bluuebunny/crossref_metadata_2025_split huggingface dataset:
Methods of transplanting nuclei from single cultured cells to unfertilized frogs’ eggs
Authors: Gurdon J. B. , Laskey R. A. 
Published: April 2021

ABSTRACT
Two methods of transplanting single nuclei from monolayers of cultured cells to unfertilized eggs of Xenopus laevis are described, illustrated, and tested.
The detached-cell method is simpler and quicker to operate and is suitable for homogeneous populations of cells which are easily removed from the substrate on which they are growing. The other, attached-cell, method is technically more elaborate, but is applicable to cells whose properties can be individually determined under the phase-contrast microscope and to cells which are not readily dissociated from other cells or from their substrate.
The dependence of duodenal differentiation in chick embryos on pars distalis hormones
Authors: Bellware F. T. , Betz T. W. 
Published: April 2021

ABSTRACT
Duodenal differentiation in normal chick embryos between 15·75 and 20·5 days of incubation was characterized by the following changes:
The dry weight increases from 4·1 to 12·4 mg. The alkaline phosphatase activity increases from less than 12 to 426 units. The length of the villi increases sixfold. The height of the epithelial cells at the villous tips increases from 12·9 to 25·9 μ. The shape of the mucosal cells changes from low columnar, to cuboidal, to high columnar. The shape of the nuclei progresses from round to ovoid. At first mitotic figures are distributed throughout the epithelium but become restricted to the crypts of Lieberkiihn. Cytoplasmic glycogen appears by day 15·75 and is mobilized by 20·5 days. A mucopolysaccharide at the brush border of the mucosal cells progressively appears at 16-75 days and increases in amount. Alkaline phosphatase activity (Gomori technique) at the brush border appears in low levels at 16-75 days and becomes more intense. Fresh body weights and third toe lengths at 19·75 and 20·5 days of incubation were recorded as indices of body growth. In ‘hypophysectomized’ embryos at 19·75–21·5 days of age: The level of duodenal differentiation approximated that of normal .16·75–17·75 day embryos. In ‘hypophysectomized’ embryos which received a pars distalis chorioallantoic homograft at 9·5 days of incubation the duodena were normal. In ‘hypophysectomized’ embryos with grafts which became atrophic the level of duodenal differentiation was not different from that of untreated ‘hypophysectomized’ embryos. In chick embryos duodenal differentiation depends on pars distalis hormones.
The effect of environmental temperature on the growth of vertebrae in the tail of the mouse
Authors: Noel Janet F. , Wright E. A. 
Published: April 2021

ABSTRACT
C3H mice were bred at 30 °C and 22 °C. At 28 days of age the lengths of the sacral and caudal vertebrae were measured from radiographs and related to the local skin temperature. Growth of the sacral and proximal caudal vertebrae was slightly retarded in the hot environment, but the distal caudal vertebrae showed increased growth which could be quantitatively related to an increase in skin temperature. This suggests that in hot climates the increased growth of peripheral organs of some mammals is due to local increases in tissue temperature.
Melanogenesis in amphibians : II. Electron microscope studies of the normal and PTU-treated pigmented epithelium of developing Notophthalmus viridescens eyes
Authors: Eppig John J. 
Published: April 2021

ABSTRACT
Electron microscopy of 11 -day-old Notophthalmus viridescens retinal pigmented epithelium reveals particulate premelanosomes which are identical to the melanosomes found in the oocyte. These organelles, when found in the pigmented epithelium, are called premelanosomes because they undergo further maturation to form relatively homogeneous, spherical melanosomes. At this stage, oocyte melanosomes found in cells other than melanocytes have not undergone this subsequent maturation.
Elongated melanosomes which develop from fibrillar premelanosomes are also found in the pigmented epithelial cells.
Treatment with phenylthiourea blocks the maturation of both the fibrillar and particulate premelanosomes.
Experimental studies on axial polarity in hydra
Authors: Wilby Owen K. , Webster Gerald 
Published: April 2021

ABSTRACT
There is evidence which suggests that the polarity of regeneration in hydra is determined by axial gradients of some sort. The mechanisms which may be involved in the establishment and maintenance of the gradients have been investigated by studying the reversal of polarity in graft combinations.
Complete polarity reversal can be effected by a grafted hypostome or by a grafted hypostome and peduncle. Partial polarity reversal can be effected by a graft of a peduncle only. Changes in regional properties associated with polarity changes have been investigated using isolation and transplantation techniques.
The experimental results suggest that the axial gradient behaves as a gradient of a substance. Such a gradient could be produced by either (a) simple diffusion of a substance from a source or (b) unidirectional transport of a substance plus back-diffusion. Some of the experimental results are incompatible with mechanism (a). All the experimental results are compatible with mechanism (b).
Some of the problems raised by the interpretation of the axial gradient in terms of a polarized transport model are briefly discussed.
The localization of morphogenetic factors in uncleaved eggs of Dentalium
Authors: Verdonk N. H. , Geilenkirchen W. L. M. , Timmermans L. P. M. 
Published: April 2021

ABSTRACT
The effect of removing parts of unfertilized and fertilized eggs of Dentalium has been studied.
Up to 70 % of the volume of a 1st polar lobe can be removed from the vegetal side of both unfertilized and fertilized eggs, without influencing apical tuft formation. The post-trochal region is reduced. These eggs form a reduced polar lobe at first cleavage.
After removal of more than 70 % of the volume of a 1st polar lobe from the vegetal side of an uncleaved egg, before or after fertilization, no polar lobe is formed and larvae develop without apical tuft or post-trochal region.
The polar lobe area is quantitatively determined in the uncleaved egg, but after fertilization of isolated vegetal fragments regulation occurs and the polar lobe becomes proportional in size to the fragment.
Feulgen-positive granules, present at the vegetal side of the uncleaved egg, can be removed without influencing apical tuft formation. They may be important as determinants for the formation of the post-trochal region or adult structures.
The genetics and development of fused and supernumerary molars in the rice rat
Authors: Sofaer J. A. , Shaw J. H. 
Published: April 2021

ABSTRACT
Analysis of breeding records suggests that the occurrence of fused and supernumerary molars in the rice rat, associated with lower body weight than normal and with reduced fertility, is dependent on a single autosomal recessive gene subject to background modification.
Molar fusion, which is preceded by stripping of the external enamel epithelium from the interdental lamina, may involve the first two molars, or all three molars of the normal series in either jaw.
The supernumerary is a posterior tooth, developing after the three molars of the normal series in either jaw. Supernumerary development usually occurs with fusion of the molars of the normal series, but occasionally a supernumerary may be present in the absence of fusion.
Other examples of association between fusion, subsequent to separation of the external enamel epithelium from the interdental lamina, and supernumerary tooth development are cited. This association suggests that there may be a single common attribute of the dental lamina predisposing to epithelial stripping and to laminal hyperactivity.
A study of meiotic germ cells in the gonads of foetal mouse chimaeras
Authors: Mclaren Anne , Chandley Ann C. , Kofman-Alfaro Susana 
Published: April 2021

ABSTRACT
The gonads of 53 foetuses (16♀, 37♂) derived from fusion of embryos at about the 8-cell stage were examined. Ovotestes were found in two of the male foetuses. When gonads were sectioned days post coitum, germ cells in meiotic prophase were seen in 6/6 female and 4/14 male foetuses. When air-dried preparations were made from gonads days post coitum, germ cells in meiotic prophase were seen in 7/7 females and 4/13 males. At days post coitum, 2/2 female but only 2/10 male foetuses showed any meiotic cells, and these were degenerating.
[3H]Thymidine injected into the mother days post coitum resulted in labelling of the meiotic germ cells, but the sex vesicle characteristic of meiotic cells in normal males was never seen. The timing of DNA synthesis and meiosis was identical to that seen in the germ cells in foetal ovaries.
We conclude that the meiotic cells seen in the testes of foetal chimaeras are probably XX in constitution, and rarely survive beyond the 19th day of gestation.
Effect of yolk-sac antibody on rat embryos grown in culture
Authors: New D. A. T. , Brent R. L. 
Published: April 2021

ABSTRACT
It has been shown that congenital malformations can be produced in rats by injection into the pregnant female of rat kidney antiserum (Brent, Averich & Drapiewski, 1961 ; Brent, 1966a, b) or heterologous placental antiserum (Brent, 1966a, b, 1967). The teratogenic factor has been localized in the gammaglobulin fraction of the serum (Brent, 1966b).
Localisation et durée des potentialités médullo-surrénaliennes des crêtes neurales chez l’ embryon de Poulet
Authors: Chevallier Alain 
Published: April 2021

ABSTRACT

The localization and duration of the capacity of neural crest cells to differentiate into medullary cells of the adrenal gland
The capacity of the neural crest cells to differentiate into medullary cells of the adrenal gland has been tested for different levels of the cephalo-caudal axis of the chick embryo and at different stages.
The procedure consisted in associating a fragment of neural crest cells containing spinal cord with a section of an embryo containing the prospective cortical territory. The latter was previously deprived in ovo of presumptive medullar adrenal cells by localized X-irradiation of its spinal cord.
The portion of the spinal cord which has the capacity to give off medulloblasts is located not only within the prospective adrenal area (somite levels 18–22), but also within a region extending over a length of six somites in front and seven somites behind the presumptive zone.
This capacity, which is restricted in space, is also limited in time. It is possessed by the portion of spinal cord defined above from 6 h before the migration of the first neural crest cells and lasts roughly for 24 h after the beginning of migration. Furthermore, the experiments indicate that the differentiation of neural crest cells into medullocytes requires the inductive influence of the cortical
Evolution de Fiode, 127I, total thyroïdien chez l’embryon de Poulet au cours de l’ incubation
Authors: Daugèras Nicole , Lachiver François 
Published: April 2021

ABSTRACT

Thyroid, iodine in the developing chick embryo
Total thyroidal 127I of chick embryo has been studied from the 7th to the 20th days of incubation. On the 7th and 8th days the thyroid concentrates 127I but this concentration is weak. The total amount of 127I, Q, increases from the 8th day (0.1 ng) to the end of incubation, where its value is nearly 4·6µg. Between the 12th and 13th days there is an abrupt rise of the daily increment, ΔQ = Q2–Q1, and of the rate of accumulation, ΔQ/Q1. Between the 17th and 18th days there is a decrease of the increment and the rate of accumulation.
Evolution of the lining bodies in the embryonic chick gonad
Authors: Rahil Kuldeep S. , Narbaitz Roberto 
Published: April 2021

ABSTRACT
Gonads from White Leghorn chick embryo of various ages ranging from 4 to 10 days of incubation, were fixed in half-strength Karnovsky’s fixative, osmicated and embedded in Araldite. Thin sections were stained with uranyl acetate and lead citrate. Our observations were especially concentrated on the germinal epithelium.
Two cytological characteristics not previously described in embryonic chick gonads were observed:A network of fine microfilaments was present in the somatic cells of the germinal epithelium. These microfilaments were especially concentrated in the apical pole of these cells and appeared to be more numerous in 5- and 6-day gonads. Since similar microfilaments have been described in other embryonic epithelia in which growth of glands or cords is taking place, their presence in the embryonic gonad may be related to the formation of sex cords.Lining bodies, organelles which are characteristic of follicular cells in the adult ovary, were found in the embryonic gonads of both sexes. They first appeared in some of the 5-day embryos and were present thereafter in all 6-day left gonads, in all left ovaries and in those left testes in which regression of the germinal epithelium had not been completed. Lining bodies were never observed in right germinal epithelia. It is classically accepted that follicular cells of the adult originate from the somatic cells of the germinal epithelium. The presence of lining bodies in the epithelial cells of young embryos appears to indicate that, despite the fact that follicles are not formed until after hatching, follicular cells initiate their differentiation much earlier. The fact that this differentiation is also present in gonads of male embryos can be interpreted in the light of current theories on sex differentiation which assume the bisexuality of embryonic gonads.Short cytoplasmic processes, representatives of a merocrine secretory process, have been described by other authors in the germinal epithelium of young embryos. We confirmed these observations and found, in addition, that these processes were smaller, both in size and number, in the right gonads. This fact, together with the previously mentioned absence of lining bodies in right gonads, appears to be the expression, at the ultrastructural level, of the well known asymmetry of the avian embryonic gonads.
The morphologic expression of each cardiac primordium in the chick embryo
Authors: Nadal-Ginard Bernardo , García María Paz 
Published: April 2021

ABSTRACT
The cardia bifida in amphibians has the bulboventricular loop of the two hemi-hearts convex towards the mid-line. In birds the two loops have been reported to be convex towards the outside because all the experimental methods of producing cardia bifida in birds, unlike amphibians, impede the closure of the foregut.
The morphologic expression of each cardiac primordium was studied without altering endodermal tubulation or altering it only to the least possible degree. It has been demonstrated that the cardia bifida in birds has the two bulboventricular loops convex towards the mid-line and that the heart loops formed by only one primordium also tend to be convex towards the mid-line. Previous studies have been confirmed in the sense that the caudal portion of the left hemi-heart is the more prominent than the right one and that the left hemi-heart has faster heating rate than the right one until stage 12.
When the caudal portion of the left cardiac primordium was removed at stage 9 of Hamburger & Hamilton, in all cases a loop convex to the right was formed. This fact excludes that this portion of the left primordium is the origin of the right bending of the cardiac tube.
The origin of the epidermis in the supernumerary regenerates of triple legs in cockroaches (Blattaria)1
Authors: Bohn Horst 
Published: April 2021

ABSTRACT
An attempt has been made to clarify the origin of the supernumerary regenerates of triple legs by transplantations between two species of cockroaches, Gromphadorhina portentosa and Leucophaea maderae. The three ways of combining stump and transplant tissues were: heteropleural, dorso-dorsal, antero-posterior (I); heteropleural, dorso-ventral, anteroanterior (II); homopleural, dorso-ventral, antero-posterior (III). The transplantations have been performed at the level of the tibia as well as at the level of the coxa.
(1) The supernumerary regenerates were partly mixed, i.e were composed of a mosaic of the tissues of both species of cockroach, partly homogeneously built up by the tissues of only one of the two species. In combination I nearly all regenerates were mixed; in the other two combinations homogeneous regenerates were relatively numerous, sometimes even the most numerous.
Both supernumerary regenerates of a triple leg might be mixed; or one was homogeneous and the second mixed; or they were both homogeneous. In the latter case one regenerate was built up by Gromphadorhina tissues, the other by Leucophaea tissues, or, more rarely, both were built by up Gromphadorhina tissues.
(2) The intraspecific transplantations simultaneously done in Leucophaea gave results which correspond in general with the results of the interspecific transplantations.
(3) From the composition of the supernumerary regenerates it must be concluded that the four different properties of a cross-section (anterior, posterior, etc.) are not yet determined irreversibly in the tissues of the cockroach legs. Thus, missing properties may be completed by the other properties to give an entire cross-section.
Experimental studies on the organization of the preimplantation mouse embryo:II. Reaggregation of disaggregated embryos
Authors: Stern M. Susan 
Published: April 2021

ABSTRACTThe reaggregation and subsequent development of a range of disaggregated embryos has been examined:Following complete dissociation embryos from 8-cell to late blastocyst reaggregated and developed to form morphologically normal blastocysts, even when blastomeres of two different developmental stages were present in the reaggregate. Dissociated mid-blastocysts could also reaggregate to form blastocysts but more commonly they produced vesiculated masses, as did disaggregates of late blastocysts. Successful fusion of pairs of mid or late blastocysts, with full cell numbers, was achieved following partial dissociation.These results are discussed in relation to blastocyst formation. It is suggested that even if the embryo derives polarity from the oocyte it is not functionally essential to normal development in view of the remarkable regulative capacity of the egg.
The effect of spatial arrangement on cell determination during mouse development
Authors: Hillman N. , Sherman M. I. , Graham Chris 
Published: April 2021

ABSTRACTThe effect of cell position on cell determination was studied in mouse embryos. Embryos and parts of embryos were combined during early preimplantation development. The differentiation of cells in these composites was followed either by prelabelling some cells with tritiated thymidine or by combining cells which synthesized different electrophoretic variants of glucose phosphate isomerase.It was found that each blastomere of a 4-cell embryo could form both the trophoblast and the inner cell mass of the blastocyst. However, when blastomeres of a 4-cell embryo were placed on the outside of other 4-cell embryos then (a) they tended to form the outside layer of the blastocyst, (b) they tended to develop into the trophoblast and the yolk sac on the 10th day of pregnancy, (c) they tended not to form the coat colour of the foetus. Four-to eight-cell embryos which were completely surrounded by other blastomeres had lost the capacity to form vesicles at the blastocyst stage.We could find no evidence for the segregation of morphogenetic factors at the 4- and 8-cell stages of mouse development and concluded that at these stages cell position could determine the development of blastomeres.
The appearance and quantitation of cytoplasmic ribonucleic acid in the early chick embryo
Authors: Wylie C. C. 
Published: April 2021

ABSTRACT
This paper seeks to extend our knowledge about RNA synthesis in early embryogenesis to the domestic fowl, Gallus domesticus. Using this species for research, apart from increasing our knowledge of higher vertebrate embryology, has certain advantages such as rapid uptake of isotopic precursors and ease of microdissection in culture.
The following results are presented:
The cell number in the whole chick embryos is shown to be increasing logarithmically between the time of laying and the early neurula stage; with a doubling time of 7·4 h. The onset of ribosomal RNA synthesis has been shown to be during mid-cleavage of the chick embryo, while development is taking place in the oviduct and uterus of the mother. In a cumulative labelling experiment, embryos were labelled at the unincubated-egg stage, allowed to develop to various morphological stages up to neurulation, and their cytoplasmic RNA prepared and analysed by gel electrophoresis. The specific activity of the precursor pool for RNA synthesis was measured at several stages, using the same labelling conditions, and the results were used to quantitate the RNA synthesis from the incorporated radioactivity. Using these techniques, it was found that newly synthesized cytoplasmic RNA accumulates steadily in the whole chick embryo, reaching a level of 104 μg by the early neurula stage. On a per cell basis, however, the amount of newly synthesized cytoplasmic RNA seems to decrease slightly.
These findings are discussed in the light of present knowledge about embryos of other vertebrates and certain invertebrates.
Localization and growth pattern of the tergite Anlage of Drosophila
Authors: Santamaria Pedro , García-Bellido Antonio 
Published: April 2021

ABSTRACT
Following cauterization in different regions of each larval segment, different effects - on growth and pattern - in the adult hemitergite were obtained. A correspondence between different segments in the larva and in the adult was found, with the exception of the Vllth abdominal segment in the male, which apparently has no adult cuticular representation. The histoblasts forming the imaginal Anlage are grouped in the central part of the larval hemisegment. Following cauterization, the viable histoblasts only partially replace the killed ones, giving rise to incomplete tergites.
Pattern damages are characteristic of the cauterized region. Cauterization in marginal regions of the abdominal segment, although not killing the histoblasts, induce specific fusions and penetrations between neighbouring colateral and contralateral hemitergites. The effects of cauterization on the number of cuticular elements and their disposition in the adult pattern are discussed.
Surface modifications of neural epithelial cells during formation of the neural tube in the rat embryo
Authors: Freeman Bruce G. 
Published: April 2021

ABSTRACT
The apical (juxtaluminal) ends of the neural epithelial cells of rat embryos were examined using light and electron microscopy during varying stages of neural tube formation. At the neural-plate stage the apical surfaces exhibit numerous microvilli. At the presomite neurula stage the microvilli are longer and more irregular. Filaments of approximately 40–60 Å diameter appear in the apical cytoplasm. By the neural-groove stage, cytoplasmic protrusions containing various organelles have begun to appear. Apical filaments are present. At the beginning of closure the apical surfaces are characterized by large, irregular protrusions that are still associated with apical filaments. Finally, at the time of neural closure, the apical protrusions as well as the apical filaments have disappeared and the apical surfaces of the neural epithelial cells are relatively smooth.
These observations bear out the proposal that contraction of the apical filaments is responsible for the folding of the neural plate and the production of apical protrusions.