bluuebunny/crossref_metadata_2025_split huggingface dataset:
Epithelial-mesenchymal interactions in the production of basement membrane components in the gut
Authors: Simon-Assmann P. , Bouziges F. , Arnold C. , Haffen K. , Kedinger M. 
Published: April 2021

Abstract
The production and deposition of extracellular matrix proteins and the cellular origin of type-IV collagen have been analysed immunocytochemically in cocultured or transplanted intestinal epithelial-mesenchymal cell associations.
In the first experimental model, rat intestinal endodermal cells were cultured on top of confluent monolayers of rat intestinal or skin fibroblastic cells. Under these conditions, interstitial matrix and basement membrane proteins were deposited within the fibroblastic layer over the whole culture period; interactions between the epithelial cells and the fibroblastic cell population, whatever their organ of origin, were required for the production of the basement membrane. In addition, its formation was progressive as assessed by the shift of a spot-like labelling to a continuous linear pattern at the epithelial–mesenchymal interface, and paralleled epithelial cell differentiation.
In the second experimental model, chick–rat epithelial-mesenchymal recombinants developed as intracoelomic grafts were used, and the immunocytochemical detection of a basement membrane protein, type-IV collagen, was performed with species-specific antibodies. The major role of the mesenchyme in the deposition of type-IV collagen is supported by the fact that anti-chick but not anti-mammalian antibodies stained this antigen in chick mesenchyme-rat endoderm recombinants.
These observations emphasize the role of tissue interactions in the formation of a basement membrane and show that the mesenchymal compartment is the principal endogenous source of type-IV collagen.
Isolation and expression of a new mouse homeobox gene
Authors: Sharpe P.T. , Miller J. R. , Evans E. P. , Burtenshaw M. D. , Gaunt1 S. J. 
Published: April 2021

Abstract
A homeobox-containing clone has been isolated from an adult mouse kidney cDNA library and shown by DNA sequence analysis to be a new isolate, Hox-6·1†. A genomic clone containing Hox-6.1 has been isolated and found to contain another putative homeobox sequence (Hox-6·2), within 7 kb of Hox-6·1. In situ hybridization of mouse metaphase chromosomes shows this Hox-6 locus to be located on chromosome 14 (14E2).
Hox-6.1 has been studied in detail and the predicted protein sequence of the homeobox is 100 % homologous to the Xenopus Xebl (formally AC1) homeobox and the human c8 homeobox (Carrasco et al. 1984; Boncinelli et al. 1985; Simeone et al. 1987). Southern blotting shows that the DNA sequence encoding Hox-6.1 is single copy.
Expression of Hox-6.1 has been studied in adult tissues and embryos by RNase protection assays, Northern blotting analysis and in situ hybridization. RNase protection assays show that Hox-6.1 transcripts are present in embryos between days and of gestation and in extraembryonic tissues at day . Adult expression is detectable in kidney and testis but not in liver, spleen and brain. One major transcript is detectable on Northern blots of kidney and day- embryo RNA. In kidney, this transcript is 2·7 kb whereas in embryos the major transcript is smaller at 1·9 kb, a much fainter band being visible at 2·7 kb. Localized expression of Hox-6.1 is observed in the spinal cord and prevertebral column of day- embryos, and in the posterior mesoderm and ectoderm of day-8) embryos. An anterior boundary of expression is located just behind the hindbrain whereas the boundary in the mesoderm is located at the level of the 7th prevertebra.
Cell-autonomous action of the testis-determining gene: Sertoli cells are exclusively XY in XX ↔XY chimaeric mouse testes
Authors: Burgoyne Paul S. , Buehr Mia , Koopman Peter , Rossant Janet , Mclaren Anne 
Published: April 2021

Abstract
The distribution of XX and XY cells in XX ↔XY chimaeric mouse testes was analysed by enzyme marker analysis of separated testicular tissues and by in situ DNA marker analysis of air-dried testicular cells and testis sections. XX cells contributed to the Leydig cells, the peritubular cells and the vascularized connective tissue of the tunica albuginea. The Sertoli cells, on the other hand, appeared to be exclusively XY. These results indicate that during the development of the testis, Sertoli cell differentiation is triggered by cell-autonomous activity of the Y chromosomal testis-determining gene Tdy. Subsequent steps in testis differentiation may be a consequence of Sertoli cell activity.
A developmental and ultrastructural study of the optic chiasma in Xenopus
Authors: Wilson M. A. , Taylor J. S. H. , Gaze R. M. 
Published: April 2021

Abstract
The structure of the optic chiasma in Xenopus tadpoles has been investigated by light and electron microscopy. Where the optic nerve approaches the chiasma, a tongue of cells protrudes from the periventricular cell mass into the dorsal part of the nerve. Glial processes from this tongue of cells ensheath fascicles of optic axons as they enter the brain. Coincident with this partitioning, the annular arrangement of axons in the optic nerve changes to the laminar organization of the optic tract.
Beyond the site of this rearrangement, all newly growing axons accumulate in the ventral-most part of the nerve and pass into the region between the periventricular cells and pia which we have called the ‘bridge’. This region is characterized by a loose meshwork of glial cell processes, intercellular spaces and the presence of both optic and nonoptic axons. In the bridge, putative growth cones of retinal ganglion cell axons are found in the intercellular spaces in contact with both the glia and with other axons.
The newly growing axons from each eye cross in the bridge at the midline and pass into the superficial layers of the contralateral optic tracts. As the system continues to grow, previous generations of axons, which initially crossed in the then existing bridge, are displaced dorsally and caudally, forming the deeper layers of the chiasma. At their point of crossing in the deeper layers, these fascicles of axons from each eye interweave in an intimate fashion. There is no glial segregation of the older axons as they interweave within the chiasma.
Localization of transcripts from the wingless gene in whole Drosophila embryos
Authors: Baker Nicholas E. 
Published: April 2021

Abstract
In situ hybridization has been used to detect transcription in whole Drosophila embryos. Improved results have been obtained by incubating the hybridized embryos in liquid emulsion prior to autoradiographic exposure. This technique has been used to map the distribution of transcripts from the segment-polarity gene wingless (wg), which is transcribed in a stripe in each segment of the trunk region. By the extended germband stage additional areas of transcription in the head and caudal regions define a total of 21 domains, comprising the foregut, six regions in the head, three thoracic and ten abdominal segments, and the hindgut. At the end of the extended germband stage, the pattern of wg transcription is no longer uniform in the dorsoventral axis: wg transcripts are absent from the lateral epidermis. This pattern of wg transcription is discussed with particular regard to the segmentation of the terminalia. Also it is suggested that the dorsoventral reorganization could be related to the specification of the imaginal disc primordia.
Analysis of germ line development in the chick embryo using an antimouse EC cell antibody
Authors: Urven Lance E. , Erickson Carol A. , Abbott Ursula K. , Mccarrey John R. 
Published: April 2021

Abstract
We have found that EMA-1, a monoclonal antibody originally raised against mouse embryonal carcinoma (Nulli SCC1) cells (Hahnel & Eddy, 1982), also labels chick primordial germ cells (PGCs). We have used this antibody in immunohistological studies to follow the development of PGCs in the chick embryo from the time of their initial appearance beneath the epiblast, through their migratory phase and subsequent colonization of the germinal epithelium. During hypoblast formation, individual EMA-l-labelled cells appeared to separate from the basal surface of the epiblast and enter the blastocoel, coincident with the appearance of morphologically identifiable PGCs in this same area. EMA-1 continued to label germ cells until the initiation of gametogenesis in each sex; specifically, labelling was absent by 7–8 days of incubation in females and started to decrease at 11 days of incubation in males. There was a recurrence of the epitope on oogonia at 15 days of incubation, but not on spermatogonia during the remainder of development through hatching. These observations are consistent with an epiblast origin for the avian germ line, and are strikingly similar to those reported for the early mouse embryo using the same antibody (Hahnel & Eddy,1986).
Reformation of specific neuromuscular connections during axolotl limb regeneration: evidence that the first contacts are correct
Authors: Wilson Steve , Jesani Meena , Holder Nigel 
Published: April 2021

Abstract
Retrograde neuronal tracing with horseradish peroxidase was used to determine the position in the spinal cord of the motor neurone pools of a proximal (biceps) and a distal (extensor digitorum) limb muscle at various times during axolotl limb regeneration. It was found that from the earliest stages of muscle redifferentiation (as judged by light and electron microscopic analysis) the vast majority of axons innervating the regenerating muscles came from cells within the bounds of the normal motor neurone pool for each muscle. A few incorrect projections were noted in that the regenerating proximal muscle was sometimes innervated by some cells caudal to its normal motor neurone pool.
The results are discussed in terms of mechanisms that may be operating in the regenerating limb to ensure that specific neuromuscular connections are made.
Replication, integration and stable germ-line transmission of foreign sequences injected into early zebrafish embryos
Authors: Stuart Gary W. , Mcmurray James V. , Westerfield Monte 
Published: April 2021

Abstract
To generate stable lines of transgenic fish, early zebrafish embryos were injected with high concentrations of a linear bacterial plasmid. After injection, the foreign DNA was converted into a high molecular weight form and then amplified approximately tenfold during the initial rapid cleavages characteristic of the early embryo prior to gastrulation. While most of this DNA was subsequently degraded during gastrulation, some of the foreign sequences survived the gastrula stage and could be found in most of the injected fish at 3 weeks of age. Only about 5 % of fish analysed 4 months after the injection retained foreign DNA in their fins, usually at less than one copy per cell. One of these fish was also found to contain about 100 copies per cell of foreign DNA in a fraction of its germ cells. Approximately 20% of the F, offspring from this germ-line-positive parent inherited the foreign DNA, whereas 50 % of F2 progeny obtained from an identified F1 individual inherited these sequences. The 50 % transmission rate in F2 progeny was as expected for a single, heterozygous genomic insert. These observations indicate that injected DNA can be integrated into the fish genome, that the resulting transgenic fish are mosaic and that some of these mosaic individuals give rise to stable lines of transgenic fish.
The fate map of the cephalic neural primordium at the presomitic to the 3-somite stage in the avian embryo
Authors: Couly Gérard , Douarin Nicole M. Le 
Published: April 2021

ABSTRACT
The fate map of the early neural plate and neural fold has been established at the cephalic level by using the quail–chick marker system (Le Douarin, 1969, 1973). The experimental design comprised the replacement of definite territories belonging to the neural plate and neural folds in the chick embryo by their counterparts from quail embryos at the same developmental stage. This technique is referred to as the isotopic and isochronic exchange of preneural tissues between these two species. The various types of experiments that were carried out are schematized in Fig. 2. The possibility of distinguishing quail from chick cells by the structure of their nuclei allowed the fate of the grafted territories to be recognized at later developmental stages ranging from 3 to 9 days of incubation (E3–E9). Fig. 1 illustrates the morphological changes in the anterior neural plate and neural ridges in the chick embryo at the early somitic stages.
Interactions and fates of avian craniofacial mesenchyme
Authors: Noden Drew M. 
Published: April 2021

ABSTRACT
Craniofacial mesenchyme is composed of three mesodermal populations - prechordal plate, lateral mesoderm and paraxial mesoderm, which includes the segmented occipital somites and the incompletely seg- mented somitomeres - and the neural crest. This paper outlines the fates of each of these, as determined using quail-chick chimaeras, and presents similarities and differences between these cephalic populations and their counterparts in the trunk.
Prechordal and paraxial mesodermal populations are the sources of all voluntary muscles of the head. The latter also provides most of the connective precur- sors of the calvaria, occipital, otic-parietal and basisphenoid tissues. Lateral mesoderm is the source of peripharyngeal connective tissues; the most rostral skeletal tissues it forms are the laryngeal and tracheal cartilages.
When migrating neural crest cells encounter seg- mented paraxial mesoderm (occipital and trunk somites), most move into the region between the dermamyotome and sclerotome in the cranial half of each somite. In contrast, most cephalic crest cells migrate superficial to somitomeres. There is, however, a small subpopulation of the head crest that invades somitomeric mesoderm. These cells subsequently segregate presumptive myogenic precursors of vis- ceral arch voluntary muscles from underlying mesen- chyme.
In the neurula-stage avian embryo, all paraxial and lateral mesodermal populations contain precursors of vascular endothelial cells, which can be detected in chimaeric embryos using anti-quail endothelial anti- bodies. Some of these angioblasts differentiate in situ, contributing directly to pre-existing vessels or forming isolated, nonpatent, cords that subsequently vesiculate and fuse with nearby vessels. Many angioblasts mi- grate in all directions, invading embryonic mesenchy- mal and epithelial tissues and participating in new blood vessel formation in distant sites.
The interactions leading to proper spatial pattern- ing of craniofacial skeletal, muscular, vascular and peripheral neural tissues has been studied by perform- ing heterotopic transplants of each of these mesoder- mal and neural crest populations. The results consist- ently indicate that connective tissue precursors, regardless of their origin, contain spatial information used by the precursors of muscles and blood vessels and by outgrowing peripheral nerves. Some of these connective tissue precursors (e.g. the neural crest, paraxial mesoderm) acquire their spatial pro- gramming while in association with the central ner- vous system or developing sensory epithelia (e.g. otic, optic, nasal epithelia).
Steroid-induced cell proliferation in vivo is associated with increased c-myc proto-oncogene transcript abundance
Authors: Rempel Sandra A. , Johnston Randal N. 
Published: April 2021

ABSTRACT
Enhanced c-myc transcript abundance has been observed in a variety of human malignancies, in normal liver tissue induced to proliferate in vivo by partial hepatectomy and in cells in culture induced to proliferate with the addition of protein hormones and growth factors. Little is known, however, about the expression of cellular proto-oncogenes in cells induced to proliferate in vivo by steroid hormones. Experiments reported here indicate that when cells of the immature chicken oviduct are induced to undergo rapid in vivo proliferation by application of the estrogen hormone 17 β-estradiol, the onset of this proliferation is associated with a rapid, large, and transient increase in c-myc transcript abundance. When estrogen is administered to chickens in which the oviduct has already differentiated, neither massive cell proliferation nor large increases in c-myc transcript abundance are induced. We conclude that the abundance of c-myc transcripts in vivo correlates well with the degree of cell proliferation induced by steroid hormone.
Ectopic expression of homeotic genes caused by the elimination of the Polycomb gene in Drosophila imaginal epidermis
Authors: Busturia Ana , Morata Gines 
Published: April 2021

Abstract
The morphological patterns in the adult cuticle of Drosophila are determined principally by the homeotic genes of the bithorax and Antennapedia complexes. We find that many of these genes become indiscriminately active in the adult epidermis when the Pc gene is eliminated. By using the Pc3 mutation and various BX-C mutant combinations, we have generated clones of imaginal cells possessing different combinations of active homeotic genes.
We find that, in the absence of BX-C genes, Pc− clones develop prothoracic patterns; this is probably due to the activity of Sex combs reduced which overrules Antennapedia. Adding contributions of Ultrabithorax, abdominal-A and Abdominal-B results in thoracic or abdominal patterns. We have established a hierarchical order among these genes: Antp &lt; Scr &lt; Ubx &lt; abd-A &lt; Abd-B. In addition, we show that the engrailed gene is ectopically active in Pc− imaginal cells.
Somitomeres: mesodermal segments of vertebrate embryos
Authors: Jacobson Antone G. 
Published: April 2021

ABSTRACT
Well before the somites form, the paraxial mesoderm of vertebrate embryos is segmented into somitomeres. When newly formed, somitomeres are patterned arrays of mesenchymal cells, arranged into squat, bilaminar discs. The dorsal and ventral faces of these discs are composed of concentric rings of cells. Somitomeres are formed along the length of the embryo during gastrulation, and in the segmental plate and tail bud at later stages. They form in strict cranial to caudal order. They appear in bilateral pairs, just lateral to Hensen’s node in the chick embryo. When the nervous system begins to form, the brain parts and neuromeres are in a consistent relationship to the somitomeres. Somitomeres first appear in the head, and the cranial somitomeres do not become somites, but disperse to contribute to the head the same cell types contributed by somites in the trunk region. In the trunk and tail, somitomeres gradually condense and epithelialize to become somites. Models of vertebrate segmentation must now take into account the early presence of these new morphological units, the somitomeres.
Somitomeres were discovered in the head of the chick embryo (Meier, 1979), with the use of stereo scanning electron microscopy. The old question of whether the heads of the craniates are segmented is now settled, at least for the paraxial mesoderm. Somitomeres have now been identified in the embryos of a chick, quail, mouse, snapping turtle, newt, anuran (Xenopus) and a teleost (the medaka). In all forms studied, the first pair of somitomeres abut the prosencephalon, but caudal to that, for each tandem pair of somitomeres in the amniote and teleost, there is but one somitomere in the amphibia. The mesodermal segments of the shark embryo are arranged like those of the amphibia.
The generation of periodic pattern during early Drosophila embryogenesis
Authors: Howard Ken 
Published: April 2021

ABSTRACT
The first indication of the formation of segment primordia in Drosophila is expression of the segment-polarity genes in particular parts of each primordium. These patterns are controlled by another class of genes, the pair-rule genes, which show characteristic two-segment periodic expression. Each pair-rule gene has a unique domain of activity and in one view different combinations of pair-rule gene products directly control the expression of the segment-polarity genes.
There is a hierarchy within the pair-rule class revealed by pair-rule gene interactions. It is unlikely that these interactions generate the periodicity de novo. Instead, pair-rule genes respond to positional information generated by a system involving zygotic gap and maternal coordinate genes. In this paper, I will concentrate on the problem of the mechanism that generates these pair-rule patterns, the first periodic ones seen during segmentation. I will review and discuss some of the relevant literature, illustrating certain points with data from my recent work.
Functional differentiation and alveolar morphogenesis of primary mammary cultures on reconstituted basement membrane
Authors: Barcellos-Hoff M. H. , Aggeler J. , Ram T. G. , Bissell M. J. 
Published: April 2021

ABSTRACT
An essential feature of mammary gland differentiation during pregnancy is the formation of alveoli composed of polarized epithelial cells, which, under the influence of lactogenic hormones, secrete vectorially and sequester milk proteins. Previous culture studies have described either organization of cells polarized towards lumina containing little or no demonstrable tissue-specific protein, or establishment of functional secretory cells exhibiting little or no glandular architecture. In this paper, we report that tissue-specific vectorial secretion coincides with the formation of functional alveoli-like structures by primary mammary epithelial cells cultured on a reconstituted basement membrane matrix (derived from Engelbreth-Holm-Swarm murine tumour). Morphogenesis of these unique three-dimensional structures was initiated by cell-directed remodelling of the exogenous matrix leading to reorganization of cells into matrix-ensheathed aggregates by 24 h after plating. The aggregates subsequently cavitated, so that by day 6 the cells were organized into hollow spheres in which apical cell surfaces faced lumina sealed by tight junctions and basal surfaces were surrounded by a distinct basal lamina.
The profiles of proteins secreted into the apical (luminal) and basal (medium) compartments indicated that these alveoli-like structures were capable of an appreciable amount of vectorial secretion. Immunoprecipitation with a broad spectrum milk antiserum showed that more than 80% of caseins were secreted into the lumina, whereas iron-binding proteins (both lactoferrin and transferrin) were present in comparable amounts in each compartment. Thus, these mammary cells established protein targeting pathways directing milk-specific proteins to the luminal compartment. A time course monitoring secretory activity demonstrated that establishment of tissue-specific vectorial secretion and increased total and milk protein secretion coincided with functional alveolar-like multicellular architecture.
This culture system is unique among models of epithelial cell polarity in that it demonstrates several aspects of epithelial cell polarization: vectorial secretion, apical junctions, a sequestered compartment and formation of a basal lamina. These lumina-containing structures therefore reproduce the dual role of mammary epithelia to secrete vectorially and to sequester milk proteins. Thus, in addition to maintaining tissue-specific cytodifferentiation and function, a basement membrane promotes the expression of tissue-like morphogenesis.