bluuebunny/crossref_metadata_2025_split huggingface dataset:
Somitogenesis in amphibia : IV. The dynamics of tail development
Authors: Elsdale Tom , Davidson Duncan 
Published: April 2021

ABSTRACT
Following neurulation, the frog segments c.40 somites and concurrently undergoes a striking elongation along the anteroposterior axis. This elongation (excluding the head) is largely the result of a presegmental extension of posterior tissue with a lesser contribution from the extension of segmented tissue.
Presegmental extension is entirely the result of activity within a narrow zone of extension that occupies the central region in the tail bud. Within the zone of extension, a minimum of six prospective somites undergo an eightto ten-fold extension along the axis. The zone passes posteriorly across the tissue of the tail tip. The anterior of the tail bud contains three extended prospective somites in the course of segmentation. The anterior boundary of the zone of extension coincides in space exactly with the anterior boundary of the zone of abnormal segmentation that results from temperature shock. This means that extension ceases immediately before the sudden tissue change associated with segmentation.
Postnatal muscle fibre histochemistry in the rat
Authors: Ho K. W. , Heusner W. W. , Huss J. Van , huss W. D. Van 
Published: April 2021

ABSTRACT
Histochemical techniques were used to study the postnatal muscle fibre differentiation patterns in the plantaris and soleus muscles of male Sprague-Dawley rats. Nine groups of animals (n = 6/group) were killed at 1, 6, 11, 16, 21, 26, 31, 36, and 140 days of age. Serial transverse sections of the two muscles were stained with H & E, NADH-D, and myofibrillar ATPase with acid (pH 4·35) or alkali (pH 10·4) preincubation. In each of the age groups, all available fibres across the muscle sections were classified. Obtained data show that fibre types are basically undifferentiated at birth in both muscles.
In the plantaris muscle there are about 99 % type IIA and less than 1 % type I fibres at 6 days of age. Type IIB fibres can be identified at 11 days of age. There are increases in the percentages of type I fibres (from 0·7 % to 3·5 %) and type IIB fibres (from 1·1 % to 6·5 %) between 6 and 11 days and between 16 and 21 days respectively. By 36 days of age the relative numbers of type IIA, IIB, and type I fibres in the plantaris are approximately 80 %, 14 %, and 6 %, respectively. A gradual change in fibre-type composition continues until it becomes 47 % for type IIA, 43 % for type IIB, and 10 % for type I at 140 days of age.
In the soleus muscle there are approximately 73 % type IIA and 26 % type I fibres at both 6 and 11 days of age. However, type IIA fibres decrease to 44 % and type I fibres increase to 56 % at 16 days of age. This rapid shift in fibre composition continues up to 31 days of age when the distribution becomes 25 % for type IIA and 74 % for type I fibres. Thereafter, the differentiation rate is much slower. At 140 days of age, there are 17 % type IIA and 83 % type I fibres in the soleus muscle.
The results of this study show that the fibre populations in the plantaris and soleus muscles of the rat undergo a postnatal differentiation process. In both muscles the adult fibre population is established by 140 days of age. Although relatively rapid increases of type I and type IIB fibres occur in the plantaris during the second and third weeks of life, differentiation in that muscle appears to be an essentially continuous process. There is a notable shift in the fibre composition of the soleus muscle during the second postnatal week. Differences between the patterns of differentiation in the two muscles are apparent.
Further analysis of the effect of ultra-violet irradiation on the formation of the germ line inXenopus laevis
Authors: Thomas V. , Heasman J. , Ford C. , Nagajski D. , Wylie C. C. 
Published: April 2021

ABSTRACTUltra-violet (u.v.) irradiation of the vegetal pole of newly fertilized eggs has three documented effects: reduction of primordial germ cells (PGCs), cytological damage to the vegetal hemisphere and disruption of the normal mechanism by which the vegetal yolk mass induces the formation of the dorsal axis of the embryo.In this study, we find that 90° rotation of the egg for various periods after irradiation rescues the dorsal axial structures but does not restore the number of PGCs found in the dorsal mesentery of the gut; neither is there any correlation between reduced numbers of PGCs and disruption of cleavage at the vegetal pole. We therefore conclude that the effect on the germ line is separate from the other two phenomena.Secondly, 90° rotation of non-irradiated eggs was found to significantly reduce germ cell numbers migrating in the dorsal mesentery of the gut.
H-2 antigens as markers of cellular genotype in chimaeric mice
Authors: Ponder B. A. J. , Wilkinson M. M. , Wood Maureen 
Published: April 2021

ABSTRACTWe describe an immunohistochemical method, using monoclonal anti-H-2 antibodies, for demonstrating H-2 antigens in cryostat sections of a variety of mouse tissues. Double staining allows simultaneous demonstration of both cell populations in tissue sections from H-2b H-2k aggregation chimaeras.
Evidence for specific feedback signals underlying pattern control during vertebrate embryogenesis
Authors: Cooke Jonathan 
Published: April 2021

ABSTRACTExperiments are described in which sectors including dorsolateral mesoderm from early-neurula-stage amphibian embryos are grafted to the mid-ventral region of gastrula-stage hosts. The grafted tissue pursues an autonomous developmental sequence, though integrated into the host mesodermal mantle, so that such embryos develop a ventral strip of ectopic somite tissue, occasionally with a pronephric formation at one side. When the proportions in which mesodermal tissue has been assigned to the four basic territories of the host’s mediolateral pattern are assayed, a significant deficit in somite is characteristically found, though the phenomenon is variable in magnitude. It seems that the size of the host’s prone-phric territory may be diminished in a similar way, if an earlier differentiating ectopic pronephros is already joined to the system. These phenomena are discussed in relation to theories of biological pattern formation.
Transplantation of turtle embryonic thymus, into quail embryo : colonization by quail cells
Authors: Vasse J. 
Published: April 2021

ABSTRACT
Turtle (Emys orbicularis L. ) embryo thymuses grafted in the somatopleure or onto the quail embryo chorioallantoic membrane developed in these heterotopic sites for 2–12 days.
When the thymus was removed from embryos at early stages such that no thymocytes were yet present during normal development, epithelial cells with mitoses were observed in the explants but no turtle thymocytes developed whatever the duration of explantation. An extrinsic origin of lymphoid precursor cells can explain such results. Quail lymphoid-like cells distinguishable from turtle cells by their nuclear structure began entering the explants 5 days after grafting. Their number increased progressively until the 12th day, when all the grafts were retrieved.
When an already lymphoid thymus was removed from embryos at later stages, turtle thymocytes remained fairly abundant in the explants until 5 days. Beyond this period, they gradually disappeared. After 11–12 days, none were left and only epithelial tissue from the turtle was present, showing excellent development. Quail lymphoid-like cells entered this more mature thymus following the same time course as they did in the early rudiment.
Thus we observed no difference between attraction of quail lymphoid cells by the precolonization thymic epithelium or by the lymphoid thymus.
Brachial muscles in the chick embryo: the fate of individual somites
Authors: Beresford Bonnie 
Published: April 2021

ABSTRACT
The wing and wing-associated muscles of the shoulder and thorax in the bird all cleave from common myogenic masses in the developing wing bud and are referred to collectively as brachial muscles. In this study the precise embryonic origin of the brachial muscles was determined using chick-quail chimaeras. Such chimaeras consisted of a graft of one somite taken from a 2-day quail donor embryo transplanted to the equivalent location in a 2-day chick host embryo. The chimaeras were analysed at 9·5-10·0 days in ovo to determine the location of the grafted cells and therefore the structures that were derived from the transplanted somite. The somites that were studied in this manner were somites 13 to 23 inclusive. The results show that only somites 16 to 21 inclusive contribute cells to the brachial musculature; moreover, the cells from a given somite are not distributed randomly among the brachial muscles but populate specific muscles only: thus it has been possible to map the somitic origin of individual brachial muscles. Moreover, there is an indication that each somite plays a unique role in the development of the brachial muscles.
Non-random X-chromosome inactivation in mouse X-autosome translocation embryos—location of the inactivation centre
Authors: Rastan Sohaila 
Published: April 2021

ABSTRACTX-chromosome inactivation was investigated cytologically using the modified Katida method which differentially stains inactive X-chromosome material at metaphase in balanced -day female embryos heterozygous for four X-autosome rearrangements, reciprocal translocations T(X;4)37H, T(X;11)38H and T(X;16)16H (Searle’s translocation) and the insertion translocation Is(7;X)1Ct (Cattanach’s translocation). In all cases non-random inactivation was found. In the reciprocal translocation heterozygotes only one translocation product ever showed Kanda staining. In addition in a proportion of cells from T(X;4)37H, T(X;11)38H and Is(7;X)1Ct the Kanda staining revealed differential staining of X-chromosome material and attached autosomal material within the translocation product.In a study of -day female embryos doubly heterozygous for Searle’s translocation and Cattanach’s translocation two unbalanced types of embryo were found. In one type of unbalanced female embryo of the karyotype 40(X(7)/X16;16/16) no inactivated X-chromosomal material is found. A second unbalanced type of female embryo, of the presumptive karyotype 40(X(7)/XN;16x/16) was found in which two inactivated chromosomes were present in the majority of metaphase spreads. A simple model for the initiation of X-chromosome inactivation based on the presence of a single inactivation centre distal to the breakpoint in Searle’s translocation explains these findings.
20-hydroxyecdysone stimulates tissue-specific yolk-protein gene transcription in both male and femaleDrosophila
Authors: Bownes Mary , Blair Mairearad , Kozma Robert , Dempster Maureen 
Published: April 2021

ABSTRACTThe yolk polypeptides of Drosophila are normally synthesized in the fat body and ovarian follicle cells of adult females. In response to 20-hydroxyecdysone males synthesize yolk polypeptides. The actual level of yolk polypeptides synthesized in males is not always a direct reflection of the YP-transcripts present. Initially YP-transcripts are efficiently translated into polypeptides whereas later they are not and the YP-transcripts can have a half-life of less than 8h in males. We suggest that the expression of the genes coding for the yolk polypeptides in males may be regulated at transcriptional and translational levels. Treatment of females with 20-hydroxyecdysone leads to a transient increase in YP-transcript accumulation, but the response is difficult to assess in whole flies due to the high variability in transcript levels during normal development.Analysing the response to 20-hydroxyecdysone at the level of specific tissues shows that transcript accumulation is dramatically increased in body walls (fat-body cells, epidermis and oenocytes) of both males and females. Gut, Malpighian tubules, testis and ovaries are not affected. Treatment of females with 20-hydroxyecdysone followed by measuring YP-transcript accumulation over the next 24 h in ovaries and body walls separately, confirms that only body walls respond to the hormone. There is an increase in yolk-polypeptide synthesis during the period of increased YP-transcript accumulation in females.We conclude that the response of the YP-genes to 20-hydroxyecdysone is tissue-, but not sex-specific.
Dorsalization and neural induction: properties of the organizer inXenopus laevis
Authors: Smith J. C. , Slack J. M. W. 
Published: April 2021

ABSTRACTWe have studied the action of the organizer in Xenopus laevis using grafts labelled with horseradish peroxidase (HRP). Orthotopic grafts of the dorsal marginal zone (the organizer) from an HRP-labelled embryo into an unlabelled host showed that this region contributes to the anterior archenteron wall, to the entire craniocaudal extent of the notochord and to a few cells in the somites. Little or no contribution was made to the neural tube. Orthotopic grafts of the ventral marginal zone (the tissue that responds to a grafted organizer) indicated that it only contributes to the posterior half of the embryo. Within this region it spreads around the entire ventrolateral mesoderm, occasionally contributing a few cells to the somites. The posterior endoderm was also heavily labelled.When the dorsal marginal zone from an HRP-labelled embryo was inserted into a slit cut in the ventral marginal zone of an unlabelled host a mirror-symmetrical double-dorsal duplicated embryo resulted, in which only the notochord and a few cells in the somites of the secondary embryo were derived from the graft. The bulk of the secondary somites was, therefore, derived from host ventral marginal zone tissue which normally makes very little contribution to the somites. This indicates that host ventral marginal zone becomes dorsalized by the graft. The neural tube of the secondary embryo was also unlabelled, showing that it was induced by the influence of the graft on the overlying ectoderm, which normally forms ventral epidermis.We have also grafted ventral marginal zone tissue into a slit cut into the dorsal marginal zone of a host embryo. HRP-labelled tissue was grafted into an unlabelled embryo and vice versa. This graft did not produce a double ventral embryo and this reinforces the traditional view that the dorsal marginal zone is a special signalling region. Instead, the resulting embryos usually had a twinned notochord with the graft tissue in between, differentiated as somite. This confirms that juxtaposing ventral and dorsal marginal zone ‘dorsalizes’ the ventral tissue but does not affect the dorsal tissue which differentiates, as usual, as notochord. Thus, our results allow us to conclude that the organizer mediates two distinct interactions in bringing about the formation of duplicated embryos. The first is dorsalization of adjacent ventral mesoderm and the second is the induction of neuroepithelium from ectoderm overlying the new archenteron roof.
Homeotic transformations of the abdominal segments ofDrosophilacaused by breaking or deleting a central portion of the bithorax complex
Authors: Morata Gines , Botas Juan , Kerridge Stephen , Struhl Gary 
Published: April 2021

ABSTRACTIn Drosophila, genes in the centromere-proximal portion of the bithorax complex (BX-C) have been shown to control the development of the metathorax, and parts of the mesothorax and first abdominal segment. Here, we explore the roles of genes positioned more distally by examining the larval and adult phenotypes caused by a breakpoint and deletion in the middle of the complex. We find that both aberrations affect only abdominal segments, transforming the more anterior segments towards the first abdominal segment, and the remaining segments into a graded series of novel segment types which are partially transformed towards more anterior abdominal segments. Moreover, the adult transformations, which we have observed in somatic clones of mutant cells, are in close accord with the transformations observed in mutant first instar larvae, and appear to be expressed in a cell autonomous fashion. We discuss these results in the light of current views of the organization and function of the complex.
Development and motor innervation of a distal pair of fast and slow wing muscles in the chick embryo
Authors: Laing N. G. , Lamb A. H. 
Published: April 2021

ABSTRACT
The chick wrist muscle ulnimetacarpalis dorsalis (umd) has two heads. Using myosin ATPase and acetylcholinesterase (ACh.E) staining it was shown that one of the heads is composed almost entirely of acid-stable muscle fibres with multiple end plates (slow muscle fibres) and the other of acid-labile fibres with single end plates (fast muscle fibres). The development of the muscle was traced from E7 (Stage 32-33) when it is a relatively homogeneous mass, to E18. The two heads of the muscle are first distinguishable, by ATPase staining, at E8 (Stage 33-34) prior to their cleaving. Both heads of the muscle are innervated by motoneurons positioned laterally in the lateral motor column in spinal segments 15 and 16. There is no observable difference in the positions of the motoneuron pools to the two heads. At E18 the motoneurons innervating the fast head tend to be slightly larger than those innervating the slow head.
Epithelial enhancement of connective tissue differentiation in explanted somites
Authors: Swalla Billie J. , Solursh Michael 
Published: April 2021

ABSTRACT
This paper examines the differentiation of somites from stage-16 or -17 chick embryos cultured with or without notochord in explant cultures. Histological sections of the cultures were stained with a trichrome stain to identify the different kinds of connective tissues formed. Both anterior and posterior (epithelial) somites made muscle, cartilage and loose connective tissue in explant culture. The extent of cartilage differentiation was enhanced by the presence of the notochord, confirming earlier studies. The presence of 1 mM-dibutyryl cAMP in the culture medium increased the amount of muscle found in the explants but by histological criteria did not inhibit chondrogenesis, contrary to earlier reports. The addition of quail ectoderm to the explants stimulated loose connective tissue to form directly beneath it, suggesting for the first time a role of the ectoderm in dermatome differentiation. These results suggest that the epithelial somite has the capacity to differentiate into all three connective tissue types even before it has separated into sclerotome and dermamyotome. The relative amount of different connective tissue types can be influenced by environmental factors, such as adjacent epithelia like the notochord or ectoderm.
The nature of intercellular coupling within the preimplantation mouse embryo
Authors: Goodall H. , Johnson M. H. 
Published: April 2021

ABSTRACT
The changing nature of intercellular coupling during the 4- and 8-cell stages of mouse early development has been investigated by iontophoretic injection of carboxyfluorescein, horseradish peroxidase and current into individual blastomeres in either the intact embryo or after their disaggregation and reaggregation into pairs. Coupling junctions that allowed only molecules of low molecular weight (putative gap junctions) were found not to appear until 2– 5 h beyond the 3rd cleavage division (8-cell stage). However, intercellular junctions that were not size selective were detected in intact embryos only throughout the 4- and 8-cell stages. It is proposed that this junctional communication results from the persistence of midbodies through all or part of the two, and in a few cases the three, cell cycles following their formation at the first and second cleavage divisions. We conclude that the cells of the early mouse embryo may be linked in a more extensive syncytial network than was hitherto suspected.
La compétition entre les éléments osseux du zeugopode de Poulet
Authors: Hampé par Armand 
Published: April 2021

ABSTRACT
En traitant les bourgeons de patte de Xenopus avec une substance toxique, Tschumi (1954) observe une réduction progressive du nombre de doigts à mesure que la dose de substance toxique augmente. C’est d’abord le premier doigt qui disparaît, puis le quatrième et ensuite le deuxième. Le troisième doigt subsiste en dernier lieu. Cette règle s’observe aussi chez les Oiseaux. L’irradiation aux rayons X du bourgeon de patte par M. Schué (1951) conduit à une perte successive des 1er, 4ème, 2ème et 3ème doigts; cet ordre est toujours respecté. Étant donné que tous les éléments osseux présumés sont touchés et partiellement détruits par l’irradiation, on peut admettre que tous les éléments cellulaires disponibles, quelle que soit leur origine, sont mobilisés par priorité vers la formation du troisième doigt. S’il y en a davantage, ce sont les 2ème, 4ème et 1er doigts qui seront constitués.
Quelques précisions sur la cinématique de la ligne primitive chez le Poulet
Authors: Vakaet par L. 
Published: April 2021

ABSTRACT
Isolated anterior and posterior fragments of very young blastoderms at the primitive-streak stage, transected in front of the streak, have been cultured for 24 hours. The posterior fragments were marked by carbon particles. Our results stress the importance, during bird gastrulation, of the transition region between the area opaca and the area pellucida, especially at the site of formation of the primitive streak. Considering this region as an extension centre, forward and backward, of the primitive streak enables us to understand the radically opposed opinions of Pasteels and Spratt by furnishing illustrations of the influence of in vitro culture circumstances. We have seen, indeed, that under Spratt’s marking conditions on whole blastoderms, absence of epiboly practically inhibits all forward movement in the blastoderm. On the contrary, however, this last tendency is seen very clearly in our experiments where, by releasing it from the hindrance formed by the anterior part of the blastoderm in vitro, we enable the streak to stretch forward. Our results, therefore, confirm the findings of Pasteels with regard to his controversy with Spratt and show that the anterior end of the very young primitive streak already contains the material of the future Hensen’s node. Using Spratt’s technique we arrive at a confirmation of Pasteels’s opinions based on in ovo staining.
It seems worth while to note that our experiments and those of our predecessors tend to localize the ‘organization centre’ in the region where earlier the formation of the endophyll started and as a consequence its contact with the ectophyll is the most precocious and the most intimate. This is stated without any implication as to the exact mode of formation of the inner germ layer. On the other hand, this point in the midst of the primitive streak is the point of convergence of Hensen’s node and the posterior node, and the place where the tail-bud will arise, as we have previously shown (Vakaet, 1960).
The Effect of Benzimidazole on the Differentiation of Ectodermal Explants from the Gastrulae of Xenopus laevis
Authors: Billett F. , Brahma S. K. 
Published: April 2021

ABSTRACT
The survival of ectodermal explants taken from early to late gastrulae of Xenopus laevis does not appear to be affected by culturing them, for up to 3 days, in solutions containing 50–100 μg./ml. of benzimidazole. This compound does not prevent neural differentiation. Cell damage only becomes apparent after about 48 hours when it is confined to the differentiating neural tissues and the surrounding cells. The histological appearance of the ectoderm cells and the fact that they develop functional cilia suggest that they are not affected by the treatment. The results suggest that tissue in the process of differentiation is highly susceptible to benzimidazole. This susceptibility may be a consequence of the high rate of turnover of RNA in differentiating tissue.