17 are lost, leaving the mature innervation from segments 14 and 15. We have also observed the loss of innervation of the biceps muscle by segment 16 using electrophysiological recording of compound action potentials in the biceps nerve and by measurement of the local contraction of the biceps muscle in response to stimulation of the segmental nerves. Similar changes in the innervation of the triceps, extensor metacarpi radialis, flexor carpi ulnaris and flexor digitorum profundus muscles have also been observed.

These results are discussed in relation to the hypothesis that (i) the motoneuron pools and muscles in the developing spinal cord and forelimb are matched, (ii) that some axons which arrive in a particular muscle during early development are unable to form a stable connexion and (iii) that the inability of an axon terminal to form a stable connexion in a muscle results in the death of the motoneuron.

Intracellular recording from muscle cells at stage 35 shows that the synaptic site on each cell is innervated by about three separate axons. Over the next few stages, however, all but one of the innervating axons is lost. From our contraction studies it is clear that the removal of the excess axon terminals after stage 35 is not associated with the establishment of the mature segmental innervation pattern of the muscle.
Ventral horn cell counts in a Xenopus with naturally occurring supernumerary hind limbs
Authors: Lamb Alan H.
Published: April 2021

In a Xenopus toad, two partially functioning supernumerary hind limbs developed naturally on the right side and were innervated by the ipsilateral side of the spinal cord. The number of ventral horn cells on the right was 18% higher than on the left while the combined mass of limb muscle on the right was estimated to be a 100 % greater. This result corroborates studies with transplanted supernumerary limbs.
A mutant ofTetrahymena thermophilewith a partial mirror-image duplication of cell surface pattern: I. Analysis of the phenotype
Authors: Jerka-Dziadosz Maria , Frankel Joseph
Published: April 2021

Cells of a mutant clone, CU-127, of Tetrahymena thermophila (formerly T. pyriformis, syngen 1) manifest three anatomical abnormalities. First, the stable number of ciliary meridians is 21-25, above the usual number (17-21) in this species. Second, up to 30 % of the cells have two oral apparatuses (OAs), one normal and the other abnormal. Third, more than one-half of the cells possess two distinct sets of contractile vacuole pores (CVPs). In some living cells two contractile vacuoles are seen. These abnormalities have persisted unchanged during more than 500 generations of vegetative propagation, and are similarly expressed in subclones. The normal and abnormal OAs are topographically segregated, with normal OAs developing along the ‘primary oral axis’ and abnormal OAs developing along a ‘secondary oral axis’ that is situated 170° of the cell circumference to the cell’s right of the primary oral axis. CVPs always appear within this 170° arc and never within the complementary 190° arc to the left of the primary oral axis.

A unique feature of the CU-127 clone is the commonly expressed mirror image reversal of the structural pattern of OAs that develop along the secondary oral axis. The primordia of such OAs initially appear (as usual) to the cell’s left of a ciliary meridian, but as membranelies develop they frequently come to be oriented in a mirror image of the normal pattern, and an undulating membrane sometimes develops on the wrong (left) side of the oral primordium. When two sets of CVPs are formed, their average positions are roughly equidistant with respect to the two oral axes, with the two sets located 50-60° to the right and left respectively of the primary and secondary oral axes. Such cells are thus bilaterally symmetrical about a plane defined by the central longitudinal axis and the halfway point between the two CVP sets (see Fig. 25). This plane bisects the cell into a normal and a ‘reversed’ half-cell. However, only oral asymmetry and large-scale CVP positioning are subject to such reversal ; all ciliary meridians remain of normal asymmetry and all CVPs are situated on the left side of CVP meridians. The fact that major aspects of large-scale cellular organization can be reversed while the ‘fine-positioning’ associated with the ciliary meridians remains normal indicates that the two aspects of cell organization are distinct.
Culture of early somite mouse embryos during organogenesis
Authors: Sadler T. W.
Published: April 2021

Early somite (2-4) mouse embryos were explanted and then maintained in culture for 24 or 48 h intervals. Various types of media were tested and it was determined that rat serum supported normal growth over a period of 48 h, based on total protein analysis and histological comparisons with in vivo specimens. Other media including fetal calf serum and fetal calf serum + Waymouth’s (1:1) supported some growth, but did not equal the success of using rat serum alone. During the 48 h culture period in rat serum, embryos developed to stages indistinguishable from embryos maintained for a similar time in vivo.
Long-term Changes in the Size and Collagen Content of Scars in the Skin of Rats
Authors: Abercrombie M. , James D. W.
Published: April 2021

A description is provided of the changes in area, wet weight, and collagen content of the scar left by a small skin wound in young adult rats during the period between 15 days and 300 days after wounding. The corresponding changes in normal skin were also followed. A standard square area of skin of about 20 mm.2 was marked by tattooing on the back of each of a number of rats, averaging about 250 g. in body-weight. The area was then excised and its collagen content estimated by the hydroxyproline technique of Neuman & Logan (1950). The wound was allowed to heal without dressing. At 15, 50, 100, 200, and 300 days after wounding groups of the animals were killed, the scars measured, and their hydroxyproline content estimated. Control areas of normal skin, similarly tattooed at the same time as the wounded area, were measured in the 100-, 200-, and 300-day groups, and excised for collagen estimation at the same time as the scars. After the period of contraction and the following phase of stationary area, which according to previous work lasts until about 25 days after wounding, the scar starts to expand, and probably continues to do so throughout the period of observation. The expansion is rapid at first, but diminishes in rate. An initially comparable area of normal skin also grows throughout at a diminishing rate per day, but, at least up to about 50 days after wounding, at a lower rate per unit of area already present than the scar. The wet weight of the scar increases proportionately to its increase in area. The wet weight of normal skin probably increases a little faster than its area, and the wet weight per unit of area of normal skin eventually surpasses that of the scar. Collagen formation in the scar probably occurs throughout the period of scar expansion, at such a rate as to increase the content per unit of area and of wet weight. Normal skin is at the same time also increasing its collagen content per unit of area and of wet weight, but not so fast as the scar. Consequently by about 50 days the scar concentration per unit of wet weight or of area has caught up with that of control skin; by 100 days the scar clearly surpasses the normal skin in collagen per unit of wet weight, and by 200 days in collagen per unit of area. The growth of the scar is interpreted according to the hypothesis of Billingham & Medawar (1955), as a response to tension.
The relationship between retinal and tectal growth in larvalXenopus:implications for the development of the retino-tectal projection
Authors: Gaze R. M. , Keating M. J. , Ostberg A. , Chung S-H.
Published: April 2021

The modes of retinal and tectal histogenesis, as well as the patterns of terminal distribution of optic axons in larval Xenopus were studied, using anatomical techniques. We show that the retina grows by adding strips of cells at its ciliary margin. The pattern of retinal growth is asymmetrical along the dorso-ventral axis of the retina. On the other hand, the tectum grows by adding newly formed cells caudo-medially. The most rapid tectal growth takes place between stages 50 and 53, and thereafter only a small proportion of cells are added near the midline of the caudal tectum. Despite such incongruent modes of retinal and tectal growth, retinotopic order is maintained throughout larval life.

We present here further evidence supporting the idea that connexions between the arrays of retinal and tectal cells shift progressively caudo-medially on the tectum during the period of growth. When the temporal pole of the retina is destroyed at various developmental stages, the density of degenerating synapses is always highest in the rostral pole of the tectum. Moreover, optic terminals stemming from the central retina spread caudally, invading newly maturing regions of the tectum. Quantitative analysis of the terminal distributions of optic axons suggest that orderly shifts in synaptic contacts between optic axons and tectal dendrites take place in the course of development. Ultrastructural observations on the maturing tectal neuropil are consistent with this view.
Surface potentials and the control of amphibian limb regeneration
Authors: Lassalle B.
Published: April 2021

The relationship between surface potentials and amphibian limb regeneration is examined. The wound surface becomes increasingly positive for several days after amputation but then decreases again, often becoming negative for a variable period during blastemal growth. The same changes of surface potentials are observed during wound healing alone, in the absence of amputation and following amputation of irradiated or denervated limbs. Similar changes occur in non-regenerating frog arms. These observations and other cited reasons lead to the conclusion that surface potentials do not control regeneration.
The use of avian double monsters in studies on induction of the nervous system
Authors: Ulshafer R. J. , Clavert A.
Published: April 2021

Ninety-eight duck double monsters (siamese twins) were studied between 48 and 72 h of incubation in whole-mount or serial-sectioned preparations. Each case was classified into one of four categories depending on the orientations of the two embryonic axes. In all classes, defects in primary neural induction of various parts of the embryonic nervous system were observed which depended to a large extent on the distance separating the anterior tips of the two notochords or on the relative positions of the notochords. Our observations suggest that: when the same inducing field of one embryo overlaps to a critical extent with that of the twin, the two inducers act as one; induction of forebrain and optic vesicles is purely prechordal; the notochord exerts an inhibition on induction of forebrain by prechordal mesoderm; and the presence of rhombencephalic structures depends on both prechordal and chordamesodermal interactions.
Somitogenesis in amphibia: II. Origins in early embryogenesis of two factors involved in somite specification
Authors: Elsdale Tom , Pearson Murray
Published: April 2021

A somite pre-pattern is established shortly before visible segmentation. The pre-pattern results from the interaction of two components: a wave of cell behavioural change that passes along the axis, and, an underlying co-ordination of the cells that is the basis for their association into large somite-sized groupings. The evidence is derived from studies of the zones of abnormal segmentation that follow temperature shocks delivered between the neurula and tail-bud stages (Pearson & Elsdale, 1979).

Temperature shock given earlier at the mid-gastrula stage is however ineffective in inducing abnormalities in somitogenesis. Shocks given before the mid-gastrula stage reveal a prior period of sensitivity stretching back into the blastula. Thus early and late sensitive periods can be defined separated by a short refactory period. Quite different patterns in the distribution of somite abnormalities characterize the results of shock during the two sensitive periods, suggesting different aetiologies.

It is concluded that the wave of rapid cell change is set up early in embryogenesis during the blastula stage, and each cell of the prospective paraxial mesoderm carries a determination to change after a specific length of time, i.e. a countdown is set in each cell. As a result of the movements of gastrulation, the prospective paraxial mesoderm cells become laid out along the axis of the neurula in the order (antero-posterior sequence) in which they will change. The achievement of the correct redistribution of the cells depends crucially on the conservation of the sequence in the blastula by the maintenance of topological integrity throughout gastrulation. It is suggested that early shock disturbs gastrulation movements, causing some mixing up of the cells resulting in incoherence of the wavefront.

Whereas early shocks are thus assumed to affect the wave, the evidence suggests that late shock undoes co-ordination. It is concluded therefore that co-ordination is established later, after the refractory period, around the late gastrula stage.
Cell number in relation to primary pattern formation in the embryo of Xenopus laevis: II. Sequential cell recruitment, and control of the cell cycle, during mesoderm formation
Authors: Cooke Jonathan
Published: April 2021

Morphological evidence is presented that definitive mesoderm formation in Xenopus is best understood as extending to the end of the neurula phase of development. A process of recruitment of cells from the deep neurectoderm layers into mesodermal position and behaviour, strictly comparable with that already agreed to occur around the internal blastoporal ‘lip’ during gastrula stages, can be shown to continue at the posterior end of the presumptive body pattern up to stage 20 (earliest tail bud).

Spatial patterns of incidence of mitosis are described for the fifteen hours of development between the late gastrula and stage 20–22. These are related to the onset of new cell behaviours and overt cyto-differentiations characterizing the dorsal axial pattern, which occur in cranio-caudal and then medio-lateral spatial sequence as development proceeds. A relatively abrupt cessation of mitosis, among hitherto asynchronously cycling cells, precedes the other changes at each level in the presumptive axial pattern. The widespread incidence of cells still in DNA synthesis, anterior to the last mitoses in the posterior-to-anterior developmental sequence of axial tissue, strongly suggests that cells of notochord and somites in their prolonged, non-cycling phase are G2-arrested, and thus tetraploid. This is discussed in relation to what is known of cell-cycle control in other situations.

Best estimates for cell-cycle time in the still-dividing, posterior mesoderm of the neurula lie between 10 and 15 h. The supposition of continuing recruitment from neurectoderm can resolve an apparent discrepancy whereby total mesodermal cell number nevertheless contrives to double over a period of approximately 12 h during neurulation when most of the cells are leaving the cycle.

Because of pre-existing evidence that cells maintain their relative positions (despite distortion) during the movements that form the mesodermal mantle, the patterns presented in this paper can be understood in two ways: as a temporal sequence of developmental events undergone by individual, posteriorly recruited cells as they achieve their final positions in the body pattern, or alternatively as a succession of wavefronts with respect to changes of cell state, passing obliquely across the presumptive body pattern in antero-posterior direction. These concepts are discussed briefly in relation to recent ideas about pattern formation in growing systems.
On the ‘clock’ mechanism determining the time of tissue-specific enzyme development during ascidian embryogenesis
Authors: Satoh Noriyuki
Published: April 2021

During ascidian embryogenesis a tissue-specific enzyme, muscle acetylcholinesterase (AChE) may first be detected histochemically in the presumptive muscle cells of the neurula. In order to investigate the ‘clock’ or counting mechanism that is determining the time when AChE first appears, Whittaker’s experiment (1973) has been repeated using eggs of the ascidian, Halocynthia roretzi.

Embryos that had been permanently cleavage-arrested with cytochalasin B were able to differentiate AChE in their muscle lineage blastomeres. The time of first AChE occurrence in embryos that had been cleavage-arrested in the 32-cell stage with cytochalasin B was about the same as in normal embryos. This result indicates that the clock is not apparently regulated by the events of cytokinesis.

The early gastrulae which had been arrested with colchicine or with colcemid could develop AChE activity, although no histochemically detectable AChE activity was observed in the cleavage-stage embryos that had been arrested with either drug. Therefore the clock does not seem to be controlled by the mitotic cycle of the nucleus. It is suggested that the cycle of DNA replication may be related to the regulation of the clock that is determining the time of development of histospecific protein.
Muscle-forming potential of the non-somitic cells of the early avian limb bud
Authors: McLachlan John C. , Hornbruch Amata
Published: April 2021

It has recently been shown that the musculature of the chick wing arises by migration of cells from the somites, and that on morphological grounds this process begins at about stage 14.

We have carried out grafts of wing anlagen separate from the somites from quail donors to the extra-embryonic coelom of chicks, and find that anlagen from as early as stage 10 (11 pairs of somites) can give rise to muscle. We discuss the possible reasons for this finding, and conclude that in the absence of the cells normally giving rise to the musculature, mesodermal cells themselves can give rise to muscle.
The differentiation and proliferation of follicle cells during oocyte growth in Lacerta sicula
Authors: Filosa S. , Taddei C. , Andreuccetti P.
Published: April 2021

The follicular epithelium of the lizard oocytes undergoes structural and morphological modifications throughout oocyte growth. During this process the number of follicle cells increases and the epithelium acquires a multilayered and polymorphic organization which is characterized by the appearance of large follicle cells (intermediate and pyriform’cells). The number of large cells also increases during oocyte growth and this increase parallels that of small cells. However, only the small cells become labelled one hour after [3H-]thymidine administration. Large cells have been found labelled after a longer period of time, i.e. 4–5 months after isotope injection.

All these results together indicate that large follicle cells arise from the differentiation of small cells.
The role of extracellular matrix in the formation of the sclerotome
Authors: Solursh Michael , Fisher Marilyn , Meier Stephen , Singley Carl T.
Published: April 2021

The development of the sclerotome is considered as a model for the formation of mesenchyme from an epithelium. In early epithelial somites, transmission and scanning electron microscopy indicate considerable ultrastructural similarity between the future sclerotome and dermamyotomal regions. Subsequently, these two regions diverge in their development. In the forming dermamyotome, junctional complexes become more extensive and the cells become elongated, closely applied to each other, and have angular surface contours. In the forming sclerotome, there is an early reduction in apical junctions. The cells elongate, keeping their original polarity, and acquire numerous filopodia which contain punctate junctions at sites of cell-to-cell contact. Associated with cellular extension is an expansion of the intercellular spaces which do not contain any ultrastructurally recognizable material.

Evidence for a role of hyaluronic acid in the expansion of the intercellular spaces is presented. As identified by the susceptibility of cetylpyridinium chloride precipitates to Streptomyces hyaluronidase and chromatographic separation of chondroitinase ABC digestion products, as much as 64 –68 % of the [3H]glucosamine-labeled glycosaminoglycans synthesized by explanted somites is hyaluronic acid. In addition, hyaluronidase-sensitive label is localized in the intercellular spaces of the sclerotome, as demonstrated by autoradiography. When Streptomyces hyaluronidase is injected in ovo into living embryos, the sclerotomal mesenchyme differentiates morphologically, but intercellular spaces are drastically reduced. It is hypothesized that the sclerotomal cells produce a hyaluronate-enriched extracellular matrix which is inflated by hydration to mediate the expansion of the sclerotomal mass towards the notochord.
The formation of muscles in regenerating limbs of the newt after denervation of the blastema
Authors: Grim Miloš , Carlson Bruce M.
Published: April 2021

The purpose of this experiment was to examine the relationship, if any, between nerve fibers and the formation of muscle pattern in the regenerating amphibian limb. During embryogenesis, nerve fibers grow into the limb bud at the time when the common muscle blastemas subdivide into individual muscle primordia, whereas in regeneration nerve fibers are always present. In order to learn whether or not the muscle pattern could be laid down in the absence of nerves we amputated 58 limbs of newts (Notophthalmus viridescens) at the mid humeral level and allowed them to regenerate to the medium-bud or late-bud stage. The limbs were then denervated. The majority of limbs denervated at the medium-bud stage either regressed or failed to regenerate further. Regeneration after denervation failed in 9 of 25 limbs denervated at the late-bud stages.

In those limbs that continued to regenerate after denervation, the formation of individual muscle primordia did occur, following the same sequence with respect to the gross stage of regeneration as innervated regenerates. In comparing these results with our previous results on the development of muscular pattern in aneurogenic limbs of the axolotl, we conclude that in neither the embryonic nor the regenerating amphibian limb are nerve fibers directly involved in the subdivision of common muscle blastemas into the primordia of individual muscles.
Histochemistry of the developing notochord, perichordal sheath and vertebrae in Danforth’s short-tail (Sd) and normal C57BL/6 mice
Authors: Paavola Laurie G. , Wilson Doris B. , Center Elizabeth M.
Published: April 2021

The development of the notochord, perichordal sheath and vertebrae was studied in C57BL/6 and Danforth’s short-tail (Sd) mutant mice on days 9–14 of gestation, using histochemical stains to detect possible extracellular matrix (ECM) components or precursors. Stains used were periodic-acid Schiff (PAS) after diastase treatment (glycoproteins, neutral polysaccharides) and alcian blue (glycosaminoglycans). Embryos from C57BL/6Sfd mice were analyzed to establish a normal baseline. In 9-day normal (C57BL/6Sfd; +/ + ) embryos the notochord is an uninterrupted structure and contains PAS-positive, diastaseresistant granules, whereas in abnormals (Sd/+ ; Sd/Sd) the notochord is discontinuous and exhibits few, if any, granules. A notochordal sheath is present in normal and abnormal embryos on day 10 and stains with PAS, alcian blue and aniline blue; subsequently, it increases in thickness in normal, but not defective, embryos. In normal embryos, the notochord shows dilatations, and notochordal cells become vacuolated from 13 to 14 days. In contrast, the notochordal fragments of abnormals never develop dilatations, nor do the cells vacuolate. Organization of mesenchymal cells into specific patterns is observed initially in 11-day normal embryos; further mesenchymal organization into vertebral and intervertebral disc analgen occurs during days 12–14. In abnormal embryos, disturbance of mesenchymal cell organization is evident as early as day 11, and by day 12 aberrant patterns of organization have emerged. Mesenchymal cells of abnormal embryos also lack the typical distribution of PAS-positive, diastase-resistant granules that occurs in normal specimens. The possible relationship of these granules in notochordal and mesenchymal cells to ECM materials is discussed.
Embryonic axis orientation in the mouse and its correlation with blastocyst relationships to the uterus: Part 1. Relationships between 82 hours and days
Authors: Smith L. J.
Published: April 2021

Up until at least days p.c., the orientation of all axes in the mouse conceptus, embryonic axis included, is directly correlated with two orientations of the 82 h blastocyst within the lumen. These two are: the almost horizontal position of the blastocyst’s inner cell mass-abembryonic pole axis and the fixation of its abembryonic pole to either the right wall of the uterine horn (type-R orientation) or to the left (type-L orientation). At 88 h and at and days equal numbers of conceptuses are found in type R and L orientations. Axes of symmetry also are recognizable in some developmentally advanced 82 h blastocysts and in all older conceptuses. For example, when the inner cell mass-abembryonic pole axis has become vertically oriented within the lumen by days, the inner cell mass is oblique to this axis. It is concluded that the 82 h blastocyst’s orientation to the uterine walls and floor provides it with positional information used in the location of its axes.
Acetylcholinesterase development in extra cells caused by changing the distribution of myoplasm in ascidian embryos
Authors: Whittaker J. R.
Published: April 2021

This research shows that myoplasmic crescent material of the ascidian egg has both functional autonomy and functional specificity in establishing the differentiation pathway of muscle lineage cells. The cytoplasmic segregation pattern in eggs of Styela plicata was altered by compression of the embryos during third cleavage. This caused a meridional division instead of the normal equatorial third cleavage; first and second cleavages are meridional. Since eggs of S, plicata have a pronounced yellow myoplasmic crescent, one observes directly that third cleavage under compression resulted in a flat 8-cell stage with four cells containing yellow myoplasm instead of the two myoplasm-containing cells that would be formed by normal equatorial division at third cleavage. If such altered 8-cell-stage embryos were released from compression and kept from undergoing further divisions by continuous treatment with cytochalasin B, some embryos eventually developed histospecific acetylcholinesterase in three and four cells instead of in just the two muscle lineage cells found in cleavage-arrested normal 8-cell stages. The wider myoplasmic distribution effected by altering the division plane at third cleavage apparently caused a change in developmental fate of the extra cells receiving myoplasm. This meridional third cleavage also resulted in a changed nuclear lineage pattern. Two nuclei that would ordinarily be in ectodermal lineage cells after third cleavage were now associated with yellow myoplasm. Acetylcholinesterase development in these cells demonstrates that nuclear lineages are not responsible for muscle acetylcholinesterase development in the ascidian embryo.
Specification of retinotectal connexions during development of the toadXenopus laevis
Authors: Sharma S. C. , Hollyfield J. G.
Published: April 2021

The specification of central connexions of retinal ganglion cells was studied in Xenopus laevis. In one series of experiments, the right eye primordium was rotated 180° at embryonic stages 24 – 32. In the other series, the left eye was transplanted into the right orbit, and vice versa, with either 0° or 180° rotation. After metamorphosis the visual projections from the operated eye to the contralateral optic tectum were mapped electrophysiologically and compared with the normal retinotectal map. In all cases the visual projection map was rotated through the same angle as was indicated by the position of the choroidal fissure. The left eye exchanged into the right orbit retained its original axes and projected to the contralateral tectum. These results suggest that retinal ganglion cell connexions are specified before stage 24.
Effects of juvenile hormone, ecdysterone, actinomycin D, and mitomycin C on the cuticular proteins ofTenebrio molitor
Authors: Roberts P. Elaine , Willis Judith H.
Published: April 2021

Juvenile hormone (JH), ecdysterone and some antibiotics cause Tenebrio molitor to form a second pupa or pupal-adult intermediate. Incorporation of labelled leucine into the cuticular proteins of JH-induced second pupae did not differ from incorporation in normal pupae, and the soluble cuticular proteins from these young second pupae were identical to those extracted from normal pupal exocuticle when analysed by SDS-polyacry lamide gel electrophoresis. However, as these second pupae aged, the major early bands did not undergo a normal decrease in staining intensity, indicating a JH effect on protein insolubilization (sclerotization). The transport of protein into the cuticle may also have been altered by JH; electrophoretic analysis of the new cuticle of treated animals showed intense staining of bands with RF’s similar to those of blood proteins.

The new exocuticle produced after treatment of pupae with ecdysterone had soluble proteins which were typical of normal pupae, but extracts from such animals aged prior to cuticle removal yielded bands characteristic of normal adults. Pupae treated with actinomycin D occasionally form new abdominal cuticle with characteristic pupal morphology. These cuticles yielded soluble proteins which, upon analysis, had pupal, pupal and adult, or adult banding patterns. Animals treated with mitomycin C, although retaining vestiges of pupal abdominal characters, had adult cuticular proteins.
Fibroblast progenitor cells of the embryonic chick limb
Authors: Newman Stuart A.
Published: April 2021

A population of mesenchymal cells derived from the stage-25 chick wing tip gives rise to progeny of a similar morphology and to authentic fibroblasts when grown in low density culture. Mixed clones containing both cell types are often observed. As the more rapidly proliferating fibroblasts begin to predominate in these cultures, collagen biosynthesis rises from the basal mesenchymal level to a level characteristic of mature fibroblasts. The fibroblast progenitor is discussed relative to the other cell types of the mesodermal lineage of the developing limb.
Ribonucleic acid synthesis in embryonic chick muscle, rates of synthesis and half-lives of transfer and ribosomal RNA species
Authors: Nwagwu Mark , Nana Mohammed
Published: April 2021

In this study the term ‘rates of synthesis’ does not refer to rates of transcription but to rates of accumulation of newly synthesized RNA.

The rates of synthesis and half-lives of tRNA, 18S and 28S rRNA of 14-day and 17-day embryonic chick muscle were determined by following the accumulation of radioactive AMP in RNA after administration of [3H]8-adenosine to chick embryos and correcting for the average specific activity of the precursor ATP pool. Transfer RNA of 14-day embryonic chick muscle is synthesized at a rate of 2·4 × 105 molecules per min per 2 N DNA content and decays with a half-life of 50 h. Transfer RNA of 17-day embryonic chick muscle is synthesized, and decays, at similar rates. Ribosomal RNA, 18S and 28S, are synthesized at a rate of 9·94 × 103 and 8·48 ×103 molecules per min per 2N DNA, respectively, in 14-day embryonic chick muscle. The rates of rRNA syntheis in 17-day embryonic muscle are also similar. In both 14-day and 17-day embryonic muscle, 18S and 28S rRNA each decays with a half-life of 65 h. We conclude that the constant level of tRNA and rRNA in embryonic chick muscle from 14 to 17 days (Nwagwu & Nana, 1974) is maintained also by a constant rate of synthesis and turnover.
The genesis of membrane bone in the embryonic chick maxilla: epithelial-mesenchymal tissue recombination studies
Authors: Tyler Mary S. , McCobb David P.
Published: April 2021

In the present study, the question of whether a relatively non-specific epithelial requirement exists for membrane bone formation within the maxillary mesenchyme was investigated. Organ rudiments from embryonic chicks of three to five days of incubation (HH .18 –25) were enzymatically separated into the epithelial and mesenchymal components. Maxillary mesenchyme (from embryos HH 18 –19) which in the absence of epithelium will not form bone was recombined with epithelium from maxillae of similarly aged embryos (homotypic-homochronic recombination) and of older embryos (HH 25) (homotypic-heterochronic recombination). Heterotypic recombinations were made between maxillary mesenchyme (HH 18 –19) and the epithelium from wing and hind-limb buds (HH 19 –22). Recombinants were grown as grafts on the chorioallantoic membranes of host chick embryos. Grafts of intact maxillae, isolated maxillary mesenchyme, and isolated epithelia from the maxilla, wing-, and hind-limb buds were grown as controls. The histodifferentiation of grafted intact maxillae was similar to that in vivo; both cartilage and membrane bone differentiated within the mesenchyme. Grafts of maxillary mesenchyme (from embryos HH 18 –19) grown in the absence of epithelium formed cartilage but did not form membrane bone. Grafts of maxillary mesenchyme (from embryos HH 18 –19) recombined with epithelium in homotypic-homochronic, homotypic-heterochronic, and heterotypic tissue combinations formed membrane bone in addition to cartilage. These results indicate that maxillary mesenchyme requires the presence of epithelium to promote osteogenesis and that this epithelial requirement is relatively non-specific in terms of type and age of epithelium.
Viability and proliferation of epithelia and the initiation of osteogenesis within mandibular ectomesenchyme in the embryonic chick
Authors: Hall B. K.
Published: April 2021

Ectomesenchyme, a derivative of the embryonic neural crest, forms the membrane bones of the mandibular skeleton, but will only do so after undergoing an inductive interaction with mandibular epithelium. Previously, non-mandibular epithelia have been shown to act as effective substitutes for the mandibular epithelium in this interaction. The role of epithelial viability was examined by enzymatically separating the mandibular epithelium from its ectomesenchyme, killing the epithelium, recombining the epithelium with vital ectomesenchyme and either organ culturing the recombinant or grafting it to the chorioallantoic membrane of a host embryo. Epithelia killed by distilled water, air drying, 80% ethanol, freeze-thawing or with 2500 rad of gamma irradiation did not elicit osteogenesis from the ectomesenchyme while vital epithelia did. Exposure of epithelia to gamma irradiation at doses between zero and 2000 rad resulted in a progressive reduction in the incidence of osteogenesis in ectomesenchyme. However, the incidence of osteogenesis progressively increased after irradiation of the mandibular epithelium with 3000 to 5000 rad, only to decrease again after 10000 rad. [3H]thymidine autoradiography was used to show that this pattern of induction of bone by irradiated epithelia could be correlated with the proliferative activity of the epithelia. A similar pattern of induced osteogenesis and epithelial proliferation was seen after epithelia were treated with colchicine. It was concluded that the ability of the mandibular epithelium to permit osteogenesis within mandibular ectomesenchyme was correlated with some property of epithelial proliferation. Several possibilities are discussed and related to other instances of induction of heterotopic bone by epithelia.
Dr Elizabeth Marion Deuchar (1927–1979)
Authors: Bellairs Ruth
Published: April 2021

Elizabeth Deuchar, who died of cancer in January 1979 at the age of 52, was an embryologist of distinction. After studying Zoology at Oxford she moved in 1948 to the Institute of Animal Genetics in Edinburgh as a Ph.D. student with the late C. H. Waddington. Her earliest papers, published under his influence, were on embryonic induction, a topic to which she returned many times. These studies culminated in 1975 in a book synthesizing many of her ideas (8).