bluuebunny/crossref_metadata_2025_split huggingface dataset:
Parthenogenetic development of mouse embryosin vivo: I. Preimplantation development
Authors: Witkowska Anna 
Published: April 2021

ABSTRACTNewly ovulated eggs from CBA-p and CBA-T6T6 inbred strains were activated in situ with an electric shock of 20–50 V. Both spontaneously ovulating females mated with vasectomized males (strain A) and those induced to ovulate and kept apart from males were used. The immediate reaction of eggs was examined 5–7 h after activation and their subsequent development was followed every day up to the 6th day (eggs examined on the 5th and 6th day were tube-locked by a ligature). In spontaneous ovulators the highest yield of activated eggs was obtained following 30 V shock (75%), with a mean for four series (20, 30, 40 and 50 V) of 46·1%. The most common reaction is extrusion of the second polar body (2 PB) and formation of one pronucleus (about 70% of activated eggs). Other types of reaction include: immediate cleavage, suppression of 2 PB with formation of two or, very rarely, one pronucleus. Thus the majority of eggs are potentially haploid. No relationship between the frequency of various types of reaction and the strength of the shock (voltage) was observed. Up to the 3rd day cleavage proceeds at a normal rate and appears to slow down during the 4th day. In spontaneously ovulating females the incidence of blastocysts among developing eggs rises from 3·4% on the 4th day to 52·5% on the 5th day; the corresponding figures for induced ovulations are 10% and 23·6%. Some embryos despite being composed of a large number of cells (40–120) do not undergo cavitation and remain morulae.On the basis of karyological examination of 60 embryos with analysable metaphase plates 60% were classified as haploid, 16·7% as diploid, 1·7% as tetraploid and 21·6% as haploid/diploid mosaics. During early cleavage binucleate blastomeres (a presumed step in regulation from tt to 2n) were observed only in eggs from induced ovulations. In embryos developed from spontaneously ovulated eggs n/2n mosaics were observed for the first time on the 5th day. In general, spontaneously ovulated eggs developed better after activation (both in quantitative and qualitative terms) than those obtained following hormonal treatment.
Feather pattern stability and reorganization in cultured skin
Authors: Novel Genevieve 
Published: April 2021

ABSTRACT
The formation of the feather pattern has been studied in skin explants obtained from the lumbar region of the spinal pteryla of -to -day chick embryos. Explants were cultured in vivo on the chorioallantoic membrane (CAM) or in vitro, either on semi-solid natural media (containing whole chick embryo extract (JE) or chick brain extract (EC)), or in a liquid synthetic medium (199). Feather pattern development was dependent on the culture method and also on the way the explants were excised and treated before cultivation. When the mid-dorsal initial row of rudiments was preserved at explantation, the feather pattern was stable on all media and initial feather rudiments progressively gave rise to feather buds. When the mid-dorsal initial row of rudiments was damaged at explantation, explants of younger stages (A, B or C) cultured on media JE or EC underwent a complete reorganization of their initial feather pattern; in other explants (of older stage D, or those of any stage cultured in medium 199 or on the CAM) the initial feather pattern was stable. When the initial rudiments were destroyed by dermo-epidermal dissociation and recombination, feather pattern reorganization was observed in explants of any stage cultured in vitro (on medium EC or in medium 199) (Table 1, p. 625). Feather pattern reorganization was characterized by the following events: during the first 24 – 30 h of culture the initial feather rudiments gradually vanished; dermal condensations and epidermal placodes disappeared; after which a new ‘primary’ row differentiated parallel to the longitudinal edges of the explant’s dermis, its distance from the medial dermal edge was larger when the explant was obtained at a more advanced stage. The newly formed feathers were arranged in longitudinal rows parallel to the cephalo-caudal axis of the dermis, which was thus solely responsible for the polarity of the reorganized feather pattern. The capacity of the feather pattern to reorganize shows that it is still labile at the time of explantation and that the site of subsequent feathers is not yet determined in the unpatterned dermis. The pattern is determined progressively from prospective row to prospective row starting from the primary row. In normal development in situ, the role of the primary row is supposedly played by the mid-dorsal row in the lumbar region of the spinal pteryla. Just prior to the formation of feather condensations the dermal cells appear to be the transitory seat of a passing peak of morphogenetic activity moving from the mid-dorsal line to the lateral edges of the spinal tract.
A clonal analysis of segment development inOncopeltus(Hemiptera)
Authors: Lawrence Peter A. 
Published: April 2021

ABSTRACTX-irradiation of eggs and larvae of Oncopeltus fasciatus results in the development of clonal patches of epidermal cells of unusual pigmentation. The frequency, size and distribution of these patches is dependent on the dose and timing of irradiation. Analysis of these clones in the abdomen has shown that the presumptive epidermis becomes effectively segmented during blastoderm formation and thereafter the clones are restricted to within a segment quadrant (dorsal or ventral, left or right). There are approximately 10 presumptive epidermal cells per segment quadrant. The shape of the clones and the orientation of mitoses in larvae suggest that both early and late cells of the anterior margin of the segments divide with a preferred orientation (cleavage plane parallel to the antero-posterior axis). Elsewhere in the larval segment the mitoses are randomly oriented, and the segment grows evenly all over. The number of mitoses/cell/moult cycle is not precisely determined, but the amount of cell division is perhaps under a general probabilistic control. It is suggested that the segmental gradient may be involved in this control.
Positional information and pattern regulation in hydra: the formation of boundary regions following axial grafts
Authors: Hicklin J. , Hornbruch A. , Wolpert L. , Clarke M. 
Published: April 2021

ABSTRACT
A two-gradient model is proposed for regulation and regeneration of the head end of hydra in terms of positional information. One gradient is set up by a diffusible substance made at the head end, which may be regarded as a positional signal, and the other is a more stable cellular parameter which is the positional value. The rule for head end formation is that the concentration of the diffusible substance falls a threshold amount below the positional value. A variety of instantaneous axial grafts have been carried out which are discussed in terms of this model. Some simple computer simulations of diffusion are provided. There is some evidence that the source of the positional signal is localized at the head end. Some experiments on changes in polarity are given. It also seems that the positional signal from the head end inhibits foot end formation.
Positional information and pattern regulation in hydra: the effect of γ-radiation
Authors: Hicklin J. , Wolpert L. 
Published: April 2021

ABSTRACT
Hydra exposed to high doses of γ-irradiation (25000 rad) are still capable of regeneration although no normal mitotic figures could be seen for up to 48 h after irradiation. Irradiated heads could still inhibit head formation in other regions in graft combinations. The time for head end determination in irradiated animals appeared to be increased. It is concluded that head end regeneration need not involve cell division.
A propos d’un effet paradoxal de la cycloheximide sur l’œuf Anemia salina
Authors: Fautrez J. , Fautrez-Firlefyn N. 
Published: April 2021

ABSTRACT
Cycloheximide, an inhibitor of protein synthesis at the ‘translation’ level, has a very strong antimitotic activity upon the egg of Artemia salina, during segmentation. At extremely low concentrations, on the contrary, it enables eggs, extracted from the uterus just after fertilization, to enter into segmentation, while the controls remain undivided. From these results it is argued that synthesis of a protein in the immature egg could have an inhibitory influence upon too early cell division. The synthesis of this factor could be extremely sensitive to cycloheximide action.
Further observations on the distribution of cytoplasmic substances among the cleavage cells in Lymnaea stagnalis
Authors: Raven Chr. P. 
Published: April 2021

ABSTRACT
The period of development from the 4th cleavage to the 24-cell stage was studied. Both during 4th and 5th cleavage a wave of mitosis passes over the egg from the vegetative to the animal pole. At 5th cleavage it does not spread over the cells of the first quartet, however, and cell division stops for 3 h at the 24-cell stage. Nucleoli are now formed in the interphase nuclei, and many of them are extruded whole into the cytoplasm. After 5th cleavage the cleavage cavity is gradually reduced and finally disappears altogether. All cells then extend towards the centre of the egg. In this process one of the macromeres (3D) finally becomes preponderant, gets a central position and applies itself against the inner side of the animal cells. This is preceded by a period of seemingly haphazard variation in macromere positions. Lipid globules and mitochondria accumulate in the central parts of the first quartet cells. The special cytoplasm (SCA-plasm) found in the most vegetative part of the macromeres at the 8-cell stage is distributed among the cells at the next cleavages. Part of it passes into the 2nd micromeres, another part into the 3rd micromeres, while the rest remains concentrated in the vegetative part of the macromeres around the vegetative cross-furrow. At this place coarse dark composite granules, of a special kind and very rich in RNA, become visible at the 16-cell stage. At the 24-cell stage they begin to move inwards along the cell walls, and finally condense into the compact RNA-rich ‘ectosomes’ at the central ends of the macromeres. The significance of the SCA-plasm and of the ‘ectosomes’ for the determination of dorso-ventrality in Lymnaea is discussed.
Morphogenesis of the trigeminal mesencephalic nucleus in the hamster: cytogenesis and neurone death
Authors: Alley Keith E. 
Published: April 2021

ABSTRACTThe chronology of cellular development in the trigeminal mesencephalic nucleus of the hamster has been studied by light and electron microscopy. Major developmental features are compressed into a two-week period that spans pre- and postnatal maturation. Special emphasis is focused on the sequence of developmental events, with the following points analyzed in this report: cell proliferation, cytological and axonal development, cell death, and cluster formation.These centrally located primary sensory neurones seem to arise from a separate germinal population found in the alar plate of the midbrain and pons. The neurones are remarkable for their precocious formation and characteristic appearance. In hamster embryos they are first detected when the neural tube is only a couple of cell layers thick. Prenatally, the neurones grow rapidly and have doubled in diameter by birth. Axons form shortly after the cells are formed. This is marked by a sudden upsurge in cytoplasmic tubules and filaments in one end of the soma. Postnatally, cellular growth continues at a reduced rate. However, shortly after birth many small spines protrude from the cell body, thus increasing the surface area available for nutritive exchange. Myelination of the axon commences 6 days after birth.Cell counts on a series of pre- and postnatal animals detected a considerable overproduction of neurones in the mesencephalic nucleus. Prior to birth there is a rapid elimination of almost 50% of these cells. Degenerating cells were identified in both light and electron microscopes. The temporal relationship between peripheral innervation, cell death and synaptogenesis suggests a developmental mechanism that provides some flexibility in the formation of synaptic connexions in the mesencephalic nucleus.Clusters of 2 –4 tightly packed neurones are a characteristic feature of the developing and adult mesencephalic nucleus. Specialized junctions connect adjacent neurones and are thought to provide the basis for electrotonic coupling within the nucleus. Macula adhaerens plaques were present in both pre- and postnatal hamsters. However, close appositions were only identified postnatally.
Ein invasives Neoplasma aus embryonalen Zellen vonDrosophila melanogasterin Dauerkulturin vivo
Authors: Hauri Hans-Peter 
Published: April 2021

ABSTRACTAn invasive neoplasm from embryonic cells of Drosophila melanogaster cultured permanently in vivoThe neoplasm H 126, obtained from the posterior half of a 6 ± 1-h-old embryo of Droso-phila melanogaster, was cultivated in adult female flies over more than 120 transfer generations (more than 4 years). Four sub-lines were derived from it.The neoplasm H 126 invades the ovaries of the host flies, whereas the intestinal tract and the fat body are only surrounded very tightly, but not invaded by these abnormal cells. The neoplasm is lethal to the host 8–14 days after implantation into the abdomen (cultivation temperature: 25 °C).Egg deposition of neoplasm-bearing hosts decreases 5 days after abdominal implantation.After 4 years of cultivation the sub-lines differ specifically from one another in their chromosomal content; however, all of them show a karyotype near tetraploidy.Ultrastructural features of these neoplasm cells are: (a) the nearly complete absence of membrane specializations correlated with weak cell adhesion, (b) the abundance of cyto-plasmic processes and (c) 36 nm virus-like particles in the nucleus and in the cytoplasm.Invasiveness, alterations of the karyotype, the origin of the neoplasm H .126, and the presence of virus-like particles are discussed.
The structure of a morphogenetic cytoplasm, present in the polar lobe ofBithynia tentaculata(Gastropoda, Prosobranchia)
Authors: Dohmen M.R. , Verdonk N.H. 
Published: April 2021

ABSTRACTIn the first polar lobe of the egg of Bithynia tentaculata a cup-shaped mass of small vesicles is described, which fills the greater part of the lobe. It is named the ‘vegetal body’. With methyl green-pyronin the vegetal body stains clearly, but after treatment with RNase no staining occurs, thus indicating the presence of RNA. The first polar lobe of Bithynia is of great importance for further development of the embryo and it is argued that the vegetal body could be a morphogenetic cytoplasm, responsible for the developmental effects of the polar lobe.
In vitroactivation of mouse eggs
Authors: Graham C. F. , Deussen Z. A. 
Published: April 2021

ABSTRACTUnfertilized mouse eggs were activated in vitro with hyaluronidase. Subsequently they were exposed to culture medium at different osmolarities. In full strength White’s culture medium they tended to form one pronucleus and a second polar body. The majority of these eggs were haploid. In 4/5 and 3/5 dilutions of this medium, the second polar body formation was sup-pressed and eggs tended to form with one or two pronuclei. Those with one pronucleus were diploid and those with two pronuclei could either form a diploid or form a haploid mosaic. Old eggs tended to immediately cleave and form haploid mosaics.DNA synthesis was studied in activated eggs using tritiated thymidine and autoradiography. DNA synthesis occurred at a similar time in fertilized and activated eggs.
The effect of osmolarity on mouse parthenogenesis
Authors: Kaufman M. H. , Surani M. A. H. 
Published: April 2021

ABSTRACTEggs from (C57BI × A2G)F1 mice were activated by treatment with hyaluronidase, which removed the follicle cells, and cultured in vitro. Observations were made 6–8 h after hyaluronidase treatment to determine the frequency of activation and the types of parthenogenones induced. Cumulus-free eggs resulting from hyaluronidase treatment were incubated for in culture media of various osmolarities. The frequency of activation was found to be dependent on the postovulatory age of oocytes, while the types of parthenogenones induced were dependent on the osmolarity of the in vitro culture medium and their postovulatory age.Culture in low osmolar medium suppressed the extrusion of the second polar body (2PB). This decreased the incidence of haploid eggs with a single pronucleus and 2PB and immediately cleaved eggs from 97·5% to 42·3 % of the activated population. Where 2PB extrusion had been suppressed, 97·4 % of parthenogenones contained two haploid pronuclei. Very few were observed with a single and presumably diploid pronucleus.Serial observations from 11 to 18 h after hyaluronidase treatment were made on populations of activated eggs as they entered the first cleavage mitosis after incubation in medium either of normal (0·287 osmol) or low (0·168 osmol) osmolarity. A delay in the time of entry into the first cleavage mitosis similar to the duration of incubation in low osmolar medium was observed.Further, eggs were incubated in control and low osmolar culture media containing uniformly labelled [U−14C]amino acid mixture to examine the extent of protein synthesis in recently activated eggs subjected to these culture conditions. An hypothesis is presented to explain the effect of incubation in low osmolar culture medium in delaying the first cleavage mitosis.
The interaction of the organizing regions in hydra and its possible relation to the role of the cut end in regeneration
Authors: Newman Stuart A. 
Published: April 2021

ABSTRACT
Regeneration in hydra does not necessarily involve cell division, so that the problem of pattern regulation is essentially one of finding the processes by which a given population of cells are assigned appropriate functions in the correct positions. The restoration and nature of the organizers or ‘dominant regions’ must also be explained.
Lateral transplants of the two different organizer tissues (hypostome and basal disc) into the digestive regions of host animals unexpectedly antagonize one another’s inductive ability, suggesting that the heretofore separately studied distal and proximal developmental fields may in fact be interconnected. A model based on this idea, incorporating the extinction results with classical findings, leads to the hypothesis of a role for leakage from the cut surface as a trigger for the regenerative process. This is tested using a ligature technique in which the cut surface is minimized when the hypostome is removed, and the degree of regeneration is found to be significantly lowered, in agreement with prediction.
These results are discussed in relation to ‘positional information’ and ‘special substance’ models for pattern formation.
Cell redundancy in the zona-intact preimplantation mouse blastocyst: a light and electron microscope study of dead cells and their fate
Authors: El-Shershaby A. M. , Hinchliffe J. R. 
Published: April 2021

ABSTRACTIn the zona pellucida-intact 95 h post coition mouse blastocyst, electron-microscopic studies reveal the presence, as a part of normal development, of 1–2 dead cells lying free on the surface of the inner cell mass (1CM) or trophoblast cells, and of 4–5 dead cells phago-cytosed by I.CM cells. Such dead cells are electron-dense and show characteristic chromato-pycnosis of the nucleus, and swelling of the endoplasmic reticulum. In addition, 1–2 digestive vacuoles with granular contents and myelin figures are found, principally in ICM cells, and corresponding with basophilic bodies observed with the light microscope. The results are interpreted as indicating that a relatively large number (i.e. a minimum of 6–8, or approximately 10%) of blastocyst cells die and are phagocytosed and digested, usually by the ICM cells, but probably also by trophoblast cells. This process does not, however, affect the future differentiation of the ingesting cell. Simultaneously a small number of epithelial cells adjacent to the blastocyst die, either singly or in small groups. These findings confirm the view that previous reports of penetration of the uterine epithelium by ‘primary invasive cells’ originating in the ICM were due to confusion between two separate groups of dead cells, namely the embryonic dead cells of the ICM and the single dead cells in the adjacent uterine epithelium, which appear to be phagocytosed by trophoblast cells following loss of the zona pellucida.
Polarizing and maintenance activities in two polydactylous mutants of the fowl: diplopodia
1 and talpid
2
Authors: Maccabe Jeffrey A. , Abbott Ursula K. 
Published: April 2021

ABSTRACT
In two polydactylous mutants, talpid2 and diplopodia1, polarizing activity appears to be present only in the normal location in the posterior corner of the limb-bud. There is, thus, a preaxial extension of maintenance activity without an accompanying extension of demon-strable polarizing activity. Experiments involving apex exchanges between normal and talpid2 wing-buds suggest that the movement of ‘maintenance factor’ per se from preaxial talpid2 limb tissue into a normal apex does not occur.
Some aspects of the development of the notochord in mouse embryos
Authors: Jurand A. 
Published: April 2021

ABSTRACTPrenotochordal cells are derived by proliferation from the pluripotential ectoderm in the Hensen’s node area, and they migrate in the cephalic direction to be incorporated into the roof of the archenteron. Later, after separation from the archenteron, the notochord probably includes some endodermal cells. Topographically it occupies an intermediate position between the ectoderm and endoderm. In this way it assumes a mesodermal-like character. After separation fiom the archenteron, the differentiation of the organ and its cells follows a cranio-caudal gradient. At the time of separation the basal lamina, originally covering the dorsal side of both the prenotochordal and endodermal cells, remains continuous between the endoderm and the notochord. Its presence from the earliest stages of morphogenesis of the notochord presumably indicates that it plays an important formative role.The cells of Hensen’s node contain numerous microtubules, centrioles and cilia. In later stages fibrillogenesis in the prenotochordal and notochordal cells and excortication (ecdysis) occur. The intracellular fibrillar material in the notochordal cells may first form the basal lamina and later the perichordal sheath. In 12 to 13-day-old embryos, during excortication of the fibrillar material, the basal lamina undergoes disruption and eventually disappears. From the 10th day onwards, the outer plasma membrane shows an active endocytosis, by the formation of micropinocytic vesicles. Vacuolization occurs in the later stages of morpho-genesis and it is suggested that this is due to dilation of endoplasmic reticulum and mito-chondria.There is no evidence of a syncytial stage in the development of the notochord in mouse embryos.