bluuebunny/crossref_metadata_2025 huggingface dataset:
Pax6 regulates specification of ventral neurone subtypes in the hindbrain by establishing progenitor domains
Authors: Takahashi Masanori , Osumi Noriko
Published: April 2021

Recent studies have shown that generation of different kinds of neurones is controlled by combinatorial actions of homeodomain (HD) proteins expressed in the neuronal progenitors. Pax6 is a HD protein that has previously been shown to be involved in the differentiation of the hindbrain somatic (SM) motoneurones and V1 interneurones in the hindbrain and/or spinal cord. To investigate in greater depth the role of Pax6 in generation of the ventral neurones, we first examined the expression patterns of HD protein genes and subtype-specific neuronal markers in the hindbrain of the Pax6 homozygous mutant rat. We found that Islet2 (SM neurone marker) and En1 (V1 interneurone marker) were transiently expressed in a small number of cells, indicating that Pax6 is not directly required for specification of these neurones. We also observed that domains of all other HD protein genes (Nkx2.2, Nkx6.1, Irx3, Dbx2 and Dbx1) were shifted and their boundaries became blurred. Thus, Pax6 is required for establishment of the progenitor domains of the ventral neurones. Next, we performed Pax6 overexpression experiments by electroporating rat embryos in whole embryo culture. Pax6 overexpression in the wild type decreased expression of Nkx2.2, but ectopically increased expression of Irx3, Dbx1 and Dbx2. Moreover, electroporation of Pax6 into the Pax6 mutant hindbrain rescued the development of Islet2-positive and En1-positive neurones. To know reasons for perturbed progenitor domain formation in Pax6 mutant, we examined expression patterns of Shh signalling molecules and states of cell death and cell proliferation. Shh was similarly expressed in the floor plate of the mutant hindbrain, while the expressions of Ptc1, Gli1 and Gli2 were altered only in the progenitor domains for the motoneurones. The position and number of TUNEL-positive cells were unchanged in the Pax6 mutant. Although the proportion of cells that were BrdU-positive slightly increased in the mutant, there was no relationship with specific progenitor domains. Taken together, we conclude that Pax6 regulates specification of the ventral neurone subtypes by establishing the correct progenitor domains.
Regulation ofAPETALA3floral homeotic gene expression by meristem identity genes
Authors: Lamb Rebecca S. , Hill Theresa A. , Tan Queenie K.-G. , Irish Vivian F.
Published: April 2021

The Arabidopsis APETALA3 (AP3) floral homeotic gene is required for specifying petal and stamen identities, and is expressed in a spatially limited domain of cells in the floral meristem that will give rise to these organs. Here we show that the floral meristem identity genes LEAFY (LFY) and APETALA1 (AP1) are required for the activation of AP3. The LFY transcription factor binds to a sequence, with dyad symmetry, that lies within a region of the AP3 promoter required for early expression of AP3. Mutation of this region abolishes LFY binding in vitro and in yeast one hybrid assays, but has no obvious effect on AP3 expression in planta. Experiments using a steroid-inducible form of LFY show that, in contrast to its direct transcriptional activation of other floral homeotic genes, LFY acts in both a direct and an indirect manner to regulate AP3 expression. This LFY-induced expression of AP3 depends in part on the function of the APETALA1 (AP1) floral homeotic gene, since mutations in AP1 reduce LFY-dependent induction of AP3 expression. LFY therefore appears to act through several pathways, one of which is dependent on AP1 activity, to regulate AP3 expression.
An experimental approach to the development of the ear capsule in the turtle, Chelydra serpentina
Authors: Toerien M. J.
Published: April 2021

With the exception of part of the floor which is of basal plate origin, the cartilaginous ear capsule is absent following complete extirpation of the otocyst at the 12-20 somite stages. Cartilaginous structures occupying the metotic fissure are similarly absent. A metotic cartilage is present in Chelonia and develops independently of the ear capsule. The full development of the stapes footplate is inhibited by the absence of the ear capsule.
The energetics of cleavage in Planorbis exustus
Authors: Sherbet Gajanan V. , Lakshmi M. S.
Published: April 2021

The effect of sodium azide on the processes of cleavage in Planorbis exustus has been studied. The phase of cleavage division at which treatment is begun and the delay caused in subsequent divisions have a definite relationship to each other. The delay caused by azide, after it becomes apparent, does not progressively increase but is maintained. The results are discussed from the point of view of the energy mechanism involved. A reservoir system, probably of phosphorylated compounds, seems to operate. When carbohydrate metabolism is selectively inhibited at some point in the Embden-Meyerhof pathway, the embryos seem to be capable of metabolizing fats for the purposes of deriving energy for the cleavage processes.
An experimental approach to the problem of the derivation of the vaginal epithelium
Authors: Forsberg John-Gunnar
Published: April 2021

In earlier papers the present author (Forsberg, 1963, 1965a, b;Forsberg & Olivecrona, 1964) has presented studies of the derivation and differentiation of the vaginal epithelium by morphological, histochemical and autoradiographic methods and by counts of mitotic rates. These investigations favour the view that the vaginal epithelium in mouse and rat has a dual origin: the anterior part being derived from the Müllerian epithelium and the posterior part from the sinus epithelium. This means that in these species the pseudostratified columnar Müllerian epithelium in the vaginal region undergoes a transformation into a stratified squamous epithelium. The possible mechanism behind this transformation has been discussed (Forsberg & Olivecrona, 1965). Results from estradiol treatment of neonatal mice during the differentiation of the vaginal epithelium support the above-mentioned investigations. (For a detailed review on the problem of the derivation of the vaginal epithelium, see Forsberg, 1963.)
Further studies of the effects of deprivation of sulfate on the early development of the sea urchin Paracentrotus lividus
Authors: Immers J. , Runnström J.
Published: April 2021

The morphological effects of sulfate-free medium on sea urchin embryos were described in detail by Herbst (1904). Further studies were carried out by Lindahl (1936,1942). He was the first to consider metabolic aspects of the rôle of sulfate in the development of the sea urchin. Immers (1956, 1959, 1961a and b, 1962) studied the distribution and function of acid mucopolysaccharides in early developmental stages of sea urchins, mainly Paracentrotus lividus. A dominant group of these acid polysaccharides are sulfated. Their location in the blastocoel, in the hyaline layer and in the lumen of the intestine could be demonstrated by staining of sectioned specimens with the ferri-acetic reagent of Hale (1946). In blastulae or gastrulae raised in sulfate-free sea water these regions are negative with respect to Hale staining (Immers, 1961b). On the other hand, the ectodermal nuclei of the animal region of the embryos are stained with the Hale reagent although the nuclei of the vegetal region remained unstained (l.c.).
Histological studies of whisker regeneration in the hooded rat
Authors: Oliver R. F.
Published: April 2021

A histological study has been made of the follicular changes which occur in vibrissa follicles both after the removal of the dermal papilla alone and the removal of various lengths of follicle root (‘root ends’). The dermal papilla of the vibrissa follicle is not always a discrete and permanent entity, as it has been suggested to be in the feather follicle, since it can be regenerated. No whisker is produced from a follicle or follicle remnant unless a dermal papilla is first regenerated. Dermal papillae regenerate by tissue reorganization at, or just above, the puncture in the base of, or the cut across, the capsule. After removal of the dermal papilla alone, a new papilla of apparently normal size is regenerated, but dermal papillae which regenerate after removal of root ends are smaller than normal. Examination of follicles after the removal of root ends demonstrates that the regeneration of dermal papillae and then whiskers occurs only within the lower third of the vibrissa follicle; there is little or no permanent lengthening, or shortening, of the follicle remnant—whether whiskers are regenerated or not. However, lengths of follicle remaining after removing root ends from within the upper two-thirds of the follicle persist—even though dermal papillae do not regenerate and no fibre production occurs. The histological evidence strongly suggests that cells from the mesenchymal layer contribute to and possibly become the new dermal papilla. After removal of the dermal papilla or root end the outer root sheath cells coalesce to form a column or rod. Basophilia arises within the proximal end of this rod, over which the mesenchymal cells aggregate. These cells form the dermal papilla, first as a small indentation which then increases in size whilst acquiring a strongly basophilic ectodermal matrix.
A study of the effects of colchicine on the process of morphogenesis and induction in chick embryos
Authors: Diwan B. A.
Published: April 2021

The importance of sulfhydryl groups in the process of morphogenesis and induction has been discussed by several workers (Rapkine & Brachet, 1951; Seilern-Aspang, 1959; Brachet, 1960; Pohl & Quertier, 1963; Brachet, 1964). Lakshmi (1962a, b) studied the effects of chloroacetophenone on the develop-ment of chick embryos and emphasized the importance of sulfhydryl groups in morphogenesis and induction. Colchicine is known to affect cell division, probably by its action on sulfhydryl groups of the spindle proteins (Dustin, 1947; Mazia & Dan, 1952). In the present work the effect of colchicine on the processes of morphogenesis and induction in chick embryos has been studied. In order to gain further insight into the mechanism of action of the chemical it is useful to see if its action is reversible. Therefore, an attempt has been made to reverse the action of colchicine by cysteine.
A new gene affecting the morphogenesis of the vestibular part of the inner ear in the mouse
Authors: Deol M. S. , Lane Priscilla W.
Published: April 2021

The discovery of a new semi-dominant gene in the mouse is reported. It is called ‘dancer’, and it belongs to the linkage group XII. The homozygotes have cleft palate and cleft lip, and die soon after birth. The heterozygotes have ab-normal behaviour and a white spot on the head. An examination of the inner ear in the heterozygotes revealed a reduction of the vestibular ganglion, absence of some of its nerves, and widespread mal-formations in the vestibular region. Developmental studies showed that the malformations appear about 2 days after the abnormalities of the ganglion and nerves, and since they are virtually confined to the parts with affected nerve supply they are probably consequent on these abnormalities. A complete correlation between the defects of the semicircular ducts and of their nerves strongly suggests that the nerve plays an essential part in the morphogenesis of the proximal end of the duct. The failure of the otoliths to form in the utricle in the absence of the macula indicates that the otoliths are probably secreted by the macula.
On the constancy of the number of villi in the duodenum of the post-embryonic domestic fowl
Authors: Clarke Rufus
Published: April 2021

Counts performed on whole mounts of late embryonic and of adult chicken duodenum demonstrate that the number of villi present at these two stages of development is approximately the same. Growth occurs by increase in the size of the villi. The crypts of Lieberkühn increase greatly in number and depth, but change little in diameter.
Studies on induction by substances containing sulphydryl groups in post-nodal pieces of chick blastoderm
Authors: Waheed M. Abdul , Mulherkar Leela
Published: April 2021

The importance of sulphydryls in morphogenesis is being increasingly recognized. In the study of the role of thiols in amphibian and avian development one of the methods of approach has been to subject early embryonic stages to the action of reagents such as chloroacetophenone, monoiodoacetic acid, oxidized glutathione and mercaptoethanol (Beatty, 1949; Rapkine & Brachet, 1951; Deuchar, 1957; Brachet & Delange-Cornil, 1959; Pohl & Brachet, 1962; Lakshmi, 1962a). One common effect seen in most of the above experiments is that in treated embryos the nervous system is affected, in that it remains an open thick plate.
The pathogenesis of hydrocephalus in newborn rats deficient in vitamin B12
Authors: Woodard James Carroll , Newberne Paul M.
Published: April 2021

Richardson & Hogan (1946) produced hydrocephalus in rats by feeding a purified casein diet containing all the vitamins available at that time. Almost 2% of the young from females fed the experimental diet were hydrocephalic; female rats fed the same diet supplemented with liver extract gave birth to normal young. It is now thought that this diet was marginally deficient in vitamin B12 (Newberne & O’Dell, 1961). Animals which showed no gross evidence of lesions in the central nervous system had reduced maze-learning abilities as compared to animals on control diets (Whitley, O’Dell & Hogan, 1951).
Developmental genetics of the mutant grandchildless of Drosophila subobscura
Authors: Fielding C. J.
Published: April 2021

A study of the embryology of female-sterile mutants can provide information on the course of normal development, particularly when several mutants affect the same organ system. A favourable situation for an investigation of this kind arises with the formation and migration of the pole cells in Drosophila species. A number of genetic characters are known whose expression in the embryology of the offspring of affected mutant females involves the complete loss of pole cells or a change in their distribution after gastrulation. Thus the sex-linked female sterile mutant fs nasA (Counce & Ede, 1957), and the sex-linked lethals Lf11 (Ede, 1956a), X2 (Ede, 1956b), X27 (Ede, 1956c) and X10 (Ede, 1956d) all show disturbances of the pole cell complement.
Immunochemical investigations on the origin of serum albumin in the chick embryo
Authors: Zaccheo D. , Grossi C. E.
Published: April 2021

Information concerning physical and chemical properties of serum albumin during the development of the chick has been collected by different techniques, e.g. paper, gel and continuous flow electrophoresis, ultracentrifugation and immunochemical methods. However, the results of the various authors are not always in full agreement. The main questions deal with the precise stage of development when serum albumin can first be detected in the circulating blood, and with the heterogeneity of the molecular types in the group of serum albumins. Other aspects of the problem concern the possibility of different origins of serum albumin at various stages and the metabolism of this protein which probably has peculiar features at each intra- and extra-ovular developmental period (Iványi, Hraba & Cerny, 1964).
The ultrastructure of implantation in the golden hamster (Cricetus auratus)
Authors: Young M. P. , Whicher J. T. , Potts D. M.
Published: April 2021

Previous work on the early development of the golden hamster includes the investigation of Ochs (1908), Graves (1945) and Ward (1948), all at the level of the light microscope. Austin (1963) has examined the ultrastructure of the oocytes of the golden hamster while Enders & Schlafke (1965) have observed the pre-implantation stages of pregnancy.
Development of embryonic rat eyes in organ culture
Authors: Armstrong R. Christy , Elias Joel J.
Published: April 2021

Abnormalities of the ocular system which appear in organ culture in Way-mouth’s medium with freshly added glutamine (Armstrong & Elias, 1968) resemble those caused by transitory pteryolglutamic acid (PGA or folic acid) deficiency in vivo (Armstrong & Monie, 1966). The configurations of such malformations as lens herniations, retinal diverticula, and rosette-like formations of the retina are remarkably similar in both cases. The experiments reported in this paper were undertaken in an effort to understand the mechanisms involved in the production of similar abnormalities by two very different experimental conditions: the addition of glutamine in vitro and the transitory deficiency of PGA in vivo.

One series of experiments involved the effects of manipulation of the PGA and glutamine content of the culture medium on eye development in vitro. Parallel studies on PGA-deficiency in vivo were undertaken in conjunction with organ-culture experiments in order to compare the effects on abnormal eye morphogenesis.
Induction neurale chez les Oiseaux à travers un filtre millipore: étude au microscope optique et électronique
Authors: Gallera Par J. , Nicolet G. , Baumann M.
Published: April 2021

Chez les Amphibiens le contact direct entre l’inducteur et l’ectoblaste n’est pas indispensable. Des substances inductrices solubles, probablement de nature pro-téinique, peuvent traverser un filtre millipore et déclencher des inductions neurales (Saxén, 1961; Nyholm, Saxén, Toivonen & Vainio, 1962). Ce filtre constitue pourtant une barrière difficilement franchissable, puisque le pour-centage et la puissance des inductions obtenues sont nettement plus faibles que dans les conditions normales.
Evolution of flowers and inflorescences
Authors: Coen Enrico S. , Nugent Jacqueline M.
Published: April 2021

Plant development depends on the activity of meristems which continually reiterate a common plan. Permutations around this plan can give rise to a wide range of morphologies. To understand the mechanisms underlying this variation, the effects of parallel mutations in key developmental genes are being studied in different species. In Antirrhinum, three of these key genes are: (1) floricaula (flo) a gene required for the production of flowers (2) centrora- dialis (cen), a gene controlling flower position (3) cycloidea (eye), a gene controlling flower symmetry. Several plant species, exhibiting a range of inflorescence types and floral symmetries are being analysed in detail. Comparative genetic and molecular analysis shows that inflorescence architecture depends on two underlying parameters: a basic inflorescence branching pattern and the positioning of flowers. The flo and cen genes play a key role in the positioning of flowers, and variation in the site and timing of expression of these genes, may account for many of the different inflorescence types. The evolution of inflorescence structure may also have influenced the evolution of floral asymmetry, as illustrated by the cen mutation which changes both inflorescence type and the symmetry of some flowers. Conflicting theories about the origins of irregular flowers and how they have coevolved with inflorescence architecture can be directly assessed by examining the role of eye- and cen-like genes in species displaying various floral symmetries and inflorescence types.
Gene duplications and the origins of vertebrate development
Authors: Holland Peter W. H. , Garcia-Fernàndez Jordi , Williams Nic A. , Sidow Arend
Published: April 2021

All vertebrates possess anatomical features not seen in their closest living relatives, the protochordates (tunicates and amphioxus). Some of these features depend on develop mental processes or cellular behaviours that are again unique to vertebrates. We are interested in the genetic changes that may have permitted the origin of these inno vations. Gene duplication, followed by functional diver gence of new genes, may be one class of mutation that permits major evolutionary change. Here we examine the hypothesis that gene duplication events occurred close to the origin and early radiation of the vertebrates. Genome size comparisons are compatible with the occurrence of duplications close to vertebrate origins; more precise insight comes from cloning and phylogenetic analysis of gene families from amphioxus, tunicates and vertebrates. Comparisons of Hox gene clusters, other homeobox gene families, Wot genes and insulin-related genes all indicate that there was a major phase of gene duplication close to vertebrate origins, after divergence from the amphioxus lineage; we suggest there was probably a second phase of duplication close to jawed vertebrate origins. From amphioxus and vertebrate homeobox gene expression patterns, we suggest that there are multiple routes by which new genes arising from gene duplication acquire new functions and permit the evolution of developmental inno vations.
Can the Cambrian explosion be inferred through molecular phylogeny?
Authors: Philippe Hervé , Chenuil Anne , Adoutte Andre
Published: April 2021

Most of the major invertebrate phyla appear in the fossil record during a relatively short time interval, not exceeding 20 million years (Myr), 540-520 Myr ago. This rapid diversification is known as the ‘Cambrian explosion’. In the present paper, we ask whether molecular phyloge netic reconstruction provides confirmation for such an evo lutionary burst. The expectation is that the molecular phy logenetic trees should take the form of a large unresolved multifurcation of the various animal lineages. Complete 18S rRNA sequences of 69 extant representatives of 15 animal phyla were obtained from data banks. After elimi nating a major source of artefact leading to lack of resolu tion in phylogenetic trees (mutational saturation of sequences), we indeed observe that the major lines of triploblast coelomates (arthropods, molluscs, echinoderms, chordates…) are very poorly resolved i.e. the nodes defining the various clades are not supported by high bootstrap values. Using a previously developed procedure consisting of calculating bootstrap proportions of each node of the tree as a function of increasing amount of nucleotides (Lecointre, G., Philippe, H. Le, H. L. V. and Le Guyader, H. (1994) Mol. Phyl. Evol., in press) we obtain a more infor mative indication of the robustness of each node. In addition, this procedure allows us to estimate the number of additional nucleotides that would be required to resolve confidently the currently uncertain nodes; this number turns out to be extremely high and experimentally unfea sible. We then take this approach one step further: using parameters derived from the above analysis, assuming a molecular clock and using palaeontological dates for cali bration, we establish a relationship between the number of sites contained in a given data set and the time interval that this data set can confidently resolve (with 95% bootstrap support). Under these assumptions, the presently available 18S rRNA database cannot confidently resolve cladogenetic events separated by less than about 40 Myr. Thus, at the present time, the potential resolution by the palaeontolog ical approach is higher than that by the molecular one.
The evolving role of Hox genes in arthropods
Authors: Akam Michael , Averof Michalis , Castelli-Gair James , Dawes Rachel , Falciani Francesco , Ferrier David
Published: April 2021

Comparisons between Hox genes in different arthropods suggest that the diversity of Antennapedia-class homeotic genes present in modern insects had already arisen before the divergence of insects and crustaceans, probably during the Cambrian. Hox gene duplications are therefore unlikely to have occurred concomitantly with trunk segment diversification in the lineage leading to insects. Available data suggest that domains of homeotic gene expression are also generally conserved among insects, but changes in Hox gene regulation may have played a significant role in segment diversification. Differences that have been documented alter specific aspects of Hox gene regulation within segments and correlate with alterations in segment morphology rather than overt homeotic transformations.

The Drosophila Hox cluster contains several homeobox genes that are not homeotic genes -bicoid, fushi-tarazu and zen. The role of these genes during early development has been studied in some detail. It appears to be without parallel among the vertebrate Hox genes. No well conserved homologues of these genes have been found in other taxa, suggesting that they are evolving faster than the homeotic genes. Relatively divergent Antp-class genes isolated from other insects are probably homologues of fushi-tarazu, but these are almost unrecognisable outside of their homeodomains, and have accumulated approximately 10 times as many changes in their homeodomains as have homeotic genes in the same comparisons. They show conserved patterns of expression in the nervous system, but not during early development.
A class act: conservation of homeodomain protein functions
Authors: Manak J. Robert , Scott Matthew P.
Published: April 2021

Dramatic successes in identifying vertebrate homeobox genes closely related to their insect relatives have led to the recognition of classes within the homeodomain superfamily. To what extent are the homeodomain protein classes dedicated to specific functions during development? Although information on vertebrate gene functions is limited, existing evidence from mice and nematodes clearly supports conservation of function for the Hox genes. Less compelling, but still remarkable, is the conservation of other homeobox gene classes and of regulators of homeotic gene expression and function. It is too soon to say whether the cases of conservation are unique and exceptional, or the beginning of a profoundly unified view of gene regulation in animal development. In any case, new questions are raised by the data: how can the differences between mammals and insects be compatible with conservation of homeobox gene function? Did the evolution of animal form involve a proliferation of new homeodomain proteins, new modes of regulation of existing gene types, or new relationships with target genes, or is evolutionary change largely the province of other classes of genes? In this review, we summarize what is known about conservation of homeobox gene function.
The relation of the two blastomeres to the polar lobe in Dentalium
Authors: Verdonk N. H.
Published: April 2021

Experiments on the influence of the polar lobe on the development of molluscs have shown that after removal of the polar lobe cleavage is radially symmetrical and indications of bilateral symmetry do not appear (Wilson, 1904: Dentalium;Clement, 1952: Ilyanassa). In normal development the polar lobe fuses with one of the two cells of the trefoil stage, and this cell becomes the posterior side of the embryo.
Albumen absorption during chick embryogenesis
Authors: Carinci P. , Manzoli-Guidotti L.
Published: April 2021

In birds albumen represents a substantial part of the reserve material for their embryological development (Romanoff & Romanoff, 1949). In Gallus gallus albumen proteins form 50 % of non-incubated egg protein content (Romanoff & Romanoff, 1949). During incubation such material is absorbed and utilized, to a great extent, for the synthesis of embryonal proteins (Fiske & Boyden, 1926; Rupe & Farmer, 1955). It is not yet well understood how these processes (albumen absorption and utilization for the energetic and nutritional needs of the embryo) take place. The present available data indicate that the amount of albumen solids begins to diminish starting from 11 to 12 days of incubation (Romanoff & Romanoff, 1933; Rupe & Farmer, 1955). From 13 to 14 days, after the sero-amniotic connexion perforates, the protein content of the amniotic fluid shows a marked increase because of the passage of albumen (Needham, 1931 ; Romanoff, 1960). During the same development period albumen proteins can be recovered, in large amounts, in the yolk (Saito, Martin & Cook, 1965; Carinci, Wegelin & Manzoli-Guidotti, 1966).
Observations on CBA-p/CBA-T6T6 mouse chimeras
Authors: Mystkowska Ewa T. , Tarkowski Andrzej K.
Published: April 2021

A considerable amount of information bearing upon mouse chimeras obtained experimentally by fusion of cleaving eggs has already been accumulated (Tarkowski, 1961, 1963, 1964a, b, 1965; Mintz, 1962a, b, 1964a, b, 1965a, b, 1967). Direct and indisputable proofs of the chimerism of the individuals produced were obtained by establishing that two types of pigment cells were present in the outer layer of the retina (Tarkowski, 1963,1964a) and in the coat (Mintz, 1965a, b, 1967). The cell composition of other organs and tissues has not as yet been investigated. True hermaphroditism in some of the animals obtained was also accepted as an indirect proof of chimerism (Tarkowski, 1961, 1963, 1964b; Mintz, 1965b) but the postulate of these individuals being six-chromosome chimeras has not as yet been directly confirmed by karyological research.
Etude experimentale de Forganogenèse du poumon: nature et spécificité des interactions épithélio-mésenchymateuses
Authors: Dameron Fl.
Published: April 2021

On sait que Forganogenèse pulmonaire (Dameron, 1961a, b) s’effectue seulement lorsque les deux constituants de l’ébauche, épithélium bronchique et mésenchyme pulmonaire, sont associés. Les interactions qui s’exercent entre les deux tissus sont indispensables pour la croissance et la différenciation de l’épithélium.
Le rôle de l’épiblaste dans la chondrogénèse du bourgeon de membre chez la Souris
Authors: Milaire J. , Mulnard J.
Published: April 2021

Les facteurs qui contrôlent la morphogénèse et la croissance des bourgeons de membres ont suscité un intérêt considérable au cours de ces vingt dernières années. Tous les travaux qui y ont été consacrés se basent sur des techniques d’expérimentation directe appliquée in vivo aux bourgeons de membres du poulet, ou, dans une moindre mesure, à ceux du xénope. Leurs résultats ont fait l’objet de plusieurs articles de synthèse qui nous autorisent à n’en rappeler ici que les points essentiels (Zwilling, 1961; Tschumi, 1962; Amprino, 1965). Dès qu’il prend naissance aux dépens de la pariétopleure, le mésoblaste présomptif des membres acquiert la faculté d’induire, dans son feuillet de revêtement, la formation d’un épaississement marginal connu sous le nom de cape épiblastique apicale. Aussitôt constituée, cette structure stimule à son tour la croissance du mésoblaste sous-jacent et assure ainsi la mise en place des matériaux destinés à former les segments de plus en plus distaux du membre. Dans ce jeu d’influences réciproques, c’est le mésoblaste qui détient le rôle principal et spécifique. Non seulement il induit la formation d’une cape apicale, mais durant toute la morphogénèse il continue d’émettre, vers la périphérie du bourgeon, un facteur diffusible assurant le maintien de l’intégrité structurale et fonctionnelle de la crête épiblastique. Les informations dont nous disposons concernant le rôle de l’épiblaste sont beaucoup moins précises. Il paraît bien s’agir d’une induction non spécifique stimulant la prolifération du mésoblaste sous-jacent, mais on ignore tout des modalités de cette influence et de ses répercussions éventuelles sur les capacités d’histodifférenciation du mésoblaste.
The effect of transection of the duck blastoderm on the orientation of the embryo
Authors: Rogulska Teresa
Published: April 2021

Von Baer (1828) formulated a rule according to which the cephalo-caudal axis is perpendicular to the long axis of the shell, and the head of the embryo is directed forwards when the egg is placed with the blunt end to the left. This law has been checked in several species of bird: hen, duck, pigeon, goose, turkey (see Clavert, 1960, for references) and quail (Fargeix, 1963, 1964). Embryos obeying von Baer’s rule were found to constitute the most numerous class, but considerable interspecific as well as intraspecific differences were observed.
Cytonucleoproteins in cleaving eggs of Xenopus lœvis
Authors: Arms K.
Published: April 2021

The cytoplasm of unfertilized eggs of Xenopus laevis induces DNA synthesis in a high proportion of adult and embryonic nuclei introduced into it (Graham, Arms & Gurdon, 1966). This induction of DNA synthesis is not due merely to the fact that the egg cytoplasm supplies precursors of DNA synthesis which might be absent from the nuclei, since adult liver nuclei, at least, of those nuclei which are induced to synthesize DNA after their injection into eggs, do not do so if incubated in vitro with DNA precursors (Arms, 1968). One of the ways in which the cytoplasm of unfertilized eggs might induce DNA synthesis is by supplying other molecules, such as various enzymes, to the introduced nuclei.
The effects of embryonic pars distalis grafts and albumen on the growth of chick embryos
Authors: Betz T. W.
Published: April 2021

Normal chick embryos swallow and utilize the albumen in the egg between the 11th and 15th day of incubation (Witschi, 1949). They use approximately two-thirds of the yolk by the end of incubation (Romanoff & Romanoff, 1949). Thus the embryo has access to 4 g of protein in the albumen and 3 g of protein in the yolk (Romanoff & Romanoff, 1949). Embryos which have been hypo-physectomized by partial decapitation, which is the only practical way of hypophysectomizing chick embryos (Betz, 1965 a, see also the reviews of Benoit (1962) and of Hinni & Watterson (1963), do not develop an upper beak and do not swallow much of the albumen since most of it remains in the egg (Witschi, 1959; Betz, 1965b).
Morphogenetic analysis of the effects of juvenile hormone analogues and other morphogenetically active substances on embryos of Schistocerca gregaria (Forskål)
Authors: Novák Vladimír J. A.
Published: April 2021

One of the basic assumptions of the author’s gradient-factor theory of insect morphogenesis is that the effects of the hypothetical gradient-factor on tissue growth can be reproduced by the juvenile hormone, not only during postembryonic development, but also in the course of embryogenesis (Novák, 1951 a, b, 1956, 1966). This concept was originally based on the more or less indirect evidence supplied by the findings of Pflugfelder (1947) in Dixippus morosus and by those of Novak (1951 b) in Oncopehus fasciatus.
Le mécanisme d’ entrée des cellules germinales primordiales dans le réseau vasculaire, chez l’ embryon de Poulet
Authors: Dubois Regis
Published: April 2021

La lignée germinale des Oiseaux fait l’ objet, depuis une quinzaine d’ années, de travaux expérimentaux basés sur la technique des cultures in vitro. Ces recherches ont apporté des résultats décisifs concernant les questions du transport des cellules germinales primordiales (CGP) par la voie sanguine (technique des parabioses circulatoires in vitro, Wolff & Simon, 1957) et de la colonisation des ébauches gonadiques (technique des associations in vitro, Dubois, 1964, 1968).
Magnitude and pattern of compensatory growth in rats after cold exposure
Authors: Lee Marjorie M. C. , Chu P. C. , Chan H. C.
Published: April 2021

It is a common observation that normal growth is affected or suppressed in young individuals by environmental adversities and physical disturbances. On the other hand, when health or favorable conditions are restored, the tempo of growth promptly accelerates as if the individual is trying to make up for the growth debt incurred. Tanner has referred to this increased growth rate after diseases or starvation as compensatory or ‘catch-up’ growth, a topic on which he has written eloquently and fully in a number of articles (1963a, b). He considers this compensatory growth as a ‘self-stabilizing’ or ‘target-seeking’ phenomenon in the regulatory control of growth.
Changes in mitotic rate during compensatory renal growth in Xenopus laevis tadpoles after unilateral pronephrectomy
Authors: Chopra D. P. , Simnett J. D.
Published: April 2021

In many organs partial extirpation is followed by compensatory hypertrophy in the residual tissue which is generally brought about by a temporary increase in the rate of cell division. After unilateral nephrectomy in the rat, cell proliferation in the contralateral kidney starts after a latent period of 24 h and reaches its maximum rate about 24 h later (Goss & Rankin, 1960). Similar results were obtained in immature metamorphosed Xenopus laevis after partial extirpation of liver and kidney. In this case the increased cell proliferation starts at 3 days and reaches a maximum 6 days after the operation (Chopra, unpublished results). Although the timing of the response may thus vary according to the experimental conditions the pattern of a latent period followed by a rapid increase in the mitotic rate seems to be a general phenomenon.
Effects of trypan blue and Niagara blue 2 B on the in vitro absorption of ions by the rat visceral yolk sac
Authors: Kernis Marten M. , Johnson E. Marshall
Published: April 2021

Prior to 1927, when Brunschwig proposed that the rat visceral yolk sac is functionally a placenta, it was customary to consider the chorio-allantoic placenta as the primary organ for bringing nourishment to and taking waste from the developing embryo and growing fetus. Eight years later, Everett (1935) predicted that the visceral yolk sac is functionally at least as important as the chorio-allantoic placenta, while Noer & Mossman (1947) suggested that the yolk sac functions differently from the placenta and is therefore complementary in its role. More recently, Halliday (1955) indicated that the proximal yolk sac of the rat is capable of absorbing antibodies by day 17 of gestation. This was confirmed by Brambell & Halliday (1956), who were able to demonstrate that the vitelline epithelium and its underlying vascular system are partly responsible for antibodies penetrating into the embryo. Padykula, Deren & Wilson (1966) noted that the rat yolk sac has the ability to absorb vitamin B12 and that this ability is stimulated by the presence of intrinsic factor. The yolk sac has also been shown to be capable of actively transporting certain amino acids (Deren, Padykula & Wilson, 1966) and is able to accumulate ferritin by means of pinocytosis (Lambson, 1966).
The programming of differentiation and its control by juvenile hormone in saturniids
Authors: Willis Judith H.
Published: April 2021

Although considerable progress has been made with the chemistry of juvenile hormone (Dahm, Roeller & Trost, 1968), studies on its mechanism of action in immature insects are still in a preliminary stage. Much of the recent work has been interpreted as showing an effect of juvenile hormone on the morphogenetic program through which an insect passes in the course of its ontogeny (Williams, 1961). It is the purpose of this paper to describe three studies which illustrate the complex nature of this developmental program in saturniid moths.
Threshold phenomena versus cell heredity in the manifestation of sex-linked genes in mammals
Authors: Grüneberg Hans
Published: April 2021

The mode of action of sex-linked genes in mammals has been the subject of much discussion in recent years. This has centred round the concept that in the mammalian female, either the maternal or the paternal X-chromosome is randomly and irreversibly inactivated during development, with the result that in the female, as in the male, one X-chromosome only is active in a given cell (Lyon, 1966, and earlier papers). The Lyon Hypothesis (L.H.) is based, in part, on the mottled or striped phenotypes of heterozygotes for certain sexlinked genes affecting the coat of the mouse and other mammals: these phenotypes are regarded as a mixture of clones descended from cells in which either one or the other X-chromosome has been inactivated. As Baker (1967) rightly insists, the interpretation of a pattern as clonal must be based on known cell lineages, as without such a basis one simply postulates what should be put to the test.
Aspects of the tabby—crinkled—downless syndrome : I.The development of tabby teeth
Authors: Sofaer J. A.
Published: April 2021

The sex-linked gene tabby, Ta (Falconer, 1953), and two autosomal mimics of tabby, crinkled (cr, linkage group XIV) (Falconer, Fraser & King, 1951; King, 1956) and downless (dl, linkage group IV) (Mouse News Letter, 1960,1966) each produce a similar mutant syndrome involving the coat and dentition of the mouse. Studies on the coats of tabby and crinkled mice point to a timed gene effect causing suppression of formation of new hair follicles between and 17 days of gestation and again from birth onwards, with a reduction in the rate of growth of the follicles that do form (Falconer et al. 1951). Associated with this is a reduction in hair calibre and a lack of differentiation of the coat into hair types (Grüneberg, 1966 b). A model to explain the timed action of the tabby gene has been proposed by Dun (1959).
Gut and nerve-cord interaction in sabellid regeneration
Authors: Fitzharris Timothy P. , Lesh Georgia E.
Published: April 2021

Studies of annelid regeneration have considered interactions which may exist between the gut and nerve-cord. Although the influence of the gut has often been assigned a secondary role (Kroeber, 1900; Morgan, 1902; Hunt, 1919; Faulkner, 1932; Sayles, 1932), the necessity for its presence has been demonstrated in certain instances (Okada, 1938). Attention therefore has been primarily directed to the nerve-cord, particularly the trophic influences of this structure at the wound site (Goldfarb, 1914; Bailey, 1930 & 1939; Avel, 1932; Crowell, 1937), and its influence posterior to the wound area, presumably hormonal in nature (Kropp, 1933; Clark, R. B. & Clark, M. E., 1959; Clark, R. B. & Bonney, 1960; Clark, M. E. & Clark, R. B., 1962; Scully, 1964; Golding, 1967a-c). Regardless of the organism or the approach used, previous investigators have pointed to one persistent problem: the independence or interdependence of these two organ systems in the structuring of the regenerate bud. Specifically, what does the gut contribute to the regenerate bud and in what manner, if any, does the nerve-cord direct the formation of the bud? Because of the lack of histological data, plus conflicting views on the exact ordering of these regenerating organ systems, this study will attempt to resolve the problem of tissue interaction involved in normal regeneration.
The effect of tetracyclin on the processes of calcification of the otoliths in the developing chick embryo
Authors: Balsamo Giuseppe , de Vincentiis Mario , Marmo Francesco
Published: April 2021

It is known that tetracyclin is fixed in calcified tissues and that it can have an inhibitory action on calcification processes under certain conditions (Saxén, 1966). The mechanism by which tetracyclin is bound to the calcified structures is not clearly understood. Some workers believe that there is simple chelation between the antibiotic and calcium (Albert, 1953); others believe that the fixation of tetracyclin is mediated by more complex mechanisms (Sternberg, 1966; Saxén, 1966). The latter hypothesis is based on the observation of the presence of both a stable complex of tetracyclin-Ca and an unstable form from which either the calcium or the tetracyclin can undergo rapid changes.
Embryonic development of the heart
Authors: Manasek Francis J.
Published: April 2021

The mature heart may be thought of as consisting of three layers, endocardium, myocardium, and an outer investing tissue called the epicardium. During early formation of the tubular heart of chick embryos, at about the 8-somite stage, two tissue layers become clearly discernible with the light microscope: the endocardium and the developing myocardial wall. The outer epicardial layer does not appear until later in development.
Epithelial and mesenchymal cell interactions with extracellular matrix material in vitro
Authors: Slavkin H. C. , Bringas P. , Cameron J. , Lebaron R. , Bavetta L. A.
Published: April 2021

Epidermal organogenesis (thyroid gland, salivary gland, feather, hair, skin, thymus gland, tooth, etc.) generally follows a basic rule; epithelium exhibits well-documented interdependence with adjacent mesenchyme for a specific path of development (Grobstein, 1967, for review). Koch (1967) demonstrated in rodent embryos that isolates of incisor epithelial and mesenchymal tissue, separated by a millipore filter, continued to develop. When homotypic tissues were placed in juxtaposition to the filter, no evidence of continued differentiation was observed.
Electron microscopic studies on developing cartilage I. The membrane system related to the synthesis and secretion of extracellular materials
Authors: Goel S. C.
Published: April 2021

The present communication describes the changing developmental pattern of the cellular organelles concerned with the synthesis and transfer of the extra-cellular materials during the process of chondrogenesis in chick limb-buds.
Experimental studies on morphogenetic factors localized in the first and the second polar lobe of Dentalium eggs
Authors: Geilenkirchen W. L. M. , Verdonk N. H. , Timmermans L. P. M.
Published: April 2021

During the development of several annelids and molluscs, a lobe of protoplasm is observed to protrude from the vegetal pole of the egg during the first cleavages. Removal of this polar lobe causes characteristic defects in the developing larvae as has been observed in the scaphopod, Dentalium (Wilson, 1904; Verdonk,1968), the annelid Sabellaria (Hatt,1932; Novikoff,1938), the gastropod Jlyanassa obsoleta (Crampton, 1896; Clement, 1952) and the lamellibranch, Mytilus edulis (Rattenbury & Berg, 1954).
Local accumulation of Feulgen-positive granules in the egg cortex of Dentalium dentale L
Authors: Timmermans Lucy P. M. , Geilenkirchen W. L. M. , Verdonk N. H.
Published: April 2021

A special feature of eggs of several species of annelids and molluscs is the formation of a polar lobe at stage-specific intervals during the cleavage phase.
Analyse autoradiographique de la localisation des différentes ébauches présomptives dans la ligne primitive de l’embryon de Poulet
Authors: Nicolet Par G.
Published: April 2021

Le problème de la localisation des ébauches présomptives chez les Oiseaux est actuellement l’un des thèmes les plus controversés de la littérature embryologique (Grâper, 1929; Wetzel, 1929, 1936; Pasteels, 1937; Rudnick, 1944, 1948; Spratt, 1955). Une nouvelle analyse de ce problème s’impose, encore faut-il que la méthode employée soit réellement capable d’obvier aux désavantages des techniques de marquage usuelles. En effet, en particulier chez les Oiseaux, ni la technique de coloration locale au bleu de Nil, ni l’apposition de fines particules ne donne la garantie formelle que la marque se rapporte strictement au même ensemble de cellules du début à la fin des expériences. Nous croyons que l’emploi de la thymidine tritiée comme marqueur nucléaire peut surmonter cet obstacle. Ce radioisotope s’incorpore spécifiquement dans l’ADN et ne se transmet qu’aux cellules-filles issues de cellules marquées. Cette technique a déjà été employée à plusieurs reprises chez le Poulet. Weston (1963) a étudié la migration des éléments de la crête neurale, Rosenquist & De Haan (1966) ainsi que Orts-Llorca & Collado (1967) ont analysé la morphogénèse du cœur. Modak (1966) s’est consacré au problème de la régénération de l’endoblaste, alors que Rosenquist (1966) et Nicolet (1965, 1967) ont précisé la destination des cellules provenant de diverses régions du blastoderme.