bluuebunny/crossref_metadata_2025_split huggingface dataset:
Changes in hair growth characteristics following the wounding of vibrissa follicles in the hooded rat
Authors: Jahoda Colin A. B. , Oliver Roy F. 
Published: April 2021

ABSTRACT
The effect on hair growth of wounding the lower region of whisker follicles, and in particular the dermal papilla, with sharply pointed tungsten needles was studied in adult hooded rats. Following injury hair growth ceased, but was subsequently resumed. While it might have been anticipated that follicle wounding would have a negative effect on whisker length, regular postoperative length measurements revealed that in follicles where cellular material was not displaced from the follicle by the original manipulation, 50 % of the subsequent hairs produced were longer than their counterparts on the opposite side of the face, with 25 % shorter and 25 % with their length unchanged. In every case increased hair length was achieved by a prolongation of the growing period of the hair. Growth rate, when altered, was reduced. These results suggest that the factors which control the duration of the hair cycle and fibre growth rate are independent in vibrissa follicles. Since removal of most of the epidermal component by plucking of the hair just prior to injury produced equivalent hair length increases, this implicated the proximal dermal components as being mainly responsible for the observed changes.
Haemoglobin and globin synthesis in the isolated primitive and definitive erythroid cells of chicken embryos. Evidence for a non-clonal mechanism at the haemoglobin switch
Authors: Schalekamp Margreet , Goor Diety Van 
Published: April 2021

ABSTRACT
Primitive and definitive erythroid cells of chicken embryos aged 4–8 days, were separated by unit gravity sedimentation and pulse labelled with [3H]- and [14C]leucine. The haemo-globin and globin synthesis in the cell populations was analysed by chromatofocussing, isoelectric focussing, urea starch gel electrophoresis, and immunofluorescence or radioimmunoassay, using globin specific antibodies.
We found that both embryonic and adult agiobins are present in primitive erythroid cells, but relatively more of the adult α-type globins are synthesized in the late primitive erythroid cells. In young definitive erythroid cells exclusively adult a-type globins are synthesized. From these findings we conclude that a command to synthesize adult agiobin is perceived in both cell types at the time of the switch. This supports an environmental model rather than a clonal model of haemoglobin switching.
Dermal cells form strong adhesions to the basement membrane during the development of feather primordia in chick skin
Authors: Davidson Duncan 
Published: April 2021

ABSTRACT
Experiments are described which provide a direct measure of the adhesion between dermis and epidermis during the development of feather primordia in chick dorsal skin in culture. The epidermis was peeled from the dermis and the surfaces so exposed were examined under the scanning electron microscope: regions of strong adhesion between the tissues were revealed as areas where their separation was incomplete. The results show that soon after primorida become morphologically distinct, cells from the surface of dermal condensations form adhesions to the basement membrane which are stronger than those between dermis and epidermis interplumar skin. These adhesions may help to hold the epidermis and dermis together during the outgrowth of the primordium.
The cellular contributions of blastema and stump to 180 ° supernumerary limbs in the axolotl
Authors: Maden M. , Mustafa K. 
Published: April 2021

ABSTRACT
By inverting triploid blastemas onto diploid stumps (and vice versa) the cellular contributions to supernumerary limbs so generated have been assessed. The four classes of 180° supernumerary limbs each had a different mixture of stump and blastemal cells. The mesoderm of normal supernumeraries was composed entirely or almost entirely of stump cells and were always of stump handedness. The mesoderm of symmetrical supernumeraries was of variable composition, it could be mostly stump, mostly blastema or half and half. In part normal/part symmetrical supernumeraries the normal part was usually of stump origin and the abberant symmetrical part of blastemal origin. In part normal/part inverted supernumeraries the normal part came from the stump and the inverted part from the inverted blastema. The handedness of each part of these supernumeraries corresponded with its cellular origin. The epidermis of the supernumeraries was not of the same relative composition as the mesoderm, it tended to have a larger stump component. The black/white marker was also used and this too tended not to conform to the mesodermal contribution patterns. These results are discussed in terms of rules for generating supernumeraries and it is concluded that with the exception of symmetrical supernumeraries the cellular contributions of stump and blastema determine their structure.
Butterfly wing patterns: how good a determining mechanism is the simple diffusion of a single morphogen?
Authors: Bard Jonathan B. L. , French Vernon 
Published: April 2021

ABSTRACT
The formation of the wing pigmentation patterns of three species of butterflies has been modelled using a mechanism based on a tripod of assumptions. First, that there may be morphogen sources in the foci of eyespots and morphogen sinks at some parts of the wing margin, all other cells being passive. Second, that the morphogen has a finite half life and diffuses simply and freely away from the sources throughout a wing of hexagonally packed cells. Third, that the overt pattern derives from cells interpreting the local morphogen concentration with respect to thresholds which determine scale colours. The final pattern thus follows lines of constant morphogen concentration and may, depending on the distribution of sources, comprise rings, curves or bands. With such a model, we have been able to compute stable patterns having the essential topology of the compound spots of Tenaris domitilla, the large rings of Diaethria marchalii and the pattern of eyespots, rings and asymmetric bands of Ragadia minoa. Quantitative analysis of the pattern-forming process shows that, with a biologically realistic diffusion constant (∽ 540−7cm2 sec−1) and a morphogen half life less than 6h, the patterns form within ∽ 12h over a wing of ∽ 1000 cells in length. The limitations of the model are that the exact morphology of the eyespots and bands do not match precisely those of the original wings, that there are edge distortions and that optimal patterns may be critically dependent on the exact positions of sources and sinks. An explanation for part of the discrepancy is that we have assumed an adult wing shape and foci coordinates in modelling a process that took place earlier in development. Nevertheless, the limitations of the model argue against a mechanism based on a single morphogen operating in vivo. However, as the model can generate many features of butterfly wing patterns, it may be considered as a degenerate case of that mechanism.
The response of denervated axolotl arms to delayed amputation
Authors: Wallace H. 
Published: April 2021

ABSTRACT
Forearms of juvenile axolotls can be kept denervated for up to 4 weeks by deflecting brachial nerves to the flank. A more orthodox second denervation prolongs this state up to a total of six weeks. The denervated arms are unable to regenerate for the whole period, but eventually become reinnervated and then regenerate normally. These results and analogous experiments on adult newts prompt a partial retraction and reinterpretation of my previous report on regeneration after prolonged denervation.
Cell replication and terminal differentiation in the embryonic chicken lens: normal and forced initiation of lens fibre formation
Authors: Zwaan Johan , Kenyon Robert E. 
Published: April 2021

ABSTRACT
The relation between cell replication and lens fibre formation was studied in normal 5-day chicken embryos and in embryos in which the lens was reversed. After this microsurgery the epithelial cells were facing the retina and were forced to start fibre differentiation. Embryos were treated with [3H]thymidine followed by autoradiography or with Colcemid to induce metaphase arrest.
About half of the control epithelial cells were actively replicating (in contrast, in the earliest stages of lens formation all cells are multiplying). Half of the non-dividing population was accounted for by the annual pad cells. The other half, probably in a resting phase (GO) of the cell cycle, was perhaps slightly more common in the central epithelium. This suggests that a germinative zone may be forming in the lens epithelium as early as 5 days of embryonic life.
Normal epithelium had a cell cycle time of about 11 h, with S-phase, M, G1 and G2 lasting 5·5, 0·5, 2, and 3 h. After reversal the labelling index remained at control levels for about 4 h and then dropped to zero at 9 h. Similarly, the mitotic index gradually decreased to zero in 15.
It appears that reversal forces the epithelial cells to cease replication when they reach Gl. Cells already in GO may form fibres without first going through DNA synthesis. The very sharp boundary between dividing and non-dividing cells at the border of the optic cup suggests that the retina may regulate the irreversible cessation of cell replication associated with lens fibre differentiation.
Trophectodermal processes regulate the expression of totipotency within the inner cell mass of the mouse expanding blastocyst
Authors: Fleming Tom P. , Warren Paul D. , Chisholm Julia C. , Johnson Martin H. 
Published: April 2021

ABSTRACT
Mouse blastocysts, aged 0, 2, 6 and 12 h from the onset of cavitation, were examined by transmission (TEM) and scanning (SEM) electron microscopy. In TEM sections, trophectoderm cells (TE) differed morphologically from those of the inner cell mass (ICM) by their flattened shape, paler cytosol staining and polarized disposition of both junctional complexes (apicolateral) and intracellular secondary lysosomes (SL; basal). Throughout this period of development, cytoplasmic processes, characterized by abundant SLs, cover approximately 80 % of the juxtacoelic face of the ICM. These processes are shown to be derived from the basal surface of TE cells intermediately placed between polar and mural regions. In SEM preparations of the juxtacoelic ICM surface, revealed by ‘cracking open’ blastocysts, the processes appear as tongue-shaped, centripetally oriented structures which terminate collectively at a central area on the ICM surface.
The potential of cultured ICMs to generate TE was demonstrated following their immunosurgical isolation from blastocysts aged up to 12 h post cavitation and by examining the sequence of ultrastructural changes associated with TE generation by ICMs from 2 h blastocysts. In contrast, the juxtacoelic cells of similarly aged ICMs observed in situ in ultrasections of intact embryos showed little or no evidence of totipotency expression as judged by the absence of TE characteristics. Since TE expression within presumptive ICM cells is thought to be generated by an asymmetry of cell contacts (Johnson & Ziomek, 1983), we propose that the juxtacoelic TE processes, by providing a cellular cover to the ICM, function in suppressing the expression in situ of ICM totipotency.
Translation and stability of ovalbumin messenger RNA injected into growing oocytes and fertilized ova of mice
Authors: Ebert Karl M. , Paynton Barbara V. , Mcknight G. Stanley , Brinster Ralph L. 
Published: April 2021

ABSTRACT
Growing mouse oocytes and fertilized ova were injected with chicken ovalbumin messenger RNA (mRNAov) and chicken conalbumin mRNA (mRNAcon) and cultured in vitro. Estimation of mRNAov and mRNAcon stability by hybridization of cDNAov and cDNAcon to extracted mRNA from injected oocytes and fertilized ova indicated a half-life of 147 and 366 h in the oocyte and 5 and 3 h in the fertilized ovum respectively. Stability of mRNAov was similar in the fertilized and unfertilized ovum. Oocytes injected with chicken ovalbumin mRNA were also labelled with βH]leucine and ovalbumin synthesis was measured by immunoprecipitation. The amount of ovalbumin synthesized during the initial 7 h was less than during the period of 18–25 or 66–73 h postinjection. The greatest percentage of ovalbumin to total protein synthesis occurred between 66–73 h. Oocytes secreted 12% of the synthesized ovalbumin during each of the 7 h periods (0–7, 18–25 and 66-73 h) indicating a stable mechanism for secretion throughout the culture period. These studies demonstrate: (1) a dramatic difference in stability of injected mRNA between the growing oocyte and the unfertilized or fertilized ovum, and (2) a gradual increase in the translation of injected mRNA by the growing oocyte during in vitro culture.
Vascular regression during the formation of the free digits in the avian limb bud: a comparative study in chick and duck embryos
Authors: Hurle J. M. , Colvee E. , Fernandez-Teran M. A. 
Published: April 2021

ABSTRACT
The pattern and structure of the blood vessels of the interdigital spaces of the leg bud have been studied by means of Indian ink injections and transmission electron microscopy in the chick and duck embryos. The results show that in the chick the interdigital necrotic process responsible for the freeing of the digits is followed by regression of the blood vessels. In the webbed foot of the duck, the interdigital necrotic processes are not followed by vascular regression. Transmission electron microscopic studies show that both in the chick and in the duck, interdigital blood vessels are immature structures lacking basal lamina. Dead cells of presumably endothelial origin were detected in the lumen of the regressing blood vessels of the chick but not in the duck. However, the intensity of this cell death process does not appear to be high enough to account by itself for the disappearance of the interdigital blood vessels. The possible relationships between interdigital mesenchymal cell death and vascular regression are discussed.
Paths taken by sensory nerve fibres in aneural chick wing buds
Authors: Swanson Gavin J. 
Published: April 2021

ABSTRACT
What constrains growing nerves to follow the paths they take during the development of peripheral nerve patterns? This paper examines two, related, topics concerning the pathways taken by sensory nerve fibres in the embryo chick wing: the constraints imposed on the nerves by limb tissues; and the timing of axon outgrowth. Sensory ganglia from 7-day-old chick embryos were grafted into younger host embryo wing buds which had been previously denervated. The resultant nerve patterns revealed that, first, nerve fibres could grow almost anywhere within the wing bud, with the exceptions of cartilage and a region just beneath the growing tip. Secondly, the younger the host wing bud at the time of grafting, the more likely the neurites were to form a thick fascicle which followed the limb’s normal nerve pathways. The wing apparently does not impose a rigid restraint on nerves to grow only along certain routes; however, if a nerve fibre reaches a normal nerve pathway, it prefers to follow it.
The distribution of the polarizing zone (ZPA) in the legbud of the chick embryo.
Authors: Hinchliffe J. Richard , Sansom Anna 
Published: April 2021

ABSTRACT
The stage-21 to 22 legbud polarizing zone (ZPA) was mapped by transplanting small blocks of posterior marginal mesenchyme preaxially into stage-20 to -22 chick wing buds and assessing the degree of duplication of the wing digital skeleton produced in the host. Blocks taken from the posterior flank, from the angle between posterior flank and the proximal base of the limb bud, and from the most anterior distal position chosen (under the AER), all had very low activity. Blocks taken from the posterior margin of the legbud, plus the next distal block under the posterior part of the AER, all had high activity. We consider that barrier and amputation results on wing and legbud, when interpreted in the light of maps of the ZPA in both limb buds, are consistent with the hypothesis that both leg and wing have their growth and anteroposterior axis of pattern formation controlled by the ZPA.
Genetic identification of tissue of origin of cellular populations within the mouse placenta
Authors: Rossant J. , Croy B. A. 
Published: April 2021

ABSTRACT
The mouse haemochorial placenta is a complex mixture of maternal cells and foetal trophectoderm and inner cell mass (ICM)-derived cells. The majority of the placental tissue is assumed to be trophoblast in origin but the exact extent and localization of the ICM and maternal contribution has not previously been determined. Using embryo transfer and reconstituted blastocyst techniques, combined with isozymal and in situ genetic markers, we have established that about 70% of the 13 to 15-day placenta is trophectoderm-derived, 30% is maternal in origin, and 4% develops from the ICM. Nearly all of the maternal contribution was confined to the spongiotrophoblast region and all of the ICM contribution was confined to the labyrinthine trophoblast region, where it formed the foetal blood capillaries and the endodermal sinuses. Using the same genetic markers, we showed that cell suspension techniques commonly used to produce ‘trophoblast’ cell preparations from placenta do not enrich for trophoblast, and, indeed, that collagenase, the preferred dissociation technique for cell viability, produced cell suspensions in which ICM and maternal cells were preferentially dissociated. No method for producing pure trophoblast populations has yet been found.
Some unusually high ICM contributions to the placenta were found in reconstituted blastocyst experiments using ICMs isolated from early 3·5-day blastocysts, suggesting that these ICMs may have contributed to the trophectoderm layer of the blastocyst. These and other experiments suggest that the inner cell mass lineage may not be closed until some time after formation of the blastocyst.
Stimulation of division in mouse 3T3 cells by coculture with embryonic chick limb tissue
Authors: Bell K. M. , McLachlan J. C. 
Published: April 2021

ABSTRACT
Two regions of the chick limb bud — the apical ectodermal ridge and the zone of polarizing activity — have been shown to influence cell division and pattern formation during normal development and following surgical manipulation. In this study, using a simple coculture system, together with autoradiography, we have shown that these morphogenetically active regions of the limb bud can stimulate quiescent 3T3 cells to initiate DNA synthesis to a significantly greater degree than comparable but morphogenetically inactive regions of the limb bud.
Normal fates and states of specification of different regions in the axolotl gastrula
Authors: Cleine J. Herman , Slack Jonathan M. W. 
Published: April 2021

ABSTRACT
A fate map was constructed for four regions of the early gastrula of Ambystoma mexicanum using orthotopic grafts from donors labelled with FLDx (fluoresceinated-lysinated-dextran). The region around the animal pole gave rise to epidermis only and did not include prospective neural plate. The dorsal marginal zone contributed to cephalic endoderm and to the whole length of the axial mesoderm (notochord and somites), the lateral marginal zone to lateroventral and somitic mesoderm, and the ventral marginal zone to lateroventral mesoderm. It was found that the dorsal marginal zone contributed relatively more to the anterior regions of the mesodermal mantle and the ventral marginal zone more to its posterior parts.
The same regions of the gastrula and also vegetal yolky tissue were cultured as explants and labelled with tritiated mannose. Their glycoprotein synthesis pattern was compared to those of the neurula tissues to which they contribute in vivo. Animal pole explants synthesized large amounts of the epidermis-specific marker epimucin. Dorsal marginal zone explants did not synthesize epimucin but did make amounts of S2 and S6 indicative of mesoderm, as well as the notochord-specific markers S2·2 and S3·2. Lateral marginal zone explants showed the same pattern as the dorsal marginal zone including the two notochord-specific markers, although they do not contribute to notochord in vivo. Ventral marginal zone explants were more variable in their behaviour. Yolky tissue from the vegetal hemisphere of the gastrula or the archenteron floor of the neurula synthesized mainly polydisperse material of high molecular weight rather than discrete glycoproteins.
The results indicate that at the early gastrula stage states of specification exist which correspond to the three germ layers, ecto-, meso- and endoderm.
The ectodermal specification of animal pole explants is quite robust and cannot easily be changed by variation of the culture conditions. However treatment with a concentrated pellet of vegetalizing factor does induce a change to mesodermal specification, which is clearly detectable in the pattern of glycoprotein synthesis. Similar inductive interactions between different regions of the early embryo are thought to occur during normal development.
Comparative effects of cathepsin inhibitors on rat embryonic development in vitro. Evidence that cathepsin D is unimportant in the proteolytic function of yolk sac.
Authors: Freeman Stuart J. , Brown Nigel A. 
Published: April 2021

ABSTRACT
The effects of two proteinase inhibitors, leupeptin and pepstatin on the development of 9·5-day rat conceptuses in vitro has been studied. All cultures were of 48 h duration and the inhibitors were present throughout the entire period. When pepstatin was added to the culture medium (5–25 μg/ml) conceptuses developed and grew to an extent that did not differ from untreated controls. However, leupeptin (1–4 μg/ml) caused severe growth retardation and abnormal development of conceptuses.
The effects of the two inhibitors on the hydrolysis of 125I-labelled BSA and haemoglobin by homogenates of 10·5-day yolk sac indicated the biochemical basis for the differential toxic effects of the two inhibitors on development. Leupeptin was highly inhibitory of the degration of both substrates whereas pepstatin caused no inhibition of 125I-labelled BSA hydrolysis, and only a slight inhibition of haemoglobin hydrolysis.
These observations demonstrate that cathepsin D, a lysosomal aspartic proteinase that is specifically inhibited by pepstatin is not involved in yolk-sac-mediated protein utilization by early organogenesis-phase conceptuses and that lysosomal cysteine proteinases, specifically inhibited by leupeptin, are of paramount importance in this yolk sac function.
Developmental variability within and between mouse expanding blastocysts and their ICMs
Authors: Chisholm Julia C. , Johnson Martin H. , Warren Paul D. , Fleming Tom P. , Pickering Susan J. 
Published: April 2021

ABSTRACT
We have attempted to reduce the developmental heterogeneity amongst populations of mouse blastocysts by synchronizing embryos to the first visible signs of blastocoel formation. Using embryos timed in this way, we have examined the extent of variation of inside and outside cell number and of inside cell size, nuclear DNA content and developmental potential, between and within embryos of a similar age postcavitation.
The overall impression gained is one of wide heterogeneity in inside: outside cell number ratios and in cell cycling and its relation to cavitation among embryos of similar age postcavitation. However, the simplest explanation of our results suggests that cavitation generally begins at a time when most outside cells are in their sixth developmental cell cycle and that outside cells, as a population, are a little ahead of inside cells in their cell cycling. Additionally we present evidence that, within at least some individual inner cell masses (ICM), there is intraembryo variation in the time at which inside cell developmental potential becomes restricted.