A reconsideration of the origins of the 'typical' Cretaceous inoceramid calcitic hinge plate in the light of new ultrastructural observations from some Jurassic 'inoceramids'

Abstract:  Marked differences occur between the hinge plates of Jurassic and Upper Cretaceous British 'inoceramid' species. Albian and Upper Cretaceous inoceramids had the poiriform calcite hinge plate with closely spaced resiliifers that is widely associated with this extinct bivalve family. The whole structure was dominated by compressible ligament. Jurassic species, in contrast, had an ultrastructurally less familiar aragonite hinge plate with widely spaced resiliifers and a ligament reminiscent of Isognomon with equally spaced elastic and compressional components. The wider taxonomic relationships of the Inoceramidae still remain uncertain, although the majority of the evidence links the family to the Pterioida. This study, however, suggests that the ancestral inoceramid did not necessarily have a calcitic hinge plate, but rather that a Jurassic 'inoceramid' species could have been developing such a structure via an aragonite precursor. Observations on British Kimmeridgian 'inoceramid' specimens indicate that calcite was being incorporated into the aragonite hinge plate by these times. Structures in the ligamentat of Jurassic species suggest that the fundamental change in mineralogy was initiated by valve architectural modification at the byssal notch, linked to inoceramid epifaunalism. Worldwide poor preservation of Lower Cretaceous inoceramids makes it very difficult to further prove this hypothesis via intermediate evolutionary stages leading to the fully poiriform calcite hinge plate observed in Albian and Upper Cretaceous species of Inoceramidae.     

The gastrocoel roof plate in embryos of different frogs

The morphology of the gastrocoel roof plate and the presence of cilia in this structure were examined in embryos of four species of frogs. Embryos of Ceratophrys stolzmanni (Ceratophryidae) and Engystomops randi (Leiuperidae) develop rapidly, provide comparison for the analysis of gastrocoel roof plate development in the slow-developing embryos of Epipedobates machalilla (Dendrobatidae) and Gastrotheca riobambae (Hemiphractidae). Embryos of the analyzed frogs develop from eggs of different sizes, and display different reproductive and developmental strategies. In particular, dorsal convergence and extension and archenteron elongation begin during gastrulation in embryos of rapidly developing frogs, as in Xenopus laevis. In contrast, cells that involute during gastrulation are stored in the large circumblastoporal collar that develops around the closed blastopore in embryos of slow-developing frogs. Dorsal convergence and extension only start after blastopore closure in slow-developing frog embryos. However, in the neurulae, a gastrocoel roof plate develops, despite the accumulation of superficial mesodermal cells in the circumblastoporal collar. Embryos of all four species develop a ciliated gastrocoel roof plate at the beginning of neurulation. Accordingly, fluid-flow across the gastrocoel roof plate is likely the mechanism of left-right asymmetry patterning in these frogs, as in X. laevis and other vertebrates. A ciliated gastrocoel roof plate, with a likely origin as superficial mesoderm, is conserved in frogs belonging to four different families and with different modes of gastrulation.     

Physiology and pathophysiology of the growth plate

Longitudinal growth of the skeleton is a result of endochondral ossification that occurs at the growth plate. Through a sequential process of cell proliferation, extracellular matrix synthesis, cellular hypertrophy, matrix mineralization, vascular invasion, and eventually apoptosis, the cartilage model is continually replaced by bone as length increases. The regulation of longitudinal growth at the growth plate occurs generally through the intimate interaction of circulating systemic hormones and locally produced peptide growth factors, the net result of which is to trigger changes in gene expression by growth plate chondrocytes. This review highlights recent advances in genetics and cell biology that are illuminating the important regulatory mechanisms governing the structure and biology of the growth plate, and provides selected examples of how studies of human mutations have yielded a wealth of new knowledge regarding the normal biology and pathophysiology of growth plate cartilage.     

Changes in leucine-rich repeat proteoglycans during maturation of the bovine growth plate

The primary growth plate of the fetal bovine tibia was studied in order to determine whether changes in the structure, abundance and expression of the leucine-rich repeat proteoglycans were occurring during tissue maturation from reserve cartilage to hypertrophic cartilage. The proteoglycans under study were decorin, biglycan, fibromodulin and lumican. Decorin was readily detectable in both the reserve and proliferating zones of the growth plate, but its abundance decreased markedly in the zones of maturation and hypertrophy where it could not be detected under the same conditions of analysis. In contrast to decorin, fibromodulin and biglycan could be detected throughout the growth plate, though their abundance was decreased in the proliferative and hypertrophic zones. Unlike the other proteoglycans, lumican could not be detected throughout the growth plate. At the message level, the expression of decorin shows a similar trend to that of protein abundance in the extracellular matrix, with its expression dropping markedly in the proliferative and hypertrophic zones. In the case of both biglycan and fibromodulin, message expression continued at a similar level throughout the growth plate. Thus, the leucine-rich repeat proteoglycans are different in the way they behave during growth plate maturation.     

High lipid order of Arabidopsis cell‐plate membranes mediated by sterol and DYNAMIN‐RELATED PROTEIN1A function

Membranes of eukaryotic cells contain high lipid‐order sterol‐rich domains that are thought to mediate temporal and spatial organization of cellular processes. Sterols are crucial for execution of cytokinesis, the last stage of cell division, in diverse eukaryotes. The cell plate of higher‐plant cells is the membrane structure that separates daughter cells during somatic cytokinesis. Cell‐plate formation in Arabidopsis relies on sterol‐ and DYNAMIN‐RELATED PROTEIN1A (DRP1A)‐dependent endocytosis. However, functional relationships between lipid membrane order or lipid packing and endocytic machinery components during eukaryotic cytokinesis have not been elucidated. Using ratiometric live imaging of lipid order‐sensitive fluorescent probes, we show that the cell plate of Arabidopsis thaliana represents a dynamic, high lipid‐order membrane domain. The cell‐plate lipid order was found to be sensitive to pharmacological and genetic alterations of sterol composition. Sterols co‐localize with DRP1A at the cell plate, and DRP1A accumulates in detergent‐resistant membrane fractions. Modifications of sterol concentration or composition reduce cell‐plate membrane order and affect DRP1A localization. Strikingly, DRP1A function itself is essential for high lipid order at the cell plate. Our findings provide evidence that the cell plate represents a high lipid‐order domain, and pave the way to explore potential feedback between lipid order and function of dynamin‐related proteins during cytokinesis.     

Internal micromorphology of the frons plate in females of the oriental hornet

Scanning electron microscopy and energy dispersive x-ray analysis (SEM/EDS) have been used to study the internal micromorphology of the frons plate in the Oriental hornet, Vespa orientalis. A conical shaped organ was described which is recessed into the frons plate and projects toward the interior of the acoustic box. The latter is located on the inner side of the frons plate. On the exterior of the conical region are observed aggregates containing Ca and Si, and a thin transparent membrane bearing a hole in its center. The innermost surface of the conical structure terminates bluntly as a convex lentiform tip, bearing a transparent oval-shaped window in its center. The conical organ, excepting the window, is enclosed in several layers of epithelium. The structure of this many-layered conical organ is highly complex; its numerous sub-structures and the possible role as a gravity sense organ are discussed. © 1993 Wiley-Liss, Inc.     

Simultaneous visualization of the actin plate and new cell partition membrane during cytokinesis in the brown alga Sphacelaria rigidula (Sphacelariales,Phaeophyceae)

In many brown algae, cytokinesis is accomplished through the centrifugal expansion of the membrane structure formed by the fusion of Golgi vesicles and flat cisternae. In contrast, it has been reported that cytokinesis in Sphacelaria rigidula progresses centripetally by adding Golgi vesicles and flat cisternae to cleaving furrows of the plasma membrane. The reason why this cytokinetic pattern was observed only in Sphacelaria species is unknown. In either cytokinesis pattern, a plate-like actin structure (the actin plate) coincides with the cytokinetic plane between the daughter nuclei. However, it is unclear how the actin plate is related to cytokinesis progression. In this study, we re-examined cytokinesis in the apical cells of S. rigidula using transmission electron microscopy. Double staining of the actin plate and the developing membrane was followed by fluorescence microscopy analysis to determine the relationship between these two formations. The results showed that cytokinesis in S. rigidula, as in many brown algae, was completed by centrifugal growth of the new cell partition membrane. A furrow of the plasma membrane was observed at the beginning of cytokinesis; however, further invagination did not occur. The actin plate arose at the center of the cytokinetic plane before membrane fusion and extended parallel to the expansion of the new cell partition membrane. When cytokinesis was slow due to insufficient Golgi vesicle supply to the cytokinetic plane in the cells under brefeldin A treatment, the extension of the actin plate was also suspended. In this study, the spatiotemporal relationship between the occurrence and expansion of the actin plate and the new cell partition membrane was revealed. These observations indicate that the actin plate might promote membrane fusion or lead to the growth of a new cell partition membrane.     

Bovine floor plate explants secrete SCO-spondin

SCO-spondin is a large-molecular mass glycoprotein, secreted by the subcommissural organ (SCO), which has been implicated in neuronal development during ontogeny of the central nervous system. The expression of SCO-spondin is not restricted to the SCO but it also occurs in the floor plate, a key structure participating in neuronal differentiation and patterning of the neural tube. It has been postulated that SCO-spondin detected in the floor plate is released into the lumen of the neural tube, but this new route of secretion of floor plate cells needs to be further substantiated. For this purpose, we standardized long-term organ culture of bovine floor plate and performed morphological, immunological, biochemical, and gene expression analyses. The study of floor plate explants and their conditioned media allowed us to demonstrate that: (1) organ-cultured floor plate cells are actively secretory for up to 25 days; (2) SCO-spondin gene is actively transcribed and translated by the cultured floor plate cells; (3) SCO-spondin is released into the culture medium via the apical cell pole; and (4) upon release, SCO-spondin does not aggregate in the conditioned medium but remains soluble. Furthermore, in the cultured floor plate cells, SCO-spondin may be secreted through a route bypassing the Golgi apparatus.     

Evaluation of a new character for the phylogenetic analysis of Ostracoda (Crustacea): the podocopan maxillular branchial plate

A data set of the number of setae on the maxillular branchial plate of podocopan ostracods was compiled from published drawings and our own dissections. A total of 168 species in six superfamilies were covered, with the Cytheroidea, Cypridoidea and Bairdioidea being best represented. The number of setae is shown to be independent of the size of the ostracod and the environment in which the species lives, but to have phylogenetic significance at superfamily level. Ontogenetic data suggest that the low number of branchial plate setae in many cytheroidean families is a paedomorphic phenomenon.     

Force plate for measuring the ground reaction forces in small animal locomotion

The importance of kinetic force plate studies of locomotion in small animals has grown recently with the increasing use of rodent models for studies of musculoskeletal diseases. However, the force plates for use with animals much smaller than a cat are difficult to design and use. Here we present data on a commercially available small force plate that accurately collects whole-body and, in a modified form, single-limb ground reaction forces in mice. The method used here is convenient, inexpensive, and readily adaptable for use with a variety of small species.     

Caffeine inhibition of cytokinesis: Dynamics of cell plate formation-deformationin vivo

Summary The effect of caffeine on cell plate formation inTradescantia stamen hair cells has been studiedin vivo using Nomarski differential interference contrast microscopy. It is well known that caffeine is a potent inhibitor of cell plate formation. Direct examination of drug-treated cells reveals that the cell plate always arises and grows centrifugally until almost complete. Up to this point drug-treated cells are indistinguishable from controls. However in the presence of caffeine the plate never reaches completion but rather appears to melt away until no refractile structure remains. Even after cells have been cultured for 24 hours in caffeine a cell plate always arises only to subsequently break down. Studies on the time of caffeine action show that within minutes before the onset of cell plate formation, the drug efficiently reaches the target site. This effect is partially reversible by washing out the caffeine with HEPES/KCl buffer, however the time required for the cell plate to reach completion is prolonged and in some instances the plate appears to be fragmented. Adenosine is also partially effective in reversing the caffeine inhibition of cell plate formation.     

Structure of lateral-line scales in representatives of families of the order pleuronectiformes

Structure of nonmodified scales and lateral-line scales (Sll) is compared in 179 species of 105 genera of 13 families of the order Pleuronectiformes. Morphological diversity of Sll depends on the level of development and of interaction of two component parts—the scale plate and the tubular part. Of the considered characters, the most individually variable character is whether the tubular part is complete or incomplete. The interspecies differences may manifest themselves in structure of the scale plate, the level of unification of opening of the tubular part and of the cutaneous canaliculus, or in completeness or incompleteness of the tubular part. As a rule, Sll in species of the same genus is similar in structure. In some cases, special traits of this structure may be diagnostic characters of genera and contribute to the solution of controversial issues of generic position of species. The families of Pleuronectiformes are characterized by a different ratio of taxa with certain involved characters of nonmodified scales and Sll. However, their distribution in this order does not give a simple idea on their relationships and on the direction of evolutionary transformations. This follows from the fact that the structure of Sll depends on a wide complex of factors—morphogenesis of nonmodified scales, level of ossification of trunk canal, time of anlage, and mutual influence of these structures at early stages of ontogenesis.     

Response properties of motion-sensitive visual interneurons in the lobula plate of Drosophila melanogaster

The crystalline-like structure of the optic lobes of the fruit fly Drosophila melanogaster has made them a model system for the study of neuronal cell-fate determination, axonal path finding, and target selection. For functional studies, however, the small size of the constituting visual interneurons has so far presented a formidable barrier. We have overcome this problem by establishing in vivo whole-cell recordings from genetically targeted visual interneurons of Drosophila. Here, we describe the response properties of six motion-sensitive large-field neurons in the lobula plate that form a network consisting of individually identifiable, directionally selective cells most sensitive to vertical image motion (VS cells). Individual VS cell responses to visual motion stimuli exhibit all the characteristics that are indicative of presynaptic input from elementary motion detectors of the correlation type. Different VS cells possess distinct receptive fields that are arranged sequentially along the eye's azimuth, corresponding to their characteristic cellular morphology and position within the retinotopically organized lobula plate. In addition, lateral connections between individual VS cells cause strongly overlapping receptive fields that are wider than expected from their dendritic input. Our results suggest that motion vision in different dipteran fly species is accomplished in similar circuitries and according to common algorithmic rules. The underlying neural mechanisms of population coding within the VS cell network and of elementary motion detection, respectively, can now be analyzed by the combination of electrophysiology and genetic intervention in Drosophila.     

Endocrine regulation of the growth plate

Longitudinal bone growth occurs at the growth plate by endochondral ossification. Within the growth plate, chondrocyte proliferation, hypertrophy, and cartilage matrix secretion result in chondrogenesis. The newly formed cartilage is invaded by blood vessels and bone cells that remodel the newly formed cartilage into bone tissue. This process of longitudinal bone growth is governed by a complex network of endocrine signals, including growth hormone, insulin-like growth factor I, glucocorticoid, thyroid hormone, estrogen, androgen, vitamin D, and leptin. Many of these signals regulate growth plate function, both by acting locally on growth plate chondrocytes and also indirectly by modulating other endocrine signals in the network. Some of the local effects of hormones are mediated by changes in paracrine factors that control chondrocyte proliferation and differentiation. Many human skeletal growth disorders are caused by abnormalities in the endocrine regulation of the growth plate. This review provides an overview of the endocrine signals that regulate longitudinal bone growth, their interactions, and the mechanisms by which they affect growth plate chondrogenesis.     

A force plate study of avian gait

OBJECTIVE: To test the force plate as a gait analysis system for broilers and to determine how the ground reaction force (GRF) patterns change in these birds with growth and administration of analgesia. MATERIALS AND METHODS: Thirty-three male Ross 308 chicks were raised on either an ad libitum or restricted-feeding regime, and subsequently treated with carprofen or a placebo. Vertical, craniocaudal and mediolateral GRFs were measured as the birds walked across a standard force plate. RESULTS: The data were easy to collect, and peak vertical forces of an equivalent percentage of bodyweight as seen in human walking were identified. Mediolateral forces were 2-3 times greater than those demonstrated in other species. GRF patterns showed significant changes during growth, but analgesia did not have a significant effect on the speed of walking, or GRF patterns. CONCLUSIONS AND CLINICAL RELEVANCE: The force plate is a suitable research tool for recording GRFs from avian bipeds. The large mediolateral forces identify a particularly inefficient aspect of avian gait; however, the role of pain remains to be determined.     

Endocytosis of cell surface material mediates cell plate formation during plant cytokinesis

Dividing plant cells perform a remarkable task of building a new cell wall within the cytoplasm in a few minutes. A long-standing paradigm claims that this primordial cell wall, known as the cell plate, is generated by delivery of newly synthesized material from Golgi apparatus-originated secretory vesicles. Here, we show that, in diverse plant species, cell surface material, including plasma membrane proteins, cell wall components, and exogenously applied endocytic tracers, is rapidly delivered to the forming cell plate. Importantly, this occurs even when de novo protein synthesis is blocked. In addition, cytokinesis-specific syntaxin KNOLLE as well as plasma membrane (PM) resident proteins localize to endosomes that fuse to initiate the cell plate. The rate of endocytosis is strongly enhanced during cell plate formation, and its genetic or pharmacological inhibition leads to cytokinesis defects. Our results reveal that endocytic delivery of cell surface material significantly contributes to cell plate formation during plant cytokinesis.     

Regeneration of the growth plate

The occurrence of growth plate regeneration has been doubted. However, in 5 different series of experiments reported between 1950 and 1986 regeneration of injured parts of growth plates in long bones of rabbits and pigs could be demonstrated. The 1st series implied partial X-ray injury of growth plates in rabbits aged 3-6 weeks. The 2nd series implied autotransplantation of the head of the fibula in rabbits aged 10-21 days. The 3rd, 4th and 5th series implied transplantation of autologous fat grafts into provoked defects of growth plates in rabbits and pigs. The findings show that regeneration of a growth plate occurs when a part of it is injured in such a manner that a bone bridge is not formed between the epiphysis and the metaphysis. Regeneration of a plate is much faster in relation to the growth in length of the bone in the rabbit than in the pig. The 1st and 2nd series suggest that regeneration takes place by interstitial proliferation of cells from the germinal layer of the uninjured parts of the plate. Signs of partial regeneration of growth plates have been seen in radiographs after operation for partial closure of growth plates in children.     

Relating the chondrocyte gene network to growth plate morphology: from genes to phenotype

During endochondral ossification, chondrocyte growth and differentiation is controlled by many local signalling pathways. Due to crosstalks and feedback mechanisms, these interwoven pathways display a network like structure. In this study, a large-scale literature based logical model of the growth plate network was developed. The network is able to capture the different states (resting, proliferating and hypertrophic) that chondrocytes go through as they progress within the growth plate. In a first corroboration step, the effect of mutations in various signalling pathways of the growth plate network was investigated.     

Spatiotemporal distribution of heparan sulfate epitopes during murine cartilage growth plate development

Heparan sulfate proteoglycans (HSPGs) are abundant in the pericellular matrix of both developing and mature cartilage. Increasing evidence suggests the action of numerous chondroregulatory molecules depends on HSPGs. In addition to specific functions attributed to their core protein, the complexity of heparan sulfate (HS) synthesis provides extraordinary structural and functional heterogeneity. Understanding the interactions of chondroregulatory molecules with HSPGs and their subsequent outcomes has been limited by the absence of a detailed analysis of HS species in cartilage. In this study, we characterize the distribution and variety of HS species in developing cartilage of normal mice. Cryo-sections of femur and tibia from normal mouse embryos were evaluated using immunostaining techniques. A panel of unique phage display antibodies specific to particular HS species were employed and visualized with secondary antibodies conjugated to Alexa-fluor dyes. Confocal microscopy demonstrates that HS species are dynamic structures within developing growth plate cartilage and the perichondrium. GlcNS6S-IdoUA2S-GlcNS6S species are down regulated and localization of GlcNS6S-IdoUA-GlcNS6S species within the hypertrophic zone of the growth plate is lost during normal development. Regional differences in HS structures are present within developing growth plates, implying that interactions with and responses to HS-binding proteins also may display regional specialization.