bluuebunny/crossref_metadata_2025_split huggingface dataset:
Epithelial-mesenchymal interactions are required for msx 1 and msx 2 gene expression in the developing murine molar tooth
Authors: Jowett Adrian K. , Vainio Seppo , Ferguson Mark W. J. , Sharpe Paul T. , Thesleff Irma 
Published: April 2021

ABSTRACT
Duplication of the msh-like homeobox gene of Drosophila may be related to the evolution of the vertebrate head. The murine homologues of this gene, msx 1 and msx 2 are expressed in the developing craniofacial complex including the branchial arches, especially in regions of epithelial-mesenchymal organogenesis including the developing tooth.
By performing in vitro recombination experiments using homochronic dental and non-dental epithelial and mesenchymal tissues from E10 to E18 mouse embryos, we have found that the maintenance of homeobox gene expression in the tooth is dependent upon tissue interactions. In homotypic recombinants, dental-type tissue interactions occur, leading to expression of both genes in a manner similar to that seen during in vivo development. msx 1 is expressed exclusively in mesenchyme, both in the dental papilla and follicle. msx 2 is expressed in the dental epithelium and only in the mesenchyme of the dental papilla. In heterotypic recombinants, the dental epithelium is able to induce msx 1 expression in non-dental mesenchyme, this potential being lost at the bell stage. In these recombinants msx 2 was induced by presumptive dental epithelium prior to the bud stage but not thereafter. The expression of msx 1 and msx 2 in dental mesenchyme requires the presence of epithelium until the early bell stage. However, whereas non-dental, oral epithelium is capable of maintaining expression of msx 1 in dental mesenchyme throughout tooth development, induction of msx 2 was temporally restricted suggesting regulation by a specific epithelial-mesenchymal interaction related to the inductive events of tooth formation.
msx 1 and msx 2, as putative transcription factors, may play a role in regulating the expression of other genes during tooth formation. We conclude that expression of msx 1 in jaw mesenchyme requires a non-specific epithelial signal, whereas msx 2 expression in either epithelium or mesenchyme requires reciprocal interactions between specialized dental cell populations.
Ontogeny of hyaluronan secretion during early mouse development
Authors: Brown Jeremy J. G. , Papaioannou Virginia E. 
Published: April 2021

ABSTRACT
The ontogeny of hyaluronan (HA) secretion during early mouse embryogenesis has been investigated using a biotin-labelled HA-binding complex from cartilage proteoglycan. HA is first secreted by visceral endoderm cells of the early egg cylinder on day 5.5 post coitum (p.c.), predominantly into the expanding yolk cavity. On day 6.5 p.c., HA is present in both the yolk and proamniotic cavities, but pericellular staining is restricted to the visceral endoderm and a population of embryonic ectoderm cells at the antimesometrial end of the proamniotic cavity. By the primitive streak stage, HA is secreted into the ectoplacental, exocoelomic, amniotic and yolk cavities, whilst the only cells exhibiting pericellular staining are those of the embryonic and extraembryonic mesoderm, including the allantois. Comparisons of HA-staining patterns of cultured whole blastocysts, microdissected trophectoderm fragments and immuno-surgically isolated inner cell masses, revealed no trophoblast-associated HA secretion during outgrowth in vitro but significant synthetic activity by the endodermal derivatives of differentiating inner cell masses. To identify the cell lineages responsible for secretion of HA into the embryonic cavities and to investigate the origin of the HA observed around migrating mesoderm cells, day 7.5 p.c. primitive streak stage conceptuses were dis-sected into their various embryonic and extraembryonic cell lineages. HA secretion was observed after shortterm suspension culture of mesoderm, embryonic ectoderm and embryonic endoderm, but was undetectable in fragments of ectoplacental cone, parietal yolk sac (primary giant trophoblast and parietal endoderm), extraembryonic ectoderm or extraembryonic endoderm. The level of synthesis by the HA-positive tissues was markedly enhanced by culture in medium containing serum, compared with that obtained following culture in medium supplemented with a defined serum substitute containing insulin, transferrin, selenous acid and linoleic acid. This suggests that additional growth factors, present in serum but absent from the serum substitute, are required for optimal HA synthesis by the HA-secreting tissues in vitro, and probably also in vivo. The implications of these events for implantation and the development of peri- and early post-implantation mouse embryos are discussed, and a new role for HA in the initial formation and expansion of the embryonic cavities is proposed.
Conservation of regulatory elements controlling hairy pair-rule stripe formation
Authors: Langeland James A. , Carroll Sean B. 
Published: April 2021

ABSTRACT
The hairy (h) gene is one of two pair-rule loci whose striped expression is directly regulated by combinations of gap proteins acting through discrete upstream regulatory fragments, which span several kilobases. We have undertaken a comparative study of the molecular biology of h pair-rule expression in order to identify conserved elements in this complex regulatory system, which should provide important clues concerning the mechanism of stripe formation. A molecular comparison of the h locus in Drosophila virilis and Drosophila melanogaster reveals a conserved overall arrangement of the upstream regulatory elements that control individual pair-rule stripes. We demonstrate that upstream fragments from D. virilis will direct the proper expression of stripes in D. melanogaster, indicating that these are true functional homologs of the stripe-producing D. melanogaster regulatory elements, and that the network of trans-acting proteins that act upon these regulatory elements is highly conserved. We also demonstrate that the spatial relationships between specific h stripes and selected gap proteins are highly conserved. We find several tracts of extensive nucleotide sequence conservation within homologous stripe-specific regulatory fragments, which have facilitated the identification of functional subelements within the D. melanogaster regulatory fragment for h stripe 5. Some of the conserved nulceotide tracts within this regulatory fragment contain consensus binding sites for potential trans-regulatory (gap and other) proteins, while many appear devoid of known binding sites. This comparative approach, coupled with the analysis of reporter gene expression in gap mutant embryos suggests that the Kr and gt proteins establish the anterior and posterior borders of h stripe 5, respectively, through spatial repression. Other, as yet unidentified, proteins are certain to play a role in stripe activation, presumably acting through other conserved sequence tracts.
RNA and protein localisations of TGFβ2 in the early mouse embryo suggest an involvement in cardiac development
Authors: Dickson Marion C. , Slager Hans G. , Duffie Elizabeth , Mummery Christine L. , Akhurst Rosemary J. 
Published: April 2021

ABSTRACT
We have performed a detailed analysis of the localisations of RNAs for TGFβ2 and β3, and of TGFβ2 protein in mouse embryos from 6.5 to 9.5 days post coitum, using in situ hybridisation and immunohistochemistry on serial sections, and whole-mount in situ hybridisation to complete embryos. TGFβ3 RNA was not seen in any of the tissue sections, but very low levels of the RNA were seen by whole-mount in situ hybridisation around the outflow tract of the heart at 8.5 days post coitum. TGFβ2 RNA is expressed at high levels in all cells with the potential to differentiate into cardiomyocytes. Additionally, the foregut endoderm, juxtaposed to the heart, and the neuroepithelium at the rostral extremity of the foregut, express very high levels of TGFβ2 RNA, between 8.5 and 9.5 days post coitum. As cardiomyogenesis proceeds, TGFβ2 RNA levels diminishes within the myocytes, with a concomitant increase in staining for TGFβ2 protein. TGFβ2 protein staining of cardiomyocytes persists throughout development and in the adult, in the absence of detectable levels of the corresponding RNA. Superimposed upon this myocardial pattern of expression, there is an upregulation of TGFβ2 RNA in the myocardium of the outflow tract and atrioventricular canal between 8.5 and 9.5 days post coitum, which returns to low levels by 11.5 days post coitum. The results are discussed in terms of a potential role of TGFβ2 in controlling cardiomyogenesis and in induc-tive interactions leading to cardiac cushion tissue formation.
Actin depolymerisation induces process formation on MAP2-transfected non-neuronal cells
Authors: Edson Kathryn , Weisshaar Brigitte , Matus Andrew 
Published: April 2021

ABSTRACT
We have previously shown that microtubules in non-neuronal cells form long, stable bundles after transfection with the embryonic neuronal microtubule-associated protein MAP2c. In this study, we found that treating MAP2c-transfected cells with the actin depolymerising drug cytochalasin B led to the outgrowth of microtubule-containing processes from the cell surface. This effect was specific to MAP2c and did not occur in untransfected cells whose microtubules had been stabilised by treatment with taxol. The outgrowth and retraction of these processes during repeated cycles of cytochalasin addition and removal was followed by video time-lapse microscopy and was suggestive of a physical interaction between compressive forces exerted by the MAP2c-stabilised microtubule bundles and tensile forces originating in the cortical actin network. We suggest that MAP2c confers three properties on cellular microtubules that are essential for process out-growth: stability, bundling and stiffness. The latter probably arises from the linking together of neighbouring tubulin subunits by three closely spaced tubulin-binding motifs in the MAP2 molecule that limits their motion relative to one another and thus reduces the flexibility of the polymer. Similar multimeric tubulin-binding domains in other proteins of the MAP2 class, including tau in axons and MAP4 in glial cells, may play the same role in the development and support of asymmetric cell morphology. Axial bundles of microtubules are found in growing neurites but not in growth cones, suggesting that the regulated expression of these MAP-induced properties makes an important contribution to the establishment of a stable process behind the advancing growth cone.
Activins are expressed in preimplantation mouse embryos and in ES and EC cells and are regulated on their differentiation
Authors: Albano Rodolpho M. , Groome Nigel , Smith J. C. 
Published: April 2021

ABSTRACT
Members of the activin family have been suggested to act as mesoderm-inducing factors during early amphib- ian development. Little is known, however, about meso- derm formation in the mammalian embryo, and as one approach to investigating this we have studied activin expression during early mouse development.
Activins are homo- or heterodimers of the βA or βB subunits of inhibin, itself a heterodimer consisting of one of the β subunits together with an α subunit. Our results indicate that the oocyte contains mRNA encoding all three subunits, and antibody staining demonstrates the presence of both α and β protein chains. From the fer- tilized egg stage onwards, α subunit protein cannot be detected, so the presence of β subunits reflects the pres- ence of activin rather than inhibin.
Maternal levels of activin protein decline during early cleavage stages but increase, presumably due to zygotic transcription (see below), in the compacted morula. By 3.5 days, only the inner cell mass (ICM) cells of the blas- tocyst express activin, but at 4.5 days the situation is reversed; activin expression is confined to the trophec- toderm. Using reverse transcription-PCR, neither βA nor βB mRNA was detectable at the two-cell stage but transcripts encoding both subunits were detectable at the morula stage, with βB mRNA persisting into the blastocyst.
We have also analyzed activin and inhibin expression in ES and EC cells. Consistent with the observation that activins are expressed in the ICM of 3.5-day blastocysts, we find high levels of βA and βB mRNA in all eight ES cell lines tested. F9 EC cells express only activin βB, together with low levels of the inhibin αchain. When ES and EC cells are induced to differentiate, levels of activin fall dramatically. These results are consistent with a role for activins in mesoderm formation and other steps of early mouse development.
Somite pattern regulation in the avian segmental plate mesoderm
Authors: Packard David S. , Zheng Rui-Zhen , Turner David C. 
Published: April 2021

ABSTRACT
Previous experimental evidence suggested that the avian segmental pattern is already specified in the apparently unsegmented paraxial (segmental plate) mesoderm, but is susceptible to modification and reconstitution. We explored capacities of embryos to alter the specified pat-tern and restore it after disruption. In control experi-ments, right segmental plates of chicken or Japanese quail embryos were removed after about 48 hours of incubation and immediately replaced. Hensen’s node and the primitive streak were removed to halt further segmental plate formation and the embryos were cul-tured for about 18 hours more. Somite numbers on the operated and unoperated sides were nearly identical (r=0.904, n=31, P&lt;0.001); no species differences were noted. Right segmental plates of chicken hosts were then replaced with right segmental plates from quail donors. The numbers of somites formed by donors and grafts were not significantly correlated (r=0.305, n=30, P&lt;0.1), but the correlation between the graft and the host’s unoperated side was significant (r=0.666, n=30, P&lt;0.001). The host is therefore able to alter the number of somites formed by the graft to one more compatible with the host’s pattern. From orthostereoscopic recon-tructions, it appeared that the location and size of somites could also be adjusted by the host. Similar results were obtained for tandem grafts of anterior halves of segmental plates and for grafts of minced seg-mental plates, though in the latter case contact with tissues near the midline was necessary for somite for-mation.
Expression of the Drosophila optomotor-blind gene transcript in neuronal and glial cells of the developing nervous system
Authors: Poeck Burkhard , Hofbauer Alois , Pflugfelder Gert O. 
Published: April 2021

ABSTRACT
Mutations in the complex gene locus optomotor-blind (omb) can lead to defects in the development of both the optic lobes and external features of the adult fly. We describe here the expression of omb in the developing and adult nervous system using in situ hybridization. During embryogenesis, omb expression is first observed in the optic lobe anlagen. It later expands to a larger part of the developing larval brain and to the gnathal lobes. Cells in the ventral and peripheral nervous systems begin to express omb after completion of germ band extension. Later in embryonic development, expression declines and only persists in the antennomaxillary complex and in part of the brain hemispheres. During the larval and pupal stages, omb expression in the brain is confined to the developing optic lobes and contiguous regions of the central brain. At these stages, only a few cells show expression in the ventral ganglion. In the eye imaginal disc, transcript accumulation is most conspicuous in a group of presumptive glia precursor cells posterior to the morphogenetic furrow and in the optic stalk. In the adult brain, expression is prominent in several regions of the optic lobe cortex and along the border between central brain and optic lobes. In the mutation In(1)ombH31, 40 kb of regulatory DNA, downstream from the transcription unit, are removed from the omb gene. In(1)ombH31 is characterized by the lack of a set of giant interneurons from the lobula plate of the adult optic lobes. We find that, already during embryogenesis, there is a drastic difference between wild type and In(1)ombH31 in the level of the omb transcript in the optic lobe primordia. The adult mutant phenotype may thus be caused by omb misexpression during embryonic development.
Altered Epidermal Growth Factor-like sequences provide evidence for a role of Notch as a receptor in cell fate decisions
Authors: Heitzler Pascal , Simpson Pat 
Published: April 2021

ABSTRACT
In Drosophila each neural precursor is chosen from a group of cells through cell interactions mediated by Notch and Delta which may function as receptor and ligand (signal), respectively, in a lateral signalling path-way. The cells of a group are equipotential and express both Notch and Delta. Hyperactive mutant Notch molecules, (Abruptex), probably have an enhanced affinity for the ligand. When adjacent to wild-type cells, cells bearing the Abruptex proteins are unable to produce the signal. It is suggested that in addition to the binding of Notch molecules on one cell to the Delta molecules of opposing cells, the Notch and Delta proteins on the surface of the same cell may interact. Binding between a cell’s own Notch and Delta molecules would alter the availability of these proteins to interact with their counterparts on adjacent cells.
Appearance and evolution of calcium currents and contraction during the early post-fusional stages of rat skeletal muscle cells developing in primary culture
Authors: Cognard Christian , Constantin Bruno , Rivet-Bastide Michèle , Imbert Nathalie , Besse Colette , Raymond Guy 
Published: April 2021

ABSTRACT
Primary cultures from enzymatically dissociated satellite cells of newborn rat skeletal muscles enabled developmental in vitro studies of mechanical and electrical properties during the first steps of myogenesis. The present work focused on the appearance, evolution and roles of two types of calcium currents (ICa,T and ICa,L) and of depolarization-induced contractile activity during the early stages of muscle cell development in primary culture. Prefusional mononucleated cells (myoblasts), young myotubes of 1 day (with less than 10 nuclei) or 2-3 days (more than 9 nuclei) and myoballs from 4-6, 7-9, 10-12 and 13-16 days cultures were patchclamped (whole-cell configuration), and calcium currents and contraction simultaneously recorded. Sodium but not calcium currents could be recorded at the myoblast stage. In young myotubes (1 day), ICa,L was present with high incidence as compared to ICa,T, which was poorly expressed. Contractile responses appeared at the next stage (2-3 days) while the occurrence of ICa,T progressively increased. This developmental evolution of the calcium currents and contraction expression was accompanied by some changes in their characteristics: the ICa,T/ICa,L amplitudes ratio progressively increased and the time-to-peak of contraction progressively decreased with the age of myoballs. Physiological functions for calcium currents in developing muscle are suggested and discussed: ICa,T, which is transiently expressed, could be involved in the pacemaker-like activity while ICa,L could serve as an early contraction triggering mechanism and/or initially to fill and then to maintain the intracellular calcium stores.
Intrinsic and extrinsic factors in the mechanism of neurulation: effect of curvature of the body axis on closure of the posterior neuropore
Authors: Straaten H.W.M. van , Hekking J.W.M. , Consten C. , Copp A.J. 
Published: April 2021

ABSTRACT
Neurulation has been suggested to involve both factors intrinsic and extrinsic to the neuroepithelium. In the curly tail (ct) mutant mouse embryo, final closure of the posterior neuropore is delayed to varying extents resulting in neural tube defects. Evidence was presented recently (Brook et al., 1991, Development 113, 671-678) to suggest that enhanced ventral curvature of the caudal region is responsible for the neurulation defect, which probably originates from an abnormally reduced rate of cell proliferation affecting the hindgut endoderm and notochord, but not the neuroepithelium (Copp et al., 1988, Development 104, 285-295). This axial curvature probably generates a mechanical stress on the posterior neuropore, opposing normal closure. We predicted, therefore, that the ct/ct posterior neuropore should be capable of normal closure if the neuroepithelium is isolated from its adjacent tissues. This prediction was tested by in vitro culture of ct/ct posterior neuropore regions, isolated by a cut caudal to the 5th from last somite. In experimental explants, the neuroepithelium of the posterior neuropore, together with the contiguous portion of the neural tube, were separated mechanically from all adjacent non-neural tissues. The posterior neuropore closed in these explants at a similar rate to isolated posterior neuropore regions of non-mutant embryos. By contrast, control ct/ct explants, in which the caudal region was isolated but the neuroepithelium was left attached to adjacent tissues, showed delayed neurulation. To examine further the idea that axial curvature may be a general mechanism regulating neurulation, we cultured chick embryos on curved substrata in vitro. Slight curvature of the body axis (maximally 1° per mm axial length), of either concave or convex nature, resulted in delay of posterior neuropore closure in the chick embryo. Both incidence and extent of closure delay correlated with the degree of curvature that was imposed. We propose that during normal embryogenesis the rate of neurulation is related to the angle of axial curvature, such that experimental alterations in curvature will have differing effects (either enhancement or delay of closure) depending on the angle of curvature at which neurulation normally occurs in a given species, or at a given level of the body axis.
Involvement of leukemia inhibitory factor and nerve growth factor in the development of dorsal root ganglion neurons
Authors: Murphy Mark , Reid Kate , Brown Melissa A. , Bartlett Perry F. 
Published: April 2021

ABSTRACT
Leukemia inhibitory factor (LIF) was recently shown to stimulate the generation of sensory neurons from the murine neural crest in vitro. Here, we examine the respective activities of LIF and nerve growth factor (NGF) throughout the embryonic development of sensory neurons in dorsal root ganglia (DRG) and neural crest. In cultures of embryonic day 12 (E12) DRG, which contain sensory neuron precursor cells, a combination of both LIF and NGF are required for the differentiation of mature sensory neurons from their neurofilament negative (NF) precursors. The primary differentiation step from NF cell to NF+ immature neuron is promoted by LIF, whereas the survival and further maturation of the newly differentiated neurons depends on NGF. In cultures of sensory neurons isolated at the time of target innervation (E14 and E15 DRG), the survival of the majority of the neurons is dependent on NGF. However, LIF acts as a survival agent for a discrete population of NGF non-responsive neurons. From E16, the number of neurons maintained by LIF increases to &gt;90% by birth. Consistent with the in vitro observations, LIF mRNA could be detected at early developmental stages (E12-E13), within the spinal column and DRG as well as the limbs and, later (after E15), in areas of sensory innervation (skin, limbs, feet and gut). This supports the idea that LIF, as well as NGF, may regulate sensory development in vivo.