Hydrodynamic stress and phenotypic plasticity of the zebrafish regenerating fin

Understanding how extrinsic factors modulate genetically encoded information to produce a specific phenotype is of prime scientific interest. In particular, the feedback mechanism between abiotic forces and locomotory organs during morphogenesis to achieve efficient movement is a highly relevant example of such modulation. The study of this developmental process can provide unique insights on the transduction of cues at the interface between physics and biology. Here, we take advantage of the natural ability of adult zebrafish to regenerate their amputated fins to assess its morphogenic plasticity upon external modulations. Using a variety of surgical and chemical treatments, we are able to induce phenotypic responses to the structure of the fin. Through the ablation of specific rays in regenerating caudal fins, we generate artificially narrowed appendages in which the fin cleft depth and the positioning of rays bifurcations are perturbed compared to normal regenerates. To dissect the role of mechanotransduction in this process, we investigate the patterns of hydrodynamic forces acting on the surface of a zebrafish fin during regeneration by using particle tracking velocimetry on a range of biomimetic hydrofoils. This experimental approach enables us to quantitatively compare hydrodynamic stress distributions over flapping fins of varying sizes and shapes. As a result, viscous shear stress acting on the distal margin of regenerating fins and the resulting internal tension are proposed as suitable signals for guiding the regulation of ray growth dynamics and branching pattern. Our findings suggest that mechanical forces are involved in the fine-tuning of the locomotory organ during fin morphogenesis.

Hydrodynamic stress and phenotypic plasticity of the zebrafish regenerating fin

Understanding how extrinsic factors modulate genetically encoded information to produce a specific phenotype is of prime scientific interest. In particular, the feedback mechanism between abiotic forces and locomotory organs during morphogenesis to achieve efficient movement is a highly relevant example of such modulation. The study of this developmental process can provide unique insights on the transduction of cues at the interface between physics and biology. Here, we take advantage of the natural ability of adult zebrafish to regenerate their amputated fins to assess its morphogenic plasticity upon external modulations. Using a variety of surgical and chemical treatments, we are able to induce phenotypic responses to the structure of the fin. In particular, fin cleft depth and the bifurcation of the bony rays are modulated by the surface area of the stump. To dissect the role of mechanotransduction in this process, we investigate the patterns of hydrodynamic forces acting on the surface of a zebrafish fin during regeneration by using particle tracking velocimetry on a range of biomimetic hydrofoils. This experimental approach enables us to quantitatively compare hydrodynamic stress distributions over flapping fins of varying sizes and shapes. As a result, viscous shear stress acting on the tip of the fin and the resulting internal tension are proposed as suitable signals for guiding the regulation of ray growth dynamics and branching pattern. Our findings suggest that mechanical forces are involved in the fine-tuning of the locomotory organ during fin morphogenesis.

Comparative genomic analysis of the secondary flagellar (flag-2) system in the order Enterobacterales

Background The order Enterobacterales encompasses a broad range of metabolically and ecologically versatile bacterial taxa, most of which are motile by means of peritrichous flagella. Flagellar biosynthesis has been linked to a primary flagella locus, flag -1, encompassing ~ 50 genes. A discrete locus, flag -2, encoding a distinct flagellar system, has been observed in a limited number of enterobacterial taxa, but its function remains largely uncharacterized. Results and Discussion Comparative genomic analyses showed that orthologous flag -2 loci are present in 592/4,028 taxa belonging to 5/8 and 31/76 families and genera, respectively, in the order Enterobacterales. Furthermore, the presence of only the outermost flag- 2 genes in many taxa suggests that this locus was far more prevalent and has subsequently been lost through gene deletion events. The flag -2 loci range in size from ~3.4 to 81.1 kilobases and code for between five and 102 distinct proteins. The discrepancy in size and protein number can be attributed to the presence of cargo gene islands within the loci. Evolutionary analyses revealed a complex evolutionary history for the flag -2 loci, representing ancestral elements in some taxa, while showing evidence of recent horizontal acquisition in other enterobacteria. Conclusions The flag -2 flagellar system is a fairly common, but highly variable feature among members of the Enterobacterales. Given the energetic burden of flagellar biosynthesis and functioning, the prevalence of a second flagellar system suggests it plays important biological roles in the enterobacteria and we postulate on its potential role as locomotory organ or as secretion system.

Comparative genomic analysis of the secondary flagellar (flag-2) system in the order Enterobacterales

Background The order Enterobacterales encompasses a broad range of metabolically and ecologically versatile bacterial taxa, most of which are motile by means of peritrichous flagella. Flagellar biosynthesis has been linked to a primary flagella locus, flag -1, encompassing ~ 50 genes. A discrete locus, flag -2, encoding a distinct flagellar system, has been observed in a limited number of enterobacterial taxa, but its function remains largely uncharacterized.Results and Discussion Comparative genomic analyses showed that orthologous flag -2 loci are present in 592/4,028 taxa belonging to 5/8 and 31/76 families and genera, respectively, in the order Enterobacterales. Furthermore, the presence of only the outermost flag- 2 genes in many taxa suggests that this locus was far more prevalent and has subsequently been lost through gene deletion events. The flag -2 loci range in size from ~3.4 to 81.1 kilobases and code for between five and 102 distinct proteins. The discrepancy in size and protein number can be attributed to the presence of cargo gene islands within the loci. Evolutionary analyses revealed a complex evolutionary history for the flag -2 loci, representing ancestral elements in some taxa, while showing evidence of recent horizontal acquisition in other enterobacteria.Conclusions The flag -2 flagellar system is a fairly common, but highly variable feature among members of the Enterobacterales. Given the energetic burden of flagellar biosynthesis and functioning, the prevalence of a second flagellar system suggests it plays important biological roles in the enterobacteria and we postulate on its potential role as locomotory organ or as secretion system.

Comparative genomic analysis of the secondary flagellar (flag-2) system in the order Enterobacterales

Background The order Enterobacterales encompasses a broad range of metabolically and ecologically versatile bacterial taxa, most of which are motile by means of peritrichous flagella. Flagellar biosynthesis has been linked to a primary flagella locus, flag -1, encompassing ~ 50 genes. A discrete locus, flag -2, encoding a distinct flagellar system, has been observed in a limited number of enterobacterial taxa, but its function remains largely uncharacterized.Results and Discussion Comparative genomic analyses showed that orthologous flag -2 loci are present in 592/4,028 taxa belonging to 5/8 and 31/76 families and genera, respectively, in the order Enterobacterales. Furthermore, the presence of the outermost flag- 2 genes only in many taxa suggest that this locus was far more prevalent and has subsequently been lost through gene deletion events. The flag -2 loci range in size from ~3.4 to 81.1 kilobases and code for between five and 102 distinct proteins. The discrepancy in size and protein number can be attributed to the presence of cargo gene islands within the loci. Evolutionary analyses revealed a complex evolutionary history for the flag -2 loci, representing ancestral elements in some taxa, while showing evidence of recent horizontal acquisition in other enterobacteria.Conclusions The flag -2 flagellar system is a relatively common, but highly variable feature among members of the Enterobacterales. Given the energetic burden of flagellar biosynthesis and functioning, the prevalence of a second flagellar system suggests it plays important biological roles in the enterobacteria and we postulate on its potential role as locomotory organ or as secretion system.

Understanding form and function of the stem in early flattened echinoderms (pleurocystitids) using a microstructural approach

Pleurocystitid rhombiferans are among the most unusual echinoderms whose mode of life has been long debated. These echinoderms are usually interpreted as vagile epibenthic echinoderms, moving over the sea bottom by means of a flexible stem. Although their life habits and posture are reasonably well understood, the mechanisms that control the movement of stem are highly controversial. Specifically, it is unknown whether the stem flexibility was under the control of muscles or ligamentary mutable collagenous tissues (MCTs). Here, we reconstruct palaeoanatomy of the two Ordovician pleurocystitid rhombiferans (PleurocystitesandAmecystis) based on stereom microstructure. We show that the articular facets of columnals in pleurocystitid rhombiferans are composed of fine labyrinthic stereom. Comparison with modern echinoderms suggests that this type of stereom was associated with muscles implying that their stem was a muscular locomotory organ supporting an active mode of life.

Corticotropin-Releasing Factor Is Cytoprotective in Xenopus Tadpole Tail: Coordination of Ligand, Receptor, and Binding Protein in Tail Muscle Cell Survival

Upon metamorphosis, amphibian tadpoles lose their tails through programmed cell death induced by thyroid hormone (T3). Before transformation, the tail functions as an essential locomotory organ. The binding protein for the stress neuropeptide corticotropin-releasing factor (CRF; CRF-BP) is strongly up-regulated in the tail of Xenopus tadpoles during spontaneous or T3-induced metamorphosis. This finding led us to investigate physiological roles for CRF and CRF-BP in tadpole tail. We found CRF, CRF-BP, and functional CRF1 receptor in tail and CRF and functional CRF1 receptors, but not CRF-BP, in the tail muscle-derived cell line XLT-15. CRF, acting via the CRF1 receptor, slowed spontaneous tail regression in explant culture and caused a reduction in caspase 3/7 activity. CRF increased, but stable CRF-BP overexpression decreased, [3H]thymidine incorporation in XLT-15 cells. Overexpression of CRF-BP in vivo accelerated the loss of tail muscle cells during spontaneous metamorphosis. Lastly, exposure of tail explants to hypoxia increased CRF and urocortin 1 but strongly decreased CRF-BP mRNA expression. We show that CRF is expressed in tadpole tail, is up-regulated by environmental stressors, and is cytoprotective. The inhibitory binding protein for CRF is regulated by hormones or by environmental stressors and can modulate CRF bioactivity.

The development of Neomenia carinata Tullberg (Mollusca Aplacophora)

The chance finding of a single adult specimen of the solenogastre Neomenia carinata Tullberg 1875 rendered possible an embryological study of this species. Little is known concerning the ontogeny of the Aplacophora and a number of important questions, such as the fate of the larval test, the nature of the abapical depression visible during gastrulation and the presence or absence of any evidence of metamery, remain to be elucidated. Embryos, larvae and post-larvae were maintained in laboratory culture a t 10 °C. No description can be given of the early cleavage stages since the eggs when found were always well advanced. Each egg is enclosed by a single membrane. Gastrulation begins on the second day, by a process of immigration of the abapical cells; the abapical depression, often called a blastopore, is shown to be of an unusual character and is to be referred to as a pseudo -blastopore. This pseudo-blastopore is merely a relatively shallow depression marking the area at which immigration is occurring. After the completion of gastrulation, the cells lining the pseudo-blastopore are the prospective trunk ectoderm. The endoderm and mesoderm lie within the embryo and have no communication with the exterior. The remaining cells form the larval test, except for an apical quartet which will develop into the larval apical plate and for six small patches of cells which will give rise to much of the definitive nervous system. The apical/abapical axis of the gastrula is coincident with the antero-posterior axis of the adult solenogastre. The embryos leave their egg membranes on the third day and swim by means of the cilia of the larval test. This test becomes organized into a series of tiers of regularly shaped cells. The main tier is the prototroch, on which is developed a strong equatorial band of locomotory cilia. The larvae are not negatively geotactic and swim close to the bottom of a culture vessel. Proliferation of the definitive nervous tissue begins just before hatching, from six areas of larval test ectoderm on the future ventral side. Nervous elements are cut off inwards at the bases of shallow ectodermal depressions; they come to aggregate into cerebral and ventral (pedal) ganglia. By the seventh day the rudiment of the adult trunk is visible, protruding through the pseudo-blastopore. On its tip is the yolk-laden, ciliated, larval telotroch. The remainder of the trunk is 'Unciliated (except for a median longitudinal ventral ciliated band) but bears numerous pointed calcareous spicules. The length of the trunk rudiment increases by repeated division of the ectodermal cells within the pseudo-blastopore. The midgut passes down into the trunk and with it travel mesodermal elements and a pair of bands of nervous tissue which will form the ventral (pedal) cords. Proctodaeal and stomodaeal invaginations place the midgut in communication with the exterior but the larvae do not feed. The ‘ pygidial ’ development of the trunk of Neomenia resembles strongly that process as found in many annelids but it must be noted that no trace of metameric segmentation of this trunk is visible at any stage in the development of Neomenia . At no stage does the trunk bear overlapping dorsal spicules like those described by Pruvot for Nematomenia ; it seems probable on embryological grounds that the solenogastres are more closely allied to the primitive Lamellibranchia than to the Polyplacophora. Metamorphosis is considered to include only those changes occurring from the tenth to the thirteenth days, during which period the larva exchanges a pelagic for a benthic life. The trunk comes to form by far the greater proportion of the late larva and swimming becomes impossible. The larval test cells lose their orderly arrangement, the prototroch ceases to exist as a co-ordinated locomotory organ and the whole larval test becomes enclosed within the blastocoel of the trunk by the anterior extension and fusion of folds of definitive ectoderm. Similarly, the larval telotroch enters the trunk blastocoel posteriorly. From the blastocoel these yolk-laden cells of the larval locomotory and sensory apparatus pass through the midgut wall into the digestive cells; here they are broken down into small clusters of yolk granules which form the main identifiable food reserve of the post-larva. The mouth and anus, which, before metamorphosis, were directed posteriorly, are now directed ventrally; they lie at the anterior and posterior extremities of a median ventral longitudinal ciliated groove, the so-called pedal groove of the post-larva. This groove is at no stage employed as a pedal sole. The sites from which nervous elements were proliferated during larval life are obliterated at metamorphosis. In the post-larva, two new pairs of ectodermal nervous depressions develop. Both give rise to tubular strands of nervous tissue which extend to and fuse with the cerebral ganglia. Lateral (pleural) cords develop as outgrowths from the cerebral ganglia. Post-larval stages lived in the laboratory without food for up to 10 weeks; they were subsisting entirely on their food reserves. The natural diet of the species is unknown. During the ninth week after metamorphosis the atrium appeared, as a capacious invagination around the mouth. No radula, gills, cloaca, heart, coelomoducts or gonads developed before the young stages died; all but the first are known to be present in the adult Neomenia . A bibliography of works dealing with the ontogeny of Aplacophora is given.

Tetraplatia , a coronate scyphomedusan

The true relationships of the pelagic coelenterate Tetraplatia have long been a matter of controversy. The most recent and widely held view, that it is a highly modified trachyline medusa, is here demonstrated to be untenable because it has no velum, it has gastric filaments, a sense organ that is a rhopalium with an endodermal statolith, and gonads that originate in the endoderm. A reinvestigation based on adequate samples shows that it is a scyphomedusan. It is suggested first, that Tetraplatia has no ephyral stage and the planula develops directly into a juvenile, and secondly, that Tetraplatia evolved from a coronate scyphomedusan in which the normal radial expansion of the ephyra larva was arrested at an early stage and replaced by accelerated growth in the oral-aboral axis. Later, or accompanying the increased growth rate on the oral-aboral axis, four pairs of pouches were formed causing displacement and crowding of the eight ephyran lappets into four pairs and finally their fusion into a single locomotory organ. Thus, there were four locomotory lappets separated by four pairs of pouches. T. chuni remains essentially unaltered from this basic pattern, but in T. volitans the pouches fuse to form the well-known flying buttresses. Tetraplatia should now be placed in the Coronate Scyphomedusae, near the Ephyropsidae and Periphyllidae, in a family of its own, the Tetraplatidae. For this study, supplies of material of both T. volitans and T. chuni have been available.