Foregut Organs Research Articles

Pancreaticoduodenectomy in Patients With Coeliac or Superior Mesenteric Artery Stenosis: A Review of the Literature.

Pancreaticoduodenectomy (Whipple's procedure) is a technically demanding operation performed for malignant and premalignant conditions of the pancreatic head, duodenum and bile duct. Awareness of the vascular anatomy, variations, and pathology of this area is essential to achieve safe surgery and good outcomes. The operation involves division of the gastroduodenal artery (GDA) which provides communication between the foregut and midgut blood supply. In patients with coeliac or superior mesenteric artery (SMA) stenosis, this can lead to reduced blood supply to the foregut or midgut organs, with consequent severe ischaemic complications leading to significant morbidity and mortality. Coeliac artery stenosis is caused by median arcuate ligament syndrome (MALS) in the majority of patients with atherosclerosis being the second most common cause. SMA stenosis is much less common and is caused in the majority of cases by atherosclerosis. A review of preoperative imaging and intraoperative gastroduodenal artery clamp test is important to identify cases that may need additional procedures to preserve the blood supply. In this paper, we present a literature review for studies reporting patients undergoing Whipple's operation with concomitant coeliac axis stenosis (CAS) or SMA stenosis. Analysis of causes of stenosis or occlusion, prevalence, risk factors, different management strategies and outcomes was conducted.

Paleocene origin of a streamlined digestive symbiosis in leaf beetles

Timing the acquisition of a beneficial microbe relative to the evolutionary history of its host can shed light on the adaptive impact of a partnership. Here, we investigated the onset and molecular evolution of an obligate symbiosis between Cassidinae leaf beetles and Candidatus Stammera capleta, a γ-proteobacterium. Residing extracellularly within foregut symbiotic organs, Stammera upgrades the digestive physiology of its host by supplementing plant cell wall-degrading enzymes. We observe that Stammera is a shared symbiont across tortoise and hispine beetles that collectively comprise the Cassidinae subfamily, despite differences in their folivorous habits. In contrast to its transcriptional profile during vertical transmission, Stammera elevates the expression of genes encoding digestive enzymes while in the foregut symbiotic organs, matching the nutritional requirements of its host. Despite the widespread distribution of Stammera across Cassidinae beetles, symbiont acquisition during the Paleocene (∼62 mya) did not coincide with the origin of the subfamily. Early diverging lineages lack the symbiont and the specialized organs that house it. Reconstructing the ancestral state of host-beneficial factors revealed that Stammera encoded three digestive enzymes at the onset of symbiosis, including polygalacturonase-a pectinase that is universally shared. Although non-symbiotic cassidines encode polygalacturonase endogenously, their repertoire of plant cell wall-degrading enzymes is more limited compared with symbiotic beetles supplemented with digestive enzymes from Stammera. Highlighting the potential impact of a symbiotic condition and an upgraded metabolic potential, Stammera-harboring beetles exploit a greater variety of plants and are more speciose compared with non-symbiotic members of the Cassidinae.

Extracellular symbiont colonizes insect during embryo development.

Insects typically acquire their beneficial microbes early in development. Endosymbionts housed intracellularly are commonly integrated during oogenesis or embryogenesis, whereas extracellular microbes are only known to be acquired after hatching by immature instars such as larvae or nymphs. Here, however, we report on an extracellular symbiont that colonizes its host during embryo development. Tortoise beetles (Chrysomelidae: Cassidinae) host their digestive bacterial symbiont Stammera extracellularly within foregut symbiotic organs and in ovary-associated glands to ensure its vertical transmission. We outline the initial stages of symbiont colonization and observe that although the foregut symbiotic organs develop 3 days prior to larval emergence, they remain empty until the final 24h of embryo development. Infection by Stammera occurs during that timeframe and prior to hatching. By experimentally manipulating symbiont availability to embryos in the egg, we describe a 12-h developmental window governing colonization by Stammera. Symbiotic organs form normally in aposymbiotic larvae, demonstrating that these Stammera-bearing structures develop autonomously. In adults, the foregut symbiotic organs are already colonized following metamorphosis and host a stable Stammera population to facilitate folivory. The ovary-associated glands, however, initially lack Stammera. Symbiont abundance subsequently increases within these transmission organs, thereby ensuring sufficient titers at the onset of oviposition ~29days following metamorphosis. Collectively, our findings reveal that Stammera colonization precedes larval emergence, where its proliferation is eventually decoupled in adult beetles to match the nutritional and reproductive requirements of its host.

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.

A single-cell–resolution fate map of endoderm reveals demarcation of pancreatic progenitors by cell cycle

Significance During embryonic development, an early-stage progenitor cell could generate different types of descendant cells. Developmental biologists keep dreaming of making all the descendant cell types generated by each early-stage progenitor cell clear. Here, we focus on one germ layer, the endoderm. Early foregut endoderm generates foregut digestive organs, including the pancreas, liver, and digestive tract. The central point of this work is the establishment of a full-coverage, single-cell–resolution fate map of zebrafish early foregut endoderm through unbiased labeling of every single endodermal progenitor cell and tracing its descendant cells. Based on the maps, we reveal a link of the cell cycle state and pancreatic fate propensity, providing an example of how the maps could facilitate understanding cell fate determination.

Papers presented at the fall 2020 Pediatric Urologic Oncology Work Group of the Societies of Pediatric Urology meetingBladder Duplication in a Setting of VACTER Association

Bladder duplication is a rare anomaly classified as sagittal or coronal, depending on the axis of the septum. VACTER association involves congenital anomalies affecting the vertebrae, anus, heart, trachea, esophagus, kidney and genitourinary system. This is the first description of a case of coronal bladder duplication in a patient that also presented with anomalies on the foregut and other organs that correspond to VACTER association. Pertinent literature is systematically reviewed and compared with our case.

Midline morphogenesis of zebrafish foregut endoderm is dependent on Hoxb5b

During vertebrate embryonic development complex morphogenetic events drive the formation of internal organs associated with the developing digestive tract. The foregut organs derive from hepatopancreatic precursor cells that originate bilaterally within the endoderm monolayer, and subsequently converge toward the midline where they coalesce to produce the gut tube from which the liver and pancreas form. The progenitor cells of these internal organs are influenced by the lateral plate mesoderm (LPM), which helps direct them towards their specific fates. However, it is not completely understood how the bilateral organ precursors move toward the embryonic midline and ultimately coalesce to form functional organs. Here we demonstrate that the zebrafish homeobox gene hoxb5b regulates morphogenesis of the foregut endoderm at the midline. At early segmentation stages, hoxb5b is expressed in the LPM adjacent to the developing foregut endoderm. By 24 hpf hoxb5b is expressed directly in the endoderm cells of the developing gut tube. When Hoxb5b function is disrupted, either by morpholino knockdown or sgRNA/Cas9 somatic disruption, the process of foregut morphogenesis is disrupted, resulting in a bifurcated foregut. By contrast, knockdown of the paralogous hoxb5a gene does not alter gut morphology. Further analysis has indicated that Hoxb5b knockdown specimens produce endocrine pancreas cell types, but liver cells are absent. Finally, cell transplantation experiments revealed that Hoxb5b function in the endoderm is not needed for proper coalescence of the foregut at the midline. Together, our findings imply that midline morphogenesis of foregut endoderm is guided by a hoxb5b-mediated mechanism that functions extrinsically, likely within the LPM. Loss of hoxb5b function prevents normal coalescence of endoderm cells at the midline and thus disrupts gut morphogenesis.

Isolation of Embryonic Tissues and Formation of Quail-Chicken Chimeric Organs Using The Thymus Example.

The capacity to isolate embryonic tissues was an essential step for establishing the quail-chicken chimera system, which in turn has provided undisputed contributions to unveiling key processes in developmental biology. Herein is described an optimized method to isolate embryonic tissues from quail and chickens by microsurgery and enzymatic digestion while preserving its biological properties. After isolation, tissues from both species are associated in an in vitro organotypic assay for 48 h. Quail and chicken tissues can be discriminated by distinct nuclear features and molecular markers allowing the study of the cellular cross-talk between heterospecific association of tissues. This approach is, therefore, a useful tool for studying complex tissue interactions in developmental processes with highly dynamic spatial modifications, such as those occurring during pharyngeal morphogenesis and the formation of the foregut endoderm-derived organs. This experimental approach was first developed to study the epithelial-mesenchymal interactions during early-stages of thymus formation. In this, the endoderm-derived prospective thymic rudiment and mesoderm-derived mesenchyme, were isolated from quail and chicken embryos, respectively. The capacity of the associated tissues to generate organs can be further tested by grafting them onto the chorioallantoic membrane (CAM) of a chicken embryo. The CAM provides nutrients and allows gas exchanges to the explanted tissues. After 10 days of in ovo development, the chimeric organs can be analyzed in the harvested explants by conventional morphological methods. This procedure also allows studying tissue-specific contributions during organ formation, from its initial development (in vitro development) to the final stages of organogenesis (in ovo development). Finally, the improved isolation method also provides three-dimensionally (3D) preserved embryonic tissues, that can also be used for high-resolution topographical analysis of tissue-specific gene-expression patterns.

The University of Chicago contribution to the treatment of gastroesophageal reflux disease and its complications: a tribute to David B. Skinner 1935-2003.

To highlight the contributions from the University of Chicago under the leadership of Dr David B. Skinner to the understanding of gastroesophageal reflux disease (GERD) and its complications. The invention of the esophagoscope confirmed that GERD was a premorbid condition. The medical world was divided between those who believed in a morphological lower esophageal sphincter (LES) and those who did not. Those who did not believe attempted to rearrange the anatomy of the foregut organs to stop reflux with minimal success. The discovery of the LES focused attention on the sphincter as the main deterrent to reflux and the hope that measurement of a low LES pressure would mark the presence of GERD. This turned out not to be so. In July 1973, with this history of confusion, Dr Skinner at the age of 36 assumed the chair of surgery at the University of Chicago. The publications of the University of Chicago's esophageal group were collected from private and public (PubMed) databases, reviewed, and seminal contributions selected. Twenty-four-hour esophageal pH monitoring led to the understanding of the LES, its contribution to GERD, and the complication of Barrett's esophagus. The relationship of Barrett's to adenocarcinoma was clarified. The rising incidence of esophageal adenocarcinoma led to contributions in the staging of esophageal cancer and its treatment with an en bloc resection. Ten years after the death of Dr Skinner, we can appreciate the monumental contributions to benign and malignant esophageal disease under his leadership.

Huge clusters of embryonic stem cells in human embryos: a morphologic study.

Nothing is known about huge clusters (HC) of embryonic stem cells (ESC) in human fetal organs (HFO). To know the status of HC-ESC in HFO. Morphology and immunohistochemistry (IHC) in 32 HFO of 7-40 gestational weeks (GW). HC-ESC were seen in many HFO including central nervous system, spinal cords, spine, soft tissue, bone, skin, thyroid, lung, liver, pancreas, gall bladder, extrahepatic bile duct, adrenal, kidney, bladder, foregut, midgut, hindgut, female and male genital organs, and neurons. HC-ESC's were composed of two populations depending on constituting cells. One were large cells with ample acidophilic cytoplasms with vesicular nuclei and nucleoli. The other were small cells with scant cytoplasm with hyperchromatic nuclei without nucleoli, resembling lymphocytes. The HC-ESC were frequently showed neuronal differentiation. HC-ESC were positive for NCAM, synaptophysin, NSE, chromogranin, PDGFRA, AFP, ErbB2, bcl-2, KIT, MET. They were negative for CD45, CD3, CD20, EMA, CEA, CA19-9, cytokeratin (CK) 7, CK8, CK18, CK19, MUC1, MUC2, MUC5AC, and MUC6. The mean Ki-67 labeling index (LI) was 13% ± 7%. HC-ESC showed a little glycogen but lacked mucins. These HC-ESC were seen in 7-25 GW, and they were rarely seen in 26-40 GW. The morphology, IHC, and ontogeny of HC-ESC were described.

Endodermal and mesenchymal cross talk: a crossroad for the maturation of foregut organs

The developmental stages of each foregut organ are intimately linked to the development of the other foregut organs such that the ultimate function of any one foregut organ, such as the metabolic function of the liver, depends on organizational changes associated with the maturation of multiple foregut organs. These changes include: (i) proliferation of the intrahepatic bile ducts and hepatoblasts within the liver coinciding with parenchymal expansion, (ii) elongation of extrahepatic bile ducts, which allows for proper gallbladder (GB) formation, and (iii) duodenal elongation and rotation, which coincides with all of the above to connect the intrahepatic, extrahepatic, and pancreatic ductal systems with the intestine. It is well established that cross talk between endodermal and mesenchymal components of the foregut occurs, particularly regarding the vascularization of developing organs. Furthermore, genetic mutations in mesenchymal and hepatic compartments of the developing foregut result in similar foregut pathologies: hypoplastic liver, absence of GB, biliary atresia (intrahepatic and/or extrahepatic), and failure of gut elongation and rotation. Finally, these shared pathologies can be linked to deficiencies in genes specific to the septum transversum mesenchyme (Hes1, Hlx, and Foxf1) or liver (Hhex and Hnf6), illustrating the complexity of such cross talk.

Cincinnati Regional Incidence, Morbidity, and Mortality of Neonatal Foregut Defects and High Coincidence with Cardiovascular Malformations

The first trimester fetal foregut generates organs from larynx to ligament of Treitz. The incidence and clinical impact of many of the 29 congenital malformations arising from the foregut organs remain under characterized. We performed a retrospective chart review on patients from a geographically defined area born between 2006 and 2008 admitted to Cincinnati Children’s Hospital Neonatal Intensive Care Unit with diagnoses consistent with one or more congenital foregut malformations. We found foregut malformations occurred in 1 in 801 births and determined the incidence for each individual foregut malformation, including some that have not previously been reported. We report a high rate of multiple congenital foregut malformations within an individual with coincidence of foregut malformations of 51.5%, and a high association with cardiovascular malformations (40%). Hospital stay was prolonged (32 days versus 5days). Need for assisted feeding (51%) and respiratory support (27%) at discharge were higher when compared to control patients (12 and 6%, respectively). Mortality was 7% in patients with foregut malformations. These data provide needed quantitation of the incidence, morbidity, and mortality related to congenital foregut defects present in inpatient neonates. The coincidence of foregut malformations with cardiovascular malformations underscores the need for further research into their coordinated embryologic formation to aid their prevention and treatment.

Selective feeding on nutrient-rich particles by gizzard shad Dorosoma cepedianum does not involve mechanical sorting

Previous field and laboratory studies have concluded that suspension-feeding detriti - vorous fish such as gizzard shad Dorosoma cepedianum selectively ingest nutrient-rich particles using either mechanical sorting within the oropharyngeal cavity or behavioral selectivity within the environment, but none have distinguished between these hypothesized selection mecha- nisms. To determine whether mechanical selectivity occurs within the oropharyngeal cavity, giz- zard shad were fed particles of standardized size but different carbon and nitrogen content in homogeneous particle suspensions vs. non-homogeneous particle distributions. By comparing foregut and epibranchial organ contents with the particles available in a homogeneous suspen- sion, we demonstrated that the fish did not use mechanical selection for nutrient-rich particles. Previously published hypotheses for intraoral selection of nutrient-rich particles in gizzard shad using crossflow filtration or gustatory receptors were not supported. However, when particles with different nutrient content were allowed to settle in a heterogeneous distribution, the nutrients in the foregut and epibranchial organs were 1.5 times higher than those of particles in the water and 2.5 times higher than those of settled particles (p ≤ 0.0001). As a test of one potential behavioral mechanism of particle selection, disturbance of the sedimentwater interface resulted in signifi- cantly higher organic carbon (p = 0.01) and nitrogen (p = 0.001) within 1 to 2 cm of the bottom com- pared to the overlying water and the bottom sediment. Thus, future laboratory and field studies should focus on potential behavioral mechanisms of particle selectivity in detritivorous fish sus- pension feeding on non-homogeneous distributions of small particles (<< 1 mm).

Three new species of Pruvotinidae (Mollusca: Solenogastres) from Antarctica and NW Spain

The family Pruvotinidae (Solenogastres, Cavibelonia) includes thirty species of fifteen genera grouped in five subfamilies. These subfamilies are defined by the combination of the presence or absence of hollow hook-shaped sclerites, the presence or absence of a dorsopharyngeal gland and the type of ventrolateral foregut glandular organs: type A, type C or circumpharyngeal. In this paper, three new species of the family Pruvotinidae are described: Pruvotina artabra n. sp. and Gephyroherpia impar n. sp. from NW Spain, and Pruvotina manifesta n. sp. from Antarctic Peninsula. These new descriptions increase the global knowledge of Solenogastres biodiversity.

A gene regulatory network controlling hhex transcription in the anterior endoderm of the organizer

The homeobox gene hhex is one of the earliest markers of the anterior endoderm, which gives rise to foregut organs such as the liver, ventral pancreas, thyroid, and lungs. The regulatory networks controlling hhex transcription are poorly understood. In an extensive cis-regulatory analysis of the Xenopus hhex promoter, we determined how the Nodal, Wnt, and BMP pathways and their downstream transcription factors regulate hhex expression in the gastrula organizer. We show that Nodal signaling, present throughout the endoderm, directly activates hhex transcription via FoxH1/Smad2 binding sites in the proximal −0.44 Kb promoter. This positive action of Nodal is suppressed in the ventral–posterior endoderm by Vent 1 and Vent2, homeodomain repressors that are induced by BMP signaling. Maternal Wnt/β-catenin on the dorsal side of the embryo cooperates with Nodal and indirectly activates hhex expression via the homeodomain activators Siamois and Twin. Siamois/Twin stimulate hhex transcription through two mechanisms: (1) they induce the expression of Otx2 and Lim1 and together Siamois, Twin, Otx2, and Lim1 appear to promote hhex transcription through homeobox sites in a Wnt-responsive element located between −0.65 to −0.55 Kb of the hhex promoter. (2) Siamois/Twin also induce the expression of the BMP-antagonists Chordin and Noggin, which are required to exclude Vents from the organizer allowing hhex transcription. This study reveals a complex network regulating anterior endoderm transcription in the early embryo.

Wnt2/2b and β-Catenin Signaling Are Necessary and Sufficient to Specify Lung Progenitors in the Foregut

Patterning of the primitive foregut promotes appropriate organ specification along its anterior-posterior axis. However, the molecular pathways specifying foregut endoderm progenitors are poorly understood. We show here that Wnt2/2b signaling is required to specify lung endoderm progenitors within the anterior foregut. Embryos lacking Wnt2/2b expression exhibit complete lung agenesis and do not express Nkx2.1, the earliest marker of the lung endoderm. In contrast, other foregut endoderm-derived organs, including the thyroid, liver, and pancreas, are correctly specified. The phenotype observed is recapitulated by an endoderm-restricted deletion of beta-catenin, demonstrating that Wnt2/2b signaling through the canonical Wnt pathway is required to specify lung endoderm progenitors within the foregut. Moreover, activation of canonical Wnt/beta-catenin signaling results in the reprogramming of esophagus and stomach endoderm to a lung endoderm progenitor fate. Together, these data reveal that canonical Wnt2/2b signaling is required for the specification of lung endoderm progenitors in the developing foregut.

A Review of Porcine Foregut Anatomy for the Beginning Endoscopic Researcher

Purpose: Recently, there has been a rise in endolumenal and natural orifice translumenal endoscopic surgery (NOTES) research, most of which utilizes a porcine model. The size and function of the swine GI tract make it suitable for studying techniques with human equipment, but there are key anatomic differences. This abstract reviews porcine foregut anatomy for the beginning endoscopic researcher, highlighting relevant differences from human anatomy. Methods: We reviewed laboratory NOTES recordings to identify procedural difficulties related to porcine anatomy. Results: Esophagus: A 3–4 cm pharyngeal diverticulum is encountered in the caudal pharynx. The endoscope must be directed ventrally into the esophagus to avoid perforating the pharynx. Gastro-esophageal Junction (GEJ): The GEJ is located within the caudal mediastinum. Entry into this space during transesophageal procedures may lead to hemodynamic instability from vena cava compression. In addition, esophageal mucosa extends past the mechanical GEJ into the stomach; in contrast to the human, where the transition to gastric mucosa occurs in the esophagus. Stomach: The left extremity of the swine stomach is a conical blind pouch. Feed may be retained here, leading to potential contamination of the surgical site. Additionally, the stomach has greater mobility when insufflated than the human stomach, in part because of thinner omentum and loose attachments to surrounding organs. This mobility allows gastric rotation, which affects the reproducibility of gastrotomy creation. Furthermore, the stomach is U-shaped, making passage into the duodenum challenging. Pylorus: The torus pyloricus, a protuberance of muscle and fat, projects from the lesser curve near the pylorus, reducing the luminal size. This also complicates entry into the duodenum. Liver: The liver is large, multi-lobular and extremely convex on the diaphragmatic surface. The gall bladder is found in a fossa mainly on the right medial lobe but also partly on the left medial lobe. This location, and deep interlobular fissures, can make it challenging to access the gall bladder. The cystic duct and artery are smaller, less defined and longer in length than in humans. This increases the difficulty of identification and manipulation. Spleen: The spleen is large and mobile, characteristics which increase the chance of iatrogenic injury. Conclusion: The size of porcine foregut organs make them amenable to endoscopic research, but novice researchers must be cognizant of anatomical differences from humans when performing interventions.

Three new species of Simrothiellidae (Solenogastres) associated with the hot-vent biotope

Solenogastres specimens collected during three French cruises at different hydrothermal vent sites represent three undescribed species, all belonging to the family Simrothiellidae (order Cavibelonia): Helicoradomenia parathermalis n. sp. comes from five stations of the Southeast Pacific Rise, Sensilloherpia pholidota n. sp, n. gen., is recorded from two stations of the Northeast Pacific Rise, and Diptyaloherpia insolita n. sp, n. gen., originates from one station of the Northeast Pacific Rise. The organization of the three species is systematically compared, and the two new genera are defined; they enlarge our knowledge of the organizational diversity of Solenogastres. The definitions of Simrothiellidae and of the order Cavibelonia are emended correspondingly. The common characters of all hot vent Solenogastres and adaptations in relation to this particular biotope are discussed; these include a particular anterior sense organ, solid mantle sclerites, latero-ventral foregut glandular organs of the clustered type, and a non-cnidarian diet, probably of polychaetes.

Cdx4 is required in the endoderm to localize the pancreas and limitβ-cell number

Cdx transcription factors have crucial roles in anteroposterior patterning of the nervous system and mesoderm. Here we focus on the role of cdx4 in patterning the endoderm in zebrafish. We show that cdx4 has roles in determining pancreatic beta-cell number, directing midline convergence of beta-cells during early pancreatic islet formation, and specifying the anteroposterior location of foregut organs. Embryos deficient in cdx4 have a posteriorly shifted pancreas, liver and small intestine. The phenotype is more severe with knockdown of an additional Cdx factor, cdx1a. We show that cdx4 functions within the endoderm to localize the pancreas. Morpholino knockdown of cdx4 specifically in the endoderm recapitulates the posteriorly shifted pancreas observed in cdx4 mutants. Conversely, overexpression of cdx4 specifically in the endoderm is sufficient to shift the pancreas anteriorly. Together, these results suggest a model in which cdx4 confers posterior identity to the endoderm. Cdx4 might function to block pancreatic identity by preventing retinoic acid (RA) signal transduction in posterior endoderm. In support of this, we demonstrate that in cdx4-deficient embryos treated with RA, ectopic beta-cells are located well posterior to the normal pancreatic domain.

Rhopalomenia glandulosa spec. nov., and the restoration of Entonomenia Leloup (Mollusca: Solenogastres)

A new species of Solenogastres from the Rockall Basin (NW of Scotland) at 1270 m is described. The organisation of Rhopalomenia glandulosa spec. nov. coincides with that of the type species R. aglaopheniae (Kowalevsky &amp; Marion, 1887) in the presence of two different types of foregut glandular organs (characterised as type A or extraepithelial and type C or intraepithelial). Compared with other Rhopalomeniidae, this condition is generic and leads to the restoration of the currently synonymised genus Entonomenia Leloup, 1948, which has glandular organs consisting of ducts with subepithelially/extraepithelially arranged glandular cells only (= type A ). Besides E. atlantica Leloup, 1948 (type species), six species described as Rhopalomenia are transferred to Entonomenia.