bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of activin and lithium on isolated Xenopus animal blastomeres and response alteration at the midblastula transition
Authors: Kinoshita Kei , Asashima Makoto 
Published: April 2021

ABSTRACT
Dorsoventral mesoderm patterning in the amphibian embryo involves a series of interactions mediated by several peptide growth factors. Animal blastomeres isolated at the 8-cell stage are useful for studying mesoderm patterning, since they contain the prospective (uninduced) mesoderm region and allow examination of the default state of animal cells. When activin is applied to these dorsal and ventral animal half explants, a competence prepattern for responding to activin is observed. In order to investigate the characteristics of prepatterning, we treated animal blastomeres with the embryo dorsalizing agent LiCl. Treatment with lithium alone did not induce normal trunk mesoderm in either blastomere. Lithium did, however, alter the competence of animal blastomeres to activin. Dorsal mesoderm was formed in the ventral blastomeres, as well as in the dorsal blastomeres. This result reveals that the early dorsoventral polarity in the animal hemisphere is not fixed.
Using goosecoid(gsc) and Xwnt-8 genes as dorsal and ventral mesoderm markers, it was verified that lithium modifies the competence to activin. Unexpectedly, lithium treatment on its own resulted in gsc expression in the animal half explants. This suggests that embryo goosecoid expression may be induced by the effect of dorsal determination activity, but not by mesoderm induction. However, lithium induced also the expression of brachyury (Xbra) gene at very low levels. This would indicate the formation of dorsal-anterior mesoderm, which was not identified by the tissue observations.
Expression of Xwnt-8, a ventral mesoderm marker usually induced in blastula animal caps by activin, was hardly induced in the blastomere explants. We isolated whole animal half explants at the 8-cell stage and exposed to activin at different stages. It was found that the same concentration of activin induces gsc before the midblastula stage, and induces Xwnt-8 at later stages. This suggests that the response of animal blastomeres alters depending on the stage of activin signaling.
A 25.7×103Mr hydra metalloproteinase (HMP1), a member of the astacin family, localizes to the extracellular matrix of Hydra vulgaris in a head-specific manner and has a developmental function
Authors: Yan Li , Pollock Gail H. , Nagase Hideaki , Sarras Michael P. 
Published: April 2021

ABSTRACT
Hydra extracellular matrix (ECM) is composed of a number of components seen in vertebrate ECM such as laminin, type IV collagen, fibronectin, and heparan sulfate proteoglycan. A number of functional studies have shown that hydra ECM plays an important role in pattern formation and morphogenesis of this simple metazoan. The present study was designed to identify matrix degrading proteinases in hydra and determine their potential function in hydra morphogenesis. Using SDS-PAGE gelatin-zymography, five gelatinolytic bands were identified with relative molecular masses of 67×103, 51-58×102 (a triplet) and 25-29×103, respectively. Inhibition studies indicated that all of these gelatinases were metalloproteinases. Gelatin-zymography indicated that there was a differential distribution of these gelatinases along the longitudinal axis of hydra, with the 67×103Mr gelatinase being concentrated in the body column, while the 51-58×103Mr gelatinase triplet and the 25-29×103Mr gelatinase concentrated in the head region. Purification procedures were successfully developed for the 25-29×103Mr metalloproteinase which has been termed hydra metalloproteinase 1 (HMP1) and which appeared as a single band with a SDS-PAGE mobility of 25.7×103Mr.
The N-terminal sequence of purified HMP1 indicated that it has structural homology with metalloproteinases that belong to the astacin family. Subsequent cloning and sequencing of cDNA clones confirmed the identification of HMP1 as an astacin-like metalloproteinase. Immunocytochemical studies with antibodies generated against the purified enzyme and to a synthetic peptide indicated that HMP1 was localized to the ECM of tentacles. Functional studies were performed in which purified HMP1, anti-HMP1 IgG, or suspected substrates of HMP1 (e.g. growth factors such as TGF-β1) were introduced into the inter-epithelial compartment of hydra using a ‘DMSO loading’ procedure. These studies indicated that HMP1 has a functional role during a number of developmental processes such as head regeneration and cell differentiation/trans-differentiation of tentacle battery cells.
Transcriptional control of tektin A mRNA correlates with cilia development and length determination during sea urchin embryogenesis
Authors: Norrander J. M. , Linck R. W. , Stephens R. E. 
Published: April 2021

ABSTRACT
Previous studies have shown that tektin A, one of three integral filamentous protein components of outer doublet microtubules, is synthesized in sea urchins in an amount correlating to the length of embryonic cilia initially assembled or experimentally regenerated. To investigate further the molecular mechanism for the regulation of tektin synthesis, tektin cDNA clones were used to assess mRNA levels during ciliogenesis, zinc-induced animalization, deciliation-induced regeneration and theophylline-induced elongation. Possibly involved in centriole replication, low, near-constant levels of mRNA for all three tektins are present in the unfertilized egg and during cleavage stages. Preceded by new synthesis of tektin B and C mRNAs, tektin A mRNA is up-regulated during ciliogenesis, but only tektin A mRNA levels correlate directly with ciliary length in animalized embryos; the others augment larger, non-limiting pools of tektins B and C. Tektin mRNAs decrease to steady-state levels after ciliogenesis, but are up-regulated again when the embryos are deciliated, correlating with the length of cilia to be deployed. In a species where a 3-fold ciliary length increase can be induced by theophylline treatment of zinc-arrested embryos, the mRNAs accumulate to proportionately higher levels during arrest but are not translated until induction, whereupon they decrease inversely with ciliary elongation. This suggests transcriptional control with respect to mRNA amounts but post-transcriptional control with respect to the expression of this phenotype. These data are consistent with a model in which (1) tektin filaments serve as linear determinants of microtubule doublet structure, and (2) the fixed amount of tektin A mRNA and protein synthesis consequently limit the length of doublets that can be co-assembled from larger pools of tektins B and C, tubulin, and other components.
TGFα can act as a chemoattractant to perioptic mesenchymal cells in developing mouse eyes
Authors: Reneker Lixing W. , Silversides David W. , Patel Kavita , Overbeek Paul A. 
Published: April 2021

ABSTRACT
Growth factors are believed to play an important role in regulating cell fate and cell behavior during embryonic development. Transforming growth factor α (TGFα), a member of the epidermal growth factor (EGF) superfamily, is a small polypeptide growth factor. Upon binding to its receptor, the EGF receptor (EGFR), TGFα can exert diverse biological activities, such as induction of cell proliferation or differentiation. To explore the possibility that TGFα might regulate cell fate during murine eye development, we generated transgenic mice that express human TGFα in the lens under the control of the mouse αA-crystallin promoter. The transgenic mice displayed multiple eye defects, including corneal opacities, cataracts and microphthalmia. At early embryonic stages TGFα induced the perioptic mesenchymal cells to migrate abnormally into the eye and accumulate around the lens. In situ hybridization revealed that the EGFR mRNA is highly expressed in the perioptic mesenchyme, suggesting that the migratory response is mediated by receptor activation. In order to test this model, the TGFα transgenic mice were bred to EGFR mutant waved-2 (wa-2) mice. We found that the eye defects of the TGFα transgenic mice are significantly abated in the wa-2 homozygote background. Because the EGFR mutation in the wa-2 mice is located in the receptor kinase domain, this result indicates that the receptor tyrosine kinase activity is critical for signaling the migratory response. Taken together, our studies demonstrate that TGFα is capable of altering the migratory decisions and behavior of perioptic mesenchyme during eye development.
Cytoskeletal elements link calcium channel activity and the cell cycle in early sea urchin embryos
Authors: Yazaki Ikuko , Tosti Elisabetta , Dale Brian 
Published: April 2021

ABSTRACT
Using the whole-cell clamp technique, we show that L-type calcium channels are activated in early sea urchin blastomeres during M-phase and subsequently inactivated in S-phase. This cyclical channel behaviour occurs in the absence of the nucleus suggesting cytoplasmic regulation independent of the centrosome cycle. Puromycin at 100–400 μM does not prevent inactivation of the current showing that this phase, at least, does not require protein synthesis. Cytochalasin B at 2 μg/ml inhibits the cyclical activity in both M and S phases, while 100 μg/ml of colchicine inactivates the L-type current in M-phase and activates a large T-type calcium current in S-phase, suggesting that channel behaviour is regulated by cytoskeletal elements. Since, fragmentation experiments show the calcium channels to be clustered in the apical membrane, and some L-type calcium channel inhibitors induced a significant delay in the cell cycle, the channel may play a role in regulating cytokinesis possibly by contributing to local intracellular calcium gradients.
Axonal localisation of the CAM-like tyrosine phosphatase CRYPα: a signalling molecule of embryonic growth cones
Authors: Stoker Andrew W. , Gehrig Bernhard , Haj Fawaz , Bay Boon-Huat 
Published: April 2021

ABSTRACT
Migrating embryonic growth cones require multiple, membrane-associated signalling molecules to monitor and respond to guidance cues. Here we present the first evidence that vertebrate cell adhesion molecule-like protein tyrosine phosphatases are likely to be components of this signalling system. CRYPα, the gene for an avian cell adhesion molecule-like phosphatase, is strongly expressed in the embryonic nervous system. In this study we have immunolocalised the protein in the early chick embryo and demonstrated its predominant localisation in axons of the central and peripheral nervous systems. This location suggests that the major, early role of the enzyme is in axonal development. In a study of sensory neurites in culture, we furthermore show that this phosphatase localises in migrating growth cones, within both the lamellipodia and filopodia. The dependence of growth cone migration on both cell adhesion and signalling through phosphotyrosine turnover, places the cell adhesion molecule-like CRYPα phosphatase in a position to be a regulator of these processes.
Drosophila nonmuscle myosin II is required for rapid cytoplasmic transport during oogenesis and for axial nuclear migration in early embryos
Authors: Wheatley Sally , Kulkarni Sanjay , Karess Roger 
Published: April 2021

ABSTRACT
The X-linked Drosophila gene spaghetti squash (sqh) encodes the regulatory light chain of nonmuscle myosin II. To assess the requirement for myosin II in oogenesis and early embryogenesis, we induced homozygous germline clones of the hypomorphic mutation sqh1 in otherwise het-erozygous mothers. Developing oocytes in such sqh1 germline clones often failed to attain full size due to a defect in ‘dumping’, the rapid phase of cytoplasmic transport from nurse cells. In contrast to other dumpless mutants described to date, sqh1 egg chambers showed no evidence of ring canal obstruction, and no obvious alteration in the actin network. However the distribution of myosin II was abnormal. We conclude that the molecular motor responsible for cytoplasmic dumping is supplied largely, if not exclusively, by nurse cell myosin II and we suggest that regulation of myosin activity is one means by which cytoplasmic transport may be controlled during oocyte development. The eggs resulting from sqh1 clones, though smaller than normal, began development but exhibited an early defect in axial migration of cleavage nuclei towards the posterior pole of the embryo, in a similar manner to that seen in early cleavage eggs in which the actin cytoskeleton is disrupted. Thus both nurse cell dumping and axial migration require a maternally supplied myosin II.
Polydactylous limbs in Strong’s Luxoid mice result from ectopic polarizing activity
Authors: Chan David C. , Laufer Ed , Tabin Cliff , Leder Philip 
Published: April 2021

ABSTRACT
Strong’s Luxoid (lstD) is a semidominant mouse mutation in which heterozygotes show preaxial hindlimb polydactyly, and homozygotes show fore- and hindlimb polydactyly. The digit patterns of these polydactylous limbs resemble those caused by polarizing grafts, since additional digits with posterior character are present at the anterior side of the limb. Such observations suggest that lstD limb buds might contain a genetically determined ectopic region of polarizing activity. Accordingly, we show that mutant embryos ectopically express the pattern-determining genes fibroblast growth factor 4 (fgf-4), sonic hedgehog (shh), and Hoxd-12 in the anterior region of the limb. Further, we show that anterior mesoderm from mutant limbs exhibits polarizing activity when grafted into host chicken limbs. In contrast to an experimentally derived polydactylous transgenic mouse, forelimbs of homozygotes show a normal pattern of Hoxb-8 expression, indicating that the duplication of polarizing tissue here occurs downstream or independently of Hoxb-8. We suggest that the lst gene product is involved in anteroposterior axis formation during normal limb development.
The role of Hoxa-3 in mouse thymus and thyroid development
Authors: Manley Nancy R. , Capecchi Mario R. 
Published: April 2021

ABSTRACT
Targeted disruption of Hoxa-3 results in a number of regionally restricted defects in tissues and structures derived from or patterned by mesenchymal neural crest. However, analysis of mutant embryos with injections of a carbocyanine dye or with molecular markers that label these cells indicates that neither the amount nor the migration patterns of this neural crest population are grossly affected. Therefore, it appears that the loss of Hoxa-3 affects the intrinsic capacity of this neural crest cell population to differentiate and/or to induce proper differentiation of the surrounding pharyngeal arch and pouch tissues. Hoxa-3 mutant mice are athymic and show thyroid hypoplasia. Thymus development is first evident as an expansion of mesenchymal neural crest in the posterior part of the 3rd pharyngeal pouch. Prior to this expansion, a marked reduction in pax-1 expression is observed in these cells in the mutant embryos. As pax-1 mutant mice also show thymic hypoplasia, these results suggest that Hoxa-3 may be required to maintain pax-1 expression in these cells and that the reduction of pax-1 expression is part of the athymic teleology in Hoxa-3 mutant mice. The thyroid gland is formed from the fusion of two structures of separate embryonic origin, the thyroid diverticulum, which is formed from endodermal epithelium in the floor of the pharynx, and the ultimobranchial body, formed from mesenchymal neural crest in the 4th pharyngeal pouch. Both of these sites express Hoxa-3 and are defective in mutant mice. Often a vesicle is observed in mutant mice that is exclusively composed of calcitonin-producing cells, suggesting the persistence of an ultimobranchial body. Both aspects of the thyroid phenotype show variable expressivity among mutant animals, even on the two sides of the same mutant animal. This variability suggests the presence of a compensating gene or genes, whose utilization is stochastic. A reasonable candidate for providing this compensatory function is the paralogous gene Hoxb-3.
How do sea urchins invaginate? Using biomechanics to distinguish between mechanisms of primary invagination
Authors: Davidson Lance A. , Koehl M. A. R. , Keller Raymond , Oster George F. 
Published: April 2021

ABSTRACT
The forces that drive sea urchin primary invagination remain mysterious. To solve this mystery we have developed a set of finite element simulations that test five hypothesized mechanisms. Our models show that each of these mechanisms can generate an invagination; however, the mechanical properties of an epithelial sheet required for proper invagination are different for each mechanism. For example, we find that the gel swelling hypothesis of Lane et al. (Lane, M. C., Koehl, M. A. R., Wilt, F. and Keller, R. (1993) Development 117, 1049-1060) requires the embryo to possess a mechanically stiff apical extracellular matrix and highly deformable cells, whereas a hypothesis based on apical constriction of the epithelial cells requires a more compliant extracellular matrix. For each mechanism, we have mapped out a range of embryo designs that work. Additionally, the simulations predict specific cell shape changes accompanying each mechanism. This allows us to design experiments that can distinguish between different mechanisms, all of which can, in principle, drive primary invagination.
Role of the proneural gene, atonal, in formation of Drosophila chordotonal organs and photoreceptors
Authors: Jarman Andrew P. , Sun Yan , Jan Lily Y. , Jan Yuh Nung 
Published: April 2021

ABSTRACT
The Drosophila gene atonal encodes a basic helix-loop-helix protein similar to those encoded by the proneural genes of the achaete–scute complex (AS-C). The AS-C are required in the Drosophila PNS for the selection of neural precursors of external sense organs. We have isolated mutants of atonal, which reveal that this gene encodes the proneural gene for chordotonal organs and photoreceptors. In atonal mutants, all observable adult chordotonal organs, and almost all embryonic chordotonal organs fail to form; all adult photoreceptors are missing. For both types of sense organ, this defect is already apparent at the level of precursor formation. Therefore it is a failure in the epidermal-neural decision process i.e. a proneural defect. The failure to form photoreceptors results in atrophy of the atonal mutant imaginal disc, due to apoptosis and lack of stimulation of division. Lack of photoreceptors should also eliminate signalling that arises from differentiating photoreceptors and is required for morphogenetic furrow movement in the wild-type eye disc. Nevertheless, a remnant morphogenetic furrow is still observed in the atonal mutant disc. This presumably reflects the process of furrow initiation, which would not depend on signals from developing photoreceptors.
Transient and restricted expression during mouse embryogenesis of Dll1, a murine gene closely related to Drosophila Delta
Authors: Bettenhausen Berthold , Hrabê de Angelis Martin , Simon Dominique , Guénet Jean-Louis , Gossler Achim 
Published: April 2021

ABSTRACT
The Drosophila Delta (Dl) gene is essential for cell-cell communication regulating the determination of various cell fates during development. Dl encodes a transmembrane protein, which contains tandem arrays of epidermal-growth-factor-like repeats in the extracellular domain and directly interacts with Notch, another transmembrane protein with similar structural features, in a ligand-receptor-like manner. Similarly, cell-cell interactions involving Delta-like and Notch-like proteins are required for cell fate determinations in C. elegans. Notch homologues were also isolated from several vertebrate species, suggesting that cell-to-cell signaling mediated by Delta- and Notch-like proteins could also underlie cell fate determination during vertebrate development. However, in vertebrates, no Delta homologues have yet been described.
We have isolated a novel mouse gene, Dll1 (delta-like gene 1), which maps to the mouse t-complex and whose deduced amino acid sequence strongly suggests that Dll1 represents a mammalian gene closely related to Drosophila Delta. Dll1 is transiently expressed during gastrulation and early organogenesis, and in a tissue-restricted manner in adult animals. Between day 7 and 12.5 of development, expression was detected in the paraxial mesoderm, closely correlated with somitogenesis, and in subsets of cells in the nervous system. In adult animals, transcripts were detected in lung and heart. Dll1 expression in the paraxial mesoderm and nervous system is strikingly similar to the expression of mouse Notch1 during gastrulation and early organogenesis. The overlapping expression patterns of the Dll1 and Notch1 genes suggest that cells in these tissues can communicate by interaction of the Dll1 and Notch1 proteins. Our results support the idea that Delta- and Notch-like proteins are involved in cell-to-cell communication in mammalian embryos and suggest a role for these proteins in cellular interactions underlying somitogenesis and development of the nervous system.
Epithelial planar polarity in the developing Drosophila eye
Authors: Wehrli Marcel , Tomlinson Andrew 
Published: April 2021

ABSTRACT
Experiments with the insect ectoderm have suggested that planar polarity in epithelia results from the local orientation of cells to the slope of a gradient of positional information. Here we show that planar polarity in the Drosophila eye is inverted when the morphogenetic wave that sweeps through the presumptive retinal epithelium is induced to move in the reverse direction. We suggest that the movement of the morphogenetic wave may be causal in establishing the planar polarity of this epithelium.
Dynamics of thin filopodia during sea urchin gastrulation
Authors: Miller Jeffrey , Fraser Scott E. , McClay David 
Published: April 2021

ABSTRACT
At gastrulation in the sea urchin embryo, a dramatic rearrangement of cells establishes the three germ layers of the organism. Experiments have revealed a number of cell interactions at this stage that transfer patterning information from cell to cell. Of particular significance, primary mesenchyme cells, which are responsible for production of the embryonic skeleton, have been shown to obtain extensive positional information from the embryonic ectoderm. In the present study, high resolution Nomarski imaging reveals the presence of very thin filopodia (0.2-0.4 μm in diameter) extending from primary mesenchyme cells as well as from ectodermal and secondary mesenchyme cells. These thin filopodia sometimes extend to more than 80 μm in length and show average growth and retraction rates of nearly 10 μm/minute. The filopodia are highly dynamic, rapidly changing from extension to resorption; frequently, the resorption changes to resumption of assembly. The behavior, location and timing of active thin filopodial movements does not correlate with cell locomotion; instead, there is a strong correlation suggesting their involvement in cell-cell interactions associated with signaling and patterning at gastrulation. Nickel-treatment, which is known to create a patterning defect in skeletogenesis due to alterations in the ectoderm, alters the normal position-dependent differences in the thin filopodia. The effect is present in recombinant embryos in which the ectoderm alone was treated with nickel, and is absent in recombinant embryos in which only the primary mesenchyme cells were treated, suggesting that the filopodial length is substratum dependent rather than being primary mesenchyme cell autonomous. The thin filopodia provide a means by which cells can contact others several cell diameters away, suggesting that some of the signaling previously thought to be mediated by diffusible signals may instead be the result of direct receptor-ligand interactions between cell membranes.