bluuebunny/crossref_metadata_2025_split huggingface dataset:
Developmental stages of fetal-type Leydig cells in prepubertal rats
Authors: Kuopio T. , Tapanainen J. , Pelliniemi L. J. , Huhtaniemi I. 
Published: April 2021

ABSTRACT
Fetal Leydig cells were studied in rats during and after the perinatal-neonatal period by comparing changes in morphology, number and volume with changes in testicular steroids and serum luteinizing hormone (LH) concentration. Stereologic examination indicated regression of fetal Leydig cells in testis by showing that their total volume as well as the average cell volume decreased between prenatal day 20 and postnatal day 3. The total number and total volume of cells both increased between postnatal days 3 and 11 but the average cell volume did not change during the same time period. Determination of serum LH showed a close correlation between an increase in LH concentration and increases in total number and volume of cells. The combined number of fetal- and adult-type Leydig cells on day 20 was more than 20 times the number of fetal cells at 3 days of age. Electron microscopic analysis showed that fetal Leydig cells after birth formed conspicuous clusters, which were surrounded by a layer of envelope cells and extracellular material. Occasional dividing fetal Leydig cells and possible precursors of fetal or adult Leydig cells were observed. Mitoses of spindle-shaped pericordal cells were frequent during the neonatal period. During and after the second postnatal week fetal Leydig cells again showed signs of regression, indicated by disintegration of the cell clusters, a decrease in cell size, accumulation of collagen between the cells and a decrease in steroid content per cell. The cytoplasm showed no degenerative changes, but the shape of the nuclei changed from spherical into irregular.
The present results suggest that the perinatal regression of fetal Leydig cells is followed by an LH-induced phase of growth. This growth period precedes a second phase of regression that coincides with early development of adult-type cells reported earlier. Contrary to the present concept of a biphasic pattern of Leydig cell development in rat, we suggest three consecutive stages: fetal (fetal cells in fetal testis), early juvenile (fetal cells during neonatal-early juvenile life) and juvenile-adult (adult cells before and after puberty). The regression of the fetal cells suggests that they have only a minor role in testicular hormone production after the appearance of adult-type Leydig cells prior to puberty.
Fibroblast growth factor (FGF) induces different responses in lens epithelial cells depending on its concentration
Authors: McAvoy J. W. , Chamberlain C. G. 
Published: April 2021

ABSTRACT
We reported previously that epithelial cells in expiants from neonatal rat lenses, when cultured in the presence of fibroblast growth factor (FGF), showed increased proliferation, cell migration and fibre differentiation; moreover, fibre differentiation in response to the basic form of FGF (bFGF) was virtually completely blocked by an anti-bFGF antibody. In the present study, we report a detailed analysis of the effects of bFGF on cells in the central region of lens epithelial explants. Proliferation in explants was assessed by measuring [3H]thymi-dine incorporation. Cell migration was measured by labelling cells in explants with fluorescein isothiocyanate (FITC)-dextran and monitoring them by UV fluorescence microscopy. Fibre differentiation in explants was assessed on the basis of β-crystallin accumulation. This study showed that half maximal activities for the three responses, proliferation, migration and fibre differentiation, were achieved at different concentrations of bFGF, namely, 0·15, 3 and 40 ng ml-1, respectively. Thus, the response of lens epithelial cells to bFGF varied qualitatively, as well as quantitatively, as the concentration increased. Monitoring FITC-dextran injected cells for up to 5 days after exposure to bFGF allowed analysis of the interrelation between various responses to bFGF in individual cells. As expected some cells divided in response to FGF, mainly within the first three days. However, whether or not they divided, all labelled cells responded to FGF by migrating and elongating. Maximal migration occurred during the first day of culture and maximal elongation was achieved by day 4. It was also found that [3H]thymidine incorporation and cell migration were substantially inhibited (90–93 %) by the anti-bFGF antibody shown previously to inhibit fi-crystallin accumulation, providing strong support for the conclusion that FGF is the molecule responsible for inducing all three responses. All these findings lead us to suggest that variations in FGF concentration in the different ocular media may be involved in controlling and maintaining lens polarity and lens growth patterns.
Cellular insertion of primary and secondary myotubes in embryonic rat muscles
Authors: Duxson M. J. , Usson Y. 
Published: April 2021

ABSTRACT
Mammalian muscles develop from two populations of myotubes; primary myotubes appear first and are few in number; secondary myotubes appear later and form most of the muscle fibres. We have made an ultrastructural study to investigate how primary and secondary myotubes in embryonic rat muscles transmit tension during the period of their development. Primary myotubes extend from end to end of the muscle from the earliest times, and attach directly to the tendon. In contrast, newly formed secondary myotubes are short cells which insert solely into the primary myotubes by a series of complex interdigitating folds along which adhering junctions occur. As the secondary myotubes lengthen and mature, their insertion is progressively transferred from the primary myotube to the tendon proper. We suggest that this variable insertion of immature secondary myotubes, combined with complex patterns of innervation and electrical coupling in developing muscle, makes it difficult to predict the overall contribution of secondary myotubes to muscle tension development. This work extends other studies showing the unique relationship between a primary myotube and its associated secondary myotubes, indicating that these may constitute a developmental compartment.
Cell lines with developmental potential restricted to mesodermal lineages isolated from differentiating cultures of pluripotential P19 embryonal carcinoma cells
Authors: Rudnicki Michael A. , Reuhl Kenneth R. , McBurney Michael W. 
Published: April 2021

ABSTRACT
Embryonal carcinoma (EC) cells are developmentally pluripotential cells which can be induced to differentiate in cell culture to form a wide variety of cell types. To investigate the lineage relationships between cells of different types, we set out to isolate cell lines with multiple but restricted developmental potentials from differentiating cultures of P19 cells, a line of EC. By selecting for differentiated cells capable of anchorage independent growth, we isolated cell lines which differentiated in high density cultures to form at least two cell types; myocytes that resembled fetal skeletal muscle cells and loose connective tissue cells that secreted large amounts of type I collagen. These results suggest that skeletal myocytes and connective tissue share a common precursor and that stem cells with limited but multiple developmental potentials can be isolated from differentiating cultures of P19 cells.
Ontogeny and tissue distribution of leukocyte-common antigen bearing cells during early development of Xenopus laevis
Authors: Ohinata Hiroshi , Tochinai Shin , Katagiri Chiaki 
Published: April 2021

ABSTRACT
To analyze the ontogenic emergence of leukocytes during early development, a mouse monoclonal antibody (IgG1), designated as XL-1, was produced against the peritoneal macrophages of adult Xenopus laevis. The XL-1 determinant was expressed on all types of leukocytes, including lymphocytes, granulocytes, thrombocytes and macrophages, but not on erythrocytes of either larvae or adults. Immunohistochemical observations of the hemopoietic organs revealed that the XL-1+ cells with granulocyte and/or macrophage morphology appeared at st.36–37 in the liver, at st.44–45 in the mesonephric and the thymus rudiments, and at st.47 in the spleen. The XL-1 determinant was expressed on the precursor cells of T lymphocytes in the thymus rudiments at st.46–47, on the pre-B cells in the liver rudiments at st.47, and on lymphocytes in the spleen at st.48–49. A few XL-1+ cells were present in the ventral blood island of the st.35/36 embryos, where differentiating erythrocytes had predominated since st.28. XL-1+ cells with a macrophage-like morphology were found in several locations of the mesenchyme in the st.32 embryos, before the establishment of vascularization at st.33/34 and far earlier than the emergence of lymphocytes.
Bone formation following intrarenal transplantation of isolated murine chondrocytes: chondrocyte-bone cell transdifferentiation?
Authors: Moskalewski Stanislaw , Malejczyk Jacek 
Published: April 2021

ABSTRACT
Isolated syngeneic epiphyseal chondrocytes transplanted into a muscle formed cartilage in which matrix resorption and endochondral ossification began at the end of the second week after transplantation. After 56 days cartilage was converted into an ossicle. In 7-day-old intrarenal transplants, epiphyseal chondrocytes formed nodules of cartilage. In 10-day-old transplants, islands of bone appeared. Slight resorption of cartilage was first noted in 14-day-old transplants of chondrocytes. After eight weeks, transplants contained mainly bone. Intramuscularly transplanted rib chondrocytes formed cartilage which did not ossify. Nevertheless, bone islands appeared in intrarenal transplants of rib chondrocytes. Bone was not formed in allogeneic intrarenal transplants of epiphyseal or rib chondrocytes, but appeared in such transplants in animals immunosuppressed by anti-thymocyte serum and procarbazine. When spleen cells from animals immunized with allogeneic chondrocytes were transferred to immunosuppressed chondrocyte recipients two weeks after intrarenal chondrocyte transplantation, the majority of osteocytes in bone islands was dead. On the other hand, endochondral bone formed in intramuscular transplants of allogenic epiphyseal chondrocytes in immunosuppressed recipients was not damaged by sensitized spleen cells. This suggested that bone in 10- to 14-day-old intrarenal transplants of chondrocytes arose from injected cells and not by induction. To see whether bone was formed by chondrocytes or by some cells contaminating the chondrocyte suspension, the superficial layer of rib cartilage was removed by collagenase digestion and only more central chondrocytes were used for transplantation. Intrarenal transplants of these chondrocytes also yielded bone. Furthermore, in some experiments intrarenal transplants of syngeneic rib chondrocytes were stained in toto by Alcian blue and Alizarin red S 7 and 14 days after transplantation and examined under a dissecting microscope. In 7-day-old transplants only cartilage nodules could be found while in the older ones cartilage and bone or only bone islands were present. These results strongly suggest that in intrarenal transplants epiphyseal and rib chondrocytes transdifferentiated into bone cells. It also seems that chondrocytes first formed cartilage matrix which, after their transdifferentiation, was substituted by bone matrix.
Cell lineage and pattern formation in the earthworm embryo
Authors: Storey Kate G. 
Published: April 2021

ABSTRACT
The pattern of segmental contribution of teloblasts in the earthworm embryo was examined by injection of the lineage tracer HRP and by studying the timing and symmetry of the first few divisions in each teloblast bandlet . The changing spatial relationship of the ectoteloblasts during development was also used to assess segmental contributions. A mathematical method for determining the cell cycle time of each teloblast is presented. The teloblasts and their immediate progeny, the blast cells, were found to undergo unique and highly stereotyped patterns of division which lead to equally stereotyped patterns of contribution in the segments apparent in the later embryo.
Delayed determination of claw laterality in lobsters following loss of target
Authors: Govind C. K. , Pearce Joanne 
Published: April 2021

ABSTRACT
Lateralization of the paired claws into a major crusher and a minor cutter type is determined during the 4th and 5th stages of juvenile development of the lobster, Homarus americanus. Loss of both claws during this critical period delays the determination of laterality until the 6th stage when regenerate claws are present. Continued loss into the 6th stage, and beyond, however, suppresses laterality, resulting in lobsters with paired cutter claws.
The critical period for determining claw laterality may therefore be extended for a brief time to cater for claw loss, which is especially common in these early juvenile stages.
Desmin and titin expression in early postimplantation mouse embryos
Authors: Schaart G. , Viebahn C. , Langmann W. , Ramaekers F. 
Published: April 2021

ABSTRACT
The expression of the intermediate filament (IF) constituents desmin, vimentin and keratin, as well as the striated-muscle-specific marker titin, was studied in mouse embryos of 8.0 to 9.5 days post coitum (d.p.c.), using the indirect immunofluorescence technique in combination with polyclonal and monoclonal antibodies. During the development of the embryo, desmin was first detected at 8.25 d.p.c. in the ectoderm, where it was transiently coexpressed with keratin and vimentin. At later stages, the ectoderm contained only keratin and to a certain extent also vimentin IF. At 8.5 d.p.c., desmin was found exclusively in the heart rudiment, and remained present with increasing intensity in the myocardial cells during later cardiogenesis. Striation of desmin in the heart muscle cells was observed in 9.5 d.p.c. embryos. At these stages (8.5–9.5 d.p.c.), triple expression of the IF proteins desmin, vimentin and keratin was evident in these cells. From 9.0 d.p.c. onwards, desmin could be detected in the myotomes as well. Immunoblotting studies of 9.5 d.p.c. mouse embryos confirmed the immunohistochemical data.
Titin was found in the early heart anlage at stage 8.25 d.p.c., when no desmin expression was observed in this tissue. At this stage the titin appeared in a punctate pattern, similar to that observed in cardiac myofibrils of early chicken embryos (Tokuyasu and Maher, 1987; J. Cell Biol. 105, 2781–2793). In 8.5 d.p.c. mouse embryos, this punctate titin staining pattern was still observed, while, at this stage, a filamentous staining reaction could be seen with the desmin antibodies. During further development, cross-striation was detected within myocardial cells using the polyclonal titin antibody from 9.0 d.p.c. onwards, i.e. before such striation could be detected with the desmin antibodies.
From these data, we conclude that titin synthesis may anticipate desmin expression in the developing mouse myocard, although the level of expression of the former protein remains low until 9.0 d.p.c.
Spatial aspects of neural induction in Xenopus laevis
Authors: Jones E. A. , Woodland H. R. 
Published: April 2021

ABSTRACT
A monoclonal antibody, 2G9, has been identified and characterised as a marker of neural differentiation in Xenopus. The epitope is present throughout the adult central nervous system and in peripheral nerves. Staining is first detected in embryos at stage 21 in the thoracic region. By stage 29 it stains the whole central nervous system, except the tail tip. The epitope is present in a 65K Mr protein, and includes sialic acid. The antibody also reacts with neural tissue in mice and axolotls and newts. 2G9 was used to show that both notochord and somites are capable of neural induction, and the stimulus is present as late as stage 22. Attempts to demonstrate the induction of nervous system by developing nervous system (homoiogenetic induction) were unsuccessful. The view that the lateral extent of the nervous system might be determined by that of the inductive stimulus is discussed. Neural induction was detected as early as stage 10 and occurs in embryos without gastrulation and without cell division from stage .
Pre-existing neuronal pathways in the leg imaginal discs of Drosophila
Authors: Tix Simone , Bate Michael , Technau Gerhard M. 
Published: April 2021

ABSTRACT
Injection of a cell lineage tracer (HRP) into Drosophila embryos before cellularization provides a way of selectively labelling cells at later stages that have undergone only a few mitoses. All cells born and differentiating during embryogenesis become labelled, whereas further proliferation and growth during postembryonic development causes an almost complete dilution of the marker in the adult cell complement. Early born neurons visualized in this way are good candidates for executing a pioneering function during postembryonic differentiation of the adult nervous system.
In all three pairs of leg imaginal discs, a stereotyped set of larval sense organs becomes selectively labelled. Their axons fasciculate with a larval nerve, which connects the leg disc with the central nervous system. Larval sense organs are not present in the other imaginal discs.
Larval neurons are not present in the transformed antennal discs of Antp 73B flies. Nonetheless adult axons successfully navigate to the base of these discs as they differentiate to form ectopic legs. We conclude that embryonically formed larval nerves are not essential for the guidance of adult axons within the leg discs.
Steroid hormone receptor homologs in development
Authors: Oro Anthony E. , Umesono Kazuhiko , Evans Ronald M. 
Published: April 2021

ABSTRACT
The steroid/thyroid receptor superfamily are liganddependent transcription factors which consist of distinct functional domains required for transcriptional control of a network of genes. Members of this superfamily are beginning to be studied for their contribution to embryogenesis. Two human receptors for the vertebrate morphogen retinoic acid have been isolated and further characterized on model promoters. Moreover, the presence of homologs of these receptors in Drosophila reveals that members of this superfamily predate the divergence of the vertebrates and Invertebrates. One locus is knirps-related (knrl), whose product is closely related to that of the gap segmentation gene knirps (kni). knrl is one of the most diverged steroid receptor-like molecules and displays a spatially restricted blastoderm pattern.
Segmental polarity and identity in the abdomen of Drosophila is controlled by the relative position of gap gene expression
Authors: Lehmann Ruth , Frohnhöfer Hans Georg 
Published: April 2021

ABSTRACT
The establishment of the segmental pattern in the Drosophila embryo is directed by three sets of maternal genes: the anterior, the terminal and the posterior group of genes. Embryos derived from females mutant for one of the posterior group genes lack abdominal segmentation. This phenotype can be rescued by transplantation of posterior pole plasm into the abdominal region of mutant embryos. We transplanted posterior pole plasm into the middle of embryos mutant either for the posterior, the anterior and posterior, or all three maternal systems and monitored the segmentation pattern as well as the expression of the zygotic gap gene Kriippel in control and injected embryos. We conclude that polarity and identity of the abdominal segments do not depend on the relative concentration of posterior activity but rather on the position of gap gene expression. By changing the pattern of gap gene expression, the orientation of the abdomen can be reversed. These experiments suggest that maternal gene products act in a strictly hierarchical manner. The function of the maternal gene products becomes dispensable once the position of the zygotically expressed gap genes is determined. Subsequently the gap genes will control the pattern of the pair-rule and segment polarity genes.
The decapentaplegic gene: a TGF-β homologue controlling pattern formation in Drosophila
Authors: Gelbart William M. 
Published: April 2021

ABSTRACT
The type β transforming growth factor (TGF-β) family of secreted factors encompasses a wide range of structurally related proteins that control the state of determination or differentiation in a wide variety of cell types. For all members of the family that have been studied at the protein level, the active moieties arise as dimers of the C-terminal ∼110 amino acid fragment derived from much longer precursor polypeptides. The hallmark of the family is a series of 7 completely conserved cysteine residues in the C-terminus; other conserved amino acid sequences generally cluster in the vicinity of 6 of these 7 cysteines. This report focuses on our current understanding of the genetic structure and developmental role of the decapentaplegic (dpp) gene in Drosophila, the only member of the TGF-β family thus far identified in invertebrates. The dpp polypeptide bears a sufficiently close relationship to two bone morphogenesis proteins (BMP-2A and BMP-2B) identified in mammals (Wozney et al. 1988, Science 242, 1528-1534) to warrant the suggestion that dpp and the BMP-2s are the descendants of a common ancestral gene. The protein-coding information for dpp is contained within a 6 kb DNA segment. An elaborate cis-regulatory apparatus, encompassing a &gt;55 kb DNA segment, has evolved to control expression of the dpp gene, which is required for determination of dorsal ectoderm in the early embryo, for normal distal outgrowth of the adult appendages, and for sundry other developmental events, which are currently less well-defined. Studies of chimeric individuals and observations of transcript accumulation in situ have demonstrated that the dpp gene is expressed along the A/P boundary of the imaginai disks. A possible role of dpp in elaborating positional information in imaginai disk development is discussed.
Early determination in the C. elegans embryo: a gene, cib-1, required to specify a set of stem-cell-like blastomeres
Authors: Schnabel Ralf , Schnabel Heinke 
Published: April 2021

ABSTRACT
The early somatic blastomeres founding the tissues in the C. elegans embryo are derived in a stem-cell-like lineage from the P cells. We have isolated maternal effect lethal mutations defining the gene cib-1 in which the P cells, Pi-P3, skip a cell cycle and acquire the fates of only their somatic daughters. Therefore, the cib-1 gene is required for the specification of the stem-cell-like fate of these cells.
The analysis of the development of these mutants suggests that the clock controlling the cell cycles in the early embryo is directly coupled to the fate of a cell and that there must be another developmental clock that activates the determinative inventory for the early decision-making.