bluuebunny/crossref_metadata_2025_split huggingface dataset:
Apoptotic cell death and tissue remodelling during mouse mammary gland involution
Authors: Strange Robert , Li Feng , Saurer Susanne , Burkhardt Arne , Friis Robert R. 
Published: April 2021

Abstract
During post-lactational mammary gland involution, the bulk of mammary epithelium dies and is reabsorbed. This massive cell death and tissue restructuring was found to be accompanied by a specific pattern of gene expression. Northern blot analysis showed that weaning resulted in a dramatic drop in ODC, a gene involved in synthesis of a component of milk, and the nearly simultaneous induction of SGP-2, a gene associated with apoptotic cell death. These changes were followed by decreases in expression of milk protein genes to basal levels and expression of genes associated with regulation of cell proliferation and differentiation, p53, c-myc and TGF-β1. Subsequently, additional genes implicated in stress response, tissue remodelling, and apoptotic cell death were transiently expressed, expression peaking at about 6 days post-weaning. A non-random degradation of DNA yielding the oligonucleosomal length fragmen-tation pattern typical of apoptotic cell death (Wyllie, 1980; Wyllie et al., 1980) was detected in association with morphological changes and gene expression. The correlations between: (a) changes in morphology, (b) pattern of gene expression and (c) changes in DNA integrity suggest that complementary programs for cell death and tissue remodelling direct post-lactational mammary gland involution.
Establishment and maintenance of stable spatial patterns in lacZ fusion transformants of Polysphondylium pallidum
Authors: Vocke Cathy D. , Cox Edward C. 
Published: April 2021

Abstract
Polysphondylium pallidum cells were transformed with a construct containing the Dictyostelium discoideum ecmA promoter fused to a lacZ reporter gene. Two stably transformed lines, one in which β-galactosidase (β-gal) is expressed in apical cells of the fruiting body (p63/2.1), and one in which it is expressed in basal cells (p63/D), have enabled us to infer how cells move during aggregation and culmination. Several types of cell movement proposed to occur during slime mold culmination, such as random cell mixing and global cell circulation, can be ruled out on the basis of our observations.
Cells of the two transformant lines express β-gal very early in development. In both cases, stained cells are randomly scattered in a starving population. By mid to late aggregation, characteristic spatial patterns emerge. Marked cells of p63/2.1 are found predominantly at tips of tight aggregates; those of p63/D accumulate at the periphery. These patterns are conserved throughout culmination, showing that marked cells maintain their relative positions within the multicellular mass following aggregation.
Neither the apical nor the basal pattern appears to be regulated within the primary sorogen by de novo gene expression or by cell sorting as whorls are formed. However, marked cells within a whorl re-establish the original pattern in secondary sorogens. This must be achieved by cell migration, since β-gal is not reexpressed.
Localized expression of a Xenopus POU gene depends on cell-autonomous transcriptional activation and induction-dependent inactivation
Authors: Frank Dale , Harland Richard M. 
Published: April 2021

Abstract
We have cloned a cDNA encoding a Xenopus POU domain protein, XLP0U91, which is expressed at high levels in gastrula embryos. XLP0U91 transcription initiates at the midblastula transition, and declines to low levels by late neurula stages. In early neurula embryos, XLP0U91 transcripts are enriched 35-fold in the most ventroposterior versus anterior regions. Initial transcriptional activation of the gene is cell autonomous; the gene is activated in dissociated gastrula stage embryos as well as in animal cap explants. Cell-cell communication is needed for proper temporal downregulation of XLP0U91 expression in late neurula embryos; cell dissociation during blastula stages or removal of explants from the embryo prevents normal transcriptional shut down. Explants treated with peptide growth factors (PGFs) mimic the normal temporal and spatial shut down in whole embryos. This negative regulatory pathway may be important for determining cell fate or maintaining an inducible state in the ventroposterior region of the embryo.
Analysis of Xwnt-4 in embryos of Xenopus laevis: A Wnt family member expressed in the brain and floor plate
Authors: Mcgrew L. Lynn , Otte Arie P. , Moon Randall T. 
Published: April 2021

Abstract
This study characterizes the temporal and spatial expression during early Xenopus development of Xwnt-4, a member of the Wnt gene family. The Xwnt-4 protein contains all of the sequence motifs that are hallmarks of the Wnt gene family and is 84% identical to the mouse homolog, Wnt-4. The highest level of Xwnt-4 expression occurs during the early neurula stage of development although its expression persists throughout embryogenesis and can be found in the adult testis, brain and epithelium. Consistent with its localization to head and dorsal regions of microdissected embryos, the expression of Xwnt-4 is enhanced in anterodorsalized embryos resulting from treatment with LiCl, and the expression of XWNT-4 is suppressed in UV-ventralized embryos that lack anterior neural tissue. These results suggested that expression of XWNT-4 is dependent on the induction of neural tissue. This idea was tested using induction experiments with dorsal or ventral ectoderm from a stage 10 embryo, recombined with dorsal marginal zone mesoderm from the same embryo. Recombinant tissue and ectoderm alone were cultured until stage 14, when Xwnt-4 expression was assayed using Northern analysis. In the recombinant assay, Xwnt-4 expression does not occur in the uninduced ectoderm but is expressed in both the dorsal and ventral recombinants. Xwnt-4 expression in neural ectoderm was confirmed in isolated, induced neural ectoderm, dissected away from the dorsal mesoderm, in a stage 12.5 embryo. Whole-mount in situ hybridization confirmed the dissection studies and demonstrated that Xwnt-4 transcripts are expressed in the dorsal midline of the midbrain, hindbrain and the floor plate of the neural tube. Collectively, the data indicate that Xwnt-4 is a unique member of the Wnt family whose expression is dependent on neural induction. The specific pattern of expression following neural induction suggests that Xwnt-4 plays a role in the early patterning events responsible in the formation of the nervous system in Xenopus.
Role of the chicken homeobox-containing genes GHox-4.6 and GHox-8 in the specification of positional identities during the development of normal and polydactylous chick limb buds
Authors: Coelho Caroline N. D. , Upholt William B. , Kosher Robert A. 
Published: April 2021

Abstract
During early stages of normal chick limb development, the homeobox-containing (HOX) gene GHox-4.6 is expressed throughout the posterior mesoderm of the wing bud from which most of the skeletal elements including the digits will develop, whereas GHox-8 is expressed in the anterior limb bud mesoderm which will not give rise to skeletal elements. In the present study, we have examined the expression of GHox-4.6 and GHox-8 in the wing buds of two polydactylous mutant chick embryos, diplopodia-5 and talpid2, from which supernumerary digits develop from anterior limb mesoderm, and have also examined the expression of these genes in response to polarizing zone grafts and retinoic acid-coated bead implants which induce the formation of supernumerary digits from anterior limb mesoderm. We have found that the formation of supernumerary digits from the anterior mesoderm in mutant and experimentally induced polydactylous limb buds is preceded by the ectopic expression of GHox-4.6 in the anterior mesoderm and the coincident suppression of GHox-8 expression in the anterior mesoderm. These observations suggest that the anterior mesoderm of the polydactylous limb buds is “posteriorized” and support the suggestion that GHox-8 and GHox-4.6, respectively, are involved in specifying the anterior non-skeletal and posterior digit-forming regions of the limb bud. Although the anterior mesodermal domain of GHox-8 expression is severely impaired in the mutant and experimentally induced polydactylous limb buds, this gene is expressed by the prolonged, thickened apical ectodermal ridges of the polydactylous limb buds that extend along the distal anterior as well as the distal posterior mesoderm. These findings indicate that the anterior mesodermal and apical ectodermal ridge domains of GHox-8 expression are independently regulated, and provide further support for the concept that GHox-8 expression is involved in apical ectodermal ridge function.
A maternal factor, OZ-1, activates embryonic transcription of the Xenopus laevis GS17 gene
Authors: Ovsenek Nick , Zorn Aaron M. , Krieg Paul A. 
Published: April 2021

Abstract
We describe the identification of an enhancer sequence and a sequence-specific DNA-binding protein required for developmental expression of the Xenopus laevis GS17 gene. Using microinjection of recombinant plasmids into fertilized frog eggs, we have shown that a 14 base pair CT-rich sequence element, normally located about 700 bases upstream of the GS17 promoter, is sufficient to activate transcription of a heterologous reporter gene in gastrula stage embryos. This regulatory element has been called the OZ sequence. Sequences closely related to OZ are located in the promoter regions of several other genes expressed during Xenopus development. Extracts prepared from Xenopus embryos show the presence of a DNA-binding factor, OZ-1, that specifically recognizes the OZ sequence. Mutations within the OZ element that abolish OZ-1 binding also abolish enhancer activity. The OZ-1 factor contains at least two proteins of approximate Mr 76 X 103 and 100 x 103. The sequence-specific binding activity accumulates during oogenesis and remains present at approximately constant levels throughout early development.
Activin can generate ectopic axial structures in chick blastoderm explants
Authors: Ziv T. , Shimoni Y. , Mitrani E. 
Published: April 2021

ABSTRACT
We have recently shown that activin can induce the formation of axial structures from chick blastulae and that activin beta-B is transcribed, in the hypoblast of the chick, at the same stage that axial mesoderm is being induced. It was not clear, however, whether activin was merely allowing the central epiblastic cells to express a differentiated phenotype for which they were already prepared. This report shows that activin-containing medium (ACM) can act as an instructive inductor, which can change the fate of competent cells and bring about the formation of an ectopic embryonic axis. Further more, we show data that suggest that during normal development only one axis is obtained as a result of a carefully controlled inhibitory process.
Spatial and temporal expression of the I factor during oogenesis in Drosophila melanogaster
Authors: Lachaume Philippe , Bouhidel Karim , Mesure Michelle , Pinon Hubert 
Published: April 2021

ABSTRACT
The I factor is a functional non-viral retrotransposon, or LINE, from Drosophila melanogaster. Its mobility is associated with the I-R hybrid dysgenesis. In order to study the expression pattern of this LINE in vivo, a translational fusion between the first ORF of the I factor and the lacZ gene of Escherichia coli has been carried out and introduced in the genome of reactive (R) flies. Homozygous transgenic Drosophila lines have been established and analysed. ORF1 expression is limited to germ-line cells (nurse cells and oocyte) between stage 2 and 10 of oogenesis. No somatic expression is found. Position effects may limit the level of expression of a given transgene but do not modify its basic pattern of expression during the development of the fly. This reproducible control demonstrates both that I factor is driven by its own promoter, probably the internal one suggested by Mizrokhi et al. (Mizrokhi, L. J., Georgevia, S. G. and Ilying, Y. V. (1988). Cell 54, 685-691), and that tissuespecific regulatory sequences are present in the 5 untranslated part of the I factor. The nuclear localization of the fusion protein reveals the presence of nuclear localization signals (NLS) in the ORF1-encoded protein correlating with the possible structural and/or regulatory role of this protein. This expression is restricted to dysgenic and reactive females, and is similar in the two conditions. All the results obtained in this work suggest that I factor transposition occurs as a meiotic event, between stage 2 and 10 of the oogenesis and is regulated at the transcriptional level. It also appears that our transgene is an efficient marker to follow I factor expression.
Developmental regulation of chromatin composition during mouse embryogenesis: somatic histone H1 is first detectable at the 4-cell stage
Authors: Clarke Hugh J. , Oblin Colette , Bustin Michael 
Published: April 2021

ABSTRACT
We have examined the distribution of histone H1 in oocytes and preimplantation embryos of the mouse, using a polyclonal antibody raised against the histone H1 sub-types present in somatic cells. Immunofluorescence and immunoblotting analyses failed to detect somatic histone H1 in germinal vesicle (GV)-stage oocytes. In contrast, somatic histone H1 was detectable by immunofluorescence in the nuclei of GV oocytes previously injected with histone H1 as well as the nuclei of ovarian granulosa cells, and by immunoblotting in 8-cell embryos. 1- and 2-cell embryos examined by immuofluorescence did not contain detectable somatic histone H1. At the early 4-cell stage (54–56 hours post-hCG), 5 of 52 embryos contained somatic histone H1 in one or more nuclei. By the late 4-cell stage (66–68 hours post-hCG), however, 58 of 62 embryos contained somatic histone H1. In 8-cell embryos, morulae and blastocysts, all nuclei contained somatic histone H1 in every case. When embryos were exposed to the transcriptional inhibitor, -amanitin, beginning at the late 2-cell stage, they cleaved to the 4-cell stage but fewer than 10% developed histone H1 immunoreactivity. When treatment began at the early 4-cell stage, the embryos that remained at the 4-cell stage in the presence of the drug developed histone H1 immunoreactivity in half of the cases. Embryos that reached the 5-to 8-cell stage in the presence of the drug developed histone H1 immunoreactivity in every case. The protein synthesis inhibitor, puromycin, prevented development of histone H1 immunoreactivity in most embryos when added either at the late 2-cell or early 4-cell stage. When embryos were exposed to the DNA replication inhibitor, aphidicolin, beginning at the late 2-cell stage, they cleaved to the 4-cell stage, but developed only a very weak histone H1 immunoreactivity. These results indicate that oocytes and 1- and 2-cell embryos contain little or no somatic histone H1, which may imply that these cells contain immunologically distinct histone H1 subtypes. The somatic subtypes first appear at the 4-cell stage, through a process requiring embryonic transcription and DNA replication during the third cell cycle. These results suggest that the deposition of somatic histone H1 on chromatin is developmentally regulated during mouse embryogenesis.
BHK-21-derived cell lines that produce basic fibroblast growth factor, but not parental BHK-21 cells, initiate neuronal differentiation of neural crest progenitors
Authors: Brill Gilat , Vaisman Nora , Neufeld Gera , Kalcheim Chaya 
Published: April 2021

ABSTRACT
We present evidence that basic fibroblast growth factor (bFGF)-producing cells stimulate primary differentiation of neurons from neural crest progenitors. Baby hamster kidney (BHK-21) cells were stably cotrans-fected with plasmid pSV2/neo, which contains the gene conferring resistance to the neomycin analog G418 and expression vectors containing the human bFGF cDNA. Various clones, which differed in their bFGF production levels, were isolated. Homogeneous neural crest cells were cultured on monolayers of bFGF-producing, BHK-21-derived cell lines. While the parental BHK-21 cells, which do not produce detectable bFGF, had poor neurogenic ability, the various bFGF-producing clones promoted a 1.5-to 4-fold increase in neuronal cell number compared to the parental cells. This increase was correlated with the levels of bFGF produced by the different transfected clones, which ranged between 2.3 and 140 ng/mg protein. In contrast, no stimulation of neuronal differentiation was observed when neural crest cells were grown on monolayers of parental BHK cells transfected with plasmid pSV2/neo alone, or on a parental BHK-derived clone, which secretes high amounts of recombinant vascular endothelial growth factor (VEGF). Furthermore, the neuron-promoting ability of bFGF-producing cells could be mimicked by addition of exogenous bFGF to neural crest cells grown on the parental BHK line. A similar treatment of neural crest cells grown on laminin substrata, instead of BHK cells, resulted in increased survival of non-neuronal cells, but not of neurons (see also Kalcheim, C. 1989, Dev. Biol. 134, 1-10). Taken together, these results suggest that bFGF stimulates neuronal differentiation of neural crest cells by a cell-mediated signalling mechanism.
Spatial and developmental changes in the respiratory activity of mitochondria in early Drosophila embryos
Authors: Akiyama Takahiro , Okada Masukichi 
Published: April 2021

ABSTRACT
Mitochondria of early Drosophila embryos were observed with a transmission electron microscope and a fluorescent microscope after vital staining with rhodamine 123, which accumulates only in active mitochondria. Rhodamine 123 accumulated particularly in the posterior pole region in early cleavage embryos, whereas the spatial distribution of mitochondria in an embryo was uniform throughout cleavage stages. In late cleavage stages, the dye showed very weak and uniform accumulation in all regions of periplasm. Polar plasm, sequestered in pole cells, restored the ability to accumulate the dye. Therefore, it is concluded that the respiratory activity of mitochondria is higher in the polar plasm than in the other regions of periplasm in early embryos, and this changes during development. The temporal changes in rhodamine 123-staining of polar plasm were not affected by u.v. irradiation at the posterior of early cleavage embryos at a sufficient dosage to prevent pole cell formation. This suggests that the inhibition of pole cell formation by u.v. irradiation is not due to the inactivation of the respiratory activities of mitochondria. In addition, we found that the anterior of Bicaudal-D mutant embryos at cleavage stage was stained with rhodamine 123 with the same intensity as the posterior of wild-type embryos. No pole cells form in the anterior of Bic-D embryos, where no restoration of mitochondrial activity occurs in the blastoderm stage. The posterior group mutations that we tested (staufen, oskar, tudor, nanos) and the terminal mutation (torso) did not alter staining pattern of the posterior with rhodamine 123.
Development of the D. melanogaster caudal segments involves suppression of the ventral regions of A8, A9 and A10
Authors: Kuhn D. T. , Sawyer M. , Packert G. , Turenchalk G. , Mack J. A. , Sprey TH. E. , Gustavson E. , Kornberg T. B. 
Published: April 2021

ABSTRACT
Whereas the segmental organization of the thorax and anterior abdomen is morphologically delineated in both the Drosophila larva and adult, segments in the head and caudal regions lack such well-defined boundaries. Consequently, the organization of these regions has been difficult to decipher. In this study, transformations caused by the bithorax-complex homeotic mutants 48, M3, Ultraabdominal-1 (Uab1) and tumorous-head-3 (tuh3), as well as the patterns of engrailed gene expression have been analyzed to investigate the segmental organization of the caudal segments. A special emphasis was placed on sense organs appearing in abdominal segments 8, 9 and 10 (A8–A10): We find that: (1) transformations in the caudal segments obey parasegmental borders; (2) the sense organs on A8, A9, and A10 are probably homologous to the pits and hairs in anterior A1–A7; (3) except for the larval anal tuft and the anterior side of A8, all structures in larval segments A8, A9 and A10 are dorsal/lateral in origin; and (4) dorsalization of embryonic A8 and A9 cells leaves space ventrally for A10, as it follows the contracting ventral nervous system during the embryological process of germ band contraction.
Expression and potential functions of G-protein α subunits in embryos of Xenopus laevis
Authors: Otte Arie P. , Mcgrew L. Lynn , Olate Juan , Nathanson Neil M. , Moon Randall T. 
Published: April 2021

ABSTRACT
During early embryonic development, many inductive interactions between tissues depend on signal transduction processes. We began to test the possibility that G-proteins participate in the signal transduction pathways that mediate neural induction. The expression during Xenopus development of three Gα subunits, Gαo, Gαi-1 and Gαs-1, was characterized. The three maternally expressed genes showed different expression patterns during early development. Whole-mount in situ hybridization revealed that all three genes were expressed almost exclusively in the gastrula ectoderm and predominantly in the neuroectoderm in the neurula embryo. In order to investigate the involvement of these proteins in neural induction, we overexpressed the G-protein a subunits by injecting the Gα mRNAs into fertilized eggs. Overexpression of Gαs-1 increased the ability of gastrula ectoderm to become induced to neural tissue approximately four-fold. Overexpression of Gαo and Gαi-1had less pronounced effects on neural competence, and inhibition of the Gαo and Gαi-1 proteins by pertussis toxin did not change the neural competence of the exposed gastrula ectoderm. Overexpression of the Gαo and Gαi-1genes did, however, inhibit the normal disappearance of the blastocoel during gastrulation, suggesting a role for these G-proteins in regulating this process. The data also suggest a specific role for the Gas subunit in mediating the initial phases of neural induction.