Posterior Processes Research Articles

Morphological identification and DNA barcoding of a new species of Parabrachiella (Siphonostomatoida: Lernaeopodidae) with aspects of their intraspecific variation

We present a detailed morphological description and a DNA barcoding of Parabrachiella platensis n. sp. collected from Mugil liza Valenciennes in Samborombon Bay (Buenos Aires, Argentina). This new species was compared with two Parabrachiella species parasitic on mugilids: Parabrachiella exilis (Shiino, 1956) and Parabrachiella mugilis (Kabata, Raibaut et Ben Hassine, 1971). Parabrachiella platensis n. sp. differs from those species in the shape of posterior processes, the anal slit with two pairs of bipartite papillae, the size of cephalothorax, the trunk, the maxilla, the microhabitat on the host, and the lack of caudal rami. On the host, the new species was in the nostrils (a new site for a species of the genus Parabrachiella) and in the fins base. Some minor morphological differences were observed in relation to the locations on the host. The molecular analysis conducted based on mtDNA-COI between specimens of the new species on the fins and nostrils showed a genetic similarity of 99.8%. This percentage supports that the specimens found in nostrils and fins base could represent a single species. New studies on P. platensis n. sp., including infection of the same fish with the two forms, could bring some new information. Anyway according to the genetic information provided and the minimal morphological differences spotted we conclude that the two forms are a single specie. The differences observed are possibly influenced by the place of the host where the two forms of copepods were found, nostrils and fins. The new species was also molecularly compared to other five species of Parabrachiella including P. exilis (parasitizing mugilid from Chile), Parabrachiella anisotremis, Parabrachiella auriculata, Parabrachiella merluccii, and P. hugu (the last two sequences were taken from the GenBank). The genetic distance of 9% among P. platensis n. sp. and P. exilis, which is the close morphological related species, allow to states that these two copepods on mugilids belong to different species and then validating the morphological differences found between them.

An investigation of dimensional scaling using cervical spine motion segment finite element models.

The paucity of experimental data for validating computational models of different statures underscores the need for appropriate scaling methods so that models can be verified and validated using experimental data. Scaling was investigated using 50th percentile male (M50) and 5th percentile female (F05) cervical spine motion segment (C4-C5) finite element models subject to tension, flexion, and extension loading. Two approaches were undertaken: geometric scaling of the models to investigate size effects (volumetric scaling) and scaling of the force-displacement or moment-angle model results (data scaling). Three sets of scale factors were considered: global (body mass), regional (neck dimensions), and local (segment tissue dimensions). Volumetric scaling of the segment models from M50 to F05, and vice versa, produced correlations that were good or excellent in both tension and flexion (0.825-0.991); however, less agreement was found in extension (0.550-0.569). The reduced correlation in extension was attributed to variations in shape between the models leading to nonlinear effects such as different time to contact for the facet joints and posterior processes. Data scaling of the responses between the M50 and F05 models produced similar trends to volumetric scaling, with marginally greater correlations. Overall, the local tissue level and neck region level scale factors produced better correlations than the traditional global scaling. The scaling methods work well for a given subject, but are limited in applicability between subjects with different morphology, where nonlinear effects may dominate the response.

Review of the subgenus Xizicus (Xizicus) Gorochov, 1993 (Orthoptera: Tettigoniidae: Meconematinae) from China.

Gorochov (1993) erected the subgenus Xizicus (Xizicus), with the type species Xizicus (Xizicus) fascipes (Bey-Bienko, 1955). This subgenus is distinguished from the other subgenera of Xizicus by the following characters: male tenth abdominal tergite with a pair of contiguous posterior processes in the middle; subgenital plate simple, styli slender, located on the apices or subapices of lateral margins; posterior margin of female subgenital plate rounded.

Growth changes in the anterior and middle cranial bases assessed with cone-beam computed tomography in adolescents.

Initially, cone-beam computed tomography images from dry skulls were used to 3 dimensionally evaluate intrarater and interrater reliabilities and accuracy of selected 3-dimensional landmarks located in the anterior and middle cranial bases. Thereafter, dimensional changes of the anterior and middle cranial bases with growth were evaluated by using the previously selected landmarks. Cone-beam computed tomography images of 10 dry skulls were used to identify useful landmarks from different areas of the anterior and middle cranial bases based on their reliability and accuracy. These selected landmarks were identified in the images of an already available sample of adolescents (n=60) taken at 2 time points (19months apart) to assess dimensional changes with growth. The majority of the proposed 3-dimensional landmarks with the exception of the lesser wing of the sphenoid showed acceptable intrarater and interrater reliabilities. The distances measured between foramina and canals in the transverse dimension showed evidence of increases in size. However, the mean amounts of increase in these transverse distances were equal to or less than 1.05mm (from 1.1% to 4.1%). No change was observed between the right and left anterior and posterior clinoid processes. The vertical dimensions showed evidence of some changes, but these were within 2% of the original distances. In this adolescent sample, minor growth-related changes were observed in the anterior and middle cranial bases. The midsagittal area of the anterior cranial base (foramen caecum to presphenoid) was stable. The right and left anterior and posterior clinoid processes can be used for transverse superimposition.

Ixodes kangdingensis (Acari: Ixodidae), a new species from the Siberian weasel, Mustela sibirica (Carnivora: Mustelidae) in China

SUMMARY The female and nymph of Ixodes (Pholeoixodes) kangdingensis n. sp. are described based on both morphology and analysis of 16S rRNA gene sequences. Specimens of this new tick species were collected from a Siberian weasel (Mustela sibirica) in Kangding County, Sichuan Province, China. The morphological features of the female and nymph are unique to distinguish I. kangdingensis n. sp. from other members of the subgenus Pholeoixodes, including the presence of distinctly shaped cornua, anterior and posterior processes on palpal article I and a large angular projection on each side of the hypostome. Partial sequence of 16S rRNA gene grouped this species with Ixodes arboricola and Ixodes lividus with sequence divergence of new species from I. arboricola 4·16% and from I. lividus 8·49%. Data on the phylogenetic position, hosts, geographic distribution and key to females of closely related species are also provided.

Morphological Diversity and Evolution of the Jugal in Dinosaurs.

In dinosaurs, as in other reptiles, the homologue of the mammalian zygomatic bone is the jugal. The dinosaurian jugal was primitively triradiate, with posterior, dorsal and anterior processes that respectively contacted the quadratojugal, the postorbital, and the maxilla and lacrimal. However, the jugal evolved along different lines in the three major dinosaurian clades. In theropods this cranial element remained relatively conservative in morphology, apart from being reduced to a rod-like structure in most birds and a few non-avians. In sauropodomorphs the jugal eventually became small, plate-like and nearly restricted to the area below the orbit, even being excluded from the ventral margin of the skull in many derived taxa. Among ornithischians the jugal was highly variable, but in many cases became large and/or adorned with ornamental features such as horns, flanges, and rugosities. The jugal does not appear to have been a site of muscle attachment in most non-avian dinosaurs, but represented an important structural element in the akinetic dinosaurian skull. The conspicuous jugal ornaments seen in many ornithischian dinosaurs, like the less striking ones documented in some saurischians, may have played an important role in the social behavior of the species that possessed them. In many cases they have a weapon-like aspect suggesting use in aggressive displays, if not actual combat, adding to the evidence that agonistic behavior was likely widespread among ornithischians in particular. Anat Rec, 300:30-48, 2017. © 2016 Wiley Periodicals, Inc.

A new species of Pentamera Ayres, 1852 from the Brazilian coast (Holothuroidea, Dendrochirotida, Phyllophoridae).

Pentamera paraibanensis sp. n. is described from more than 3000 specimens as a new species of Phyllophoridae from northeast Brazil, in the tropical southwestern Atlantic. It is distinguished from its congeners by the shape of the calcareous ring with moderate posterior processes, and by the tables in the body wall with a usually quadrilocular disc and a low, toothed spire composed of two pillars. The body is brown, with the tube feet in double rows per ambulacrum, and tentacles more lightly colored. The species was found inside rodoliths in large numbers. This paper contains a morphological description of the specimens, and an account of their habitat characteristics.

Prediction error and somatosensory insula activation in women recovered from anorexia nervosa.

Previous research in patients with anorexia nervosa showed heightened brain response during a taste reward conditioning task and heightened sensitivity to rewarding and punishing stimuli. Here we tested the hypothesis that individuals recovered from anorexia nervosa would also experience greater brain activation during this task as well as higher sensitivity to salient stimuli than controls. Women recovered from restricting-type anorexia nervosa and healthy control women underwent fMRI during application of a prediction error taste reward learning paradigm. Twenty-four women recovered from anorexia nervosa (mean age 30.3 ± 8.1 yr) and 24 control women (mean age 27.4 ± 6.3 yr) took part in this study. The recovered anorexia nervosa group showed greater left posterior insula activation for the prediction error model analysis than the control group (family-wise error- and small volume-corrected p < 0.05). A group × condition analysis found greater posterior insula response in women recovered from anorexia nervosa than controls for unexpected stimulus omission, but not for unexpected receipt. Sensitivity to punishment was elevated in women recovered from anorexia nervosa. This was a cross-sectional study, and the sample size was modest. Anorexia nervosa after recovery is associated with heightened prediction error-related brain response in the posterior insula as well as greater response to unexpected reward stimulus omission. This finding, together with behaviourally increased sensitivity to punishment, could indicate that individuals recovered from anorexia nervosa are particularly responsive to punishment. The posterior insula processes somatosensory stimuli, including unexpected bodily states, and greater response could indicate altered perception or integration of unexpected or maybe unwanted bodily feelings. Whether those findings develop during the ill state or whether they are biological traits requires further study.

Multifunctional ion transport properties of human SLC4A11: comparison of the SLC4A11-B and SLC4A11-C variants.

Congenital hereditary endothelial dystrophy (CHED), Harboyan syndrome (CHED with progressive sensorineural deafness), and potentially a subset of individuals with late-onset Fuchs' endothelial corneal dystrophy are caused by mutations in the SLC4A11 gene that results in corneal endothelial cell abnormalities. Originally classified as a borate transporter, the function of SLC4A11 as a transport protein remains poorly understood. Elucidating the transport function(s) of SLC4A11 is needed to better understand how its loss results in the aforementioned posterior corneal dystrophic disease processes. Quantitative PCR experiments demonstrated that, of the three known human NH2-terminal variants, SLC4A11-C is the major transcript expressed in human corneal endothelium. We studied the expression pattern of the three variants in mammalian HEK-293 cells and demonstrated that the SLC4A11-B and SLC4A11-C variants are plasma membrane proteins, whereas SLC4A11-A is localized intracellularly. SLC4A11-B and SLC4A11-C were shown to be multifunctional ion transporters capable of transporting H+ equivalents in both a Na+-independent and Na+-coupled mode. In both transport modes, SLC4A11-C H+ flux was significantly greater than SLC4A11-B. In the presence of ammonia, SLC4A11-B and SLC4A11-C generated inward currents that were comparable in magnitude. Chimera SLC4A11-C-NH2-terminus-SLC4A11-B experiments demonstrated that the SLC4A11-C NH2-terminus functions as an autoactivating domain, enhancing Na+-independent and Na+-coupled H+ flux without significantly affecting the electrogenic NH3-H(n)+ cotransport mode. All three modes of transport were significantly impaired in the presence of the CHED causing p.R109H (SLC4A11-C numbering) mutation. These complex ion transport properties need to be addressed in the context of corneal endothelial disease processes caused by mutations in SLC4A11.

Relationship Between Bridging and Dimensions of Sella Turcica and Antero-Posterior Skeletal Malocclusions in Children

Background: Interclinoid ligament calcification and dimensional changes in Sella Turcica seen on cephalometric radiographs are associated with some bone abnormalities as well as normal variations. Merging of anterior and posterior clinoid processes, known as Sella Turcica bridging or roofing and other changes in this area may occur as a part of large skeletal growth changes in body and may have association with craniofacial skeletal patterns development. Objectives: The aim of the present study was to compare Sella Turcica bridging and dimensions of patients with various skeletal patterns to investigate whether there is a correlation between Sella Turcica region changes with skeletal patterns or not, and on the other hand, to know if these changes could be used as predictive indices for growing patients skeletal patterns. Materials and Methods: A total of 108 cephalometric radiographs (36 Class I, 36 Class II, and 36 Class III) were randomly selected for evaluation. Sella Turcica was traced on acetate paper and scanned to produce digital images. The dimensions of Sella Turcica were measured with computer software using the Silverman, Kisling, and Axelsson method. To determine bridging, Leonardi’s method was employed. To determine the association of Sella Turcica bridging and dimensions with different malocclusions, chi-squared test and one-way ANOVA were used. Results: The means of Sella Turcica lengths in three groups were significantly different (P = 0.01). Mean depth and diameter, however, were not significantly different between malocclusions. In addition, bridging was not significantly different among three malocclusions evaluated. Conclusions: According to the results, mean length of Sella Turcica, rather than depth and diameter, was significantly associated with the type of malocclusion. Sella Turcica cavity length is larger in Cl III patients in comparison with Cl I ones and may have predictive value in some instances.

TU‐AB‐BRA‐01: Abdominal Synthetic CT Generation in Support of Liver SBRT Dose Calculation

Purpose:To demonstrate and validate a technique for generating MRI‐derived synthetic CT volumes (MRCTs) in support of adaptive liver SBRT.Methods:Under IRB approval, ten hepatocellular carcinoma patients were scanned using a single MR sequence (T1 Dixon‐VIBE), yielding inherently‐registered water, fat, and T1‐weighted images. Air‐containing voxels were identified by intensity thresholding. The envelope of the anterior vertebral bodies was segmented from the fat image by fitting a shape model to vertebral body candidate voxels, then using level sets to expand the contour outward. Fuzzy‐C‐Means (FCM) was then used to classify each non‐air voxel in the image as fat, water, bone, or marrow. Bone and marrow only were classified within the vertebral body envelope. The MRCT was created by integrating the product of the FCM class probability with the assigned class density for each voxel. The resulting MRCTs were deformably aligned with planning CTs and 2‐ARC SBRT VMAT plans were optimized on the MRCT density maps. Fluence was copied onto the CT density grids and dose recalculated.Results:The MRCTs faithfully reproduced most of the features visible in the corresponding CT image volumes, with exceptions of ribs and posterior spinous processes. The liver, vertebral bodies, kidneys, spleen and cord all had median HU differences of less than 75 between MRCT and CT images. PTV D99% values had an average 0.2% difference (standard deviation: 0.46%) between calculations on MRCT and CT density grids. The maximum difference in dose to 0.1cc of the PTV was 0.25% (std:0.49%). OAR dose differences were similarly small (mean:0.03Gy, std:0.26Gy). The largest normal tissue complication percentage (NTCP) difference was 1.48% (mean:0.06%, std:0.54%).Conclusions:MRCTs from a single abdominal imaging sequence are promising for use in SBRT dose calculation. Future work will focus on extending models to better define bones in the upper abdomen.Supported by NIHR01EB016079 and NIH1L30CA199594‐01

Functional Connectivity of Ventral and Dorsal Visual Streams in Posterior Cortical Atrophy.

Posterior cortical atrophy (PCA) induces progressive dysfunction of ventral and dorsal visual networks. Little is known, however, about corresponding changes in functional connectivity (FC). To investigate FC changes in the visual networks, their relationship with cortical atrophy, and the association with Alzheimer's disease (AD) pathology. Ten PCA patients and 28 age-matched controls participated in the study. Using resting state fMRI, we measured FC in ventral and dorsal cortical visual networks, defined on the basis of a priori knowledge of long-range white matter connections. To assess the relationships with AD, we determined AD biomarkers in cerebrospinal fluid and FC in the default mode network (DMN), which is vulnerable to AD pathology. Voxel-based morphometry analysis assessed the pattern of grey matter (GM) atrophy. PCA patients showed GM atrophy in bilateral occipital and inferior parietal regions. PCA patients had lower FC levels in a ventral network than controls, but higher FC in inferior components of the dorsal network. In particular, the increased connectivity correlated with greater GM atrophy in occipital regions. All PCA patients had positive cerebrospinal fluid biomarkers for AD; however, FC in global DMN did not differ from controls. FC in PCA reflects brain structure in a non-univocal way. Hyperconnectivity of dorsal networks may indicate aberrant communication in response to posterior brain atrophy or processes of neural resilience during the initial stage of brain dysfunction. The lack of difference from controls in global DMN FC highlights the atypical nature of PCA with respect to typical AD.

Craniovertebral anomalies associated with pituitary gland duplication.

An extremely rare occurrence of the pituitary gland duplication inspired us to examine in detail the accompanying craniovertebral congenital anomalies in a patient involved. T1-wighted magnetic resonance imaging (MRI) was performed, as well as the multislice computerised tomography (MSCT) and MSCT angiography in our patient, as well as in a control group of 10 healthy subjects. In a 20-year-old male a double pituitary gland was identified, as well as hypothalamic enlargement, tuberomamillary fusion and hamartoma. In addition, the patient also showed a duplicated hypophyseal fossa and posterior clinoid processes, notch of the upper sphenoid, prominent inner relief of the skull, inverse shape of the foramen magnum, third occipital condyle, partial aplasia of the anterior and posterior arches of the atlas with a left arcuate foramen, duplication of the odontoid process and the C2 body, and fusion of the C2-C4 and T12-L1 vertebrae. The MSCT angiography presented a segmental dilatation of both vertebral arteries and the A2 segment of the anterior cerebral artery, as well as a duplication of the basilar artery. This patient is unique due to complex craniovertebral congenital anomalies associated with a duplication of the pituitary gland.

Anatomy, feeding ecology, and ontogeny of a transitional baleen whale: a new genus and species of Eomysticetidae (Mammalia: Cetacea) from the Oligocene of New Zealand.

The Eocene history of cetacean evolution is now represented by the expansive fossil record of archaeocetes elucidating major morphofunctional shifts relating to the land to sea transition, but the change from archaeocetes to modern cetaceans is poorly established. New fossil material of the recently recognized family Eomysticetidae from the upper Oligocene Otekaike Limestone includes a new genus and species, Waharoa ruwhenua, represented by skulls and partial skeletons of an adult, juvenile, and a smaller juvenile. Ontogenetic status is confirmed by osteohistology of ribs. Waharoa ruwhenua is characterized by an elongate and narrow rostrum which retains vestigial alveoli and alveolar grooves. Palatal foramina and sulci are present only on the posterior half of the palate. The nasals are elongate, and the bony nares are positioned far anteriorly. Enormous temporal fossae are present adjacent to an elongate and narrow intertemporal region with a sharp sagittal crest. The earbones are characterized by retaining inner and outer posterior pedicles, lacking fused posterior processes, and retaining a separate accessory ossicle. Phylogenetic analysis supports inclusion of Waharoa ruwhenua within a monophyletic Eomysticetidae as the earliest diverging clade of toothless mysticetes. This eomysticetid clade also included Eomysticetus whitmorei, Micromysticetus rothauseni, Tohoraata raekohao, Tokarahia kauaeroa, Tokarahia lophocephalus, and Yamatocetus canaliculatus. Detailed study of ontogenetic change demonstrates postnatal elaboration of the sagittal and nuchal crests, elongation of the intertemporal region, inflation of the zygomatic processes, and an extreme proportional increase in rostral length. Tympanic bullae are nearly full sized during early postnatal ontogeny indicating precocial development of auditory structures, but do increase slightly in size. Positive allometry of the rostrum suggests an ontogenetic change in feeding ecology, from neonatal suckling to a more specialized adult feeding behaviour. Possible absence of baleen anteriorly, a delicate temporomandibular joint with probable synovial capsule, non-laterally deflected coronoid process, and anteroposteriorly expanded palate suggests skim feeding as likely mode of adult feeding for zooplankton. Isotopic data in concert with preservation of young juveniles suggests the continental shelf of Zealandia was an important calving ground for latitudinally migrating Oligocene baleen whales.

Parameter Estimation: The Proper Way to Use Bayesian Posterior Processes with Brownian Noise

This paper studies a problem of Bayesian parameter estimation for a sequence of scaled counting processes whose weak limit is a Brownian motion with an unknown drift. The main result of the paper is that the limit of the posterior distribution processes is, in general, not equal to the posterior distribution process of the mentioned Brownian motion with the unknown drift. Instead, it is equal to the posterior distribution process associated with a Brownian motion with the same unknown drift and a different standard deviation coefficient. The difference between the two standard deviation coefficients can be arbitrarily large. The characterization of the limit of the posterior distribution processes is then applied to a family of stopping time problems. We show that the proper way to find asymptotically optimal solutions to stopping time problems, with respect to the scaled counting processes, is by looking at the limit of the posterior distribution processes rather than by the naive approach of looking at the limit of the scaled counting processes themselves. The difference between the performances can be arbitrarily large.

Study of ossified clinoid ligaments in sphenoid bone of north Indian skulls

IntroductionThe sphenoid bone lies in the base of the skull between the frontal, temporal and occipital bones. Certain parts of the sphenoid bone are connected to each other by ligaments, such as caroticoclinoid ligament and interclinoid ligament which occasionally ossify and result in the formation of foramen. MethodsThis study was performed on 40 specimens i.e. 30 dried skulls and 10 sphenoid bones, obtained from the Department of Anatomy, SRMS IMS, Bareilly. In all skulls and sphenoids the anterior, middle and posterior clinoid processes were examined to reveal their relationship and the incidence of clinoid foramina and ossification of ligaments around pituitary fossa were noted. ResultsThe incidence of anterior clinoid foramen is more as compared to posterior clinoid foramen. The ossification of caroticoclinoid ligament is more common than interclinoid ligament. The incidence of presence of anterior clinoid foramen on right and left side is same. Posterior clinoid foramen is present in one sphenoid bone only out of 40 bones. DiscussionThe knowledge of anatomy of ossified interclinoid ligament and caroticoclinoid ligament in sphenoid bone around pituitary fossa is important from diagnostic, surgical (especially surgeries involving removal of anterior clinoid process) and clinical point of view and should be evaluated by neurosurgeons before proceeding to skull based surgery. The presence of an ossified CCL ligament is likely to cause compression and straightening of the internal carotid artery thus giving rise to vascular complications.

Efficient Gaussian Process-Based Modelling and Prediction of Image Time Series.

In this work we propose a novel Gaussian process-based spatio-temporal model of time series of images. By assuming separability of spatial and temporal processes we provide a very efficient and robust formulation for the marginal likelihood computation and the posterior prediction. The model adaptively accounts for local spatial correlations of the data, and the covariance structure is effectively parameterised by the Kronecker product of covariance matrices of very small size, each encoding only a single direction in space. We provide a simple and flexible framework for within- and between-subject modelling and prediction. In particular, we introduce the Hoffman-Ribak method for efficient inference on posterior processes and its uncertainty. The proposed framework is applied in the context of longitudinal modelling in Alzheimer's disease. We firstly demonstrate the advantage of our non-parametric method for modelling of within-subject structural changes. The results show that non-parametric methods demonstrably outperform conventional parametric methods. Then the framework is extended to optimize complex parametrized covariate kernels. Using Bayesian model comparison via marginal likelihood the framework enables to compare different hypotheses about individual change processes of images.

Two new species of Tortanus (Atortus) (Copepoda, Calanoida, Tortanidae) from the Andaman Islands

Two new species of the planktonic copepod genusTortanus, subgenusAtortus, are described from inter- to sub-tidal water of South Andaman Island, India. The new species are assigned to thetropicusgroup sensu Othman (1987) and distinguished from the other members of the group by the characteristic morphology of the pair of posterior dorsolateral processes on the fifth pedigerous somite in the female and the antennule and leg 5 in the male. An analysis of previous records of thetropicusspecies group indicates their sporadic occurrence combined with high species richness in Southeast Asia, suggesting future discovery of even more species by sampling with finer geographic and habitat coverage.

Bilateral “Carotico-clinoid Foramen” With “Sella Turcica Bridge”- A Case Report

Introduction: The Carotico-clinoid foramen is the result of ossification of carotico-clinoid ligament between anterior and middle clinoid process. Whereas bony bridge between anterior and posterior clinoid processes formed by ossified dural extension connecting these two processes, is called Sella Turcica Bridge. They can be developed unilaterally or bilaterally and vary in frequency. Both these foramina may cause different presentations, i.e. compression, tightness or stretching of internal carotid artery as well as endocrinological problems affecting hypothalamus or hypophysis cerebri or neurological problems through Oculomotor or optic nerve, pituitary gland, which manifest as headache, behavioral changes, hormonal, visual, epileptic, craniofacial deviation and tooth anomalies, etc. That’s why thorough anatomical knowledge is a great clinical help for neurosurgeons, neurophysicians, endocrinologists, radiologists, anatomists and biological anthropologists. Case report: Recently during teaching medical students one dry skull having bilateral ossified interclinoid ligaments (carotico-clinoid foramen and sella Turcica Bridge) is found which is relatively very rare as per literatures. The morphologic analysis has been done.

Functional analysis of centipede development supports roles for Wnt genes in posterior development and segment generation.

The genes of the Wnt family play important and highly conserved roles in posterior growth and development in a wide range of animal taxa. Wnt genes also operate in arthropod segmentation, and there has been much recent debate regarding the relationship between arthropod and vertebrate segmentation mechanisms. Due to its phylogenetic position, body form, and possession of many (11) Wnt genes, the centipede Strigamia maritima is a useful system with which to examine these issues. This study takes a functional approach based on treatment with lithium chloride, which causes ubiquitous activation of canonical Wnt signalling. This is the first functional developmental study performed in any of the 15,000 species of the arthropod subphylum Myriapoda. The expression of all 11 Wnt genes in Strigamia was analyzed in relation to posterior development. Three of these genes, Wnt11, Wnt5, and WntA, were strongly expressed in the posterior region and, thus, may play important roles in posterior developmental processes. In support of this hypothesis, LiCl treatment of S. maritima embryos was observed to produce posterior developmental defects and perturbations in AbdB and Delta expression. The effects of LiCl differ depending on the developmental stage treated, with more severe effects elicited by treatment during germband formation than by treatment at later stages. These results support a role for Wnt signalling in conferring posterior identity in Strigamia. In addition, data from this study are consistent with the hypothesis of segmentation based on a "clock and wavefront" mechanism operating in this species.