bluuebunny/crossref_metadata_2025_split huggingface dataset:
Roles of homeobox and &gt;bHLH genes in specification of a retinal cell type
Authors: Hatakeyama Jun , Tomita Koichi , Inoue Tomoyuki , Kageyama Ryoichiro 
Published: April 2021

ABSTRACT
Previous analysis of mutant mice has revealed that the bHLH genes Mash1 and Math3, and the homeobox gene Chx10 are essential for generation of bipolar cells, the interneurons present in the inner nuclear layer of the retina. Thus, a combination of the bHLH and homeobox genes should be important for bipolar cell genesis, but the exact functions of each gene remain largely unknown. We have found that in Mash1-Math3 double-mutant retina, which exhibits a complete loss of bipolar cells, Chx10 expression did not disappear but remained in Müller glial cells, suggesting that Chx10 expression per se is compatible with gliogenesis. In agreement with this, misexpression of Chx10 alone with retrovirus in the retinal explant cultures induced generation of the inner nuclear layer cells, including Müller glia, but few of them were mature bipolar cells. Misexpression of Mash1 or Math3 alone did not promote bipolar cell genesis either, but inhibited Müller gliogenesis. In contrast, misexpression of Mash1 or Math3 together with Chx10 increased the population of mature bipolar cells and decreased that of Müller glia. Thus, the homeobox gene provides the inner nuclear layer-specific identity while the bHLH genes regulate the neuronal versus glial fate determination, and these two classes of genes together specify the bipolar cell fate. Moreover, Mash1 and Math3 promoted the bipolar cell fate, but not the other inner nuclear layer-specific neuronal subtypes in the presence of Chx10, raising the possibility that the bHLH genes may be involved in neuronal subtype specification, in addition to simply making the neuronal versus glial fate choice.
Identification of NKL, a novel Gli-Kruppel zinc-finger protein that promotes neuronal differentiation
Authors: Lamar Elise , Kintner Chris , Goulding Martyn 
Published: April 2021

ABSTRACT
The proneural basic helix-loop-helix proteins play a crucial role in promoting the differentiation of postmitotic neurons from neural precursors. However, recent evidence from flies and frogs indicates that additional factors act together with the proneural bHLH proteins to promote neurogenesis. We have identified a novel zinc finger protein, neuronal Kruppel-like protein (NKL), that positively regulates neurogenesis in vertebrates. NKL is expressed in Xenopus primary neurons and in differentiating neuronal precursors in the intermediate zone of the mouse and chick neural tube. In frog embryos, NKL is induced by overexpression of Neurogenin (Ngn), arguing that NKL is downstream of the proneural determination genes. Our results show that NKL and a NKL/VP16 fusion protein promote differentiation of neuronal precursors in the embryonic chick spinal cord. Following in ovo misexpression of NKL, neuroepithelial cells exit the cell cycle and differentiate into neurons. Similarly, NKL/VP16 induces extra primary neurons in frogs and upregulates expression of the neural differentiation factors, Xath3 and MyT1, as well as the neuronal markers, N-tubulin and elrC. Our findings establish NKL as a novel positive regulator of neuronal differentiation and provide further evidence that non-bHLH transcription factors function in the neuronal differentiation pathway activated by the vertebrate neuronal determination genes.
Regulated nuclear export of the homeodomain transcription factor Prospero
Authors: Demidenko Zoya , Badenhorst Paul , Jones Tamara , Bi Xiaolin , Mortin Mark A. 
Published: April 2021

ABSTRACT
Subcellular distribution of the Prospero protein is dynamically regulated during Drosophila embryonic nervous system development. Prospero is first detected in neuroblasts where it becomes cortically localized and tethered by the adapter protein, Miranda. After division, Prospero enters the nucleus of daughter ganglion mother cells where it functions as a transcription factor. We have isolated a mutation that removes the C-terminal 30 amino acids from the highly conserved 100 amino acid Prospero domain. Molecular dissection of the homeo- and Prospero domains, and expression of chimeric Prospero proteins in mammalian and insect cultured cells indicates that Prospero contains a nuclear export signal that is masked by the Prospero domain. Nuclear export of Prospero, which is sensitive to the drug leptomycin B, is mediated by Exportin. Mutation of the nuclear export signal-mask in Drosophila embryos prevents Prospero nuclear localization in ganglion mother cells. We propose that a combination of cortical tethering and regulated nuclear export controls Prospero subcellular distribution and function in all higher eukaryotes.
The role of Wingless signaling in establishing the anteroposterior and dorsoventral axes of the eye disc
Authors: Lee Jeffrey D. , Treisman Jessica E. 
Published: April 2021

ABSTRACT
The posteriorly expressed signaling molecules Hedgehog and Decapentaplegic drive photoreceptor differentiation in the Drosophila eye disc, while at the anterior lateral margins Wingless expression blocks ectopic differentiation. We show here that mutations in axin prevent photoreceptor differentiation and lead to tissue overgrowth and that both these effects are due to ectopic activation of the Wingless pathway. In addition, ectopic Wingless signaling causes posterior cells to take on an anterior identity, reorienting the direction of morphogenetic furrow progression in neighboring wild-type cells. We also show that signaling by Decapentaplegic and Hedgehog normally blocks the posterior expression of anterior markers such as Eyeless. Wingless signaling is not required to maintain anterior Eyeless expression and in combination with Decapentaplegic signaling can promote its downregulation, suggesting that additional molecules contribute to anterior identity. Along the dorsoventral axis of the eye disc, Wingless signaling is sufficient to promote dorsal expression of the Iroquois gene mirror, even in the absence of the upstream factor pannier. However, Wingless signaling does not lead to ventral mirror expression, implying the existence of ventral repressors.
Establishment of segment polarity in the ectoderm of the leech Helobdella
Authors: Seaver Elaine C. , Shankland Marty 
Published: April 2021

ABSTRACT
The segmented ectoderm and mesoderm of the leech arise via a stereotyped cell lineage from embryonic stem cells called teloblasts. Each teloblast gives rise to a column of primary blast cell daughters, and the blast cells generate descendant clones that serve as the segmental repeats of their particular teloblast lineage. We have examined the mechanism by which the leech primary blast cell clones acquire segment polarity – i.e. a fixed sequence of positional values ordered along the anteroposterior axis of the segmental repeat. In the O and P teloblast lineages, the earliest divisions of the primary blast cell segregate anterior and posterior cell fates along the anteroposterior axis. Using a laser microbeam, we ablated single cells from both o and p blast cell clones at stages when the clone was two to four cells in length. The developmental fate of the remaining cells was characterized with rhodamine-dextran lineage tracer. Twelve different progeny cells were ablated, and in every case the ablation eliminated the normal descendants of the ablated cell while having little or no detectable effect on the developmental fate of the remaining cells. This included experiments in which we specifically ablated those blast cell progeny that are known to express the engrailed gene, or their lineal precursors. These findings confirm and extend a previous study by showing that the establishment of segment polarity in the leech ectoderm is largely independent of cell interactions conveyed along the anteroposterior axis. Both intercellular signaling and engrailed expression play an important role in the segment polarity specification of the Drosophila embryo, and our findings suggest that there may be little or no conservation of this developmental mechanism between those two organisms.
Asymmetric Numb distribution is critical for asymmetric cell division of mouse cerebral cortical stem cells and neuroblasts
Authors: Shen Qin , Zhong Weimin , Jan Yuh Nung , Temple Sally 
Published: April 2021

Stem cells and neuroblasts derived from mouse embryos undergo repeated asymmetric cell divisions, generating neural lineage trees similar to those of invertebrates. In Drosophila, unequal distribution of Numb protein during mitosis produces asymmetric cell divisions and consequently diverse neural cell fates. We investigated whether a mouse homologue m-numb had a similar role during mouse cortical development.Progenitor cells isolated from the embryonic mouse cortex were followed as they underwent their next cell division in vitro. Numb distribution was predominantly asymmetric during asymmetric cell divisions yielding a β-tubulin III− progenitor and a β-tubulin III+ neuronal cell (P/N divisions) and predominantly symmetric during divisions producing two neurons (N/N divisions). Cells from the numb knockout mouse underwent significantly fewer asymmetric P/N divisions compared to wild type, indicating a causal role for Numb.When progenitor cells derived from early (E10) cortex undergo P/N divisions, both daughters express the progenitor marker Nestin, indicating their immature state, and Numb segregates into the P or N daughter with similar frequency. In contrast, when progenitor cells derived from later E13 cortex (during active neurogenesis in vivo) undergo P/N divisions they produce a Nestin+ progenitor and a Nestin– neuronal daughter, and Numb segregates preferentially into the neuronal daughter. Thus during mouse cortical neurogenesis, as in Drosophila neurogenesis, asymmetric segregation of Numb could inhibit Notch activity in one daughter to induce neuronal differentiation.At terminal divisions generating two neurons, Numb was symmetrically distributed in approximately 80% of pairs and asymmetrically in 20%. We found a significant association between Numb distribution and morphology: most sisters of neuron pairs with symmetric Numb were similar and most with asymmetric Numb were different. Developing cortical neurons with Numb had longer processes than those without.Numb is expressed by neuroblasts and stem cells and can be asymmetrically segregated by both. These data indicate Numb has an important role in generating asymmetric cell divisions and diverse cell fates during mouse cortical development.
The origin and continuous replacement of epidermal cells in the planarianPolycelis tenuis(lijima)
Authors: Skaer R. J. 
Published: April 2021

ABSTRACTRAY LANKESTER (1873) coined the term ‘Triploblastic’ and supposed that the gut, parenchyma and epidermis of Turbellaria corresponded to the germ layers of contemporary dogma. This idea is still current, though neither the origin, nor the maintenance of the epidermis of planarians has been investigated in detail. Most embryological studies have been restricted to early development, but Bardeen (1902) worked on embryos of a wide range of ages and claimed that their epidermal cells divide amitotically. Both Mattiesen (1904) and Fulinsky (1916), however, denied that cell division occurs there, and since this has been confirmed for the epidermis of the adult (Skaer, 1961), the cells must be recruited from elsewhere. I suggested that the entire epidermis might be continuously renewed by migration of cells from the parenchyma to the periphery.
Adult brain antigens demonstrated in chick embryos by fractionated antisera
Authors: Friedman Harvey P. , Wenger Byron S. 
Published: April 2021

ABSTRACT
Antisera produced in rabbits against homogenates of adult chicken brains and absorbed with liver and yolk were used to detect, via complement fixation, the appearance of brain antigens during development of the embryonic chick brain. Reacting antigens are found at the earliest stages studied (stages 14–16, ca. 2 days) but remain at a low level (relative to protein) until after stage 28 ( days), when a rapid increase begins, reaching the adult level by stage 38 (12 days). Antisera were fractionated on DEAE cellulose and the anti-brain activity found in two fractions, identified as 7S and 19S respectively. The 19S antibody reacted with a chloroform-methanol extract of adult brain homogenate but not with the residue, while the 7S antibody reacted only with the chloroform-methanol insoluble residue. When tested against brains of embryos at different developmental stages, the 19S antibody reacted at a low and essentially unchanging level from the earliest stages studied to the adult. The 7S antibody gave no reaction with embryonic brain until after stage 28 at which time a reacting antigen was found which reached the adult level by stage 38. Based on the appearance in detectable quantity, and the rapid accumulation, of a brain-specific protein antigen, the period between stages 28 and 38 is considered to be critical for neural differentiation.
Epsilon granules in Drosophila pole cells and oöcytes
Authors: Ullmann Suzanne L. 
Published: April 2021

ABSTRACT
The ultra-structure of the pole cells and oöcytes of Drosophila melanogaster, Drosophila willistoni and Drosophila virilis has been investigated. The eggs were dechorionated in 3 per cent, sodium hypochlorite, and the vitelline membrane removed in the fixative. Three fixatives were employed: (a) OsO4-veronal, at pH 7 · 4; (b) formol-phosphate with 7 · 5 per cent, sucrose, at pH 7 · 2; (c) gluteraldehyde, buffered at pH 7 · 4 with sodium cacodyalate. All three gave good results, but membranous structures remained rather indistinct after aldehyde fixation. Two kinds of granule occur within the pole cells, the polar and the epsilon granules. Both types may occur together within the same cell, but one or other type tends to predominate. The functions and interrelationships of these granules are obscure. Polar granules are spherical with a dense, granular cortex surrounding a less electron-opaque core, and lack a bounding membrane. Epsilon granules are ovoid and a delicate double membrane surrounds the coarse fibrous matrix, in which spaces occur. Their composition is unknown. Preliminary observations suggest that the epsilon granules arise from convolutions of the cell membranes which surround the mature oöcyte.
Cell movement within aggregates of the slime mouldDictyostelium discoideumrevealed by surface markers
Authors: Shaffer B. M. 
Published: April 2021

ABSTRACTEarlier workers examined the behaviour of foreign particles placed as markers on aggregates of D. discoideum that were migrating over the surface of the culture plate (Bonner, 1959; Francis, 1959, 1962). Comparable observations, made on aggregates in other conditions and at other stages, have now provided further information about the movement of individual cells within the aggregates. Before reporting them, the course of development must be described in some detail.
Action de la thalidomide sur l’embryon de poulet
Authors: Salzgeber par Berthe , Salaün Josselyne 
Published: April 2021

ABSTRACT
The action of thalidomide on the fowl embryo The effects of thalidomide on fowl embryos of different developmental ages (30 hr. to 3 days, stages 8-21 of Hamburger & Hamilton) have been studied. The thalidomide was administered in different forms; as a suspension in distilled water, in dioxane diluted with distilled water, as a powder, and as a sodium salt soluble in water. Since other powders, e.g. animal charcoal or egg-shell débris, are teratogenic when applied at an early stage, the results with thalidomide powder were only considered for embryos older than 50 hr. (stage 16) at the time of treatment. In all four experimental series malformed embryos were found with similar frequencies, i.e. between 20 and 30 per cent. From 15 to 22 per cent, showed malformations of the limbs. The limb malformations occurred with the following order of incidence : micromelia, phocomelia, hemimelia, ectromelia. They were nearly always associated with coelosomy or anuria. Thalidomide, though not very toxic, does, therefore, have a teratogenic effect upon the limbs, but this effect is less specific and less consistent than the effect obtained with nitrogen mustard (Salzgeber, 1963).
Effets de la puromycine sur la mitose, la synthèse des protéines et celle du DNA au cours de la segmentation de l’oeuf de Batracien
Authors: Legros par F. , Bracket J. 
Published: April 2021

ABSTRACT
The effects of puromycin on mitotis, protein synthesis and DNA synthesis during cleavage of the amphibian egg
A study has been made of the effects of puromycin injected into Pleurodeles eggs. Cleavage of the eggs is rapidly blocked by this substance, after only a few mitoses.
Autoradiography using radioactive precursors (leucine, thymidine) has revealed that puromycin has no effect on protein and DNA synthesis during the first 3 hr. following injection. Cytoplasmic protein synthesis is interrupted at the end of this delay during the interphase of the 64-blastomere stage. Occasionally this final division occurs, but even then the inhibition of protein synthesis prevents the formation of the mitotic apparatus and the reduplication of DNA. Mitotic inhibition follows, usually at the 128-blastomere stage. It may thus be concluded that the inhibition of protein synthesis in the cytoplasm precedes the blocking of DNA synthesis and nuclear protein synthesis.
Intraocular differentiation of rateggcylinders
Authors: Levak-Švajger B. , Škreb N. 
Published: April 2021

ABSTRACTThe anterior chamber of the eye is a suitable environment for testing the capacities of embryonic shields of the mouse to differentiate, as has been shown by Grobstein (1951). The development proceeds at a slower rate than usually and no morphogenesis is observed, although many identifiable tissues are found. The differentiation progressively increases as later stages are used. On the other hand, if younger stages, e.g. tubal ova or morulae, are transplanted (Runner, 1947), no histogenesis can be obtained although the germ layers are formed.
Transformations in the abdominal muscles of the blue blow-fly,Calliphora erythrocephala(Meig), during metamorphosis
Authors: Crossley A. C. S. 
Published: April 2021

ABSTRACTA re-examination of the changes at metamorphosis of certain abdominal hypodermal muscles in Calliphora is described. Methods of preparation of insect hypodermal muscles for anatomical, histological and electron microscopical studies are outlined. The anatomical changes in the abdominal hypodermal muscles were traced from larval to adult instars. Two major phases of histolysis occur. Certain larval muscles transform to adult muscles. Histological changes have been followed with various light and electron microscopical techniques. The relative importance of haemocyte phagocytosis and autolysis are considered for different groups of muscles. Evidence indicating that free-floating myoblasts, almost certainly derived from abdominal histoblast tissues, can invade modified larval muscles is presented, and electron micrographs of the invasion process are given. Redifferentiation of imaginai muscles associated with myoblast nuclei is described. Experimental denervation did not affect muscle histolysis. The results are compared with those reported in the earlier literature. Certain similarities of metamorphic and early embryonic development are pointed out.
Nouvelles recherches concernant le rôle du canal de Wolff dans la différenciation du mésonéphros de l’embryon de poulet
Authors: Bishop-Calame par Simone 
Published: April 2021

ABSTRACT
Au cours de recherches antérieures, Caíame (1961), nous avons mis en évidence le rôle inducteur du canal de Wolff dans la différenciation du mésonéphros de l’embryon du Poulet confirmant ainsi les résultats de Grünwald (1937):
Teratogenic action of the thyroid stimulating hormone and its interaction with trypan blue
Authors: Beaudoin Allan R. , Roberts James M. 
Published: April 2021

ABSTRACT
The role that the thyroid gland may play in embryonic development has been under investigation for many years. A direct relationship between thyroid gland function and development is best illustrated in the amphibia (see Kollros, 1961, for pertinent literature). Attempts to demonstrate a similar influence of thyroxin on development in mammals has led to controversial results, in part due to the difficulty of separating the metabolic from the possible developmental effects of the hormone. In order for thyroxin to exert a direct effect upon the mammalian embryo it must cross the placenta. The bulk of the evidence seems to favor the viewpoint that the placenta is rather impermeable to thyroxin during the early stages of gestation and that this permeability increases near term. This is apparently true of the rabbit and man (Osorio & Myant, 1960) and the rat (Hamburgh, Sobel, Koblin & Rinestone, 1962; Roy & Kobayashi, 1962).
The 45Ca turnover in the membranous labyrinth of chick embryos during development
Authors: De Vincentiis Mario , Marmo Francesco 
Published: April 2021

ABSTRACT
An autoradiographic study of the 45Ca turnover in the membranous labyrinth of chick embryos has shown the following.
An early presence of 45Ca in the surface of the endolymphatic duct and of the lower part of the otocyst from which the sacculus and the ductus cochlearis will originate. 45Ca is always connected to an organic matrix of mucopolysaccharide. The turnover of 45Ca in these zones is very active in embryos of 5,6,7 days of incubation (a period in which otolithic morphogenesis is occurring), while it is very low in embryos of 12 days of incubation (in which the otoliths are already formed and mineralized in large amount). These results are discussed, together with the problem of the origin of otoliths.
Enzymic differentiation of rat yolk-sac placenta as affected by a teratogenic agent
Authors: Johnson E. Marshall , Spinuzz1 Ralph 
Published: April 2021

ABSTRACT
Electrophoretic and biochemical techniques were applied to homogenates of the rat’s visceral yolk-sac. Non-specific esterase, acid phosphatase, malate and lactate dehydrogenases were shown, by electrophoretic techniques, to undergo sequential enzymic differentiation from day 10 through day 20 of gestation. The enzyme repertory on a particular day was achieved through both additions to and deletions from the repertory of the preceding day. The greatest staining intensity by esterase and acid phosphatase was late in gestation but for both malate and lactate dehydro-genase it was most intense during days 11–13. A teratogenic folic acid deficiency resulted in delayed appearance of several enzyme forms but also resulted in some forms persisting beyond their normal time for disappearance. The effects of the vitamin deficiency were quite selective in that some enzyme forms appeared on time and in apparently normal concentration in the PGA-deficient material.