bluuebunny/crossref_metadata_2025 huggingface dataset:
Spitz/EGFr signalling via the Ras/MAPK pathway mediates the induction of bract cells inDrosophilalegs
Authors: del Álamo David , Terriente Javier , Díaz-Benjumea Fernando J.
Published: April 2021

In the development of Drosophila, the activation of the EGFr pathway elicits different cellular responses at different times and in different tissues. A variety of approaches have been used to identify the mechanisms that confer this response specificity. We have analysed the specification of bract cells in Drosophila legs. We observed that mechanosensory bristles induced bract fate in neighbouring epidermal cells, and that the RAS/MAPK pathway mediated this induction. We have identified Spitz and EGFr as the ligand and the receptor of this signalling, and by ubiquitous expression of constitutively activated forms of components of the pathway we have found that the acquisition of bract fate is temporally and spatially restricted. We have also studied the role of the poxn gene in the inhibition of bract induction in chemosensory bristles.
Runx1 is required for zebrafish blood and vessel development and expression of a human RUNX1-CBF2T1 transgene advances a model for studies of leukemogenesis
Authors: Kalev-Zylinska Maggie L. , Horsfield Julia A. , Flores Maria Vega C. , Postlethwait John H. , Vitas Maria R. , Baas Andrea M. , Crosier Philip S. , Crosier Kathryn E.
Published: April 2021

RUNX1/AML1/CBFA2 is essential for definitive hematopoiesis, and chromosomal translocations affecting RUNX1 are frequently involved in human leukemias. Consequently, the normal function of RUNX1 and its involvement in leukemogenesis remain subject to intensive research. To further elucidate the role of RUNX1 in hematopoiesis, we cloned the zebrafish ortholog (runx1) and analyzed its function using this model system. Zebrafish runx1 is expressed in hematopoietic and neuronal cells during early embryogenesis. runx1 expression in the lateral plate mesoderm co-localizes with the hematopoietic transcription factor scl, and expression of runx1 is markedly reduced in the zebrafish mutants spadetail and cloche. Transient expression of runx1 in cloche embryos resulted in partial rescue of the hematopoietic defect. Depletion of Runx1 with antisense morpholino oligonucleotides abrogated the development of both blood and vessels, as demonstrated by loss of circulation, incomplete development of vasculature and the accumulation of immature hematopoietic precursors. The block in definitive hematopoiesis is similar to that observed in Runx1 knockout mice, implying that zebrafish Runx1 has a function equivalent to that in mammals. Our data suggest that zebrafish Runx1 functions in both blood and vessel development at the hemangioblast level, and contributes to both primitive and definitive hematopoiesis. Depletion of Runx1 also caused aberrant axonogenesis and abnormal distribution of Rohon-Beard cells, providing the first functional evidence of a role for vertebrate Runx1 in neuropoiesis.

To provide a base for examining the role of Runx1 in leukemogenesis, we investigated the effects of transient expression of a human RUNX1-CBF2T1 transgene [product of the t(8;21) translocation in acute myeloid leukemia] in zebrafish embryos. Expression of RUNX1-CBF2T1 caused disruption of normal hematopoiesis, aberrant circulation, internal hemorrhages and cellular dysplasia. These defects reproduce those observed in Runx1-depleted zebrafish embryos and RUNX1-CBF2T1 knock-in mice. The phenotype obtained with transient expression of RUNX1-CBF2T1 validates the zebrafish as a model system to study t(8;21)-mediated leukemogenesis.
A study of the influence of isolated calf spleen RNA on amphibian histogenesis
Authors: Finnegan Cyril V. , Biggin William P.
Published: April 2021

Ribonucleic acid (RNA) was isolated from calf spleen tissue by the new Kirby procedure followed by three phenol washings to reduce the peptide-protein contamination. Ultraviolet absorption spectra and colorimetric analyses indicated the reduction or absence of protein, peptide, DNA and, after methoxyethanol purification, polysaccharide from the isolated RNA. Ultracentrifuge sedimentation analysis showed three components in the undegraded RNA isolate: a 27S fraction, an 18S fraction and a 7-8S fraction. This ribosomal-messenger RNA was added to non-nutrient medium for induction testing. Neither embryos nor competent gastrula ectoderm of Xenopus laevis demonstrated, in a limited series, any tissue-specific inductive response, but both experimental systems in the RNA-conditioned medium did demonstrate enhanced epithelial development as compared with the control systems. Postgastrula stages of Taricha torosa and Ambystoma gracile exposed during development to reagent-grade beef liver s-RNA demonstrated hyperplasia in the dorsal mesencephalon-rhombencephalon and the anterior neural crest mesenchyme population along with an enhancement of auditory and posterior entodermal epithelial development.
The molars of the tabby mouse, and a test of the ‘single-active X-chromosome’ hypothesis
Authors: Grüneberg Hans
Published: April 2021

The sex-linked gene for tabby (Ta) in the mouse, in addition to its effects on fur and skin, has a characteristic dental syndrome (Griineberg, 1965). Some tabby heterozygotes have a spectacular mixture of molar teeth, some of which are normal, others which are tabby, and some which combine features of both. This prima facie evidence in favour of the single-active X-chromosome hypothesis of Lyon (1961) can be turned into a more exacting quantitative test of that concept. An autosomal mimic of tabby, called crinkled (cr; linkage group 14), with the same dental syndrome, offers opportunities for further tests of the hypothesis. It will be seen that, contrary to first impressions, the quantitative study reveals a situation which is not in agreement with the Lyon hypothesis.
The developmental endocrinology of the spleen in chicken embryos: II. The pars distalis and splenomegaly
Authors: Goldberg R. B. , Betz T. W.
Published: April 2021

Pars distalis-extract treatment of intact or ‘hypophysectomized’ chicken embryos resulted in a splenomegaly, perhaps of a host-versus-graft nature, by 17 and 17·5 days of incubation. Pars distalis grafts in intact embryos reduced spleen size, encouraged white-pulp follicle formation, but ‘suppressed’ red-pulp development. Adult spleen extract and bovine serum albumin did not change spleen sizes or histology appreciably in intact embryos.

Perhaps pars distalis hormones inhibit red-pulp development or stimulate white-pulp follicles which may compete with red-pulp proliferation but encourage splenic vasculogenesis alone or by stimulating adrenocorticoid, thyroid, and other hormone levels while other extract factors cause splenomegaly.
Oogenesis in Tenebrio molitor: Histological and autoradiographical observations on pupal and adult ovaries
Authors: Ullmann Suzanne L.
Published: April 2021

Nurse cells and oocytes in the telotiophic ovary of Tenebrio molitor L. (Insecta, Coleoptera-Polyphaga) are differentiated in the larval stadium. During pupation DNA synthesis occurs in the nurse cells and is probably associated with polyploidy; some of them become multinucleate. The functional significance of these events is interpreted as preparation for subsequent massive RNA synthesis. The oviducts incorporate [3H]thymidine and undergo elongation due to mitoses. This ceases at eclosion. RNA synthesis in the pupal ovary is low, but increases in the nurse cells and follicle cells just prior to eclosion. In the adult ovary, once the growth phase has been initiated, a primary oocyte takes about six days to reach maturity. The nurse cells, though apparently lacking nucleoli, synthesize much stable RNA which reaches each oocyte via a trophic cord. The follicle cells undergo continuous DNA synthesis: some nuclei contain over 64 times the haploid amount of DNA. Replication is probably asynchronous within a nucleus: this may account for the phenomenon of simultaneous DNA and RNA synthesis in the follicle cells, which also lack nucleoli. Oogenesis has been divided into nine developmental stages, three of which are vitellogenic. The oocyte chromosomes are capable of RNA synthesis both when despiralized during early previtellogenesis and after karyosome formation, which occurs at stage 6. The protein content of the oocyte appears to have a dual origin: at least part of the ooplasmic proteins form in situ; while yolk proteins are derived from the haemolymph. The extra-ovarian protein reaches the oocyte via spaces which develop between the follicle cells. The nucleoplasm becomes more heavily labelled with proteins than the ooplasm. With [3H]leucine, methionine and phenylalanine but not with tryptophane or arginine, there is an increased incorporation into the karyosome. It is suggested that this karyosomeassociated protein may function in gene masking. The significance of these findings is discussed with reference to the literature.
The development of dorsal root ganglia and ventral horns in the opossum. A quantitative study
Authors: Hughes Arthur
Published: April 2021

Numbers of cells, of mitotic figures, and of degeneration sites have been counted in dorsal root ganglia and ventral horns during the development of the opossum, from embryonic to pouch-young stages.

Tn the embryo, from forelimb bud stages onwards, the cervico-brachial ganglia growrapidly, at first with very high mitotic rates (about 5 %) and little cell degeneration. One day before birth, cell death is widespread through the whole series though cell numbers at all levels continue to increase. In the new-born, the growth of brachial ganglia is checked by very high local rates of cell death.

In the cord, cells of the lateral motor columns, or ventral horns arise by outward migration of cells from the basal half of the mantle layer. In the later embryo, these cells are recognizable at cervico-brachial levels during their migration, and are then accompanied by de-generating cells, the axial distribution of which foreshadows that of the lateral column of the new-born.

In the pouch-young, there is a slow loss of neurons from dorsal root ganglia and from ventral horns. This begins later at lumbo-sacral than at cervico-brachial levels.

Comparison of these results with data from other species emphasizes the variety of patterns in neural development among tetrapods.
Effects of insulin insufficiency on forelimb and tail regeneration in adultDiemictylus viridescens
Authors: Vethamany-Globus Swani , Liversage Richard A.
Published: April 2021

Experimental diabetes caused by pancreatectomy resulted in a marked interference in limb and tail regeneration in adult newts. Under pancreatic insufficiency, throughout the entire period of regeneration, limb and tail regenerates (26 days old) consistently showed sparse population of blastema cells, while older regenerates (58–79 days) exhibited severe abnormalities. Newts with these abnormal regenerates always had an atrophied pancreas. In the event that the cauterized pancreas regenerated, there was a subsequent recuperation in the regeneration processes of the appendages. Our data strongly indicates that a correlation exists between the normal (intact) pancreas and regeneration of the limb and tail in the adult newt.

In addition, alloxanization inhibited normal limb and tail regeneration. Again, recuperation of the pancreas from the effects of alloxan was followed by restoration of limb and tail regeneration. These results suggest an insulin role in the hormone control of regeneration. The possible actions of insulin are discussed.
The role of the tissue environment in the expression of spotting genes in the mouse
Authors: Deol M. S.
Published: April 2021

Genes causing white spotting in the mouse act in two major ways: some affect the melano-blasts, while others affect the tissue environment of the melanoblasts. The question is whether the normal tissue environment plays any role in the origin of spots in those mutants in which the melanoblasts are believed to be the site of gene activity. An earlier study, using the genotypes + /mi, Miwhl+, s/s, Wv/ + and Wv/Wv(mi = microphthalmia; Miwh= white; s = piebald; Wv= viable dominant spotting), indicated that it probably does, the evidence largely consisting in the occurrence of extremely precise pigmentation patterns on a minute scale. It seemed that more direct evidence could be obtained by comparing the pigmentation of the iris with that of the choroid and the retina in the same eye in these and other genotypes. The outer and inner layers of the iris derive their pigment cells from the choroid and the retina respectively; therefore any clear and consistent differences between the behaviour of these cells in their original and their secondary place of activity would constitute evidence for the role of the tissue environment. Such differences were found.

It was also found that in another genotype, Miwh/mi the retinal pigment cells, although unpigmented, are clearly distinguishable. This casts serious doubt on the widespread assumption that melanoblasts which do not differentiate always die.
Effects of nerve growth factor from the venom ofVipera russellion dispersed sensory ganglion cells from the embryonic chick
Authors: Banthorpe D. V. , Pearce F. L. , Vernon C. A.
Published: April 2021

A quantitative study has been made of the effects of nerve growth factor (NGF), isolated from the venom of Vipera russelli, on the growth of dispersed cells from the sensory ganglia of the embryonic chick. The main effects were to increase the viability of the sensory neurons in culture and to promote the regeneration of nerve fibres. In the presence of NGF a higher proportion of neurons produced fibres and the fibres were longer and slightly more branched than in control cultures. The number of fibres produced per neuron was unaltered. Supporting cells were unaffected by the presence of NGF. No stimulation of mitotic activity among either type of cell was observed. It is concluded that, under the stated conditions, NGF does not promote the differentiation of immature cells but acts, both in a maintenance and a stimulatory capacity, only on those cells recognizable as neurons.
Relationship between the amount of the ‘germinal plasm’ and the number of primordial germ cells in Xenopus laevis
Authors: Tanabe Kazuyuki , Kotani Minoru
Published: April 2021

Tadpoles of Xenopus laevis completely lacking primordial germ cells were obtained by irradiating the vegetal hemisphere of early 2-cell eggs with u.v. (wavelength, 253·7 nm; dose, ca. 6000 ergs/mm2). An increasing number of primordial germ cells were observed as the stage at irradiation advanced from early 2-cell to early 4-cell stages. Furthermore, early 2-cell eggs irradiated with doses ranging from 750 to 6000 ergs/mm2 grew into tadpoles carrying a decreasing number of primordial germ cells in accord with the increase of the dose. On the other hand, tadpoles developed from eggs irradiated immediately after being centrifuged at 150 g for 1 min at early 2-cell stage to displace the ‘germinal plasm’ deeper into the cytoplasm, carried a considerable number of primordial germ cells. These facts were interpreted to suggest the presence of u.v.-sensitive germ cell determinant in the ‘germinal plasm’.

It was revealed by varying the area of irradiation that the number of primordial germ cells decreased in direct proportion to the increase of the area irradiated. It was concluded that the amount of the u.v.-sensitive material(s) contained in the ‘germinal plasm’ determined the number of primordial germ cells in tadpoles.
Surface coat on the epithelium of developing palatine shelves in the mouse as revealed by electron microscopy
Authors: Greene R. M. , Kochhar D. M.
Published: April 2021

The fine structure of the surface epithelium of developing palatine shelves in the mouse was studied from days 11 through 14 of gestation. Ruthenium red, a cationic stain used as an ultrastructural indicator of acid mucopolysaccharides, was employed to detect the presence of any surface coat.

Positive staining was first observed on day 12 of gestation and was seen to be present throughout the period of shelf elevation and fusion. Tt was seen over medial and lateral surfaces as well as the inferior to of vertical shelves. The surface coat was found to be present along the entire length of the shelf, extending superiorly up the medial and lateral epithelial borders until it abruptly disappeared.

Since this surface coat first appeared approximately 48 h prior to shelf elevation, it is suggested that its appearance may be associated with the ability of palatine shelves to undergo fusion as shown by previous in vitro experiments. The time of acquisition by the shelves of this ‘fusing potential’ is also in the range of 48 h before shelf elevation.
Cellular aspects of regeneration hormone influence inNereis diversicolor
Authors: Olive P. J. W.
Published: April 2021

The histology of caudal regeneration in Nereis diversicolor is described with special reference to the role of the cerebral ‘regeneration’ hormone. Wound healing is complete after 8 days; the regenerated stump of tissue then consists of the pygidium, associated anal cirri and a prepygidial region between the pygidium and the posterior margin of the last intact segment. The term segment blastema is used to refer to the cells from which all segmental structures are derived. The segment blastema is situated in the ventral posterior margin of the prepygidial region, and consists of transverse bands of cells with large nuclei (12 μm diameter) and prominent nucleoli. Segment anlagen are formed immediately in front of the segment blastema; the development of the anlagen is described, and six stages of development are defined.

The extent of caudal regeneration in different animals is best compared with reference to the total number and stage of development reached by the segment anlagen. During normal regeneration at 18 °C, segment anlagen are first formed after 8 days, and they continue to be formed at the same rate until at least the 21st day after caudal ablation. The oldest segments reach stage 6 after about 15 days of regeneration.

Wound healing, pygidium formation, and cirrus development and establishment of the segment blastema all occur in decerebrate animals following the loss of caudal segments, but segment anlagen formation is almost completely inhibited. Implantation of ganglia taken from intact donor animals into the coelom of decerebrate animals which have lost caudal segments initiates segment anlagen formation. The segment blastema of decerebrate animals remains competent to respond in this way for at least 15 days.

The regeneration hormone produced by the cerebral ganglion is essential for continued segment anlagen production throughout the 2nd and 3rd weeks of regeneration at 18 °C. Delayed decerebration leads to an arrest of anlagen production, and anlagen younger than stage 3 fail to develop further. Older anlagen (stages 4 and 5) are independent of the regeneration hormone and can continue to differentiate in its absence.
Tissue differentiation in ectopic grafts after cultivation of rat embryonic shieldsin vitro
Authors: Škreb N. , Crnek V.
Published: April 2021

Differentiation of rat embryonic shields in vitro is inferior to that obtained in grafts under the kidney capsule. To see whether the in vitro differentiation is stable or whether it can be improved in a better environment, rat embryonic shields, isolated on gestation days 8 and 9, were transplanted under the kidney capsule after a period of 7 or 14 days in vitro.

After transfer, some tissues appear in the kidney that never appear in vitro. Many but not all tissues appear more frequently in grafts than in vitro. Most tissues differentiate further in grafts than in vitro, though skeletal muscle, when cultivated for 14 days before transplantation, is an exception.

Thus the effect on differentiation of imperfect culture conditions can be counteracted, for some tissues but not all, by grafting to the kidney. The effect depends partly on the time spent in vitro before transfer.
Morphogenesis and growth of the definitive opisthonephros during metamorphosis of anadromous sea lamprey,Petromyzon marinusL
Authors: Ooi E. C. , Youson J. H.
Published: April 2021

The definitive opisthonephros of the adult lamprey, Petromyzon marinus L., develops during metamorphosis from the nephrogenic cord confined within a nephric fold and extending from the posterior tip of the larval opisthonephros to the cloaca. This development is initiated prior to the first signs of external metamorphosis and begins with the simultaneous appearance of clusters of cells scattered along the entire length of the cord. Proliferation of these cell clusters and their elongation to connect to the closely associated archinephric duct results in the formation of rudimentary nephron units. Subsequent development involves the formation of tubular lumina, branching of the tubules, and the participation of the proximal ends of the newly formed tubules in the formation of the single renal corpuscle. Growth in size of the kidney is the result of lengthening of the existing tubules through cell proliferation rather than through the addition of new nephrons. This growth appears to be at the expense of adipose tissue within the nephric fold. During later stages of metamorphosis, cell proliferation is more prevalent in the ventral part of the nephric fold where a parallel system of tubules develops.

The development of the definitive opisthonephros during metamorphosis of lamprey may prove to be a useful model for further studies of tissue differentiation and interaction during kidney development in vertebrates.
Proportional control of organelle position by a mechanism which similarly monitors cell size of wild type and conical form-mutantTetrahymena
Authors: Lynn Denis H.
Published: April 2021

Distance between mouthparts of dividing cells of wild type and conical form-mutant Tetrahymena thermophila (formerly T. pyriformis syngen 1) is directly proportional to cell size. This distance is related to cell length in both wild type and conical cells although the proportionality is different in each cell type. However, for both wild type and conical cells the distance between mouthparts is directly and similarly proportional to the product of cell length and cell width which is an estimate of cell size. Evidence has been obtained which suggests that the new mouthparts are positioned with reference to the anterior mouthparts rather than to either pole of the cell. Determination of the site of the new mouthparts is not related to the number of basal bodies between the two sets of mouthparts.
Re-evaluation of the presence of multiple haemoglobins during the ontogeny of the mouse
Authors: Shimizu Koji , Watanabe Tomomasa
Published: April 2021

In mice, three alleles, Hbbs, Hbbd and Hbbp, have been found at the β-chain locus of haemoglobin. Analytical polyacrylamide gel electrophoresis revealed the presence of almost the same four haemoglobin bands (E-I, E-II, E-III and X) in all of the lysates of peripheral blood cells from 12-day-old foetuses of C57BL/6J (Hbbs), A/He (Hbbd) and PON (Hbbp). All were embryonic-type haemoglobins; the most anodal band (X) seemed to be a product of polymerization of E-I. Electrophoretic patterns of the haemolysates from 12-day-old foetuses were not affected by alkylation with iodoacetamide or maleic anhydride. Almost the same electrophoretic patterns in subunit analysis, using acid starch and acid-urea polyacrylamide gels, were obtained in 12-day-old foetuses of C57BL/6J, A/He and PON. E-I comprised α-and x-chains, E-Il, α-and y-chains, and E-III, α-and z-chains.

In adults, two haemoglobin bands, s and Y, were present in the haemolysate of C57BL/6J, while three, dmaj, dmin and Y, existed in A/He, and three, pmaj, pmin and Y, in PON. All were adult-type haemoglobins. Haemoglobin Y, which was not demonstrable after alkylation of the haemolysates, seemed to be a product of polymerization of major haemoglobins (s, dmaj and pmaj). Each haemoglobin possessed common a-chains, while the β-chains of major haemoglobins were different from those of minor haemoglobins.

Developmental changes of the haemolysates from foetuses of C57BL/6J, A/He and PON were similar to each other. Haemolysates of the liver cells of developing foetuses contained only adult-type haemoglobins. Our techniques used here were not able to demonstrate the presence of foetal-type haemoglobins.
Feather-forming capacities of the avian extra-embryonic somatopleure
Authors: Dhouailly Danielle
Published: April 2021

Blocks of 12·5- or 13·5-day embryonic mouse upper-lip dermis were introduced under the ectoderm of the extra-embryonic area of 2-to 3-day chick or duck embryos. Two kinds of ectopic cutaneous appendages were produced : either arrested feathers alone, or arrested feathers and full-grown feathers. The former developed in the ectoderm overlying the implanted mouse dermal cells, the latter formed in their close vicinity, but contained host dermal cells exclusively.

Thus, avian extra-embryonic somatopleure, both ectoderm and mesoderm, possesses the information for feather development: the extra-embryonic ectoderm, if it is brought in contact with an appendage-forming dermis, is able to respond to the dermal induction by initiating feather morphogenesis; the extra-embryonic mesoderm, if it is experimentally transformed into a dense dermis, can express its feather-forming capacity by specifying feather tract morphology and barb-ridge number, thus leading to the achievement of feather morphogenesis.
Production of erythropoietic colony-forming units and erythrocytes during chick embryo development: an attempt at modelization of chick embryo erythropoiesis
Authors: Samarut J. , Jurdic P. , Nigon V.
Published: April 2021

The enumeration of erythropoietic colony-forming cells in vitro has allowed us to complete previous data on changes in the various erythroid cell populations during chick embryogenesis.

Erythrocytic colony-forming units in culture (CFU-cE) which are sensitive to avian erythropoietin appear in the blastoderm as soon as the 24th hour of development. They represent most likely precursors of the megalocytic erythropoiesis, and do not seem to derive from stem cells common with normocytic erythropoiesis.

Data concerning vitelline normocytic erythropoiesis were analysed in a kinetic model based on stochastic change of the stem cells. From this model it appears that 17−20 cell divisions are required for differentiation of erythrocytes from stem cells.
The central pathways of optic fibres in Xenopus tadpoles
Authors: Steedman J. G. , Stirling R. V. , Gaze R. M.
Published: April 2021

A cobalt chloride impregnation technique was applied to the optic nerve in Xenopus tadpoles and the central optic pathways were examined in cleared, whole-mounted preparations, and in thick sections. The overall plan of the optic input was visualized in relation to the outlines of the parts of the brain and details of the structure of the tectal optic neuropil, the neuropil of Bellonci and the basal optic neuropil were seen. The fibres in the main retinotectal tract maintained an orderly disposition with respect to each other, in contrast to the fibres of the basal optic tract, in which no order was apparent. Optic fibres were seen passing caudally from the region of the basal optic neuropil.
Effect of the T-mutation on histogenesis of the mouse embryo under the testis capsule
Authors: Fujimoto H. , YANAGISAWA K. O.
Published: April 2021

Mouse embryos homozygous for the T-mutation show abnormalities, severer at the posterior embryonic regions, by day 9 of gestation and die before day .11 in utero.

To analyse developmental potentiality of the T/T embryos, fragments of their anterior and posterior portions were grafted into the testes of adult T/ + mice, and examined histologically for the tissues formed after 1 month.

The grafted tissues of the T/T embryos grew beyond the destined lethal stage and gave rise to benign teratomas composed of mature tissues. Although there were some different features of the tissues formed in the teratomas derived from different portions and stages of the embryos, their types were essentially identical between wild-type and the mutant teratomas. Statistical analysis showed that frequency of the cartilage and/or bone formation was significantly lower in the posterior mutant teratomas. It cannot be concluded, however, that this difference is essentially caused by T-mutation. The main conclusion of present experiments is that grafted portions of T/T embryos have the potentiality to develop into teratomas containing derivatives of all three germ layers.
Chemotactic cell sorting inDictyostelium discoideum
Authors: Matsukuma S. , Durston A. J.
Published: April 2021

We made mixed mounds of vitally stained prestalk cells and unstained prespore cells, from Dictyostelium discoideum (Dd), and exposed these to external 3′,5′-cyclic-AMP (c-AMP) sources. We show that prestalk cells will sort out by moving directionally toward c-AMP sources held at < 10−5 M C-AMP. This is evidence for cell sorting via chemotaxis. We present arguments that the natural cell sorting, observed during Dd development, is also chemotactic to c-AMP.
The ontogeny of erythropoiesis in the mouse detected by the erythroid colony-forming technique: I. Hepatic and maternal erythropoiesis
Authors: Rich Ivan N. , Kubanek Bernhard
Published: April 2021

Employing the erythroid colony-forming technique, it is shown that throughout hepatic erythropoiesis in the mouse, the CFU-E population remains sensitive to erythropoietin. Maximum stimulation was achieved during this period using an erythropoietin concentration of 0·075 units/ml. The peak in the CFU-E concentration occurs between the 11th and 12th day while absolute values show a maximum on the 14th day of gestation. These results are discussed in terms of changing cell populations, both of erythropoietic precursors and hepatocytes from which it is concluded that at no time during foetal erythropoiesis does the CFU-E population change or become unresponsive to erythropoietin. The BFU-E population follows closely that of the CFU-E, but declines about 24 h earlier on the 16th day of gestation.

The effect of the foetus on the mother was also studied during the second half of pregnancy. During this period of natural perturbation both femoral and, in particular, splenic erythropoiesis are increased. However, during this time an erythropoietin concentration of 0-3 units/ml was required to maximally stimulate the CFU-E population derived from these tissues. The fact that both adult and foetal erythroid tissue maintain a rather constant requirement for erythropoietin for their growth in vitro, indicates that it is an intrinsic properly of the cells. It is concluded that increased maternal erythropoiesis is due to an increased oxygen requirement causing hypoxia due to the growing foetus.
Changes in protein synthesis during the development of Xenopus laevis
Authors: Ballantine J. E. M. , Woodland H. R. , Sturgess E. A.
Published: April 2021

Patterns of protein synthesis during the development of Xenopus were studied by twodimensional gel electrophoresis. Up to the end of the blastula stage we find no newly synthesized proteins which are not already made in the oocyte. The first new proteins are seen during gastrulation, and they increase in number during neurulation. Some of these are restricted to the ‘ectodermal’ region, and some to the ‘endodermal’ region of embryos divided into two parts. These new, region-specific proteins include a-actin. When the oocyte matures the number of detectable newly synthesized proteins decreases, reaching a minimum in the unfertilized egg. Some, such as β and γ-actin, re-appear at the end of cleavage. This could not be shown to be a recovery artifact. The relation of the total mRNA to these changes in protein synthesis was studied by translation in the lysed reticulocyte cell-free system. The mRNAs that code for oocyte proteins that cease synthesis in the unfertilized egg and re-appear in blastulae are nevertheless detectable in total RNA made from eggs. These proteins therefore seem to cease and resume synthesis through translational control. mRNAs for new proteins first appear after gastrulation, just when these proteins are first detected in vivo. This strongly suggests, though it does not prove, that new gene activity is involved. It is therefore likely that region-specific gene activity is already present by the gastrula stage of development, and has an impact on the most abundant kinds of proteins made in the embryo.
Cyclic changes in the cortical layer of non-nucleated fragments of the newt’s egg
Authors: Sawai Tsuyoshi
Published: April 2021

Various changes in the cortical layer of the amphibian egg have been observed during cleavage; for example, rounding up in the animal hemisphere, increase in stiffness of the surface and reactivity of the cortex to furrow-inducing cytoplasmic components. The three kinds of change occur synchronously with the cleavage cycle.

The present experiments were aimed at determining whether the above changes in the cortical layer are caused exclusively by the nucleus or autonomously by the cytoplasm. Uncleaved fertilized eggs of the newt, Cynopspyrrhogaster, were divided into two parts, one nucleated and one non-nucleated, by cutting with a fine glass needle. Special attention was paid to the behaviour of the non-nucleated fragments, where the above-mentioned changes were also observed. The cycle of these changes did not necessarily start synchronously with the cleavage cycle of the nucleated partner, but, once started, the rhythm of both cycles had almost the same timing. These results suggest that some change in the cortex necessary for cleavage furrow formation in the amphibian egg is brought about by cyclic change in the cytoplasm, independently of the nucleus.
The mechanism of somite segmentation in the chick embryo
Authors: Bellairs Ruth
Published: April 2021

The segmentation of somites in the chick embryo has been studied by transmission and scanning electron microscopy (stages 8–14). The segmental plate mesoderm consists of loosely arranged mesenchymal cells, whereas the newly formed somites are composed of elongated, spindle-shaped cells arranged radially around a lumen, the myocoele. The diameter of each somite is thus two cells plus the myocoele.

Two major factors appear to be responsible for the change in cell shape at segmentation: (1) Each prospective somite cell becomes anchored at one end to the adjacent epithelia (i.e. the neural tube, the notochord, the ectoderm, the endoderm or the aorta) by means of collagen fibrils. These fibrils are already present in the segmental plate before the somites begin to form.(2) A change in cell-to-cell adhesiveness causes the free ends of these cells to adhere to one another. (Bellairs, Curtis & Sanders, .1978). This adhesion is then supplemented by the development of tight junctions proximally in the somite.

Because it is anchored at both ends, each somite cell is under tension in much the same way as a fibroblast cell in tissue culture is under tension. Each somite cell therefore becomes elongated and the somite as a whole accommodates its general shape to that of the space available between the adjacent tissues. The arrangement of the cells in the more differentiated somites (stages 17–18) has also been examined and it has been found that the chick resembles Xenopus in that the myotome cells undergo rotation and become orientated in an anteroposterior direction.
Concanavalin A binding to amphibian embryo and effect on morphogenesis
Authors: Boucaut J. C. , Bernard B. , Aubery M. , Bourrillon R. , Houillon Ch.
Published: April 2021

The effect of Concanavalin A (Con A) on morphogenesis in Pleurodeles waltlii has been studied. Embryos were incubated with various concentrations of the lectin for a period of 6 days. Three stages of development were examined, late blastula, young gastrula and late gastrula.

In the presence of the lectin at a concentration of 200, 150 or 100 μg/ml morphogenic movements were delayed, altered and finally blocked. At lower concentrations, 50 or 25 μg/ml, there was a slight delay in gastrulation, but in some cases development was normal. These findings indicate that Con A exerted an inhibitory effect on amphibian morphogenesis and there is evidence that the lectin effect was concentration dependent.

The effects of Con A were specific since they were totally inhibited by α-methyl-D-man-nopyranoside (0 05 M). The viability of the 24 h lectin-treated embryos was demonstrated by washing experiments.

Labelled Con A binding to the embryos was investigated before and after discarding the vitelline membrane. The results suggest a direct interaction between Con A and the cell surface and this was confirmed by using fluorescein isothiocyanate Con A.
The morphology of fetal gonads of spontaneous mouse hermaphrodites
Authors: Whitten Wesley K. , Beamer Wesley G. , Byskov Anne Grete
Published: April 2021

The gonads of .107 spontaneous, chromosomal mosaic, day-15 fetal hermaphrodites derived from BALB/cWt strain male mice are described and photographs of seven gonads representative of the major types are presented. There were 16 ovaries, 15 testes, and 183 ovotestes. The ovotestes contained on the average more testicular tissue than ovarian, and the ovarian tissue was more frequently located at the gonad poles, particularly the craniad pole. There was no difference between left and right sides with regard to gonad type, but more pure gonads were found on the left than on the right side (21/10), Meioses were observed throughout the ovarian tissue and also in some testicular cords, particularly in the caudad pole of the gonad. Some meiotic figures contained sex vesicles.

The significance of these findings is discussed in relation to several aspects of sex determination.
Interactions between optic fibres controlling the locations of their terminals in the goldfish optic tectum
Authors: Cook Jeremy E.
Published: April 2021

Removal of the caudal half of a goldfish optic tectum induces optic fibres from the entire contralateral retina to terminate retinotopically within the remaining half. This compression has been viewed by some as the result of competition between the fibres and by others as a consequence of changes, induced by the surgery, in tectal labels guiding fibres to terminal sites.

To distinguish between these possibilities, the time-course of compression has been measured by electrophysiological mapping of the visual projection. In some fish, fibres terminating in the rostral half-tectum remained intact when the caudal half was removed. In others, the optic nerve was cut at the time of tectal surgery: even after its regeneration into a half-tectum, optic terminals were first detected in the regions they normally occupy. The subsequent reorganization was gradual and retinotopic order was maintained. However, it was slower where some fibres had never been cut.

In a third series the nerve was cut 18 days before the tectal halving to reveal any dependence of compression on progressive changes in the halved tectum; but its time-course from nerve section was found to be independent of the time within the regeneration period at which the tectum was halved.

In a fourth series the nerve was cut at the time of tectal halving and then cut again after 85−97 days when compression was complete to reveal any permanent change in the halved tectum. No change was evident: the previous compression did not preclude subsequent regeneration of an uncompressed projection and its gradual recompression as before.

In a fifth series, repeated crushing of fibres normally ending in the missing caudal tectum temporarily prevented compression among the remainder, while crushing of fibres destined for rostral tectum caused transposition of the remaining projection to the rostral half.

Surgically induced changes in the labels which are thought to guide growing fibres to their normal tectal regions do not account for these results. Indeed, this guidance persists unchanged for fibres regenerating a second time after compression. Since compression is delayed while certain fibres are withheld, it appears instead to be the direct result of competition between the fibres. The maintenance of retinotopic order in compression, despite unchanged tectal guidance, may require selective interactions between fibres from different retinal regions which could contribute to the refinement of the normal visual projection.
The visuotectal projections made by Xenopus ‘pie slice’ compound eyes
Authors: Willshaw D. J. , Fawcett J. W. , Gaze R. M.
Published: April 2021

In Xenopus embryos at stages 28–32 one quarter to one third of the left eye rudiment was replaced by a similarly sized piece from a different position in a right eye rudiment. Three groups of operations were performed: (1) temporal tissue was placed in a nasal position; (2) nasal tissue was placed temporally; (3) ventral tissue was placed dorsally. The visuotectal projections made by these ‘pie-slice’ compound eyes were assessed electrophysiologically at 1 week to 6 months after metamorphosis. Of 97 animals, 71 yielded interpretable projections. In most cases two projections could be identified in each map. One, ascribed to the host part of the retina, extended over the entire tectal surface mapped. The other, identified as that from tissue derived from the pie-slice graft, projected to the tectum in register with that part of the host retina which matched the pie-slice in origin. Both projections were well ordered, and in the orientation expected if the corresponding piece of retinal tissue had participated in a normal projection. Consistent differences in pie-slice size and tectal coverage between the three groups were found. Pie-slices of nasal origin gave maps showing that they came from a relatively large portion of the retina and projected to a relatively large amount of the tectum; those of temporal origin occupied relatively small amounts of field and tectum. It was concluded that these results are further evidence for the existence of positional markers in the retina which are used for the assembly of the retinotectal map.
Effects of delayed amputation on denervated forelimbs of adult newt
Authors: Liversage Richard A. , McLAUGHLIN Danielle S.
Published: April 2021

Left forelimbs of adult newts were repeatedly denervated prior to and following amputation. Limb amputations were performed at 7–, 14–, 21–, 27– and 45-day intervals after the initial denervation. Regeneration was found in the sham-denervated and control animals but did not occur in any of the experimental cases; instead cicatrix formation and dermal wound healing ensued. Soft-tissue dedifferentiation was evident, however. We conclude from these results that forelimb regeneration in the adult newt is completely nerve dependent (for growth).
A contractile ring-like mechanism in wound healing and soluble factors affecting structural stability in the cortex ofXenopus eggsand oocytes
Authors: Merriam R. W. , Christensen Kathy
Published: April 2021

Holes or tears have been made in the surface of unfertilized Xenopus eggs or oocytes in various buffered media and the surface response to the wound has been observed with the light microscope.

In the presence of calcium ion in the medium, a pigmented ring appears around the wound and constricts in purse-string fashion until the hole is closed. A highly pigmented scar remains. We show that the surrounding pigmented cortex is moved over the denuded cytoplasm when wound healing closes a large excision wound in the pigmented surface. This movement of surface is consistent with a model of a purse string, closing the hole by pulling existing surface over the denuded cytoplasm.

The presence of cytochalasin B in the medium inhibits wound healing completely. The sensitivity to the antibiotic is similar to that of the contractile ring in cytokinesis.

Wounds made in the surface of ripe ovarian oocytes do not heal in the presence of calcium ion. The healing mechanisms, or their sensitivity to calcium, thus appear during meiotic maturation or ovulation.

The egg cortex and membrane around wounds dissociate in the absence of calcium or in the presence of cytochalasin B. The cell cortex of oocytes also dissolves around wounds even in the presence of calcium. This cortical dissolution will not occur in the isolated cortex and thus requires soluble cytoplasmic factors. Models are proposed to explain these observations.
Melanophore differentiation inXenopus laevis, with special reference to dorsoventral pigment pattern formation
Authors: Ohsugi Kojune , Ide Hiroyuki
Published: April 2021

During the development of Xenopus laevis, after stage 26, a large number of dopa-positive cells were observed in the ventral region. Electron microscopic observations revealed that these cells became localized in the epidermal layer and contained premelanosomes. In cultured ventral skin, fully matured melanophores appeared.

These results strongly suggest that a large number of melanoblasts are present in the ventral epidermis and remain there without final differentiation into melanized melanophores. Thus the positional difference of melanoblasts differentiation mainly contributes to dorsoventral pigment pattern formation of Xenopus laevis.
Blastema formation and cell division during cockroach limb regeneration
Authors: Truby Paul R.
Published: April 2021

Recent models of pattern formation in insects have been derived largely from observations on regenerated cuticular patterns. Such models make assumptions about the behaviour of the underlying epidermal cells, their movement and patterns of cell division. The present study, designed to test these assumptions, looks at the patterns of wound healing and cell division after amputation at the trochanter-femur joint of the metathoracic leg in the cockroach. It shows that the wound is closed by cell migration and that regeneration occurs by dedifferentiation of the trochanter and distal coxa to form a blastema which grows and redifferentiates to form the new limb. The extent of the spread of dedifferentiation is confirmed by a scanning electron microscope study of the coxa after the moult following amputation. The results highlight the need for a greater knowledge of cell behaviour during pattern formation before we can begin to understand the processes involved in pattern formation.