bluuebunny/crossref_metadata_2025 huggingface dataset:
Emx2regulates the proliferation of stem cells of the adult mammalian central nervous system
Authors: Galli Rossella , Fiocco Roberta , De Filippis Lidia , Muzio Luca , Gritti Angela , Mercurio Sara , Broccoli Vania , Pellegrini Massimo , Mallamaci Antonello , Vescovi Angelo L.
Published: April 2021

The appropriate control of proliferation of neural precursors has fundamental implications for the development of the central nervous system and for cell homeostasis/replacement within specific brain regions throughout adulthood. The role of genetic determinants in this process is largely unknown.

We report the expression of the homeobox transcription factor Emx2 within the periventricular region of the adult telencephalon. This neurogenetic area displays a large number of multipotent stem cells. Adult neural stem cells isolated from this region do express Emx2 and down-regulate it significantly upon differentiation into neurons and glia. Abolishing or, increasing Emx2 expression in adult neural stem cells greatly enhances or reduces their rate of proliferation, respectively. We determined that altering the expression of Emx2 affects neither the cell cycle length of adult neural stem cells nor their ability to generate neurons and glia. Rather, when Emx2 expression is abolished, the frequency of symmetric divisions that generate two stem cells increases, whereas it decreases when Emx2 expression is enhanced.
The activity of theDrosophilamorphogenetic protein Bicoid is inhibited by a domain located outside its homeodomain
Authors: Zhao Chen , York Allen , Yang Fan , Forsthoefel David J. , Dave Vrushank , Fu Dechen , Zhang Dongyi , Corado Maria S. , Small Stephen , Seeger Mark A. , Ma Jun
Published: April 2021

The Drosophila morphogenetic protein Bicoid (Bcd) is a homeodomain-containing activator that stimulates the expression of target genes during early embryonic development. We demonstrate that a small domain of Bcd located immediately N-terminally of the homeodomain represses its own activity in Drosophila cells. This domain, referred to as a self-inhibitory domain, works as an independent module that does not rely on any other sequences of Bcd and can repress the activity of heterologous activators. We further show that this domain of Bcd does not affect its properties of DNA binding or subcellular distribution. A Bcd derivative with point mutations in the self-inhibitory domain severely affects pattern formation and target gene expression in Drosophila embryos. We also provide evidence to suggest that the action of the self-inhibitory domain requires a Drosophila co-factor(s), other than CtBP or dSAP18. Our results suggest that proper action of Bcd as a transcriptional activator and molecular morphogen during embryonic development is dependent on the downregulation of its own activity through an interaction with a novel co-repressor(s) or complex(es).
Erasing genomic imprinting memory in mouse clone embryos produced from day 11.5 primordial germ cells
Authors: Lee Jiyoung , Inoue Kimiko , Ono Ryuichi , Ogonuki Narumi , Kohda Takashi , Kaneko-Ishino Tomoko , Ogura Atsuo , Ishino Fumitoshi
Published: April 2021

Genomic imprinting is an epigenetic mechanism that causes functional differences between paternal and maternal genomes, and plays an essential role in mammalian development. Stage-specific changes in the DNA methylation patterns of imprinted genes suggest that their imprints are erased some time during the primordial germ cell (PGC) stage, before their gametic patterns are re-established during gametogenesis according to the sex of individuals. To define the exact timing and pattern of the erasure process, we have analyzed parental-origin-specific expression of imprinted genes and DNA methylation patterns of differentially methylated regions (DMRs) in embryos, each derived from a single day 11.5 to day 13.5 PGC by nuclear transfer. Cloned embryos produced from day 12.5 to day 13.5 PGCs showed growth retardation and early embryonic lethality around day 9.5. Imprinted genes lost their parental-origin-specific expression patterns completely and became biallelic or silenced. We confirmed that clones derived from both male and female PGCs gave the same result, demonstrating the existence of a common default state of genomic imprinting to male and female germlines. When we produced clone embryos from day 11.5 PGCs, their development was significantly improved, allowing them to survive until at least the day 11.5 embryonic stage. Interestingly, several intermediate states of genomic imprinting between somatic cell states and the default states were seen in these embryos. Loss of the monoallelic expression of imprinted genes proceeded in a step-wise manner coordinated specifically for each imprinted gene. DNA demethylation of the DMRs of the imprinted genes in exact accordance with the loss of their imprinted monoallelic expression was also observed. Analysis of DNA methylation in day 10.5 to day 12.5 PGCs demonstrated that PGC clones represented the DNA methylation status of donor PGCs well. These findings provide strong evidence that the erasure process of genomic imprinting memory proceeds in the day 10.5 to day 11.5 PGCs, with the timing precisely controlled for each imprinted gene. The nuclear transfer technique enabled us to analyze the imprinting status of each PGC and clearly demonstrated a close relationship between expression and DNA methylation patterns and the ability of imprinted genes to support development.
Xcl1causes delayed oblique periclinal cell divisions in developing maize leaves, leading to cellular differentiation by lineage instead of position
Authors: Kessler Sharon , Seiki Sumer , Sinha Neelima
Published: April 2021

Differentiation of plant cells is regulated by position-dependent mechanisms rather than lineage. The maize Extra cell layers1 (Xcl1) mutation causes oblique, periclinal divisions to occur in the protoderm layer. These protodermal periclinal divisions occur at the expense of normal anticlinal divisions and cause the production of extra cell layers with epidermal characteristics, indicating that cells are differentiating according to lineage instead of position. Mutant kernels have several aleurone layers instead of one, indicating that Xcl1 alters cell division orientation in cells that divide predominantly in the anticlinal plane. Dosage analysis of Xcl1 reveals that the mutant phenotype is caused by overproduction of a normal gene product. This allows cells that have already received differentiation signals to continue to divide in aberrant planes and suggests that the timing of cell division determines differentiation. Cells that divide early and in the absence of differentiation signals use positional information, while cells that divide late after perceiving differentiation signals use lineage information instead of position.
The role of smooth muscle in regulating prostatic induction
Authors: Thomson Axel A. , Timms Barry G. , Barton Lesley , Cunha Gerald R. , Grace Oliver C.
Published: April 2021

We have examined the role that smooth muscle plays during prostatic organogenesis and propose that differentiation of a smooth muscle layer regulates prostatic induction by controlling mesenchymal/epithelial interactions. During development of the rat reproductive tract, an area of condensed mesenchyme involved in prostatic organogenesis is formed. This mesenchyme (the ventral mesenchymal pad, VMP) is found in both males and females, yet only males develop a prostate. We demonstrate that a layer of smooth muscle differentiates between the VMP and the urethral epithelium, and that there is a sexually dimorphic difference in the development of this layer. Serial section reconstruction showed that the layer formed at approximately embryonic day 20.5 in females, but did not form in males. In cultures of female reproductive tracts, testosterone was able to regulate the thickness of this layer resulting in a 2.4-fold reduction in thickness. We observed that prostatic buds were present in some female reproductive tracts, and determined that testosterone was able to stimulate prostatic organogenesis, depending upon the bud position relative to the smooth muscle layer. In vitro recombination experiments demonstrated that direct contact with the VMP led to the induction of very few epithelial buds, and that androgens dramatically increased bud development. Taken together, our data suggest that differentiation of a smooth muscle layer regulates signalling between mesenchyme and epithelium, and comprises part of the mechanism regulating prostatic induction.
TGFβ2 mediates the effects of Hedgehog on hypertrophic differentiation and PTHrP expression
Authors: Alvarez Jesus , Sohn Philip , Zeng Xin , Doetschman Thomas , Robbins David J. , Serra Rosa
Published: April 2021

The development of endochondral bones requires the coordination of signals from several cell types within the cartilage rudiment. A signaling cascade involving Indian hedgehog (Ihh) and parathyroid hormone related peptide (PTHrP) has been described in which hypertrophic differentiation is limited by a signal secreted from chondrocytes as they become committed to hypertrophy. In this negative-feedback loop, Ihh inhibits hypertrophic differentiation by regulating the expression of Pthrp, which in turn acts directly on chondrocytes in the growth plate that express the PTH/PTHrP receptor. Previously, we have shown that PTHrP also acts downstream of transforming growth factor β (TGFβ) in a common signaling cascade to regulate hypertrophic differentiation in embryonic mouse metatarsal organ cultures. As members of the TGFβ superfamily have been shown to mediate the effects of Hedgehog in several developmental systems, we proposed a model where TGFβ acts downstream of Ihh and upstream of PTHrP in a cascade of signals that regulate hypertrophic differentiation in the growth plate. This report tests the hypothesis that TGFβ signaling is required for the effects of Hedgehog on hypertrophic differentiation and expression of Pthrp. We show that Sonic hedgehog (Shh), a functional substitute for Ihh, stimulates expression of Tgfb2 and Tgfb3 mRNA in the perichondrium of embryonic mouse metatarsal bones grown in organ cultures and that TGFβ signaling in the perichondrium is required for inhibition of differentiation and regulation of Pthrp expression by Shh. The effects of Shh are specifically dependent on TGFβ2, as cultures from Tgfb3-null embryos respond to Shh but cultures from Tgfb2-null embryos do not. Taken together, these data suggest that TGFβ2 acts as a signal relay between Ihh and PTHrP in the regulation of cartilage hypertrophic differentiation.
LvDelta is a mesoderm-inducing signal in the sea urchin embryo and can endow blastomeres with organizer-like properties
Authors: Sweet Hyla C. , Gehring Michael , Ettensohn Charles A.
Published: April 2021

Signals from micromere descendants play a critical role in patterning the early sea urchin embryo. Previous work demonstrated a link between the induction of mesoderm by micromere descendants and the Notch signaling pathway. In this study, we demonstrate that these micromere descendants express LvDelta, a ligand for the Notch receptor. LvDelta is expressed by micromere descendants during the blastula stage, a time when signaling has been shown to occur. By a combination of embryo microsurgery, mRNA injection and antisense morpholino experiments, we show that expression of LvDelta by micromere descendants is both necessary and sufficient for the development of two mesodermal cell types, pigment cells and blastocoelar cells. We also demonstrate that LvDelta is expressed by macromere descendants during mesenchyme blastula and early gastrula stages. Macromere-derived LvDelta is necessary for blastocoelar cell and muscle cell development. Finally, we find that expression of LvDelta is sufficient to endow blastomeres with the ability to function as a vegetal organizing center and to coordinate the development of a complete pluteus larva.
ASYMMETRIC LEAVES1revealsknoxgene redundancy inArabidopsis
Authors: Byrne Mary E. , Simorowski Joseph , Martienssen Robert A.
Published: April 2021

The shoot apical meristem comprises undifferentiated stem cells and their derivatives, which include founder cells for lateral organs such as leaves. Meristem maintenance and lateral organ specification are regulated in part by negative interactions between the myb domain transcription factor ASYMMETRIC LEAVES1, which is expressed in lateral organ primordia, and homeobox transcription factors which are expressed in the shoot apical meristem (knox genes). The knox gene SHOOT MERISTEMLESS (STM) negatively regulates ASYMMETRIC LEAVES1 (AS1) which, in turn, negatively regulates other knox genes including KNAT1 and KNAT2, and positively regulates the novel gene LATERAL ORGAN BOUNDARIES (LOB). Genetic interactions with a second gene, ASYMMETRIC LEAVES2 (AS2), indicate it acts at the same position in this hierarchy as AS1. We have used a second-site suppressor screen to isolate mutations in KNAT1 and we show that KNAT1 is partially redundant with STM in regulating stem cell function. Mutations in KNAT2 show no such interaction. We discuss the regulation and evolution of redundancy among knox genes.
Distal-lessandhomothoraxregulate multiple targets to pattern theDrosophilaantenna
Authors: Dong P. D. Si , Dicks Jennifer Scholz , Panganiban Grace
Published: April 2021

The Drosophila antenna is a highly derived appendage required for a variety of sensory functions including olfaction and audition. To investigate how this complex structure is patterned, we examine the specific functions of genes required for antenna development. The nuclear factors, Homothorax, Distal-less and Spineless, are each required for particular aspects of antennal fate. Coexpression of Homothorax, necessary for nuclear localization of its ubiquitously expressed partner Extradenticle, with Distal-less is required to establish antenna fate. Here we test which antenna patterning genes are targets of Homothorax, Distal-less and/or Spineless. We report that the antennal expression of dachshund, atonal, spalt, and cut requires Homothorax and/or Distal-less, but not Spineless. We conclude that Distal-less and Homothorax specify antenna fates via regulation of multiple genes. We also report for the first time phenotypic consequences of losing either dachshund or spalt and spalt-related from the antenna. We find that dachshund and spalt/spalt-related are essential for proper joint formation between particular antennal segments. Furthermore, the spalt/spalt-related null antennae are defective in hearing. Hearing defects are also associated with the human diseases Split Hand/Split Foot Malformation and Townes-Brocks Syndrome, which are linked to human homologs of Distal-less and spalt, respectively. We therefore propose that there are significant genetic similarities between the auditory organs of humans and flies.
Dnmt3L cooperates with the Dnmt3 family of de novo DNA methyltransferases to establish maternal imprints in mice
Authors: Hata Kenichiro , Okano Masaki , Lei Hong , Li En
Published: April 2021

Genomic imprinting is regulated by differential methylation of the paternal and maternal genome. However, it remains unknown how parental imprinting is established during gametogenesis. In this study, we demonstrate that Dnmt3L, a protein sharing homology with DNA methyltransferases, Dnmt3a and Dnmt3b, but lacking enzymatic activity, is essential for the establishment of maternal methylation imprints and appropriate expression of maternally imprinted genes. We also show that Dnmt3L interacts with Dnmt3a and Dnmt3b and co-localizes with these enzymes in the nuclei of transfected cells, suggesting that Dnmt3L may regulate genomic imprinting via the Dnmt3 family enzymes. Consistent with this model, we show that [Dnmt3a–/–, Dnmt3b+/–] mice also fail to establish maternal methylation imprints. In addition, both Dnmt3a and Dnmt3L are required for spermatogenesis. Together, our findings suggest that Dnmt3L may cooperate with Dnmt3 family methyltransferases to carry out de novo methylation of maternally imprinted genes in oocytes.
Partial rescue of neural apoptosis in theLurchermutant mouse through elimination of tissue plasminogen activator
Authors: Lu Weiquan , Tsirka Stella E.
Published: April 2021

Lurcher is a spontaneous mouse mutant characterized by premature and aberrant apoptosis in the cerebellum. The phenotype has been shown to be caused by a point mutation in the δ2 glutamate receptor subunit gene that results in a large constitutive inward current, which has proved that endogenous excitotoxicity can lead to apoptotic cell death. Additional studies have suggested a direct link between this endogenous excitotoxicity and the activation of intracellular cell death enzymes. We have previously shown that excitotoxic neuronal degeneration elicited through exogenous insults (e.g. excitotoxins, stroke) is promoted by an extracellular cascade involving the serine protease tissue plasminogen activator (tPA). However, whether it is through necrotic or apoptotic mechanisms that this excitotoxic cell death occurs has remained contested. We describe the attenuation of the Lurcher cell death progression in tPA-deficient mice. Elimination of tPA delayed the apoptotic death of Purkinje and granule neurons in Lurcher mice, and reduced the phosphorylation of Jun and the activation of caspase 8. These results indicate that not only does tPA-promoted excitotoxic cell death proceed through a receptor-mediated apoptotic pathway, but that neuronal cell death in the Lurcher mouse is facilitated by extracellular cascades in addition to the already described intracellular pathways. Finally, these findings suggest that therapeutic benefits may be achieved for a wide variety of insults to the CNS by regulating tPA activity to preserve neuronal viability.
A simple technique for the preservation of vital dyes in fixed and sectioned embryos
Authors: Pertusa J.
Published: April 2021

In embryological work using vital dyes it is highly desirable to be able to study the distribution of the dyes in fixed material, whether examined in toto or after embedding in paraffin and serial sectioning. However, both fixation and dehydration present problems for the preservation of colour in vitally stained cells. Some fixatives preserve some dyes but, so far as I am aware, none will preserve all the vital dyes in common use. On the other hand, ethyl alcohol destroys or dissolves all vital dyes and its use in dehydration is thus undesirable. Among the fixatives that have been proposed are those of Golowin (1902), Mitamura (1923), Parat & Painlevé (1925), and Tchéou Tai Chuin (1930) for neutral red; that of Izquierdo (1955) for toluidine blue; that of Gérard (1925) for Trypan blue; that of Turchini (1919) for methylene blue; that of Lehmann (1929) for Nile blue.
The influence of aminopterin on limb regeneration in Ambystoma mexicanum
Authors: Gebhardt D. O. E. , Faber J.
Published: April 2021

During the last twenty-five years a number of authors have studied the influence of chemical substances on limb regeneration in amphibians. Examples of compounds which have been tested so far are: (1) the antimitotic agent, colchicine (Thornton, 1943); (2) the salt, beryllium nitrate (Thornton, 1949, 1950, 1951); (3) the carcinogens, dibenzanthracene and methylcholanthrene (Karczmar & Berg, 1952; Ruben & Balls, 1964); (4) the lathyrus factor, β-aminopropionitrile (Chang, Witschi & Ponseti, 1955); (5) the hormone, thyroxine (Hay, 1956); (6) atropine and other neuropharmacological drugs (Singer, Davis & Scheuing, 1960); (7) the metachromatic dye, toluidine blue (Csaba, Bierbauer & Tôrô, 1961); and (8) semicarbazide, an inhibitor of histamine formation (Deck & Shapiro, 1963). Most of these substances caused growth retardation as well as malformations of the limb regenerates.
The inhibitory effects of calf thymus-histone fractions on the development of the chick embryo
Authors: Sherbet Gajanan V.
Published: April 2021

The genetic potentialities of an egg are transcribed, translated and built up into a temporal-spatial organization by epigenetic processes. How are these potentialities realized? Efforts to answer this question have naturally turned towards a study of the activity of the genetic material, which according to modern ideas is entirely composed of DNA. Stedmann & Stedmann (1950) originally suggested that certain basic proteins (histones) present in the nucleus were gene inhibitors. Since then various biochemical aspects of histone metabolism have been studied (see review by Phillips, 1962). A number of distinct histones have been isolated (Butler, 1964). But tissues from different species of animals or different tissues from the same species have been found to possess very similar complements of histones (Hnilica, Johns & Butler, 1962). No specificity of interaction between histones and different parts of the DNA molecule has been observed (Johns & Butler, 1964). However, histones have been found to inhibit the synthesis of DNA-dependent RNA (Huang & Bonner, 1962; Barr & Butler, 1963; Allfrey, Littau & Mirsky, 1963; Bonner & Huang, 1964).
Onset of the acquired potentiality for fusion in the palatal shelves of rats
Authors: Pourtois M.
Published: April 2021

This paper is concerned with that phase of palate development in rats leading to fusion of the shelves in the midline. Previous experimentation in palate development in mammals has encompassed both the earlier phase of assumption of the horizontal position of the palatal shelves, and the subsequent approximation and fusion of the shelves. Since the two processes do not occur simultaneously and can theoretically be studied separately, it was possible and feasible to confine the experiment to the later fusion phase. The present research was designed to eliminate the possible confounding effects of palate rotation in vitro on the fusion of the shelves by approximation of the explanted palatal shelves in the same horizontal plane, irrespective of their original positions in the oral cavity.
Effects of ionizing radiation on meiotic maturation of frog oocytes: II. In vitro studies
Authors: Masui Yoshio
Published: April 2021

To investigate genomic activities in ovarian follicle cells and oocytes during meiotic maturation, ovarian pieces isolated from adult frogs (Rana pipiens) were irradiated with doses of X-ray ranging from 12000 to 96000 R and then treated with a pituitary extract and/or progesterone. When the ovarian tissue was treated with the pituitary extract alone or the pituitary extract plus a low dose of progesterone, irradiation with 12000 or 24000 R brought about an enhancement of ovulation, while irradiation with X-ray doses higher than 36000 R suppressed ovulation. On the contary, when the tissue was treated with high doses of progesterone, X-irradiation always suppressed ovulation. X-Irradiation at high dosages suppressed pituitary-induced maturation of oocytes with follicles, but not progesterone-induced maturation.

When oocytes irradiated with 48000 R or less were transferred into unirradiated female frogs, they proved to be fertilizable, but those irradiated with 72000 R or more were un-fertilizable. Nuclear transplantation experiments revealed that X-irradiation did not deprive the oocytes of their capability to cleave, although it did retard the emergence of this capability in maturing oocytes. The embryos from oocytes irradiated with 48000 R or less developed into tadpoles, but no embryos developed beyond the gastrula stage if the oocytes were irradiated with 72000 R or more.
The effects of isonicotinic acid hydrazide on the early chick embryo
Authors: Castellano M. A. , Tórtora J. L. , Germino N. I. , Rama F. , Ohanian C.
Published: April 2021

Unincubated White Leghorn fertile eggs were injected with isonicotinic acid hydrazide (INH) through a hole in the shell. A control group was injected with normal saline, a second group with INH plus vitamin B6, and a third group was left unopened. INH, in the doses we used, proved to be lethal for more than 50% of the early chick embryos, and also produced important developmental alterations. Alterations produced by INH were primarily observed at the level of the neural epithe-lium, particularly at its cephalic portion. The most important ones were a degenerative and necrotic process of the neural epithelium, and a distortion of the normal anatomical relations of the cephalic structures. The embryonic mortality and developmental alterations induced by INH were prevented to a considerable extent by the concurrent injection of pyridoxine hydrochloride and INH. The preventive action of vitamin B6 suggests that toxicity of INH in the chicken embryos is due to the antivitamin-B6 action of INH. Through this mechanism INH would block, specially, the amino acid metabolism. The developing nervous system was the embryonic area most sensitive to such metabolic alterations.
Effects of ionizing radiation on meiotic maturation of frog oocytes: I. In vivo studies
Authors: Masui Yoshio
Published: April 2021

In an attempt to examine genomic function of the oocyte nucleus during meiotic maturation, the effects of X-irradiation on the oocyte of the frog (Rana pipiens) vitre studied. When oocytes were irradiated with 6000-36000 R before initiation of maturation, the ovulated eggs frequently failed to be fertilized and the jelly surrounding the unfertilizable eggs was always damaged. However, the egg itself proved to retain the capability of cleaving when a nucleus was transplanted from a blastula. Also, X-irradiated eggs when invested with the jelly from unirradiated frogs recovered their capacity for fertilization. The eggs thus fertilized developed and exhibited abnormalities characteristic of X-irradiation such as arrest of gastrulation and neurulation as well as production of haploidy. Irradiation of oocytes after completion of maturation brought about developmental abnormalities more frequently than irradiation before initiation of maturation. The Hertwig effect was found only when oocytes were irradiated after completion of maturation. However, no qualitative differences were found in the developmental abnormalities produced by irradiation before maturation and those produced by irradiation after maturation.
The influence of ‘hypophysectomy’ by means of surgical decapitation on skeletal growth in the developing chick embryo
Authors: Thommes Robert C. , Hajek Anthony S. , Mcwhinnie D. J.
Published: April 2021

Wet, dry, and ash weights and calcium content were determined on demarrowed tibiae of normal and ‘hypophysectomized’ chick embryos from days 10·5 to 19·5 of incubation. All parameters noted above increased progressively through developmental time in normal embryos. ‘Hypophysectomy’ significantly affected bone wet and dry weights, and total mineral and calcium content. The data indicate that mineralization and matrix synthesis are retarded in the absence of the pituitary.
The influence of ‘hypophysectomy’ on bone growth and alkaline phosphatase activity in the chick embryo
Authors: Mcwhinnie D. J. , C. Thommes Robert
Published: April 2021

Wet weights, total bone alkaline phosphatase activity and specific alkaline phosphatase activity were determined on demarrowed femurs of normal, ‘hypophysectomized’ and pituitary-grafted chick embryos at selected intervals of incubation. In normal bones, all parameters noted above increased progressively through developmental time. ‘Hypophysectomy’ by means of surgical decapitation significantly retarded the normal increase of femur wet weight, total and specific alkaline phosphatase activity; in embryos bearing pituitary transplants, there was a return towards normal values. The possible role(s) of the pituitary in skeletal maturation and enzyme synthesis or activation is discussed.
Abnormal development of pre-implantation mouse embryos grown in vitro with [3H]thymidine
Authors: Snow M. H. L.
Published: April 2021

Mouse embryos were grown in vitro from the 2-cell stage to blastocysts in the presence of [3H]thymidine. Methyl-T-thymidine and thymidine-ó-T(n) were used and both forms found to be lethal at concentrations above 0 · 1 μ Ci/ml. Both forms of [3H]Tdr at concentrations between 0 · 01 and 0 · 1 μ Ci/ml caused a highly significant (P < 0·001) reduction in blastocyst cell number. The reduction in cell number, which was positively correlated with specific activity and tritium concentration, was associated with cell damage typical of radiation damage caused by tritium disintegration. Thymidine-6-T(n) also significantly reduced the number of 2-cell embryos forming blastocysts whereas methyl-T-Tdr did not. This difference in effect is assumed to be caused by contamination of one form of [3H]Tdr with a by-product of the tritiation process.

A study of the cleavage stages showed that almost all the reduction in cell numbers could be accounted for by selective cell death occurring at the 16-cell stage. Cells which survive that stage cleave at a normal rate. The cells that are most susceptible to [3H]Tdr damage were found to normally contribute to the inner cell mass. The [3H]Tdr-resistant cells form the trophoblast. It is possible to grow blastocysts in [3H]Tdr such that they contain no inner cell mass but are composed entirely of trophoblast. Comparatively short (12 h) incubation with [3H]Tdr at any stage prior to the 16-cell stage will cause this damage. Possible reasons for this differential effect are discussed, and also compared with damage caused by X-irradiation.
The effect of X-radiation on spermatogenesis and the fertility of Schistocerca gregaria (Forsk.)
Authors: Coggins Peter B.
Published: April 2021

Normal spermatogenesis and the effects of X-radiation on the male locust germ cells have been studied with the aid of light and electron microscopy. Adult insects were irradiated with doses of 100–500 rad (i.e. 1–5 J kg−1) and subsequently examined, at intervals, up to 55 days later. In secondary spermatogonia all doses caused nuclear fragmentation and necrosis, and in primary spermatogonia and a few spermatocytes caused a delay in division. Spermatids and the majority of spermatocytes developed into spermatozoa which were passed from the follicles to the seminal vesicles. The supply of sperm was, subsequently, temporarily stopped. The follicles were eventually repopulated by the division of the primary spermatogonia. Radiation-induced abnormalities, e.g. the formation of supernumerary centrioles, flagella and definitive mitochondria, were most common in the cytoplasm. The Golgi bodies and acrosome seemed to be unaffected. Abnormal outgrowths of the late spermatid and sperm nuclei appeared to be caused by the presence of the numerous centrioles and flagella. The bright yellow coloration of the cuticle, which is characteristic of sexually mature males, was not fully developed in irradiated males. Breeding experiments showed a significant reduction, when compared to the controls, in the number and percentage hatchability of eggs obtained from females mated to irradiated males. The doses of radiation employed did not appear to affect the longevity of the adults.
The migration of neural crest cells to the wall of the digestive tract in avian embryo
Authors: Douarin Nicole M. Le , Teillet Marie-Aimée
Published: April 2021

Isotopic and isochronic grafts of quail neural primordium in chick embryos have been made. Due to the particular structure of their nuclei, quail cells can be distinguished from chick cells and so be used as natural markers to study the migration of neural crest cells. We have been able to demonstrate by this technique that the parasympathetic enteric ganglion cells arise from two different levels of the embryonic neural axis which correspond to the vagal and lumbo-sacral parasympathetic centres. The main source of the enteric neuroblasts is located at the level of the somites 1 – 7. It gives rise to ganglion cells which migrate in the whole gut including the large intestine and rectum. The other region from which enteric neuroblasts originate is situated behind the level of the 28th somite and gives rise only to some post-umbilical gut ganglion cells. In this region of the intestine the ganglia are made up of a mixture of cells arising from the vagal and the lumbo-sacral levels of the neural axis. The part of the neural primordium between the 8th and the 28th somite does not participate in the formation of the enteric ganglia. The chronology of the enteric neuroblast migration has been studied. Most cells of vagal origin leave the neural crest before the 13-somite stage but the migration lasts sometimes until after the 16-somite stage. Those cells which have to reach the hind-gut level accomplish a long-term migration which can be evaluated at 6 days or more. The presumptive neuroblasts of lumbo-sacral origin are not found in the hind-gut before the 7th day of incubation. In our experiments we have never observed the migration of any quail cells into the endoderm of the chick host embryo. Therefore we consider that enterochromaffin cells of the digestive epithelium are not derived from the levels of the neural crest concerned in these experiments (i.e. rhombencephalic and medullary Anlagen).
In vitrostudies of the influence of hormones on tail regeneration in adultDiemictylus viridescens
Authors: Vethamany-Globus Swani , Liversage Richard A.
Published: April 2021

A total of 260 tail blastemata (13 to 15-day regenerates) of adult newts was cultured, with 170 controls, in medium no. 1760 (modified Parker’s Medium, CMRL-1415) for 98 h at 20 ±0·5 °C. Various hormones, related to the regeneration process, were added individually and in combinations. If hormones were not included in the culture medium, blastema growth and differentiation did not ensue. The results of these in vitro experiments further showed that the presence of insulin was essential in the maintenance and promotion of growth and differentiation of the explanted blastemata. In addition, thyroxine also promoted a limited amount of growth and differentiation of the blastema and maintained a normal epidermis in culture. Furthermore, advanced cartilage differentiation and maximum growth of the blaste-mata were observed in cultures treated with combinations of insulin, growth hormone and hydrocortisone; insulin, growth hormone and thyroxine or all four of these hormones. The evidence presented indicates that the collective influence of the hormones (insulin, growth hormone, hydrocortisone and thyroxine) is greater than the effect of any of them individually.

The action of insulin on the tissues and the metabolism of vertebrates is discussed and related to the regeneration process. The possible involvement of a multiple hormone action (insulin, thyroxine, hydrocortisone and growth hormone) in regeneration is discussed.
Measurements of cell adhesion I. Quantitative studies of adhesion of embryonic chick cells
Authors: Hornby Janet E.
Published: April 2021

Cell suspensions were prepared from the kidney, liver and heart of chick embryos of 5 or 8 days of incubation, and from the limb-buds of chick embryos of 5, 6, 7, 8 or 9 days of incubation. When these suspensions were aggregated under laminar shear in a Couette viscometer or random motion in a reciprocating shaker they obeyed the theoretical relationships derived for flocculating lyophobic sols. The values of the collision efficiency found for the different cell types under given conditions were used to calculate the force of interaction between cells of each type. The force of interaction ranged between 9 ×10−11 N (8-day heart) and 3 ×10−9 N (8-day liver). The forces of interaction between cells appear to be responsible for aligning the membranes of adjacent cells with a 10–20 nm gap. It is possible to arrange the cell types in a hierarchy based on the forces of interaction between them. The possible role of these forces in cell specificity is considered.
The appearance of muscle protein and myofibrils within the embryonic chick limb-bud
Authors: Thorogood P. V.
Published: April 2021

Myotubes are present in the developing hind limb of the embryonic chick at 5 days. An immunofluorescence technique was used to detect actomyosin within the myotubes. The earliest detectable appearance of this muscle protein was at six days of development, at sites located peripherally beneath the flattened dorsal and ventral surface of the limb. These dorsal and ventral loci are interpreted as representing the primordial extensor and flexor muscles. At the ultrastructural level the cytoplasm of the myotubes contains fibrillar components which are apparently aggregating to form myofibrils. A rudimentary banding pattern can be distinguished.
Évolution enzymatique destissus foetaux et placentaires de Rat en carence tératogène de riboflavine
Authors: Courcy G. Potier de , Desmettre-Miguet S. , Macquart-Moulin M. R. , Terroine T.
Published: April 2021

Enzymic changes of foetal and placental tissues of the rat in teratogenic riboflavin deficiency

The electrophoretic pattern of alkaline phosphatase was studied in teratogenic riboflavin deficiency in the whole foetus, chorioallantoic placenta and visceral yolk-sac of the rat in order to follow the course of their differentiation from day 13 to day 20 of gestation. Lactic-dehydrogenase (LDH) isozymes were chosen in the case of foetal organs (heart, intestine and kidneys) as a more sensitive test. A fluorometric analysis of alkaline phosphatase was also performed to evaluate more precisely quantitative modifications brought on by maternal riboflavin deficiency in the placenta and the whole foetus.

The importance of alkaline phosphatase in rat yolk-sac was indicated in the last period of gestation by the presence of a specific rapid isozyme band from the 16th to the 21st day, simultaneously with a greater complexity of the electrophoretic picture of this membrane. Placenta and foetus, on the other hand, were shown to possess two common bands but those concerned with the foetus appeared later and were related to the onset and increase of ossification. In the foetal organs, differentiation of LDH isozymes appeared specific for each organ studied; while the heart tissue showed five bands on the 16th day, kidney arrived at this stage only on the 21st day, indicating a slower maturation of this tissue.

At the end of gestation riboflavin deficiency delayed the appearance of rapid isoenzymes of alkaline phosphatase in the whole foetus and of LDH in the foetal kidneys, suggesting a similar delay in the course of metabolic differentiation of the skeleton and kidney tissues. Deficiency had no effect upon placental isoenzyme development but in this organ it greatly reduced the biochemical alkaline phosphatase activity, especially on day 13. This result suggests the participation of the enzyme in the general hypotrophy of the foetus by a decrease in nutrients carried by the placenta. On the other hand, the decline in the alkaline phosphatase activity of the whole foetus is related to the delayed appearance of mineralization.
Binucleate and polyploid cells in the decidua of the mouse
Authors: Ansell J. D. , Barlow P. W. , Mclaren Anne
Published: April 2021

The development of the decidua in rodents is associated with the production of multinucleate and giant cells (Fig. 1A). In the rat, binucleate cells appear throughout the secondary or antimesometrial zone of the decidua by the eighth day of pregnancy (Krehbiel, 1937), while in the mouse this region is characterized by large bi-, tri-, or tetranucleate cells (Snell & Stevens, 1966). All decidual cells may eventually enlarge, containing nuclei of a size consistent with a DNA content of four, eight and possibly even higher multiples of the haploid complement (Sachs & Shelesnyak, 1955). In the white rat spectrophotometric determination of DNA levels in decidual cells indicates that by the tenth day of gestation ploidy levels have reached 16C–32C, with maximal levels of 64 times the haploid DNA content (Zybina & Grishchenko, 1972). The mechanism of nuclear enlargement in decidual tissue is as yet unknown.
Development in vitro of mouse embryos from the two-cell egg stage to the early somite stage
Authors: Hsu Yu-Chih , Baskar John , Stevens Leroy C. , Rash John E.
Published: April 2021

About 1 –3% of mouse blastocysts, which had initially been cultured from the two-cell stage in chemically defined medium or about 3 –5% of blastocysts which were explanted from the uterus, developed to the early somite stage when cultured in vitro on collagen. Two cell eggs were initially cultivated in chemically defined medium to the blastocyst stage. Blastocysts were then transferred to Eagle’s minimal essential medium (MEM) plus 10% heat-inactivated calf serum. Two barriers to further development were overcome. First, the formation of endoderm and ectoderm from the inner cell mass immediately after attachment to collagen. Second, formation of the embryo proper from the embryonic region. Both barriers were overcome by using heat-inactivated human cord serum after the blastocysts hatched from the zona pellucida and attached to collagen. After attachment, embryos were cultured in MEM plus 20% heat-inactivated human cord serum which was changed daily until early somite stages. Apparently normal healthy development in vitro occurred, as judged by light and electron microscopic examination.
Germ cell migration in toad (Bufo bufo): effect of ventral grafting of embryonic dorsal regions
Authors: Giorgi Piero P.
Published: April 2021

Bufo bufo embryos were used at the tail-bud stage for the grafting of two different dorsal regions (cephalic and caudal tracts) into the ventral side of the embryo (cf. Fig. 1). Germ cell localization was studied at the beginning of larval life. The results seem to confirm the original finding of Gipouloux (1970) who suggested that in anurans germ cells migrate under the attraction of a substance produced by the dorsal mesodermal tissues.

The attractive action of dorsal tissue was confined to the caudal region of the embryo. In operated specimens the migration of germ cells was drastically altered. The genital ridges of host embryos were almost sterile, while numerous germ cells appeared associated with caudal grafts. A considerably smaller number of germ cells was associated with cephalic grafts.

About 80% of germ cells associated with caudal grafts were present at the same levels where a well-developed dorsal mesentery was also present. It is suggested that the formation of the dorsal mesentery plays a morphogenetic role in segregating primordial germ cells from other endodermal cells and contributes to their final localization in the genital ridges.
Ultrastructural features of ectodermal—mesenchymal relationships in the developing limb of Xenopus laevis
Authors: Tarin D. , Sturdee A. P.
Published: April 2021

Electron microscopical study of the formation of the hind limb of the toad Xenopus laevis between stages 49 and 53 of larval development has been performed with special reference to the relationships between the apical ectodermal ridge and the underlying mesenchyme. It has been found that the intervening collagenous layer is thinner in the vicinity of the ridge than elsewhere and that the subjacent mesenchymal cells are more loosely arranged. There are also fewer mesenchymal filopodia crossing the collagenous layer than proximally although the distribution of delicate vertically disposed threads, also observed at the ecto-mesenchymal junction, is uniform over the entire bud. Overall, it is concluded that the fine structural features of Xenopus limb development, during these stages, do not give clear insight into the mechanisms by which the apical region exerts its morphogenetic effects.
Normal incorporation rates for precursors of collagen and mucopolysaccharide during expression of micromelia induced by 6 -aminonico tinamide
Authors: Seegmiller Robert E. , Runner Meredith N.
Published: April 2021

Further delineation of mechanisms by which 6-aminonicotinamide (6-AN) induces micro-melia in the chick embryo was investigated by studies on rates of incorporation of thymidine, proline, glucosamine and sulfate as precursors to DNA, collagen and mucopolysaccharide, respectively. Twentyfour hours after in ovo administration of the vitamin antagonist, 6-AN, to day-4 chick embryos, hind limbs from experimental and control groups were excised and incubated for 1 h in medium containing 3 × 10 − 6 M radioactive precursor. Molar incorporation of precursors into the TCA-precipitable fraction showed, in isolated limb buds, (a) that 6-AN enhanced incorporation of thymidine, (b) that 6-AN inhibited utilization of sulfate, and (c) that 6-AN did not significantly alter utilization of glucosamine and proline.

Rates of incorporation of thymidine, glucosamine and proline indicate that 6-AN is not cytotoxic to the isolated limb bud. Enhanced incorporation of thymidine suggests expression of compensatory change 24 h after initial effects of 6-AN on DNA synthesis. Rate of in-corporation of proline suggests that, under the influence of 6-AN, tropocollagen was syn-thesized in normal quantities by limb cells. Similarly, rate of incorporation of glucosamine suggests that under the influence of 6-AN normal amounts of hexosamine sugars were being attached to the nascent core-protein of chondroitin. Inhibition of sulfation and failure to complete the chondroitin sulfate molecule seem to account for 6-AN-induced micromelia. This suggests that sulfation depends upon specific NAD-dependent dehydrogenase reactions. As far as can be established by rates of incorporation of labeled precursors, 5-day limb buds, at 24 h after exposure to teratogenic levels of 6-AN, synthesize matrix proteins and hexo-samine polysaccharides at normal rates.
The in vivo behaviour of achondroplastic cartilage from the cartilage anomaly (can/can) mouse
Authors: Johnson D. R.
Published: April 2021

Explanted cartilage from can/can mice aged 3 days shows increased protein and mucopoly-saccharide synthesis. Injection of [U-14C]glucose into 3-day-old can/can mice failed to duplicate the increased mucopolysaccharide formation. Transplanted can/can tail vertebrae grown in the renal capsule of normal sibs grew less well than those from normal litter-mates’ also suggest-ing that the increased metabolism seen in vitro is not a feature of in vivo development.
Biochemical observations on the cartilage of achondroplastic (can) mice
Authors: Johnson D. R. , Hunt D. M.
Published: April 2021

The achondroplastic can/can embryo can be distinguished from normal litter-mates at 17 days by reduced protein synthesis. After 3 days post partum protein synthesis is increased to levels well above normal, as is incorporation of glucose into mucopolysaccharides and the levels of uridine diphosphoglucose dehydrogenase and UDP-glucose-4-epimerase.
Experimentally induced aberrations in the pattern of differentiation in the cellular slime mouldDictyostelium discoideum
Authors: Farnsworth Paul
Published: April 2021

This paper describes a set of perturbatory experiments designed to elucidate aspects of the mechanism by which the normal pattern of differentiation is specified.

Experiments are described which investigate the alterations in development seen in aqueous environments, with changes in humidity and with the introduction of permeable and imperme-able barriers.

The following results are reported: The pattern of differentiation and the various morphologies of fruiting bodies formed when cell masses are placed in or on drops of buffer.The alteration of the ratio of cell types formed in aqueous environments in the presence of urethane mercaptoethanol or EDTA.Humidity dependent changes in polarity and the increase of the number of develop-mental axes with humidity.The formation of two developmental axes in cell masses bisected by impermeable barriers and a special case of bisection which induces the whole cell mass to form spores.The induction of all of any of a cell mass enclosed in a ‘cellulose’ tube to form a tissue ultrastructurally demonstrable to be the same as that of stalk.

These results are discussed in relationship to the work of other authors and the problem of the specification of the patterns of differentiation in the slime moulds. The results are pre-sented in support of a model proposed previously by the author in which the pattern of the two differentiated cell types is inherent in the morphogenetic changes of culmination, and essential requirements of such a model are correlated with these observations.