Dorsolateral Plate Research Articles

Identification and characterization of myeloid cells localized in the tadpole liver cortex in Xenopus laevis

In the present study, using transgenic frogs that express GFP specifically in myeloid cells under the myeloperoxidase enhancer sequence, we found that myeloperoxidase-positive cells are localized in the liver cortex at the late tadpole stages. Immunohistochemical analysis revealed that myelopoiesis in the liver cortex became evident after st. 50 and reached its peak by st. 56. Transplantation experiments indicated that cells with a high density at the liver cortex were derived from the dorso-lateral plate tissue in the neurula embryo. Analysis of smear samples of the cells isolated from collagenase-treated liver tissues of the transgenic tadpoles indicated that myeloid cells were the major population of blood cells in the larval liver and that, in addition to myeloid colonies, erythroid colonies expanded in entire liver after metamorphosis. Cells that were purified from the livers of transgenic tadpoles according to the GFP expression exhibited the multi-lobed nuclei. The results of present study provide evidence that the liver cortex of the Xenopus tadpole is a major site of granulopoiesis.

Treatment results of dorsolateral plate with lateral support of VA-LCPDHP for adult Humeral Condyle Fractures-Examination of Fracture Line Location

Treatment results of dorsolateral plate with lateral support of VA-LCPDHP for adult Humeral Condyle Fractures-Examination of Fracture Line Location

Biomechanical evaluation of a transcondylar screw from the dorsolateral plate support on the stabilization of orthogonal plate configuration in distal humeral fracture

IntroductionIntra-articular distal humeral fractures involving both columns require double-plate fixation. In orthogonal plate fixation, screws from the medial plate reach the radial column, while screws from the dorsolateral plate run posterior–anterior, not creating interdigitation. The Synthes LCP-DHP system has an orthogonal plate configuration that enables dorsolateral plating with support, as the radial and ulnar columns are linked via interdigitation of the distal screws. We hypothesized that the transcondylar screw from the posterolateral plate, which interdigitates with screws from the medial plate, enables more rigid stabilization of orthogonal plating in distal humeral AO type C fractures. MethodsA previous study reported the biomechanical properties of orthogonal plate fixation using an AO type 13-C2.3 intra-articular fracture model with a 1-cm supracondylar gap using artificial bones (Kudo et al., Injury, 2016). We performed a biomechanical study of the dorsolateral plate with support, and inserted one 2.7-mm locking screw through the support in the lateral-to-medial direction, creating interdigitation of the distal screws. A 0–200 N axial load was applied separately to the radial and ulnar columns. We calculated the stiffness of both columns, and the anterior displacement of the condylar fragment. We compared the biomechanical properties of orthogonal plating with versus without interdigitation. ResultsThere were no significant differences between the two groups in radial or ulnar axial compression. The ulnar column was stiffer than the radial column in both groups. There were no significant differences between groups in the angular displacements of the capitellum or trochlea. The capitellum moved more anteriorly than the trochlea during axial compression in both groups. DiscussionThe radial and ulnar columns were linked via interdigitation of the distal screws by adding one transcondylar screw from the dorsolateral plate, which did not affect radial column stiffness or capitellar anterior movement under axial compression. In the orthogonal configuration, axial compression induced more anterior displacement of the capitellum than the trochlea, which may induce secondary fragment or screw dislocation on the dorsolateral plate or nonunion at the supracondylar level. ConclusionsThe transcondylar screw from the dorsolateral plate did not affect axial compression of the radial column or capitellar anterior displacement.

A new species of Aspidoras (Siluriformes: Callichthyidae) from a small coastal drainage in northeastern Brazil

ABSTRACT A new species of Aspidoras from the rio da Dona basin, a small coastal river drainage in Bahia State, is described herein. The new taxon differs from its congeners by presenting infraorbital 1 with well-developed ventral laminar expansion, nuchal plate nearly reaching to or sometimes contacting posterior process of parieto-supraoccipital, anterior tip of nuchal plate just posterior to dorsal margin of first dorsolateral body plate, and blotches on dorsal half of dorsolateral body plates and/or ventral half of ventrolateral body plates fused with midlateral series of blotches, forming three or four enlarged and oblique black blotches.

A new species of Groenlandaspis Heintz, 1932 (Placodermi, Arthrodira), from the Famennian (Late Devonian) of Belgium

ABSTRACTA new species of the phlyctaeniid arthrodire genus Groenlandaspis from the upper Famennian of Belgium is described. The remains of Groenlandaspis potyi, sp. nov., consist of dissociated thoracic armor elements, but the specimen designated to be the holotype displays the median dorsal, anterior, and posterior dorsolateral plates in articulation. Though incomplete, the new species is characterized by an equilateral triangle-shaped median dorsal plate, a protruding posterodorsal apron of the posterior dorsolateral plate behind the overlap area for the median dorsal plate, and an overall lack of ornamentation. Groenlandaspis potyi, sp. nov., constitutes the second occurrence of a Groenlandaspis species in continental Europe after the description of Groenlandaspis thorezi from upper Famennian quarries of Belgium. Another probable new species of Groenlandaspis is also described, though of unknown locality and horizon; it can, however, be deduced to be from the upper Famennian of Belgium without more precision. Together with some unpublished material of groenlandaspidids from the Famennian tetrapod-bearing locality of Strud, this material highlights the richness of Groenlandaspididae diversity in Belgium. The discovery of Groenlandaspis potyi, sp. nov., in Belgium reinforces the Famennian global distribution of this genus during this period. Also, because these organisms have been considered as non-marine indicators, this material is another argument pleading for close relationships between Euramerica and Gondwana around the Frasnian–Famennian boundary.http://zoobank.org/urn:lsid:zoobank.org:pub:500F0661-2638-4F26-9293-95B89AF0B39B

Pax8 and Pax2 are specifically required at different steps of Xenopus pronephros development

The respective role of Pax2 and Pax8 in early kidney development in vertebrates is poorly understood. In this report, we have studied the roles of Pax8 and Pax2 in Xenopus pronephros development using a loss-of-function approach. Our results highlight a differential requirement of these two transcription factors for proper pronephros formation. Pax8 is necessary for the earliest steps of pronephric development and its depletion leads to a complete absence of pronephric tubule. Pax2 is required after the establishment of the tubule pronephric anlage, for the expression of several terminal differentiation markers of the pronephric tubule. Neither Pax2 nor Pax8 is essential to glomus development. We further show that Pax8 controls hnf1b, but not lhx1 and Osr2, expression in the kidney field as soon as the mid-neurula stage. Pax8 is also required for cell proliferation of pronephric precursors in the kidney field. It may exert its action through the wnt/beta-catenin pathway since activation of this pathway can rescue MoPax8 induced proliferation defect and Pax8 regulates expression of the wnt pathway components, dvl1 and sfrp3. Finally, we observed that loss of pronephros in Pax8 morphants correlates with an expanded vascular/blood gene expression domain indicating that Pax8 function is important to delimit the blood/endothelial genes expression domain in the anterior part of the dorso-lateral plate.

Taxonomic revision of buchanosteoid placoderms (Arthrodira) from the Early Devonian of south-eastern Australia and Arctic Russia

The ‘buchanosteid’ placoderms are best known from the Early Devonian of Australia, but also occur in China, Russia, Central Asia and the Middle East. Here we rediagnose the type species Buchanosteus confertituberculatus (Hills 1936) from the type locality at Buchan, Victoria, in the light of new material of both head and trunk shields. The superfamily Buchanosteoidea Denison, 1978 is redefined to unite taxa that share a similar skull roof with separate rostro-pineal (ethmoid) bone, and postethmoid skull pattern characterised by a large trapezoidal nuchal, strap-like short and broad preorbitals, large subrectangular centrals, small postorbitals not contacting the paranuchals, and large, elongate marginal plates. The Family Buchanosteidae is redefined on skull roof and parasphenoid shape and trunk armour features as a monotypic family within the Buchanosteoidea. A new family (Parabuchanosteidae nov.) includes taxa with the posterior lateral plate overlapping the anterior dorsolateral plate externally. Two new buchanosteids are described, Richardosteus barwickorum gen. et sp. nov., from Burrinjuck, south-eastern Australia, and Urvaspis lithuanica gen. et sp. nov., from Severnaya Zemlya, Russia.

Origin of muscle satellite cells in the Xenopus embryo

We have studied the origin of muscle satellite cells in embryos of Xenopus laevis. Fate mapping at the open neural plate stage was carried out using orthotopic grafts from transgenic embryos expressing GFP. This shows that most satellite cells originate from the dorsolateral plate rather than from the paraxial mesoderm. Specification studies were made by isolation of explants from the paraxial and dorsolateral regions of neurulae and these also indicated that the satellite cell progenitors arise from the dorsolateral plate. Muscle satellite cells express Pax7, but overexpression of Pax7 in blastomeres of whole embryos that populate the myogenic areas does not induce the formation of additional satellite cells. Moreover, a dominant-negative construct, Pax7EnR, does not reduce satellite cell formation. Neither Pax7 nor other myogenic transcription factor genes will induce satellite cell formation in animal caps treated with FGF. However, BMP RNA or protein will do so, both for FGF-treated animal caps and for paraxial neurula explants. Conversely, the induction of Noggin in dorsolateral explants from HGEM-Noggin transgenic neurulae will block formation of satellite cells, showing that BMP signaling is required in vivo for satellite cell formation. We conclude that satellite cell progenitors are initially specified in the dorsal part of the lateral plate mesoderm and later become incorporated into the myotomes. The initial specification occurs at the neurula stage and depends on the ventral-to-dorsal BMP gradient in the early embryo.

A new antiarch fish from the Upper Devonian Zhongning Formation of Ningxia, China

A new antiarch, Ningxialepis spinosa n. gen. n. sp., is described from the Zhongning Formation (Famennian, Late Devonian) of Shixiagou, Qingtongxia, Ningxia, northwestern China. It is characterized by the presence of X-shaped pit-lines, long obstantic margins, high dorsal median spine of the trunk armour formed from the anterior and posterior median dorsal plates, prominent dorsolateral and ventrolateral ridges of the trunk armour, and the anterior median dorsal plate partly overlapping the anterior dorsolateral plate. Ningxialepis is placed as the sister taxon to Jiangxilepis in the Family Jiangxilepidae from South China, based on a phylogenetic analysis of the Euantiarcha. The Jiangxilepidae is redefined. The close affinity between Ningxialepis and Jiangxilepis further corroborates the geographic proximity between the North China and South China blocks in the Late Devonian.

A new Scleromystax species (Siluriformes: Callichthyidae) from coastal rivers of southern Brazil

The recently resurrected callichthyid catfish genus Scleromystax includes species occurring in several Brazilian coastal river basins from southern Bahia to southern Santa Catarina. Several character states, especially those related to sexual dimorphism, demonstrate the monophyly of Scleromystax. Examination of Scleromystax specimens sampled from streams in the Ilha de Santa Catarina and Nova Veneza, and the rio Mampituba basin, Santa Catarina and Rio Grande do Sul States, revealed that they constitute a new taxon, and thus the southernmost record for the genus. Scleromystax salmacis, new species, has coloration similar to that of S. macropterus, differing from that species mainly by the absence of a black spot on the base of the median caudal-fin rays, and transverse blotches along the body more irregular than those in S. macropterus. In addition to differences in coloration and external and osteological characters, the new species differs from S. barbatus and S. prionotos by its more rounded snout. The new taxon is also distinguished from its congeners by the presence of a single perforated dorsolateral body plate, similar to the condition found in some Aspidoras species, orientation of the ventral keel of the scapulocoracoid, and by the absence of sexually dimorphic features.

New phyllolepids (placoderm fishes) from the Middle-Late Devonian of southeastern Australia

ABSTRACT Phyllolepid placoderms from the Devonian Boyd Volcanic Complex on the south coast of New South Wales are described as Cobandrahlepis petyrwardi, gen. et sp. nov., and Yurammia browni, gen. et sp. nov. Both are more primitive than other described phyllolepids in retaining a posterior dorsolateral plate in the trunk armor. Cobandrahlepis resembles Placolepis Ritchie, 1984, in the shape of the nuchal plate in the skull, and Austrophyllolepis Long, 1984, in the more lateral position of the sensory groove on the paranuchal plate. Yurammia, gen. nov., differs from all other phyllolepids in lacking ridged ornament on the dermal bones. These new taxa add to the diversity of early members of the order Phyllolepida from East Gondwana, before the appearance of the genus Phyllolepis in the Northern Hemisphere during the last stage of the Late Devonian (Famennian). Phyllolepid placoderms, only recorded from non-marine deposits, have a unique disjunct distribution in both time and space between the Southern and Northern hemispheres. They document a major dispersal event indicating continental connection between Gondwana and Laurussia near the Frasnian-Famennian boundary, at about the time of the Late Devonian mass extinction.

A new Middle Devonian arthrodire (placoderm fish) from the Broken River area, Queensland

Associated bones of the trunk-armour belonging to a large brachythoracid arthrodire are described as Confractamnis johnjelli n.gen. and n.sp. The specimen comes from strata of probable Eifelian age in the Broken River Group of Queensland. It shows a range of derived brachythoracid features including reduction of dermal ornament, and strong development of the dermal neck joint articulation. The posterior dorsolateral and posterior lateral plates of the trunk armour were high and narrow, and the anterior lateral plate had a distinctive narrow bilobed dorsal angle as indicated by the shape of its overlap area on the anterior dorsolateral plate. A provisional reconstruction suggests that the bones came from a large fish over 2 m in length. A cross section of the trunk armour is compared with the large arthrodire Taemasosteus from the Early Devonian of Burrinjuck, New South Wales. A possible close relative of this new taxon has been illustrated from the Early Devonian of Morocco, supporting other indications of resemblance in placoderm fish assemblages between these regions of east and north Gondwana during the Early-Middle Devonian.

Essential role of HGF (hepatocyte growth factor) in blood formation in Xenopus

AbstractIn this study, we investigated the role of hepatocyte growth factor (HGF) in blood formation during Xenopus development. First, we examined the gene expression of HGF and its receptor, c-met, by whole-mount in situ hybridization during development. Strong signals of HGF as well as c-met were detected early in the developing ventral mesoderm, which later gives rise to the ventral blood island. Furthermore, to study the role of HGF, we blocked the HGF signaling pathway in Xenopus embryos by using truncated c-met lacking the tyrosine kinase domain. Injection of truncated c-met mRNA resulted in a marked decrease in the number of circulating blood cells. Similar results were obtained using morpholino antisense HGF oligonucleotides. Moreover, we also analyzed the expression of several early primitive blood markers in the blood island of these embryos. RNA in situ analysis revealed a significant reduction (or absence) of stem cell leukemia (SCL), α-globin, and GATA-1 expression, but not GATA-2 expression. In contrast, no significant difference was observed in the levels of expression of early definitive blood markers, SCL, GATA-2, and GATA-3 in the dorsolateral plate, as analyzed by in situ hybridization. Overall, the present study demonstrated that HGF is necessary for primitive hematopoiesis by regulating the expression of SCL. (Blood. 2004;103:3320-3325)

A homostiid arthrodire (placoderm fish) from the Early Devonian of the Burrinjuck area, New South Wales

Cavanosteus, a new genus of homostiid arthrodire, with C. australis (McCoy) as type species, is erected for new material from the Early Devonian (Emsian) of the Burrinjuck area, NSW. This new material compares closely with the holotype from Buchan, Victoria, identified as the central plates from the skull; it includes lower jawbones (infragnathals) lacking denticulation also closely similar to those of Homostius from the Middle Devonian of the Baltic Province and Scotland. The only bone from the dermal trunk armour referred to the new genus is an anterior dorsolateral plate. Relationships of other large Early Devonian arthrodires assigned to the family Homostiidae are discussed. Cavanosteus gen. nov. is probably the closest relative to the type genus known from the Early Devonian.

A new buchanosteid arthrodire (placoderm fish) from the Early Devonian of the Ural Mountains

ABSTRACT A new primitive brachythoracid arthrodire, Uralosteus bashkiricus gen. et sp. nov., is described from two Emsian (late Early Devonian) localities in the Ural Mountains of the Autonomous Republic of Bashkortostan, Russia. The holotype includes bones of the skull and trunk armor associated with numerous scales from one individual, which facilitates the study of isolated microremains. The dermal ornament of distinctive tuberculate ridges suggests a relationship to Errolosteus Young, 1981 from the Emsian of southeastern Australia, but neither form is well enough known for this to be strongly supported in a character analysis. Some isolated placoderm bones with ridged ornament from southeastern Australia are figured, and interpreted to belong to a new form of williamsaspid rather than to Errolosteus. The new genus Uralosteus is referred to the family Buchanosteidae, defined by a unique overlap arrangement of the posterior lateral onto the anterior dorsolateral plate of the trunk armor. Buchanosteids, as a basal brachythoracid group, are a key to understanding the phylogeny of that clade. The type genus Buchanosteus comes from southeastern Australia, but it is now evident that the family was widely distributed in shallow marine environments during the Emsian.

Contribution of Ventral and Dorsal Mesoderm to Primitive and Definitive Erythropoiesis in the Salamander Hynobius retardatus

Previously, we found that the conversion of hemoglobins (Hbs) from the larval to the adult type occurred within a single erythroid cell population in a salamander, Hynobius retardatus (“Hb switching” model), whereas the transition involves replacement of red-blood-cell (RBC) populations (“RBC replacement” model) in many amphibians (M. Yamaguchi, H. Takahashi, and M. Wakahara, 2000, Dev. Gene Evol. 210, 180–189). To further characterize the Hb transition, developmental changes in the erythropoietic sites have been intensively analyzed using larval- and adult-specific globin antibodies and globin and GATA-3 RNA probes. Cells of the ventral blood island (VBI) and the dorsolateral plate (DLP) in embryos differentiate in situ to erythroid cells that contain larval globin mRNA, suggesting that both the VBI and the DLP contribute to “primitive” erythropoiesis. In contrast, the expression pattern of the GATA-3 gene suggests that cells of the DLP may contribute to “definitive” hematopoiesis. In order to determine whether it is possible to define a definitive erythropoiesis in H. retardatus or not, further experiments were done: (1) when metamorphosing larvae were treated with phenylhydrazine to induce anemia and then bled at the postmetamorphic stage after recovery from the anemia, a precocious Hb transition was observed in these animals; (2) an RBC population expressing only adult Hb was confirmed by subtracting the number of RBCs expressing larval Hb from the total number of RBCs during metamorphosis. All these results support the existence of a definitive erythroid cell population that contributes only adult RBCs in this species.

Embryonic sources of definitive hemopoietic stem cells

A review of one of the key problems of experimental hematology: the origin of hemopoietic stem cells in the development of vertebrates (amphibians, birds, and mammals). The appearance and functioning of two independent sources of hemopoietic stem cells (extra- and intraembryonic) were considered in amphibians, birds, and mammals. The contribution of each source to the formation of definitive hemopoietic tissue was analyzed. It was shown for amphibians and birds that intraembryonic organs such as the dorsolateral plate and the mesenchyme of dorsal aorta are involved in the formation of adult hemopoietic tissue, while the extraembryonic organs such as ventral islets and the yolk sac are devoid of true stem cells and provide only for the primary, transient hemopoiesis. New data have been considered concerning the previously unknown intraembryonic hemopoietic organ in mammals, a region of aorta-gonad-mesonephros arising in embryogenesis simultaneously with the yolk sac. Two extreme views on the involvement of stem cells of all these organs in the formation of definitive hemopoiesis have been considered. The data are provided on the interaction of the embryonic hemopoietic stem cells and the hemopoietic microenvironment of adult recipients.

Erythropoiesis and unexpected expression pattern of globin genes in the salamander Hynobius retardatus.

Transition of hemoglobin (Hb) from larval to adult types during the metamorphosis in a salamander Hynobius retardatus has been reported to occur almost independently of thyroid activity, in contrast to the case with many amphibians. In order to obtain further information on the mechanism of the transition in H. retardatus, larval and adult globin cDNAs were cloned, and the globin gene expression was analyzed in normally developing and metamorphosis-arrested animals. Northern hybridization and RT-PCR revealed that larval globin genes were initially expressed 5 days before hatching, and unexpectedly remained expressed even in juveniles 2 years old. The adult globin gene was expressed 19 days after hatching, much earlier than the initiation of morphological metamorphosis. Furthermore, the pattern of globin gene expression in metamorphosis-arrested larvae was almost identical to that in normal controls, suggesting that the transition occurs independently of thyroid hormones. In larvae recovering from anemia, precocious Hb transition, which occurs in Xenopus laevis and Rana catesbeiana, did not occur in H. retardatus. In situ hybridization convincingly demonstrated that the erythropoietic sites are the ventral blood island and the dorsolateral plate at the prehatching stage. During the ontogeny they changed to the liver, kidney, and spleen and were finally restricted to the spleen. Single erythroid cells expressed concurrently larval and adult globin genes, as demonstrated by double in situ hybridization. Thus the transition occurred within a single erythroid cell population, a unique characteristic of H. retardatus.

Genomic structure and embryonic expression of the Xenopus winged helix factors XFD-13/13′

We have isolated the gene, its corresponding cDNA and a closely related cDNA encoding the Xenopus winged helix factors XFD-13′ and XFD-13, respectively. XFD-13/13′ are regarded as pseudo-alleles and, based upon a comparison of sequences and genomic structures, represent the Xenopus orthologues to mammalian FREAC-1/HFH-8. XFD-13/13′ genes are not transcribed during oogenesis, zygotic transcription starts at late gastrula/early neurula and transcripts persist throughout embryogenesis. Expression is found within head derived neural crest cells and the dorsolateral plate (DLP). At later developmental stages, cell populations of the DLP migrate to the ventral region but exclude the most posterior part. Since they are subsequently found to accumulate in vessel like structures, we suggest that these cells represent hematopoietic/endothelial progenitor cells.

GATA factors and the origins of adult and embryonic blood in Xenopus: responses to retinoic acid

The transcription factors, GATA-1, -2 and -3 play essential roles in the differentiation of haematopoietic cells. To study the process of blood formation during vertebrate development we have used the expression of these GATA factors to locate haematopoietic cells in Xenopus embryos and to act as sensors for the effects of all-trans retinoic acid (RA), a signalling molecule which influences both anteroposterior patterning and haematopoietic differentiation. GATA factor expression was detected in the leading edge of the gastrulating mesoderm, in the ventral blood island (VBI) and dorsolateral plate (DLP) mesoderms and in a population of cells between the VBI and DLP. The VBI contributes to both embryonic and adult blood, whereas the DLP contains precursors of adult blood only, which have not been identified previously with molecular markers. The possibility that the GATA-2-expressing cells between the VBI and DLP were haematopoietic progenitors migrating from the VBI to the DLP was ruled out by transplantation analysis. Differential effects of RA on the expression of GATA-1 and GATA-2 suggest that RA has a direct action on haematopoietic differentiation, rather than on the formation of haematopoietic mesoderm.