bluuebunny/crossref_metadata_2025_split huggingface dataset:
Macrophages in haemopoietic and other tissues of the developing mouse detected by the monoclonal antibody F4/80
Authors: Morris Lynn , Graham Christopher F. , Gordon Siamon 
Published: April 2021

ABSTRACT
Macrophages are widely distributed in lymphohaemo-poietic and other tissues of the normal and diseased adult, where they play an important role in host defence and repair. Although the development of haemopoiesis has been well studied in several species, the ontogeny of the mononuclear phagocyte system remains poorly understood. We have used a highly specific mAh, F4/80, to examine the distribution of mature macrophages in the developing mouse, with special reference to their presence in the haemopoietic microenvironment. Monocytes and macrophages were first seen in embryos on day 10 in the yolk sac and liver as well as in mesenchyme. In liver, spleen and bone marrow, there was expansion of this population associated with the initiation of haemopoietic on days 11,15 and 17, respectively. Macrophages in these sites formed part of the haemopoietic stroma and their extensively spread plasma membrane processes could be seen making intimate contacts with clusters of differentiating haemopoietic cells. F4/80+ cells were widely dispersed in undifferentiated mesenchymal tissue in organs such as lung, kidney and gut.
Numbers of F4/80-labefled cells increased concomitantly with organ growth and local mitoses were evident, as well as actively phagocytic macrophages. Our studies establish that macrophages are among the earliest haemopoietic cells to be produced during development and that they are relatively abundant in fetal tissues in the absence of overt inflammatory stimuli. Their distribution is correlated with the sequential migration of haemopoiesis and they constitute a prominent component of the stroma in fetal liver, spleen red pulp and bone marrow. Apart from a role in haemopoietic cellular interactions, their highly developed endocytic and biosynthetic activities suggest that macrophages contribute major undefined functions during growth, turnover and modelling of fetal tissues.
Abbreviations: Ab, antibody; ag, antigen; mAb, monoclonal antibody; MΦ, macrophage.
Potential role of RGD-binding integrins in mammalian lung branching morphogenesis
Authors: Roman Jesse , Little Candice W. , McDonald J. A. 
Published: April 2021

ABSTRACT
Cell–matrix interactions are generally considered critical for normal lung development. This is particularly likely to be true during the glandular stage, when the primitive airways are formed through a process termed branching morphogenesis. Integrins, transmembrane receptors that bind to extracellular matrices, are likely to mediate important interactions between embryonic cells and their matrices during branching morphogenesis. In this report, we examine the role of integrin receptors in this process. Immunohistochemical studies revealed that the integrins VLA 3, VLA 5 and integrin receptors to vitronectin are expressed in the epithelium and/or mesenchyme during the glandular stage of murine lung development. To correlate expression with function, an in vitro model of murine lung branching morphogenesis was utilized to examine branching in the presence of inhibitors of ligand binding to integrin receptors. One such reagent, a hexapeptide containing the RGD (Arg-Gly-Asp) sequence, diminished branching and resulted in an abnormal morphology, whereas a control peptide RGESP (Arg-Gly-Glu-Ser-Pro) had no effect. These findings suggest a critical role for cell–matrix interactions mediated via integrin receptors in early stages of mammalian lung development.
Fate mapping and cell lineage analysis of Hensen’s node in the chick embryo
Authors: Selleck Mark A. J. , Stern Claudio D. 
Published: April 2021

ABSTRACT
Fate maps of chick Hensen’s node were generated using Dil and the lineage of individual cells studied by intracellular injection of lysine-rhodamine-dextran (LRD). The cell types contained within the node are organized both spatially and temporally. At the definitive primitive streak stage (Hamburger and Hamilton stage 4), Hensen’s node contains presumptive notochord cells mainly in its anterior midline and presumptive somite cells in more lateral regions. Early in development it also contains presumptive endoderm cells. At all stages studied (stages 3–9), some individual cells contribute progeny to more than one of these tissues.
The somitic precursors in Hensen’s node only contribute to the medial halves of the somites. The lateral halves of the somites are derived from a separate region in the primitive streak, caudal to Hensen’s node.
Autonomy and nonautonomy of sex determination in triploid intersex mosaics of C. elegans
Authors: Schedin Pepper , Hunter Craig P. , Wood William B. 
Published: April 2021

ABSTRACT
The primary sex-determining signal in Caenorhabditis elegans is the ratio of X chromosomes to sets of autosomes (X/A ratio), normally 1.0 in hermaphrodites (XX) and 0.5 in males (XO). XX triploids (X/A=0.67) are males, but if these animals carry a partial duplication of the X chromosome such that X/A ≅ 0.7, they develop as intersexes that are sexually mosaic. We have analyzed these mosaics using Nomarski microscopy and in situ hybridization to obtain information on whether sex determination decisions can be made independently in different cells and tissues, and when these commitments are made. The observed patterns of male and female cells in individual animals indicate that sex determination decisions can be influenced by anterior-posterior position and that sex determination decisions can be made as late as the third larval stage of postembryonic development. Although these decisions clearly can be made independently in different lineages, they show substantial biases toward one sex or the other in individual animals. We interpret these results to suggest that sex determination in C. elegans is not entirely cell autonomous.
Autonomous differentiation of dorsal axial structures from an animal cap cleavage stage blastomere in Xenopus
Authors: Gallagher Betty C. , Hainski Alexandra M. , Moody Sally A. 
Published: April 2021

ABSTRACT
Dorsal or ventral blastomeres of the 16- and 32-cell stage animal hemisphere were labeled with a lineage dye and transplanted into the position of a ventral, vegetal midline blastomere. The donor blastomeres normally give rise to substantial amounts of head structures and central nervous system, whereas the blastomere which they replaced normally gives rise to trunk mesoderm and endoderm. The clones derived from the transplanted ventral blastomeres were found in tissues appropriate for their new position, whereas those derived from the transplanted dorsal blastomeres were found in tissues appropriate for their original position. The transplanted dorsal clones usually migrated into the host’s primary axis (D1.1, 92 %; DI.1.1, 69 %; DI.1.2, 100 %), and in many cases they also induced and populated a secondary axis (D1.1, 43%; DI.1.1, 67%; DI.1.2, 63%). Bilateral deletion of the dorsal blastomeres resulted in partial deficits of dorsal axial structures in the majority of cases, whereas deletions of ventral midline blastomeres did not. When the dorsal blastomeres were cultured as explants they elongated. Notochord and cement glands frequently differentiated in these explants. These studies show that the progeny of the dorsal, midline, animal blastomeres: (1) follow their normal lineage program to populate dorsal axial structures after the blastomere is transplanted to the opposite pole of the embryo; (2) induce and contribute to a secondary axis from their transplanted position in many embryos; (3) are important for the normal formation of the entire length of the dorsal axis; and (4) autonomously differentiate in the absence of exogenous growth factor signals. These data indicate that by the 16cell stage, these blastomeres have received instructions regarding their fate, and they are intrinsically capable of carrying out some of their developmental program.
Curvature of the caudal region is responsible for failure of neural tube closure in the curly tail (ct) mouse embryo
Authors: Brook Frances A. , Shum Alisa S. W. , Straaten Henny W. M. Van , Copp Andrew J. 
Published: April 2021

ABSTRACTDelayed closure of the posterior neuropore (PNP) occurs to a variable extent in homozygous mutant curly tail (ct) mouse embryos, and results in the development of spinal neural tube defects (NTD) in 60 % of embryos. Previous studies have suggested that curvature of the body axis may delay neural tube closure in the cranial region of the mouse embryo. In order to investigate the relationship between curvature and delayed PNP closure, we measured the extent of ventral curvature of the neuropore region in ct/ct embryos with normal or delayed PNP closure. The results show significantly greater curvature in ct/ct embryos with delayed PNP closure in vivo than in their normal littermates. Reopening of the posterior neuropore in non-mutant mouse embryos, to delay neuropore closure experimentally, did not increase ventral curvature, suggesting that increased curvature in ct/ct embryos is not likely to be a secondary effect of delayed PNP closure. Experimental prevention of ventral curvature in ct/ct embryos, brought about by implantation of an eyelash tip longitudinally into the hindgut lumen, ameliorated the delay in PNP closure. We propose, therefore, that increased ventral curvature of the neuropore region of ct/ct embryos imposes a mechanical stress, which opposes neurulation and thus delays closure of the PNP. Increased ventral curvature may arise as a result of a cell proliferation imbalance, which we demonstrated previously in affected ct/ct embryos.
Regulation and processing of a secreted protein that mediates sensing of cell density in Dictyostelium
Authors: Yuen Ita S. , Taphouse Carl , Halfant Kerri A. , Gomer Richard H. 
Published: April 2021

ABSTRACT
During Dictyostelium development, the expression of some genes is dependent on cell density. This effect is mediated by soluble factors referred to as conditioned medium factors (CMFs) which the developing cells secrete at very low rates and simultaneously sense. There are at least two classes of CMFs: one is an 80 × 103Mr glycoprotein and the other is a heterogeneous group of molecules, with relative molecular masses between 6.5X103 and 0.65 X103. Interestingly, the two classes of molecules do not need to be combined for activity. We find that the 80x103Afr CMF but not the small CMF is sequestered in vegetative cells. The 80x103Air CMF is then secreted by cells during early development, while the small CMF appears only during late development. Like the 80x103Afr CMF, the small CMFs are trypsin-sensitive and contain N- and O-linked glycosylation. The breakdown products of a fraction containing SOxlO3 CMF cochromatographed from a Sephadex G-50 column and a reverse-phase HPLC column with small CMFs. The specific activity of CMF increases roughly 100-fold upon breakdown. The results suggest that, during differentiation, the slowly diffusing 80 × 103 Afr CMF is first produced from a precursor pool already present in vegetative cells, allowing differentiation of only those cells in the immediate vicinity of the aggregation center. The breakdown of SOxlfpAf,. CMF to a faster-diffusing, higher specific activity form then might enable cells farther from the aggregation center to differentiate.
Transient expression of XMyoD in non-somitic mesoderm of Xenopus gastrulae
Authors: Frank Dale , Harland Richard M. 
Published: April 2021

ABSTRACT
XMyoD is the earliest marker of muscle development in Xenopus embryos and is expressed in presumptive somites in the late gastrula. In the early gastrula, in situ hybridization showed XMyoD transcripts in precursors of both muscle and non-muscle mesoderm. Embryos ventralized by UV irradiation made no muscle, but expressed XMyoD transiently. Embryo explants that differentiated ventral mesoderm also expressed XMyoD transiently. These results show that the initiation of XMyoD expression is not sufficient to convert cells to muscle and suggest that XMyoD is expressed in response to a general mesodermalizing signal; expression is stabilized and enhanced only in muscle precursors that have received a dorsalizing signal.
The effects of retinoic acid on heart formation in the early chick embryo
Authors: Osmond Mark K. , Butler Andrew J. , Voon Francis C. T. , Bellairs Ruth 
Published: April 2021

ABSTRACT
The vitamin A derivative retinoic acid has previously been shown to have teratogenic effects on heart development in mammalian embryos. The craniomedial migration of the precardiac mesoderm during the early stages of heart formation is thought to depend on a gradient of extracellular fibronectin associated with the underlying endoderm. Here, the effects of retinoic acid on migration of the precardiac mesoderm have been investigated in the early chick embryo. When applied to the whole embryo in culture, the retinoid inhibits the craniomedial migration of the precardiac mesoderm resulting in a heart tube that is stunted cranially, while normal or enlarged caudally. Similarly, a local application of retinoic acid to the heart-forming area disrupts the formation of the cardiogenic crescent and the subsequent development of a single mid-line heart tube. This effect is analogous to removing a segment of endoderm and mesoderm across the heart-forming area and results In various degrees of cardia bifida. At higher concentrations of retinoic acid and earlier developmental stages, two completely separate hearts are produced, while at lower concentrations and later stages there are partial bifurcations. The controls, in which the identical operation is carried out except that dimethyl sulphoxide (DMSO) is used instead of the retinoid, are almost all normal. We propose that one of the teratogenic effects of retinoic acid on the heart is to disrupt the interaction between precardiac cells and the extracellular matrix thus inhibiting their directed migration on the endodermal substratum.
Developmental expression of two murine fibroblast growth factor receptors, fig and bek
Authors: Orr-Urtreger Avi , Givol David , Yayon Avner , Yarden Yosef , Lonai Peter 
Published: April 2021

ABSTRACT
Developmental expression of two closely related fibroblast growth factor receptors, bek and fig, is described from early postimplantation until advanced organogenesis. Transcripts of bek and fig were first seen in the primitive ectoderm of egg-cylinder-stage embryos. Later, starting with somitogenesis, and then throughout embryogenesis, they were actively transcribed both in the mesoderm and neuroectoderm. Bek was expressed also in the surface ectoderm and in various epithelia, whereas flg expression was restricted mainly to the mesenchyme. In the limb bud bek transcripts displayed a gradient-like distribution and appeared earlier than flg. The two receptors, in contrast to their almost identical ligand binding specificity, displayed distinct spatial specificities throughout development, suggesting that developmental localization may contribute to functional specificity. The role of bek and flg in gastrulation and in epithelial-mesenchymal interactions of organogenesis will be discussed.
A chondroitin sulfate proteoglycan may influence the direction of retinal ganglion cell outgrowth
Authors: Snow D. M. , Watanabe M. , Letourneau P. C. , Silver J. 
Published: April 2021

ABSTRACT
In the developing retina, retinal ganglion cell (RGC) axons elongate toward the optic fissure, even though no obvious directional restrictions exist. Previous studies indicate that axon-matrix interactions are important for retinal ganglion cell axon elongation, but the factors that direct elongation are unknown. Chondroitin sulfate proteoglycan (CS-PG), a component of the extracellular matrix, repels elongating dorsal root ganglion (DRG) axons in vitro and is present in vivo in the roof plate of the spinal cord, a structure that acts as a barrier to DRG axons during development. In this study, we examined whether CS-PG may regulate the pattern of retinal ganglion cell outgrowth in the developing retina.
Immunocytochemical analysis showed that CS-PG was present in the innermost layers of the developing rat retina. The expression of CS-PG moved peripherally with retinal development, always remaining at the outer edge of the front of the developing axons. CS-PG was no longer detectable with immunocytochemical techniques when RGC axon elongation in the retina is complete.
Results of studies in vitro showed that CS-PG, isolated from bovine nasal cartilage and chick limb, was inhibitory to elongating RGC axons and that RGC growth cones were more sensitive to CS-PG than were DRG neurites tested at the same concentrations of CS-PG. The behavior of retinal growth cones as they encounter CS-PG was characterized using time-lapse video microscopy. Filopodia of the RGC growth cones extended to and sampled the CS-PG repeatedly. With time, the growth cones turned to avoid outgrowth on the CS-PG and grew only on laminin.
While numerous studies have shown the presence of positive factors within the retina that may guide developing RGC axons, this is the first demonstration of an inhibitory or repelling molecule in the retina that may regulate axon elongation. Taken together, these data suggest that the direction of RGC outgrowth in the retina may be regulated by the proper ratio of growthpromoting molecules, such as laminin, to growthinhibiting molecules, like CS-PG, present in the correct pattern and concentrations along the retinal ganglion cell pathway.
Positive and negative control of the Antennapedia promoter P2
Authors: Riley George R. , Jorgensen Erik M. , Baker Robert K. , Garber Richard L. 
Published: April 2021

Abstract
To understand the nature of the regulatory signals impinging on the second promoter of the Antennapedia gene (Antp P2), analysis of its expression in mutants and in inhibitory drug injected embryos has been carried out. The maternally-active gene osk is identified as one of two general repressors of P2 which prevent Antp transcription until division cycle 14. Products of the zygoticaliy-active segmentation genes ftz, hb, Kr, gt and kni then act as activators or repressors of Antp P2 in a combinatorial fashion. The timing of these events, and their positive versus negative nature, is critical for generating the expression patterns normal for Antp.
Genetic analysis of leaf development in cotton
Authors: Dolan Liam , Poethig R. Scott 
Published: April 2021

Abstract
Leaf shape in cotton is regulated by the developmental age of the shoot and by several major genes that affect leaf lobing. The effect of these factors was investigated by allometric analysis, cell lineage analysis, and by studying the expression of the leaf shape mutation, Okra, in genetic mosaics. Allometric analysis of leaf growth suggests that leaf shape is determined during the initiation of the primordium rather than during the expansion phase of leaf growth. Clonal analysis demonstrates that both the rate and duration of cell division are fairly uniform throughout the leaf. Cells in the marginal region of the developing cotton leaf contribute more to the growth of the lamina than they do in tobacco. The Okra mutation acts early in the development of a leaf and appears to accentuate a developmental pattern that is also responsible for heteroblastic variation in leaf shape. The expression of this mutation in genetic mosaics demonstrates that its effect does not diffuse laterally within the leaf primordium.
Expression of the L14 lectin during mouse embryogenesis suggests multiple roles during pre- and post-implantation development
Authors: Poirier Francoise , Timmons Paula M. , Chan C.-T. J. , Guénet Jean-Louis , Rigby Peter W. J. 
Published: April 2021

Abstract
A cDNA encoding L14, the lactose-binding, soluble lectin of relative molecular mass 14 × 103, has been isolated in a differential screen designed to identify genes that are regulated during the differentiation of murine embryonic stem cells in vitro. The expression patterns of the gene and of the encoded protein during mouse embryogenesis are consistent with the lectin playing a role at several stages of development. Firstly, it is initially synthesised in the trophectoderm of expanded blastocysts immediately prior to implantation, suggesting that it may be involved in the attachment of the embryo to the uterine epithelium. Secondly, in the postimplantation embryo, the lectin is abundantly expressed in the myotomes of the somites. This observation, when taken together with data indicating a role for the lectin in myoblast differentiation in culture, suggests that the protein is important in muscle cell differentiation. Finally, within the nervous system expression of this gene is activated early during the differentiation of a particular subset of neurones.
A 102 base pair sequence of the nicotinic acetylcholine receptor delta-subunit gene confers regulation by muscle electrical activity
Authors: Chahine Kenneth G. , Walke Wade , Goldman Daniel 
Published: April 2021

Abstract
Muscle electrical activity suppresses expression of the embryonic-type (α, β, γ and δ) nicotinic acetylcholine receptor (nAChR) genes. The molecular mechanism by which electrical activity regulates these genes is not known. One approach to this problem is to identify regions of the nAChR genes that mediate electrical regulation. Here we report results from such a study of the nAChR δ-subunit gene. We cloned the rat δ-subunit promoter region and created an expression vector in which this DNA controlled the expression of a down-stream luciferase structural gene. The effect that muscle electrical activity had on the expression from this promoter was assayed by introducing this expression vector into electrically stimulated and tetrodotoxin (TTX)-treated rat primary myotubes, and assaying for luciferase activity. These myotubes, when stimulated with extracellular electrodes, suppressed endogenous embryonic-type nAChR gene expression compared to those treated with TTX. Transfection of these cells with δ-promoter-luciferase expression vectors resulted in the δ-promoter conferring electrical regulation on luciferase expression. Additional experiments using deletions from the 5’ end of theδ-promoter region have identified an element between −677 and −550 bp that suppressed δ-promoter activity and a minimal 102 bp sequence that promotes and regulates luciferase expression in response to muscle electrical activity. This latter sequence also contains all the necessary elements to confer tissue and developmental stage-specific expression.