bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regulation of expression of fibronectin and its receptor, α5β1, during development and regeneration of peripheral nerve
Authors: Lefcort Frances , Venstrom Kristine , McDonald John A. , Reichardt Louis F. 
Published: April 2021

ABSTRACT
The extracellular matrix glycoprotein, fibronectin, is a potent promoter of peripheral neurite outgrowth. Interactions of peripheral neurons with fibronectin have been shown to be primarily mediated by the β1 class of integrin heterodimers. In the present study, we have examined the expression and regulation of fibronectin and its integrin receptor, α5 β1, in developing and regenerating chick peripheral nerve. We show that fibronectin and α5β1 α5β1 are expressed at comparatively high levels in developing nerve with α5β1 expression on axons and non-neuronal cells. With nerve maturation, both proteins are less prominently expressed and the cellular pattern of α5β1,expression becomes more restricted. Following lesion of mature nerve, both fibronectin and α5β1, are strongly induced with prominent expression of α5β1, on regenerating neurites and Schwann cells. The elevation in fibronectin levels in the regenerating nerve is highest in the vicinity of the lesion, an area undergoing extensive cellular remodeling including Schwann cell migration and growth cone extension. Our results suggest that fibronectin and its receptor, α5β1, may mediate functionally important interactions in the development and regeneration of peripheral nerve.
Local and transient expression of E-cadherin involved in mouse embryonic brain morphogenesis
Authors: Shimamura Kenji , Takeichi Masatoshi 
Published: April 2021

ABSTRACT
We found that E-cadherin (uvomorulin) is transiently expressed in restricted regions of the metencephalon, mesencephalon and diencephalon of mouse embryonic brain. This expression first occurred in parts of the mes-encephalon and diencephalon at around E9.5, and subsequently extended to the primordia of cerebellum, the dorsal midline of mesencephalon and some other regions of the embryonic brain. These E-cadherin expressions ceased by E15 except at the dorsal midline. Immuno-histological analyses showed that E-cadherin-positive cells are radially arranged in the neural tube and the E-cadherin-positive regions are sharply demarcated from E-cadherin-negative regions. Axons extending from some of the E-cadherin-positive regions also expressed this molecule. When embryonic brains were dissociated into single cells and cultured as monolayers, E-cadherin-positive cells formed clusters that were seg-regated from E-cadherin-negative cells. E9.5 brain fragments containing metencephalon and mesencephalon were isolated, explanted on Nuclepore filters and cul-tured in the absence or presence of antibodies to E-cad-herin. This antibody treatment removed most of the E-cadherin molecules from the explants and consequently affected their growth pattern. To analyze cellular events induced by the antibody treatment, we stained these explants with an antiserum to En whose distribution was found to overlap in part with that of E-cadherin and found that the pattern of En staining was altered by the anti-E-cadherin antibody treatment. These results suggest that the local and transient expression of E-cad-herin in embryonic brain is involved in regional pattern formation in this organ.
The role of initial cells in maize anther morphogenesis
Authors: Dawe R. Kelly , Freeling Michael 
Published: April 2021

ABSTRACT
The near absence of cell movement in plants makes clonal analysis a particularly informative method for reconstructing the early events of organ formation. We traced the patterns of cell division during maize anther development by inducing sector boundaries that preceded the earliest events of anther initiation. In doing this, we were able to estimate the smallest number of cells that are fated to form an anther, characteristic cell division patterns that occur during anther morphogenesis, and the relationship between the pre-existing symmetry of the initial cells and the final symmetry of the mature anther. Four general conclusions are made: (1) anthers are initiated from small groups of 12 or fewer cells in each of two floral meristematic layers; (2) the early growth of the anther is more like a shoot than a glume or leaf; (3) cell ancestry does not dictate basic structure and (4) the orientation of initial cells predicts the orientation of the four pollen-containing microsporangia, which define the axes of symmetry on the mature anther. The final point is discussed with other data, and an explanation involving a ‘structural template’ is invoked. The idea is that the orientation of initial cells within the floral meristem establishes an architectural pattern into which anther cells are recruited without regard to their cellular lineages. The structural template hypothesis may prove to be generally applicable to problems of pattern formation in plants.
Tissue-specific ecdysone responses: regulation of the Drosophila genes Eip28/29 and Eip40 during larval development
Authors: Andres Andrew J. , Cherbas Peter 
Published: April 2021

ABSTRACT
The Drosophila genes Eip28/29 and Eip40 are expressed in Kc cells and are rapidly induced by the steroid hor-mone ecdysone. The molecular basis for Eip28/29’s regulation in those cells has been studied in some detail. To determine how this regulation relates to normal development, we have examined the expression of both genes throughout Drosophila development, with special attention to Eip28/29 and the final larval instar. Eip28/29 expression is complex; there are tissues in which it is never expressed, others in which it is continuously expressed at a low level and tissues in which its expression is regulated without obvious relationship to endocrine events. However high-level Eip28/29 expression always correlates with the presence of ecdysone and there is good evidence that Eip28/29 is directly regulated by the hormone in some tissues and at some stages. Most striking are the induction of Eip28/29 transcripts in numerous tissues at the last larval molt, their induction in the epidermis at the time of the ‘late 3rd transition’, their extinction in the same tissue by the premetamorphic ecdysone peak, and their induction by that peak in the lymph gland, hemocytes and proventriculus. These contrasting regulatory behaviors provide a well-defined model for studying the developmental specificity of steroid responses.
Eip40 appears to be ecdysone-inducible only in the lymph gland and there only at the premetamorphic peak. The similarities been Eip28/29 and Eip40 regulation in the lymph gland and Kc cells support the idea that Kc cells are derived from a hematopoietic ancestor.
The epithelium of the dorsal marginal zone of Xenopus has organizer properties
Authors: Shih John , Keller Ray 
Published: April 2021

ABSTRACT
We have investigated the properties of the epithelial layer of the dorsal marginal zone (DMZ) of the Xeno - pus laevis early gastrula and found that it has inductive properties similar to those of the entire Spemann orga- nizer. When grafts of the epithelial layer of the DMZ of early gastrulae labelled with fluorescein dextran were transplanted to the ventral sides of unlabelled host embryos, they induced secondary axes composed of notochord, somites and posterior neural tube. The orga- nizer epithelium rescued embryos ventralized by UV irradiation, inducing notochord, somites and posterior neural tube in these embryos, while over 90% of ven- tralized controls showed no such structures. Combina- tions of organizer epithelium and ventral marginal zone (VMZ) in explants of the early gastrula resulted in con- vergence, extension and differentiation of dorsal meso- dermal tissues, whereas similar recombinants of non- organizer epithelium and the VMZ did none of these things. In all cases, the axial structures forming in response to epithelial grafts were composed of labelled graft and unlabelled host cells, indicating an induction by the organizer epithelium of dorsal, axial morpho- genesis and tissue differentiation among mesodermal cells that otherwise showed non-axial development.
Serial sectioning and scanning electron microscopy of control grafts shows that the epithelial organizer effect occurs in the absence of contaminating deep cells adher- ing to the epithelial grafts. However, labelled organizer epithelium grafted to the superficial cell layer con- tributed cells to deep mesodermal tissues, and organizer epithelium developed into mesodermal tissues when deliberately grafted into the deep region. This shows that these prospective endodermal epithelial cells are able to contribute to mesodermal, mesenchymal tissues when they move or are moved into the deep environ- ment. These results suggest that in normal development, the endodermal epithelium may influence some aspects of the cell motility underlying the mediolateral interca- lation (see Shih, J. and Keller, R. (1992) Development 116, 901-914), as well as the tissue differentiation of mesodermal cells. These results have implications for the analysis of mesoderm induction and for analysis of variations in the differentiation and morphogenetic function of the marginal zone in different species of amphibians.
Induction of a RARβ2-lacZ transgene by retinoic acid reflects the neuromeric organization of the central nervous system
Authors: Zimmer Andreas , Zimmer Anne 
Published: April 2021

ABSTRACT
The hormone retinoic acid (RA) has been implicated in the organization of the anteroposterior (AP) body axis. In this paper, we describe the effects of RA on the activity of the RA-inducible retinoic acid receptor-2 (RAR 2) promoter. When transgenic embryos carrying a RAR 2-lacZ reporter gene were exposed to a single dose of RA between gestational days 8.5 to 10.5, lacZ expression was induced in the anterior central nervous system (CNS). Strikingly, the transgene was expressed in a segmented pattern reminiscent of that of Drosophila ‘pair-rule’ genes. RA treatment of midgastrulation embryos at day 7.5 disturbed the segmentation and pro-duced severe craniofacial defects. We discuss the possi-bility that the entire anterior CNS is segmented and that this segmentation is reflected by the RAR 2-lacZ induc-tion pattern.
Relationships between mesoderm induction and the embryonic axes in chick and frog embryos
Authors: Stern Claudio D. , Hatada Yohko , Selleck Mark A. J. , Storey Kate G. 
Published: April 2021

ABSTRACT
The hypoblast is generally thought to be responsible for inducing the mesoderm in the chick embryo because the primitive streak, and subsequently the embryonic axis, form according to the orientation of the hypoblast. However, some cells become specified as embryonic mesoderm very late in development, towards the end of the gastrulation period and long after the hypoblast has left the embryonic region. We argue that induction of embryonic mesoderm and of the embryonic axis are different and separable events, both in amniotes and in amphibians. We also consider the relationships between the dorsoventral and anteroposterior axes in both groups of vertebrates.
Fate mapping the neural plate and the intraembryonic mesoblast in the upper layer of the chicken blastoderm with xenografting and time-lapse videography
Authors: Bortier Hilde , Vakaet L. C. A. 
Published: April 2021

ABSTRACT
The disposition of the Anlage fields of the neural plate and the intraembryonic mesoblast in the upper layer of the chicken blastoderm was studied at the primitive streak stage prior to the regression of Hensen’s node (stages 5V to 6V, L. Vakaet (1970)Arch. Biol. 81, 387426). Chicken blastoderms were cultured by New’s technique on a mixture of thin egg white and agar. The anterior half of the deep layer was reflected with a tungsten needle. A circular fragment of the upper layer was punched out with a pulled out Pasteur pipette and discarded. It was replaced with an isotopic and isopolar piece of quail upper layer that was punched out with the same pipette. The deep layer was replaced and the chimeras were reincubated for 24 hours. The xenografts were followed with time-lapse videography. After fixation, the quail cells were located using Le Douarin’s quail nucleolar marker technique. Integrating the observations with time-lapse videography and the results of Feulgen stained sections, we have drawn a new fate map of the disposition of the Anlage fields in the upper layer of the chicken blastoderm at stages prior to the regression of Hensen’s node (stages 5V to 6V). The disposition of the neural plate and of the notochord, somites, nephrotome and lateral plates was therefore determined before the Anlage fields are morphologically discernible. The pathway of the fields in the upper layer towards their disposition was documented with time-lapse videography in chimeric chicken blastoderms that developed normally.
Homeostatic balance between dorsal and cactus proteins in the Drosophila embryo
Authors: Govind Shubha , Brennan Lynn , Steward Ruth 
Published: April 2021

ABSTRACT
The maternal-effect gene dorsal encodes the ventral morphogen that is essential for elaboration of ventral and ventrolateral fates in the Drosophila embryo. Dorsal belongs to the rel family of transcription factors and controls asymmetric expression of zygotic genes along the dorsoventral axis. The dorsal protein is cytoplasmic in early embryos, possibly because of a direct interaction with cactus. In response to a ventral signal, dorsal protein becomes partitioned into nuclei of cleavagestage syncytial blastoderms such that the ventral nuclei have the maximum amount of dorsal protein, and the lateral and dorsal nuclei have progressively less protein. Here we show that transgenic flies containing the dorsal cDNA, which is driven by the constitutively active hsp83 promoter, exhibits rescue of the dorsal phenotype. Transformed lines were used to increase the level of dorsal protein. Females with dorsal levels roughly twice that of wild-type produced normal embryos, while a higher level of dorsal protein resulted in phenotypes similar to those observed for loss-of-function cactus mutations. By manipulating the cactus gene dose, we found that in contrast to a dorsal/cactus ratio of 2.5 which resulted in fully penetrant weak ventralization, a cactus/dorsal ratio of 3.0 was acceptable by the system. By manipulating dorsal levels in different cactus and dorsal group mutant backgrounds, we found that the relative amounts of ventral signal to that of the dorsalcactus complex is important for the elaboration of the normal dorsoventral pattern. We propose that in a wildtype embryo, the activities of dorsal and cactus are not independently regulated; excess cactus activity is deployed only if a higher level of dorsal protein is available. Based on these results we discuss how the ventral signal interacts with the dorsal-cactus complex, thus forming a gradient of nuclear dorsal protein.
Apical-basal pattern formation in the Arabidopsis embryo: studies on the role of the gnom gene
Authors: Mayer Ulrike , Büttner Gabriele , Jürgens Gerd 
Published: April 2021

ABSTRACT
gnom is one of several genes that make substantial contributions to pattern formation along the apical-basal axis of polarity in the Arabidopsis embryo as indicated by the mutant seedling phenotype. The apical and basal end regions of the body pattern, which include the meristems of the shoot and the root, fail to form, and a minority of mutant embryos lack morphological features of apical-basal polarity. We have investigated the developmental basis of the gnom mutant phenotype, taking advantage of a large number of EMS-induced mutant alleles. The seedling phenotype has been traced back to the early embryo in which the asymmetric division of the zygote is altered, now producing two nearly equal-sized cells. The apical daughter cell then undergoes abnormal divisions, resulting in an octant embryo with about twice the normal number of cells while the uppermost derivative of the basal cell fails to become the hypophysis, which normally contributes to root development. Consistent with this early effect, gnom appears to be epistatic to monopteros in doubly mutant embryos, suggesting that, without prior gnom activity, the monopteros gene cannot promote root and hypocotyl development. On the other hand, when root formation was induced in bisected seedlings, wild-type responded whereas gnom mutants failed to produce a root but formed callus instead. These results suggest that gnom activity promotes asymmetric cell division which we believe is necessary both for apical-basal pattern formation in the early embryo and for root formation in tissue culture.
The Drosophila gene pointed encodes two ETS-like proteins which are involved in the development of the midline glial cells
Authors: Klämbt Christian 
Published: April 2021

ABSTRACT
Glial-neuronal cell interactions at the ventral midline are necessary for the proper elaboration of commissures in the embryonic CNS of Drosophila. In particular, migrating midline glial cells are required for the separation of segmental commissures. During this process the glial cells recognize specific neuronal cells at the midline, they migrate posteriorly along their cell processes and thereby separate the segmental commissures. The gene pointed (pnt) is required for this glialneuronal cell interaction, as loss of function mutations lead to a change in the migration behavior of the midline glial cells. As a consequence, anterior and posterior commissures do not become separated and appear fused. Molecular analysis of pointed has revealed two differently spliced types of transcripts, which are encoded in a region extending over 55 kb of genomic sequence. In the CNS both transcript classes are expressed in cells of the midline, including the midline glial cells. Sequence analysis of cDNA clones corresponding to both transcript types reveals two different pointed proteins which share an ETS domain common to a number of transcription factors related to the vertebrate ets oncogene. Furthermore, one pointed protein form contains an additional domain of homology of approx. 80 amino acids in length, which is shared by only a subset of the ETS protein family.
Type VI collagen expression is upregulated in the early events of chondrocyte differentiation
Authors: Quarto Rodolfo , Dozin Beatrice , Bonaldo Paolo , Cancedda Ranieri , Colombatti Alfonso 
Published: April 2021

ABSTRACT
Dedifferentiated chondrocytes cultured adherent to the substratum proliferate and synthesize large amounts of type I collagen but when transferred to suspension culture they decrease proliferation, resume the chondrogenic phenotype and the synthesis of type II collagen, and continue their maturation to hypertrophic chondrocyte (Castagnola et al., 1986, J.Cell Biol. 102, 2310-2317). In this report, we describe the developmentally regulated expression of type VI collagen in vitro in differentiating avian chondrocytes. Type VI collagen mRNA is barely detectable in dedifferentiated chondrocytes as long as the attachment to the substratum is maintained, but increases very rapidly upon passage of the cells into suspension culture reaching a peak after 48 hours and declining after 5-6 days of suspension culture. The first evidence of a rise in the mRNA steadystate levels is obtained already at 6 hours for the 3(VI) chain. Immunoprecipitation of metabolically labeled cells with type VI collagen antibodies reveals that the early mRNA rise is paralleled by an increased secretion of type VI collagen in cell media. Induction of type VI collagen is not the consequence of trypsin treatment of dedifferentiated cells since exposure to the actin-dis-rupting drug cytochalasin or detachment of the cells by mechanical procedures has similar effects. In 13-day-old chicken embryo tibiae, where the full spectrum of the chondrogenic differentiation process is represented, expression of type VI collagen is restricted to the articular cartilage where chondrocytes developmental stage is comparable to stage I (high levels of type II collagen expression). The steep rise in type VI collagen synthesis suggests that the transition of chondrocytes from a stage characterized by high levels of type I collagen to a later stage with a predominance of type II collagen (stage I chondrocytes) might be subdivided further in an early phase (stage Ia) characterized by a high and transient type VI collagen expression and a later phase (stage Ib) where type II collagen is predominant. These data might suggest a functional relationship between type VI collagen expression and the chondrogenic maturation process.
A Y-chromosomal effect on blastocyst cell number in mice
Authors: Burgoyne Paul S. 
Published: April 2021

ABSTRACT
Karyotypic and cell number analysis of 3.5 day post coitum preimplantation mouse embryos was used to determine whether XY embryos had more cells than XX embryos at the late morula/early blastocyst stage. This proved to be the case for the CD1 strain (for which it had previously been shown that XY embryos form a blastocoel earlier than XX embryos) and for the MF1 strain. However, this increased cell number was not seen in MF1 embryos carrying an RIII strain Y in place of the MF1 Y. Furthermore, interstrain crosses between CD1 and the MF1,YRIII strain showed that the cell number increase segregated with the CD1 Y but not with the RIII Y. It is concluded that the CD1 and MF1 Y chromosomes carry a factor that accelerates the rate of preimplantation development.
The triple origin of skull in higher vertebrates: a study in quail-chick chimeras
Authors: Couly Gérard F. , Coltey Pierre M. , Douarin Nicole M. Le 
Published: April 2021

ABSTRACT
We have used the quail-chick chimera technique to study the origin of the bones of the skull in the avian embryo. Although the contribution of the neural crest to the facial and visceral skeleton had been established previously, the origin of the vault of the skull (i.e. frontal and parietal bones) remained uncertain. Moreover formation of the occipito-otic region from either the somitic or the cephalic paraxial mesoderm had not been experimentally investigated. The data obtained in the present and previous works now allow us to assign a precise embryonic origin from either the mesectoderm, the paraxial cephalic mesoderm or the five first somites, to all the bones forming the avian skull. We distinguish a skull located in front of the extreme tip of the notochord which reaches the sella turcica and a skull located caudally to this boundary. The former (‘prechordal skull’) is derived entirely from the neural crest, the latter from the mesoderm (cephalic or somitic) in its ventromedial part (‘chordal skull’) and from the crest for the parietal bone and for part of the otic region. An important point enlighten in this work concerns the double origin of the corpus of the sphenoid in which basipresphenoid is of neural crest origin and the basipostsphenoid is formed by the cephalic mesoderm. Formation of the occipito-otic region of the skeleton is particularly complex and involves the cooperation of the five first somites and the paraxial mesoderm at the hindbrain level. The morphogenetic movements leading to the initial puzzle assembly could be visualized in a reproducible way by means of small grafts of quail mesodermal areas into chick embryos.
The data reported here are discussed in the evolutionary context of the ‘New Head’ hypothesis of Gans and Northcutt (1983, Science, 220, 268-274).