Ventral Organ Research Articles

Larval internal morphology of the introduced blowfly Chrysomya megacephala (Fabricius, 1794) (Diptera: Calliphoridae)

The blowfly Chrysomya megacephala (Diptera: Calliphoridae) colonizes different environments and is found in many global regions. Its importance includes its involvement in the decomposition of organic matter, forensic entomology, maggot therapy, bioprospecting, source of biodiesel, industry, stabilization of heavy metals in soil, pollination, and as a vector of diseases and causing secondary myiasis. Internal morphological studies contribute to understanding insect's function and provide basic data for applied areas with interest in this specie. The objective of this study was to describe the internal morphology of C. megacephala larvae. Post-embryonic development occurred over 240 h, equally divided into larval and pupal stages. After hatching, the larvae averaged <1 mm in length and 0.02 mg in weight, growing to 13.83 mm and 50.4 mg in the third instar. We utilized whole, third-instar larvae to perform histology. Sensory organs were observed in the cephalic region, antennae, maxillary palps, and ventral organ. The alimentary canal comprises a foregut, midgut, and hindgut, including tracheal insertions and accessory organs, such as salivary glands. The midgut is the largest organ of the alimentary canal and fat body are present in body cavity and intersegmental space. Thus, our data about the internal morphology of C. megacephala larvae describe the structure and position of the alimentary canal, salivary gland, sensory organs, and fat body.

A single-cell RNA-seq analysis of Brachyury-expressing cell clusters suggests a morphogenesis-associated signal center of oral ectoderm in sea urchin embryos

Brachyury is a T-box family transcription factor and plays pivotal roles in morphogenesis. In sea urchin embryos, Brachyury is expressed in the invaginating endoderm, and in the oral ectoderm of the invaginating mouth opening. The oral ectoderm is hypothesized to serve as a signaling center for oral (ventral)-aboral (dorsal) axis formation and to function as a ventral organizer. Our previous results of a single-cell RNA-seq (scRNA-seq) atlas of early Strongylocentrotus purpuratus embryos categorized the constituent cells into 22 clusters, in which the endoderm consists of three clusters and the oral ectoderm four clusters (Foster et al., 2020). Here we examined which clusters of cells expressed Brachyury in relation to the morphogenesis and the identity of the ventral organizer. Our results showed that cells of all three endoderm clusters expressed Brachyury in blastulae. Based on expression profiles of genes involved in the gene regulatory networks (GRNs) of sea urchin embryos, the three clusters are distinguishable, two likely derived from the Veg2 tier and one from the Veg1 tier. On the other hand, of the four oral-ectoderm clusters, cells of two clusters expressed Brachyury at the gastrula stage and genes that are responsible for the ventral organizer at the late blastula stage, but the other two clusters did not. At a single-cell level, most cells of the two oral-ectoderm clusters expressed organizer-related genes, nearly a half of which coincidently expressed Brachyury. This suggests that the ventral organizer contains Brachyury-positive cells which invaginate to form the stomodeum. This scRNA-seq study therefore highlights significant roles of Brachyury-expressing cells in body-plan formation of early sea urchin embryos, though cellular and molecular mechanisms for how Brachyury functions in these processes remain to be elucidated in future studies.

Computed Microtomography (Micro-CT) in the Anatomical Study and Identification of Solenogastres (Mollusca)

Solenogastres are vermiform marine molluscs characterised by an aculiferous mantle, a longitudinal ventral pedal groove and a terminal or subterminal pallial cavity. Their classification is based in part on the type of mantle sclerites, but identification to even the family level generally requires the study of internal anatomical characters. Taxonomically important internal characters include those related to radular structure, the type of ventrolateral glandular organs of the pharynx and the reproductive system, among others. In order to study their internal anatomical organisation, according to the classical reconstruction method, serial histological sections of specimens are made, from which the 2D internal anatomy of the specimen can be reconstructed manually. However, this is a time-consuming technique that results in destruction of the specimen. Computed microtomography or micro-CT is a non-destructive technique based on the measurement of the attenuation of X-rays as they pass through a specimen. Micro-CT is faster than histology for studying internal anatomy and it is non-destructive, meaning that specimens may be used for e.g., DNA extraction or retained as intact vouchers. In this paper, the utility of micro-CT for studying taxonomically important internal anatomical structures was assessed. Results of the 3D anatomical study of the soft parts of four specimens of three species using micro-CT are presented: Proneomenia sluiteriHubrecht, 1880, Dorymenia menchuescribanaeGarcía-Álvarez et al., 2000 and Anamenia gorgonophilaKowalevsky, 1880. Micro-CT enabled detailed study of most taxonomically important anatomical characters, precise measurements of structures, and observation of the relative position of organs from a variety of angles. However, it was not possible to observe the radula and some details of the ventral foregut organs could not be discerned. Despite these limitations, results of this study highlight micro-CT as a valuable tool to compliment histology in the study of solenogaster anatomy and in non-destructively identifying animals to the family and even genus-level.

Description of a new codling species of Physiculus from Taiwan (Gadiformes: Moridae).

A new species of codling Physiculus megastomus sp. nov. is described based on the holotype and a subadult paratype collected from northern and eastern Taiwan. The new species is classified in Physiculus by the presence of a ventral light organ on the abdomen and a chin barbel, and the absence of vomerine teeth. It is distinguished from congeners in having a large mouth with the posterior end of the maxilla extending well behind the level of the posterior margin of the orbit, its length 57.8‒60.7% in head length (HL) and the combination of the following characters: both jaws bearing caniniform teeth; snout, suborbital area, and gular region fully scaled; ventral light organ small, its length 5.5‒6.7% of distance from the interventral line to the origin of the anal fin (InV-af), located approximately at the mid-point of InV-af; five gill rakers on the upper limb of the first gill arch. DNA barcoding supported the establishment of the new species.

Contribution to the knowledge of Neanurinae of north-western Iran with description of seven new species (Collembola, Neanuridae).

Seven new species of the subfamily Neanurinae from north-western Iran are described and illustrated in detail. Endonura agnieskaesp. nov. differs from the most similar congener, E. reticulata (Axelson, 1905), in chaetotaxic details and the arrangement of tubercles on the dorsal side of the body. Endonura annaesp. nov. can be easily recognised by its wide labrum, the absence of chaetae C on the head and the presence of a toothed claw. Endonura schwendingerisp. nov. is especially distinctive due to the absence of chaetae A and Ocp on the head and the presence of the male ventral organ. Deutonura brevisetasp. nov. is related and most similar to D. persica Smolis, Shayanmehr & Yoosefi-Lafooraki, 2018, described recently and known from Mazandran Province in Iran. The new species can be easily distinguished by the following set of features: dark pigmented body, presence of chaetae C and Dl3 on the head, absence of microchaetae on the furca rudimentary, presence of thickened macrochaetae on dorsal side of body and absence of cryptopygy. The main characteristics of Deutonura sengletisp. nov. include a white body with dark pigmented eyes, the fusion of tubercles Di and De on the first thoracic segment and the presence of the male ventral organ. Deutonura iranicasp. nov. is superficially similar to D. gibbosa Porco, Bedos & Deharveng, 2010, a species known from the Alps and Jura in Europe, but it differs in the body colour and the number of labial chaetae and chaetae (L+So) on the head. Paravietnura rostratasp. nov., the first member of this enigmatic and intriguing genus known from Iran, is characterised by an unusually elongate ogival labrum and extreme reduction of dorsal chaetotaxy. Furthermore, new records of several other species of the subfamily: Cryptonura maxima Smolis, Falahati & Skarżyński, 2012; C. persica Smolis, Falahati & Skarżyński, 2012; Deutonura persica; Endonura longirostris Smolis, Shayanmehr, Kuznetsova & Yoosefi-Lafooraki, 2017; E. paracentaurea Smolis, Shayanmehr, Kuznetsova & Yoosefi-Lafooraki, 2017; Neanura deharvengi Smolis, Shayanmehr & Yoosefi-Lafooraki, 2018; N. muscorum (Templeton, 1835) and Protanura papillata Cassagnau & Delamare Deboutteville, 1955 are given. The present study is based on the rich material collected by Antoine Senglet and loaned by Peter J. Schwendinger.

Laparoscopic Pelvic Organ Prolapse Suspension (Pops) Versus Laparoscopic Ventral Mesh Rectopexy for Treatment of Rectal Prolapse: Prospective Cohort Study.

This study aimed to compare ventral mesh rectopexy (VMR) and pelvic organ prolapse suspension surgery (POPS) in management of patients presenting with rectal prolapse. Our study was a prospective cohort trial in which 120 female patients with complete rectal prolapse were included, 60 patients had had VMR and the other 60 had had POPS as a surgical management for complete rectal prolapse. Results had been compared 6months postoperatively regarding operative time, postoperative pain, hospital stay, complications of surgery including recurrence of the rectal prolapse, the efficacy of each operation in treatment of rectal prolapse and associated symptoms. The patients were assessed 6months postoperatively. There was no significant statistical difference regarding hospital stay and postoperative pain. Operative time was significantly shorter in POPS in comparison with VMR (P value < 0.05). VMR showed slight improvement regarding constipation and continence scores; however, this was statistically significant. VMR showed less complications compared to POPS. Complications with rectopexy happened only with 4 patients compared to 24 patients in POPS groups, 2 cases of recurrence in rectopexy group compared to 6 cases of recurrence in POPS. POPS is comparable to VMR in management of rectal prolapse and in improving the ODS symptoms. Thus, POPS can be used as easier, faster option to treat rectal prolapse in selected patients.

New Lobellini (Collembola: Neanuridae) from Queensland contribute to understanding distribution and ecology of Australian fauna

AbstractTwo new species from Queensland rainforest belonging to genera Hemilobella and Sphaeronura are described and illustrated with drawings and colour photographs. Hemilobella matildae sp. nov. Smolis and Greenslade is characterised by elongated tubercles laterally on body and an elongated ogival labrum. Sphaeronura ameliae sp. nov. Smolis and Greenslade differs from other taxa in the genus in chaetotaxic features and the presence of a male ventral organ. A new record of Australonura scoparia is included. The high species richness of lowland rainforests, in which these log inhabiting saproxylic species were found, is noted, and the contribution that extreme events such as cyclones in maintaining the fallen timber habitat is emphasised. The bright colour of these species may be caused by sequestered pigments from the slime moulds on which they feed. The colour probably also acts as a warning to predators that individuals are distasteful. A description of the distributions, characteristics, distinctiveness and possible genesis of Australian fauna of the subfamily Neanurinae is presented, and a checklist of species and key to all Australian genera of the subfamily is included. Species in this subfamily are predominately short‐range endemics so should be surveyed whenever wet forests are under threat from logging or urban expansion.

Deciphering and modelling the TGF-β signalling interplays specifying the dorsal-ventral axis of the sea urchin embryo.

During sea urchin development, secretion of Nodal and BMP2/4 ligands and their antagonists Lefty and Chordin from a ventral organiser region specifies the ventral and dorsal territories. This process relies on a complex interplay between the Nodal and BMP pathways through numerous regulatory circuits. To decipher the interplay between these pathways, we used a combination of treatments with recombinant Nodal and BMP2/4 proteins and a computational modelling approach. We assembled a logical model focusing on cell responses to signalling inputs along the dorsal-ventral axis, which was extended to cover ligand diffusion and enable multicellular simulations. Our model simulations accurately recapitulate gene expression in wild-type embryos, accounting for the specification of ventral ectoderm, ciliary band and dorsal ectoderm. Our model simulations further recapitulate various morphant phenotypes, reveal a dominance of the BMP pathway over the Nodal pathway and stress the crucial impact of the rate of Smad activation in dorsal-ventral patterning. These results emphasise the key role of the mutual antagonism between the Nodal and BMP2/4 pathways in driving early dorsal-ventral patterning of the sea urchin embryo.

Peptaibols from trichoderma asperellum induce apoptosis against Aedes aegypti (Diptera: Culicidae)

Blow flies of the genus Hypopygiopsis are forensically-important, as their larvae are commonly associated with human corpses. Within a forensic entomology context, species identification of specimens collected from human corpses is the initial mandatory step in the investigation. Without identification, complete interpretation of entomological evidence is challenged. In this study, the ultrastructures of eggs, all instars, and puparia of Hypopygiopsis infumata (Bigot) are presented based on assessment with scanning electron microscopy (SEM) and light microscopy (LM). Distinctive features used for species identification of all stages are highlighted. Eggs have a slightly widening median area extending almost the entire length. Larvae are vermiform-shaped, creamy white, and have a smooth integument. The pseudocephalon of larvae bears sensory structures (i.e., antennal dome, maxillary palpus and ventral organ). In the first instar, two tufts of cirri are observed along the dorsal margin of the mouth opening. In the second and third instars, six minute tubercles are present along the peripheral rims of the last abdominal segment. The anterior spiracle of the second, third instar, and puparia is fan-shape of single row, comprising 9–11 papillae. The cuticular spines between the 1st and 2nd thoracic segments of the third instar possess many rows of posteriorly-projecting acuminate spines in clusters. In puparia, at the latero-dorsal edge of the 1st abdominal segment, a cluster of ∼92 bubble membranes is present in young puparia (20–24 h). The peristigmatic tufts adjacent to the posterior spiracle of the second instar, third instar, and puparia are heavily branches of long, fine hairs. Our results demonstrate the morphology of eggs, larvae, and puparia of H. infumata are similar to other species in Hypopygiopsis. This study highlighted the main features of cephaloskeleton of H. infumata larvae as observed under LM. Particular attention is given to oral sclerite and rough surface of dorsal cornua which can distinguish between H. infumata and H. tumrasvini.

Transatlantic discovery of Notocotylus atlanticus (Digenea: Notocotylidae) based on life cycle data.

Digenean parasites feature a series of stages with a distinct appearance, reproduction mode, and lifestyle that together constitute their well-known, complex life cycle. Species descriptions of Digenea have always been based on one of these stages-the marita, or sexually reproducing adult in the final host. However, in some cases, data on the life cycle are essential for the differential diagnosis of closely related species. Here, we present the case of Notocotylus atlanticus, where different stages of its life cycle were discovered for the first time since the species description, and across the Atlantic. We used a material from a naturally infected intertidal marine snail, Ecrobia ventrosa, and several waterfowl species and also carried out infection experiments. For morphological studies, we employed light microscopy, SEM, and CLSM; molecular data obtained include sequences of ITS1 and 28S rRNA gene. We demonstrate that N. atlanticus adult worm morphology is barely sufficient to distinguish it from several other species. Cercariae morphology and identity of the first intermediate hosts provide crucial additional information. According to our preliminary phylogenetic reconstructions, two notocotylid lineages are associated with two major gastropod lineages-the Caenogastropoda and the Heterobranchia. The traditional character to identify notocotylid genera (structure of ventral organs) fails to explain the phylogeny and thus requires reassessment. Further reliable morphological, life cycle and molecular data on other species are likely to reveal more patterns in notocotylid systematics, host specificity, and evolution.

Morphology of immature blow fly Hypopygiopsis infumata (Bigot) (Diptera: Calliphoridae), a potential species of forensic importance

Blow flies of the genus Hypopygiopsis are forensically-important, as their larvae are commonly associated with human corpses. Within a forensic entomology context, species identification of specimens collected from human corpses is the initial mandatory step in the investigation. Without identification, complete interpretation of entomological evidence is challenged. In this study, the ultrastructures of eggs, all instars, and puparia of Hypopygiopsis infumata (Bigot) are presented based on assessment with scanning electron microscopy (SEM) and light microscopy (LM). Distinctive features used for species identification of all stages are highlighted. Eggs have a slightly widening median area extending almost the entire length. Larvae are vermiform-shaped, creamy white, and have a smooth integument. The pseudocephalon of larvae bears sensory structures (i.e., antennal dome, maxillary palpus and ventral organ). In the first instar, two tufts of cirri are observed along the dorsal margin of the mouth opening. In the second and third instars, six minute tubercles are present along the peripheral rims of the last abdominal segment. The anterior spiracle of the second, third instar, and puparia is fan-shape of single row, comprising 9–11 papillae. The cuticular spines between the 1st and 2nd thoracic segments of the third instar possess many rows of posteriorly-projecting acuminate spines in clusters. In puparia, at the latero-dorsal edge of the 1st abdominal segment, a cluster of ∼92 bubble membranes is present in young puparia (20–24 h). The peristigmatic tufts adjacent to the posterior spiracle of the second instar, third instar, and puparia are heavily branches of long, fine hairs. Our results demonstrate the morphology of eggs, larvae, and puparia of H. infumata are similar to other species in Hypopygiopsis. This study highlighted the main features of cephaloskeleton of H. infumata larvae as observed under LM. Particular attention is given to oral sclerite and rough surface of dorsal cornua which can distinguish between H. infumata and H. tumrasvini.

Structure and function of the male ventral organ in Onychiuroides granulosus (Collembola: Onychiuridae)

On the ventral tube of males of Onychiuroides granulosus (Stach, 1934) there is a male ventral organ, which consists of two groups of four setae that are thickened, slightly flattened and bent. All setae of the male ventral organ are inserted in a richly sculptured cuticle. At the base of each seta there are a few large cells (basal cells) that have large irregular nuclei that contain a large amount of heterochromatin. In the cytoplasm of the basal cells there are numerous mitochondria, ribosomes and a rich system of endoplasmic reticulum. The plasma membrane of the basal cells forms richly folded, deep invaginations, filled with a dense material, which also occurs in particular setae and on their surface. The present study indicates that the male ventral organ is secretory and does not confirm its previously suggested sensory function.

Comparison of ventral organ development across Pycnogonida (Arthropoda, Chelicerata) provides evidence for a plesiomorphic mode of late neurogenesis in sea spiders and myriapods

BackgroundComparative studies of neuroanatomy and neurodevelopment provide valuable information for phylogenetic inference. Beyond that, they reveal transformations of neuroanatomical structures during animal evolution and modifications in the developmental processes that have shaped these structures. In the extremely diverse Arthropoda, such comparative studies contribute with ever-increasing structural resolution and taxon coverage to our understanding of nervous system evolution. However, at the neurodevelopmental level, in-depth data remain still largely confined to comparably few laboratory model organisms. Therefore, we studied postembryonic neurogenesis in six species of the bizarre Pycnogonida (sea spiders), which – as the likely sister group of all remaining chelicerates – promise to illuminate neurodevelopmental changes in the chelicerate lineage.ResultsWe performed in vivo cell proliferation experiments with the thymidine analogs 5-bromo-2′-deoxyuridine and 5-ethynl-2′-deoxyuridine coupled to fluorescent histochemical staining and immunolabeling, in order to compare ventral nerve cord anatomy and to localize and characterize centers of postembryonic neurogenesis. We report interspecific differences in the architecture of the subesophageal ganglion (SEG) and show the presence of segmental “ventral organs” (VOs) that act as centers of neural cell production during gangliogenesis. These VOs are either incorporated into the ganglionic soma cortex or found on the external ganglion surface. Despite this difference, several shared features support homology of the two VO types, including (1) a specific arrangement of the cells around a small central cavity, (2) the presence of asymmetrically dividing neural stem cell-like precursors, (3) the migration of newborn cells along corresponding pathways into the cortex, and (4) the same VO origin and formation earlier in development.ConclusionsEvaluation of our findings relative to current hypotheses on pycnogonid phylogeny resolves a bipartite SEG and internal VOs as plesiomorphic conditions in pycnogonids. Although chelicerate taxa other than Pycnogonida lack comparable VOs, they are a characteristic feature of myriapod gangliogenesis. Accordingly, we propose internal VOs with neurogenic function to be part of the ground pattern of Arthropoda. Further, our findings illustrate the importance of dense sampling in old arthropod lineages – even if as gross-anatomically uniform as Pycnogonida – in order to reliably differentiate plesiomorphic from apomorphic neurodevelopmental characteristics prior to outgroup comparison.

Agraphorura xuae sp. nov., the First Record of Onychiuridae (Collembola) from Continental Ecuador, with a Key to the Known Species of the Genus

Abstract. The new species Agraphorura xuae sp. nov. is described from continental Ecuador, the first onychiurid species record in this region. The new species is most similar to A. gambiarius (Murphy, 1965) from West Africa, but they can be separated easily by the number and length of p-chaetae between two inner posterior pso on the head, the number of chaetae on Th. I tergum, the presence of the male ventral organ and the ratio of the empodial appendage/unguis. A key to the world known species is provided. The list of all known species from continental Ecuador is presented.

Remarkable diversity of the genus Endonura Cassagnau, 1979 (Collembola: Neanuridae: Neanurinae) in the Caucasus.

Endonura alticola (Stach, 1951) comb. nov. is redescribed based on the type material and seven new species of the genus Endonura are described from the various parts of the Caucasus. E. paracantabrica sp. nov. can be recognized by the number of chaetae (L+So) on head and a fusion of tubercles Di and De on the first thoracic segment. Specific traits of E. aibgai sp. nov. include small body size, low number of chaetae (L+So) on head, nonogival labrum, dentate claws, and long tibiotarsal chaetae B4 and B5. E. diminutichaeta sp. nov. is characterized by an unusually short chaeta Di1on abdomen IV. E. dobrolyubovae sp. nov. can be distinguished from its congeners by notably long chaeta Ocp on head and the presence of male ventral organ. The absence of chaetae E and O on head, ogival labrum, cryptopygy and dentate claws are typical of E. cryptopyga sp. nov. E. ossetica sp. nov. is most easily recognized by an unusual shape of tubercle Af on head connected with chaetae D and E. Main characteristics of E. kremenitsai sp. nov. include the presence of chaeta E and five chaetae Dl on head. A key to all known species of the genus including the above outlined taxa is given. General remarks on distribution and possible historical biogeography of the genus are also provided.

Redescription of two troglobiotic species of Deuteraphorura Absolon, 1901 &lt;br /&gt;(Collembola, Onychiuridae) from the Western Carpathians

Two species of the genus Deuteraphorura Absolon, 1901 from the Western Carpathian caves (Central Europe) are redescribed, namely D. kratochvili (Nosek, 1963) and D. schoenviszkyi (Loksa, 1967). Both species are characterized by the absence of pseudocelli on thoracic tergum I, presence of male ventral organ on abdominal terga II-III and 3 pseudocelli on hind margin of head. D. kratochvili is redescribed based on specimens from the type locality (Demänovská Cave System) and its intraspecific variability in morphological traits is discussed. Redescription of D. schoenviszkyi (Loksa, 1967) is based on specimens from the Slovak and Aggtelek Karst, the karst area where the type locality is situated. Both species are restricted to subterranean environment, thus classified as obligate cave forms (troglobionts). An identification key to Deuteraphorura species, characterized by absence of pseudocelli on thoracic segment I, is provided.

Caffeine Taste Signaling in Drosophila Larvae.

The Drosophila larva has a simple peripheral nervous system with a comparably small number of sensory neurons located externally at the head or internally along the pharynx to assess its chemical environment. It is assumed that larval taste coding occurs mainly via external organs (the dorsal, terminal, and ventral organ). However, the contribution of the internal pharyngeal sensory organs has not been explored. Here we find that larvae require a single pharyngeal gustatory receptor neuron pair called D1, which is located in the dorsal pharyngeal sensilla, in order to avoid caffeine and to associate an odor with caffeine punishment. In contrast, caffeine-driven reduction in feeding in non-choice situations does not require D1. Hence, this work provides data on taste coding via different receptor neurons, depending on the behavioral context. Furthermore, we show that the larval pharyngeal system is involved in bitter tasting. Using ectopic expressions, we show that the caffeine receptor in neuron D1 requires the function of at least four receptor genes: the putative co-receptors Gr33a, Gr66a, the putative caffeine-specific receptor Gr93a, and yet unknown additional molecular component(s). This suggests that larval taste perception is more complex than previously assumed already at the sensory level. Taste information from different sensory organs located outside at the head or inside along the pharynx of the larva is assembled to trigger taste guided behaviors.

Ultrastructure of Sensilla on Larvae and Adults ofChrysomya megacephala(Diptera: Calliphoridae)

ABSTRACT: Sensilla on insect body parts play an important role on their behavior for ovipositing and foraging. To describe the morphology and distribution of sensilla on adults and larvae of C. megacephala, scanning electron miscroscopy was applied to give detailed information. There are five types of sensilla on antenna, three on the proboscis and ovipositor, two on the haltere and leg, and only one on the wing. All body parts bear microtrichia, except for the ovipositor. Mechanoreceptors are present in all body parts of adults. Sensilla on larvae are different from those on adults. Larval antenna is a dome shaped organ located in a cavity on the cephalic region. Four papillae distribute in the ventral organ, and five coeloconic sensilla and several basiconic sensilla are located on maxillary palp of larvae. Many basiconic sensilla are situated on the ventral depression close to posterior spiracular. This is the first overall observation about sensilla on the whole body of C. megacephala adults and larva...

Ectopic hbox12 Expression Evoked by Histone Deacetylase Inhibition Disrupts Axial Specification of the Sea Urchin Embryo.

Dorsal/ventral patterning of the sea urchin embryo depends upon the establishment of a Nodal-expressing ventral organizer. Recently, we showed that spatial positioning of this organizer relies on the dorsal-specific transcription of the Hbox12 repressor. Building on these findings, we determined the influence of the epigenetic milieu on the expression of hbox12 and nodal genes. We find that Trichostatin-A, a potent and selective histone-deacetylases inhibitor, induces histone hyperacetylation in hbox12 chromatin, evoking broad ectopic expression of the gene. Transcription of nodal concomitantly drops, prejudicing dorsal/ventral polarity of the resulting larvae. Remarkably, impairing hbox12 function, either in a spatially-restricted sector or in the whole embryo, specifically rescues nodal transcription in Trichostatin-A-treated larvae. Beyond strengthen the notion that nodal expression is not allowed in the presence of functional Hbox12 in the same cells, these results highlight a critical role of histone deacetylases in regulating the spatial expression of hbox12.

External Morphology of Stable Fly (Diptera: Muscidae) Larvae.

Scanning electron microscopy was used to examine the external morphology of first-, second-, and third-instar stable flies (Stomoxys calcitrans (L.)). In the cephalic region, the antennae, labial lobe, and maxillary palpi are morphologically similar among instars. Antennae comprise a prominent anterior dome that is the primary site of olfaction, while the maxillary palpi are innervated with mechano- and chemosensilla and scolopodia. The ventral organ and facial mask, also located in the pseudocephalon, are not well-developed in first instars, but become progressively more so in the subsequent instars. When the pseudocephalon is partially retracted, anterior spines cusp around the oral ridges of the facial mask. This indicates the anterior spinose band may be used in conjunction with the facial mask in predigestion. Functional anterior spiracles are absent on first instars, but become evident as a pair of palmate spiracular processes with five to seven lobes in second and third instars. A pair of Keilin's organs, functioning as hygroreceptors, is located on each thoracic segment. Abdominal segments are marked with ventral creeping welts, the anal pad, anus, papillae, and posterior spiracles. Ventral creeping welts are thought to aid in locomotion, while the anal pad acts as an osmoregulatory structure. Posterior spiracles are modified from round spiracular discs with two straight slits in the first instar to triangular discs with two and three sinuous slits in the second and third instars, respectively.