bluuebunny/crossref_metadata_2025_split huggingface dataset:
Functional Specificity of Spinal Cord Segments in the Control of Limb Movements
Authors: Székely George 
Published: April 2021

ABSTRACTSpinal cord segments from limb levels (both brachial and lumbo-sacral) were homoplastically grafted into the place of previously removed thoracic segments in newt embryos. In other embryos the brachial segments were replaced by lumbo-sacral segments or vice versa. In early larval stages a pair of supernumerary limbs were transplanted at the level of the grafted segments in the thoracic region. The function of normal and supernumerary limbs inner-vated by heterotopic spinal cord segments was studied. When brachial segments were substituted for thoracic segments the super-numerary limbs yielded co-ordinated stepping movements, perfectly synchro-nized with the normal forelimbs. Apart from minor discrepancies arising from differences in gross anatomical structure, the same rhythm and co-ordination of stepping movements were found whether fore- or hindlimbs were transplanted. Brachial segments in lumbo-sacral positions were able to bring the normal hindlimbs into co-ordinated movement. Although there was no correlation in the movements between the four limbs, the hindlimbs showed a definite ten-dency to move in parallel with the forelimbs on the same side. Supernumerary limbs, innervated by heterotopic lumbo-sacral segments grafted into thoracic regions, showed co-ordinated movements which accom-panied the movements of the normal hindlimbs either synchronously or, in most cases, with some delay. Essentially the same movement patterns were given both by transplanted fore- and hindlimbs except that the motility of the elbow was poorer than that of a normal forelimb. This was regarded as a ‘hindlimb character’ in the movement of forelimbs innervated by lumbo-sacral segments. Orthotopic forelimbs innervated by heterotopic lumbo-sacral segments grafted into brachial regions also disclosed co-ordinated movements with a tendency to move in parallel with the hindlimbs on the same side. Well-defined ‘hindlimb character’ was verified in both the motility and the posture of such limbs. The following conclusions were drawn, (i) A special segmental apparatus, already determined in early embryonic stages, exists at limb levels of the spinal cord for controlling co-ordinated limb movements, (ii) The rhythm and character of limb movements executed by these apparatus corresponded always to the nature of the innervating segments irrespective of the nature of the innervated limbs, (iii) A secondary process of determination was assumed to provide the fore- or hindlimb character of the differentiation of these segmental apparatus. The incomplete establishment of this determination might explain the observed time lag and irregularities in function of heterotopic lumbo-sacral segments under certain experimental conditions.
Viral Susceptibility and Embryonic Differentiation.
Authors: Rapola Juhani , Vainio Tapani , Saxén Lauri 
Published: April 2021

ABSTRACTThe fact that viral susceptibility changes during embryogenesis has been pointed out by both experimental embryologists and clinical practitioners, not to mention virologists working with avian material. In attempts to find the fundamental factors which make embryonic tissue susceptible or resistant to a given virus, the metabolic and proliferative rate have been considered relevant (Williamson et al., 1953; Robertson et al., 1955; Tôndury, 1956). Experience accumulated in studies of the replication of various viruses in tissue culture has taught us that a high metabolic rate and active proliferation may not always enhance viral replication (Ginsberg, 1958). However, there seems to be justification for the view that an injurious agent leads to more severe tissue damage when it exercises its effect upon actively proliferating tissues than when it does so at the ‘resting stage’ .
Localization of specific retinoid-binding sites and expression of cellular retinoic-acid-binding protein (CRABP) in the early mouse embryo
Authors: Dencker L. , Annerwall E. , Busch C. , Eriksson U. 
Published: April 2021

ABSTRACT
Retinoids (vitamin A derivatives) are important for normal embryogenesis and retinoic acid, an acidic derivative of vitamin A, was recently proposed to be an endogenous morphogen. Several retinoids are also potent teratogens. Using an autoradiographic technique, we have identified tissues and cells in early mouse embryos that are able to specifically accumulate a radiolabelled synthetic derivative of retinoic acid. Strong accumulation of radioactivity was seen in several neural crest derivatives and in specific areas of the CNS. Gel filtration analyses of cytosols from embryos that received the radiolabelled retinoid in utero suggested that cellular retinoic acid-binding protein (CRABP) was involved in the accumulation mechanism. Immunohisto-chemical localization confirmed that cells accumulating retinoids also expressed CRABP. Strong CRABP immunoreactivity was found in neural crest-derived mesenchyme of the craniofacial area, in visceral arches, in dorsal root ganglia and in cells along the gut and the major vessels of the trunk region. In CNS, CRABP expression and retinoid binding was largely restricted to the hindbrain, to a single layer of cells in the roof of the midbrain and to cells in the mantle layer of the neural tube. Our data suggest that cells in the embryo expressing CRABP are target cells for exogenous retinoids as well as endogenous retinoic acid. Retinoic acid may thus play an essential role in normal development of the CNS and of tissues derived from the neural crest. We propose that the teratogenic effects of exogenous retinoids are due to an interference with mechanisms by which endogenous retinoic acid regulates differentiation and pattern formation in these tissues.
Treatment with β bungarotoxin blocks muscle spindle formation in fetal rats
Authors: Kucera Jan , Waldro Jon M. 
Published: April 2021

ABSTRACT
Sensory and motor fibers of peripheral nerves were irreversibly destroyed in fetal rats by administering β bungarotoxin (BTX) on embryonic day 16 or 17, after assembly of primary myotubes, but before the formation of muscle spindles. Soleus muscles of toxin-treated fetuses and their untreated littermates were removed just prior to birth and were examined by light microscopy of serial transverse sections for the presence of spindles and immunocytochemical expression of several isoforms of myosin heavy chains (MHC). Untreated muscles exhibited numerous spindles that were innervated by branches of intramuscular nerves and contained muscle fibers expressing a slow-tonic MHC isoform characteristic of the intrafusal but not extrafusal fibers. Toxin-treated muscles were devoid of intramuscular nerve bundles and perineurial structures. Encapsulations of muscle fibers resembling spindles were absent and no myotubes expressed the slow-tonic MHC isoform associated with intrafusal fibers in β BTX-treated muscles. Thus, the assembly of muscle spindles, formation of the spindle capsule, and transformation of undifferentiated myotubes into the intrafusal fibers that contain spindle-specific myosin isoforms all depend on the presence of innervation in prenatal rat muscles.
Cardiac troponin T in developing, regenerating and denervated rat skeletal muscle
Authors: Saggin Leopoldo , Gorza Luisa , Ausoni Simonetta , Schiaffino Stefano 
Published: April 2021

ABSTRACT
Fetal rat skeletal muscles express a troponin T (TnT) isoform similar to the TnT isoform expressed in the embryonic heart with respect to electrophoretic mobility and immunoreactivity with cardiac TnT-specific monoclonal antibodies. Immunoblotting analyses reveal that both the embryonic and the adult isoforms of cardiac TnT are transiently expressed during the neonatal stages. In addition, other TnT species, different from both cardiac TnTs and from the TnT isoforms expressed in adult muscles, are present in skeletal muscles during the first two postnatal weeks. By immunocytochemistry, cardiac TnT is detectable at the somitic stage and throughout embryonic and fetal development, and disappears during the first weeks after birth, persisting exclusively in the bag fibers of the muscle spindles. Cardiac TnT is re-expressed in regenerating muscle fibers following a cold injury and in mature muscle fibers after denervation. Developmental regulation of this TnT variant is not coordinated with that of the embryonic myosin heavy chain with respect to timing of disappearance and cellular distribution. No obligatory correlation between the two proteins is likewise found in regenerating and denervated muscles.
Insulin increases the cell number of the inner cell mass and stimulates morphological development of mouse blastocysts in vitro
Authors: Harvey Mark B. , Kaye Peter L. 
Published: April 2021

Abstract
Previous studies showed that insulin promotes cell proliferation and morphological development of preimplantation mouse embryos. In this report, the receptor responsible for these actions and the cell populations that are affected were investigated. Insulin’s 9 % stimulation of blastocyst cell number was entirely due to a 23 % increase in ICM cell number with an ECS0 of 0.54 pM. This and the similar degrees of stimulation of immunosurgically isolated ICMs by both physiological and supraphysiological insulin concentrations suggest that insulin receptors are present on the ICM and respond to exogenous insulin transcytosed through the TE to promote expansion of the ICM cell numbers. In morphological studies, insulin increased the number of blastocysts and decreased the number of morulae by 10 % after 54 h culture from 2-cell embryos with ECsos of about 0.95 pM. The equivalence of these ECsos suggests mediation of insulin’s stimulation of blastocyst formation via insulin receptors which are functionally expressed around the time of compaction at the 8-cell stage. These results support our hypothesis that insulin has an important role in the regulation of growth during preimplantation development.
Homeotic genes regulate the spatial expression of putative growth factors in the visceral mesoderm of Drosophila embryos
Authors: Reuter Rolf , Panganiban Grace E. F. , Hoffmann F. Michael , Scott Matthew P. 
Published: April 2021

Abstract
During Drosophila embryogenesis homeotic genes control the developmental diversification of body structures. The genes probably coordinate the expression of as yet unidentified target genes that carry out cell differentiation processes. At least four homeotic genes expressed in the visceral mesoderm are required for midgut morphogenesis. In addition, two growth factor homologs are expressed in specific regions of the visceral mesoderm surrounding the midgut epithelium. One of these, decapentaplegic (dpp), is a member of the transforming growth factor β (TGF-β) family; the other, wingless (wg), is a relative of the mammalian protooncogene int-1. Here we show that the spatially restricted expression of dpp in the visceral mesoderm is regulated by the homeotic genes Ubx and abd-A. Ubx is required for the expression of dpp while abd-A represses dpp. One consequence of dpp expression is the induction of labial (lab) in the underlying endoderm cells. In addition, abd-A function is required for the expression of wg in the visceral mesoderm posterior to the dpp- expressing cells. The two growth factor genes therefore are excellent candidates for target genes that are directly regulated by the homeotic genes.
Gonadal expression of c-kit encoded at the W locus of the mouse
Authors: Manova Katya , Nocka Karl , Besmer Peter , Bachvarova Rosemary F. 
Published: April 2021

Abstract
Recently, it has been shown that the c-kit proto-oncogene is encoded at the white spotting ( W) locus in mice. Mutations of this gene cause depletion of germ cells, some hematopoietic cells and melanocytes. In order to define further the role of c-kit in gametogenesis, we have examined its expression in late fetal and postnatal ovaries and in postnatal testis. By RNA blot analysis, c-kit transcripts were not detected in late fetal ovaries but appeared at birth. The relative amount reached a maximum in ovaries of juvenile mice, and decreased in adult ovaries, c-kit transcripts were present in increasing amounts in isolated primordial, growing and full-grown oocytes, as well as in ovulated eggs. Little was detected in early 2-cell embryos and none in blastocysts. In situ hybridization revealed c-kit transcripts in a few oocytes of late fetal ovaries and in all oocytes (from primordial to full-grown) in ovaries from juvenile and adult mice. Expression was also observed in ovarian interstitial tissue from 14 days of age onward. Using indirect immunofluorescence, the c-kit protein was detected on the surface of primordial, growing and full-grown oocytes, as well as on embryos at the 1- and 2-cell stages; little remained in blastocysts.
In situ hybridization analysis of testes from mice of different ages demonstrated expression in spermatogonia from 6 days of age onward. Using information provided by determining the stage of the cycle of the seminiferous epithelium for a given tubule and by following the age dependence of labeling, it was concluded that the period of expression of c-kit extends from at least as early as type A2 spermatogonia through type B spermatogonia and into preleptotene spermatocytes. Leydig cells were labelled at all ages examined.
The expression pattern in oocytes correlates most strongly with oocyte growth and in male germ cells with gonial proliferation.
Expression of the murine homeobox-containing gene Hox-2.3 suggests multiple time-dependent and tissue-specific roles during development
Authors: Vogels Ronald , De Graaff Wim , Deschamps Jacqueline 
Published: April 2021

Abstract
This study reports the expression pattern of the murine homeobox-containing gene Hox-2.3 during development. Using in situ hybridization, we first detect Hox-2.3 transcripts in the allantois primordium at 7.5 days post coitum (p.c.). One day later transcripts are found in embryonic ectoderm and mesoderm. In 9.5- and 10.5-day embryos Hox-2.3 expression is observed in the central nervous system (CNS) from a rostral boundary in the upper spinal cord to the caudal end. Within this anteroposterior domain, Hox-2.3 expression is also found in the peripheral nervous system, in the mesoderm and in the hindgut epithelium. The rostral boundary in the mesoderm is located at the level of the 11th somite and thus shifted posteriorwards compared to the rostral boundary in the neural tube. During subsequent development, the initially broad expression pattern in the somitic, lateral plate and intermediate mesoderm becomes restricted to structures in the urogenital system. In adults, the spinal cord and the derivatives of the Wolffian and Müllerian ducts continue to express the gene at a high level. The described temporal and tissue-specific changes in expression of Hox-2.3 are suggestive of several levels of regulation as reported for Drosophila homeotic genes and argue for more than one role of the gene during development and in adults.
Diverse expression of dsrc29A, a gene related to src, during the life cycle of Drosophila melanogaster
Authors: Katzen ALisa L. , Kornberg Thomas , Bishop J. Michael 
Published: April 2021

Abstract
We used in situ hybridization to study the RNA expression of the dsrc29A gene during Drosophila development. This gene encodes two proteins differing at their amino termini. Both gene products contain a protein-tyrosine kinase domain and resemble the protein encoded by vertebrate src. We examined most stages of development in the Drosophila life cycle: embryos, third instar larvae, pupae and adults. Our results revealed that dsrc29A expression is specialized throughout development, being prominent at various times in neural tissue, phagocytic cells, dorsal vessel, ovaries, gut, developing salivary glands, imaginai discs and disc derivatives. These findings confirm and extend previous results for the distribution of dsrc29A protein, indicating that the regulation of this gene is primarily at the level of transcription. In some tissues expression is transient, whereas in others, it is continuous, and expression occurs in proliferative, differentiating and differentiated tissue. These patterns of expression demonstrate how a single protein-tyrosine kinase might play diverse roles at different times during development. Comparison of the expression of dsrc29A and other members of the proteintyrosine kinase gene superfamily reveals that the genes are expressed in distinctive but sometimes overlapping patterns.
A cytosolic sperm factor stimulates repetitive calcium increases and mimics fertilization in hamster eggs
Authors: Swann Karl 
Published: April 2021

Abstract
Microinjection of cytosolic sperm extracts into unfertilized golden hamster eggs caused a series of increases in cytoplasmic free calcium, Ca2+i, and membrane hyperpolarizing responses, HRs. These HRs and Ca2+i, transients are similar to those seen during in vitro fertilization of hamster eggs. The sperm factor that is responsible for causing these effects appears to be of high molecular weight and protein based. Injection of sperm factor activated eggs and mimicked fertilization in causing repetitive HRs in the presence of phorbol esters and in sensitizing the egg to calcium-induced calcium release. Since these effects cannot be mimicked by injecting G-protein agonists or calcium-containing solutions, it seems unlikely that a receptor-G-protein signalling system is involved at fertilization. These data instead suggest a novel signal transduction system operates during mammalian fertilization in which a protein factor is transferred from the sperm into the egg cytoplasm after gamete membrane fusion.
Estimation of neuroblast numbers in insect neurogenesis using the lateral inhibition hypothesis of cell differentiation
Authors: Honda Hisao , Tanemura Masaharu , Yoshida Akihiro 
Published: April 2021

Abstract
Cells in the neurogenic region of an insect ectoderm have two alternative fates, making neurons or epidermis. The fates seem to be determined through a laterally inhibitory interaction among cells. That is, initially homogeneous cells are all competent to differentiate into neuroblasts. Once a cell has differentiated as a neuroblast, it inhibits its immediate neighbors from following this pathway. The differentiation process is simulated by a digital computer in a planar array of polygonal domains similar to a cell pattern. We find that the number of cells differentiating as neuronal precursors in insect neurogenesis is that expected under the hypothesis of lateral inhibition of cell differentiation between immediate neighbors.
The distribution of E-cadherin during Xenopus laevis development
Authors: Levi Giovanni , Gumbiner Barry , Thiery Jean Paul 
Published: April 2021

ABSTRACT
A vast amount of experimental evidence suggests that cell surface molecules involved in cell-to-cell and/or cell-to-substrate interactions participate in the control of basic events in morphogenesis. E-cadherin is a cell adhesion molecule directly implicated in the control of Ca2+-dependent interactions between epithelial cells. We report here the patterns of expression of E-cadherin in developmental stages of Xenopus laevis ranging from early embryo to adult using immunofluorescence microscopy. Although its distribution shares some similarities with those of L-CAM in the chicken and E-cadherin/Uvomorulin in the mouse, the distribution of E-cadherin in Xenopus presents several peculiar and unique features.
In early stages of Xenopus development, E-cadherin is not expressed. The molecule is first detectable in the ectoderm of late gastrulas (stage 13–13.5 NF). At this time both the external and the sensory layer of the non-neural ectoderm accumulate high levels of E-cadherin while the ectoderm overlying the neural plate and regions of the involuting marginal zone (IMZ) not yet internalized by the movements of gastrulation are E-cadherin-negative. Unlike most other species, endodermal cells express no or very low levels of E-cadherin up to stage 20 NF. Endodermal cells become strongly E-cadherin-positive only when a well-differentiated epithelium forms in the gut. No mesodermal structures are stained during early development. In the placodes, in contrast to other species, E-cadherin disappears very rapidly after placode thickening.
During further embryonic development E-cadherin is present in the skin, the gut epithelium, the pancreas, many monostratified epithelia and most glands. Hepatocytes are stained weakly while most other tissues, including the pronephros, are negative. In the mesonephros, the Wolffian duct and some tubules are positive.
During metamorphosis a profound restructuring of the body plan takes place under the control of thyroid hormones, which involves the degeneration and subsequent regeneration of several tissues such as the skin and the gut. All newly formed epithelia express high levels of E-cadherin. Surprisingly, degenerating epithelia of both skin and intestine maintain high levels of the protein even after starting to become disorganized and to degenerate.
In the adult, staining is strong in the skin, the glands, the lungs, the gut epithelium and the pancreas, weak in the liver and absent from most other tissues.
Our results show that the expression of E-cadherin in Xenopus is strongly correlated with the appearance of differentiated epithelia.
The homeobox gene Hox 7.1 has specific regional and temporal expression patterns during early murine craniofacial embryogenesis, especially tooth development in vivo and in vitro
Authors: Mackenzie Alasdair , Leeming Gareth L. , Jowett Adrian K. , Ferguson Mark W. J. , Sharpe Paul T. 
Published: April 2021

Abstract
Hox 7.1 is & murine homeobox-containing gene expressed in a range of neural-crest-derived tissues and areas of putative epithelial-mesenchymal interactions during embryogenesis. We have examined the expression of Hox 7.1 during craniofacial development in the mouse embryo between days 8 and 16 of development. Whereas facial expression at day 10 of gestation is broadly localised in the neural-crest-derived mesenchyme of the medial nasal, lateral nasal, maxillary and mandibular processes, by day 12 expression is restricted to the mesenchyme immediately surrounding the developing tooth germs in the maxillary and mandibular processes. Hox 7.1 expression in the mesenchyme of the dental papilla and follicle is maximal at the cap stage of development and progressively declines in the bell stage prior to differentiation of odontoblasts and ameloblasts.
Hox 7.1 expression in tooth germs is independent of overall embryonic stage of development but is dependent on stage of development of the individual tooth. Similar patterns of transient Hox 7.1 expression can also be detected in tooth germs in vitro in organ cultures of day 11 first branchial arch explants cultured for up to 7 days.
Hox 7.1 is also expressed early in development (days 10/11) in the epithelium of the developing anterior pituitary (Rathke’ s pouch), the connective tissue capsule and meninges of the developing brain, and specific regions of neuroepithelium in the developing brain.