Fgf signalling is required for gill slit formation in the skate, Leucoraja erinacea

The gill slits of fishes develop from an iterative series of pharyngeal endodermal pouches that contact and fuse with surface ectoderm on either side of the embryonic head. We find in the skate (Leucoraja erinacea) that all gill slits form via a stereotypical sequence of epithelial interactions: 1) endodermal pouches approach overlying surface ectoderm, with 2) focal degradation of ectodermal basement membranes preceding endoderm-ectoderm contact; 3) endodermal pouches contact and intercalate with overlying surface ectoderm, and finally 4) perforation of a gill slit occurs by epithelial remodelling, without programmed cell death, at the site of endoderm-ectoderm intercalation. Skate embryos express Fgf8 and Fgf3 within developing pharyngeal epithelia during gill slit formation. When we inhibit Fgf signalling by treating skate embryos with the Fgf receptor inhibitor SU5402 we find that endodermal pouch formation, basement membrane degradation and endodermal-ectodermal intercalation are unaffected, but that epithelial remodelling and gill slit perforation fail to occur. These findings point to a role for Fgf signalling in epithelial remodelling during gill slit formation in the skate and, more broadly, to an ancestral role for Fgf signalling during pharyngeal pouch epithelial morphogenesis in vertebrate embryos.

Transcervical pharyngeal pouch stapling

BACKGROUND

Pharyngeal pouches are generally treated with surgery, via either an endoscopic or an external approach. Large pouches extending to the mediastinum carry an increased risk of post-operative mediastinitis in the event of a leak following external approach surgery, and may not always be amenable to endoscopic stapling.

METHODS

Transcervical stapling is a newly described technique that uses the endoluminal stapling approach but in which the diverticuloscope is inserted into the pharynx via a neck incision.

CONCLUSIONS

This technique has been used successfully on three patients with large pharyngeal pouches, where endoscopic stapling was not possible due to access limitations.

Expression and Functional Analysis of cofilin1-like in Craniofacial Development in Zebrafish

Pharyngeal pouches, a series of outgrowths of the pharyngeal endoderm, are a key epithelial structure governing facial skeleton development in vertebrates. Pouch formation is achieved through collective cell migration and rearrangement of pouch-forming cells controlled by actin cytoskeleton dynamics. While essential transcription factors and signaling molecules have been identified in pouch formation, regulators of actin cytoskeleton dynamics have not been reported yet in any vertebrates. Cofilin1-like (Cfl1l) is a fish-specific member of the Actin-depolymerizing factor (ADF)/Cofilin family, a critical regulator of actin cytoskeleton dynamics in eukaryotic cells. Here, we report the expression and function of cfl1l in pouch development in zebrafish. We first showed that fish cfl1l might be an ortholog of vertebrate adf, based on phylogenetic analysis of vertebrate adf and cfl genes. During pouch formation, cfl1l was expressed sequentially in the developing pouches but not in the posterior cell mass in which future pouch-forming cells are present. However, pouches, as well as facial cartilages whose development is dependent upon pouch formation, were unaffected by loss-of-function mutations in cfl1l. Although it could not be completely ruled out a possibility of a genetic redundancy of Cfl1l with other Cfls, our results suggest that the cfl1l expression in the developing pouches might be dispensable for regulating actin cytoskeleton dynamics in pouch-forming cells.

Further evidence for Zenker's diverticulum in a slim woman with body figure predisposition: a case report and literature review

Zenker’s diverticulum (ZD) is a bag-like pharyngeal pouch that protrudes to the outside of the pharynx. It is thought to be an acquired disease that occurs following the dysfunction of laryngopharynx muscle, and certain body shapes may be predisposed to this condition. We report a 56-year-old female of slim build with ZD. Computed tomography scanning revealed a hypodense lesion on the left posterior side of her upper esophagus that was filled with air and had no obvious wall. To verify this finding, a barium esophagogram was carried out which showed a round pouch at the level of the 6th cervical vertebral body that communicated with the esophagus through a narrow neck. ZD was subsequently confirmed by endoscopy. These findings provide further evidence in support of a body shape predisposition for ZD.

KTP laser endoscopic cricopharyngeal myotomy and pharyngeal pouch diverticulotomy: how I do it

BACKGROUND

Various endoscopic methods of dividing the cricopharyngeus muscle and the common wall of pharyngeal pouches have been described, most commonly the carbon dioxide laser and stapler. The potassium titanyl phosphate (KTP) laser is an alternate endoscopic method of treatment.

METHODS

The KTP laser is used in a similar fashion to the carbon dioxide laser to carefully divide the cricopharyngeus muscle fibres ± the common wall of the pharyngeal pouch, under microscopic visualization.

CONCLUSION

The KTP laser is an alternative and safe technique for these surgeries.

Pharyngeal pouches provide a niche microenvironment for arch artery progenitor specification

The paired pharyngeal arch arteries (PAAs) are transient blood vessels connecting the heart with the dorsal aorta during embryogenesis. Although PAA malformations often occur along with pharyngeal pouch defects, the functional interaction between these adjacent tissues remains largely unclear. Here, we report that pharyngeal pouches are essential for PAA progenitor specification in zebrafish embryos. We reveal that the segmentation of pharyngeal pouches coincides spatiotemporally with the emergence of PAA progenitor clusters. These pouches physically associate with pharyngeal mesoderm in discrete regions and provide a niche microenvironment for PAA progenitor commitment by expressing BMP proteins. Specifically, pouch-derived BMP2a and BMP5 are the primary niche cues responsible for activating the BMP/Smad pathway in pharyngeal mesoderm, thereby promoting progenitor specification. In addition, BMP2a and BMP5 play an inductive function in the expression of the cloche gene npas4l in PAA progenitors. cloche mutants exhibit a striking failure to specify PAA progenitors and display ectopic expression of head muscle markers in the pharyngeal mesoderm. Therefore, our results support a crucial role for pharyngeal pouches in establishing a progenitor niche for PAA morphogenesis via BMP2a/5 expression.

The second pharyngeal pouch is generated by dynamic remodeling of endodermal epithelium in zebrafish

Pharyngeal arches (PAs) are segmented by endodermal outpocketings called pharyngeal pouches (PPs). Anterior and posterior PAs appear to be generated by different mechanisms, but it is unclear how the anterior and posterior PAs combine. Here, we addressed this issue with precise live imaging of PP development and cell tracing of pharyngeal endoderm in zebrafish embryos. We found that two endodermal bulges are initially generated in the future second PP (PP2) region, which separates anterior and posterior PAs. Subsequently, epithelial remodeling causes contact between these two bulges, resulting in the formation of mature PP2 with a bilayered morphology. The rostral and caudal bulges develop into the operculum and gill, respectively. Development of the caudal PP2 and more posterior PPs is affected by impaired retinoic acid signaling or pax1a/b dysfunction, suggesting that the rostral front of posterior PA development corresponds to the caudal PP2. Our study clarifies an aspect of PA development that is essential for generation of a seamless array of PAs in zebrafish.

Zebrafish Pax1a and Pax1b are required for pharyngeal pouch morphogenesis and ceratobranchial cartilage development

Pharyngeal arches are derived from all three germ layers and molecular interactions among the tissue types are required for proper development of subsequent pharyngeal cartilages; however, the mechanisms underlying this process are not fully described. Here we report that in zebrafish, Pax1a and Pax1b have overlapping and essential functions in pharyngeal pouch morphogenesis and subsequent ceratobranchial cartilage development. Both pax1a and pax1b are co-expressed in pharyngeal pouches, and time-lapse imaging of a novel Tg(pax1b:eGFP) enhancer trap line further revealed the sequential segmental development of pharyngeal pouches. Zebrafish pax1a^-/-; pax1b^-/- double mutant embryos generated by CRISPR-Cas9 mutagenesis exhibit unsegmented pharyngeal pouches 2-5 with small outpocketings. Endodermal expression of fgf3, tbx1 and edn1 is also absent in pharyngeal pouches 2-5 at 36 h post fertilization (hpf). Loss of ceratobranchial cartilage 1-4 and reduced or absent expression of dlx2a and hand2 in the pharyngeal arches 3-6 are observed in CRISPR mutant and morphant embryos that are deficient in both zebrafish pax1a and pax1b at 96 or 36 hpf. These results suggest that zebrafish Pax1a and Pax1b both regulate pharyngeal pouch morphogenesis by modulating expression of fgf3 and tbx1. Furthermore, our data support a model wherein endodermal Pax1a and Pax1b act through Fgf3 and Tbx-Edn1 signaling to non-autonomously regulate the development of ceratobranchial cartilage via expression of dlx2a and hand2.

Diminution of pharyngeal segmentation and the evolution of the amniotes

BACKGROUND

The pharyngeal arches are a series of bulges found on the lateral surface of the head of vertebrate embryos, and it is within these segments that components of the later anatomy are laid down. In most vertebrates, the post-otic pharyngeal arches will form the branchial apparatus, while in amniotes these segments are believed to generate the larynx. It has been unclear how the development of these segments has been altered with the emergence of the amniotes.

RESULTS

In this study, we examined the development of pharyngeal arches in amniotes and show that the post-otic pharyngeal arches in this clade are greatly diminished. We find that the post-otic segments do not undergo myogenesis or skeletogenesis, but are remodelled before these processes occur. We also find that nested DLX expression, which is a feature of all the pharyngeal arches in anamniotes, is associated with the anterior segments but less so with the posterior arches in amniotes. We further show that the posterior arches of the mouse embryo fail to properly delineate, which demonstrates the lack of function of these posterior segments in later development.

CONCLUSION

In amniotes, there has been a loss of the ancestral "branchial" developmental programme that is a general feature of gnathostomes; myogenesis and skeletogenesis This is likely to have facilitated the emergence of the larynx as a new structure not constrained by the segmental organisation of the posterior pharyngeal region.

Can patients determine the level of their dysphagia?

AIM

To determine if patients can localise dysphagia level determined endoscopically or radiologically and association of gender, age, level and pathology.

METHODS

Retrospective review of consecutive patients presenting to dysphagia hotline between March 2004 and March 2015 was carried out. Demographics, clinical history and investigation findings were recorded including patient perception of obstruction level (pharyngeal, mid sternal or low sternal) was documented and the actual level of obstruction found on endoscopic or radiological examination (if any) was noted. All patients with evidence of obstruction including oesophageal carcinoma, peptic stricture, Schatzki ring, oesophageal pouch and cricopharyngeal hypertrophy were included in the study who had given a perceived level of dysphagia. The upper GI endoscopy reports (barium study where upper GI endoscopy was not performed) were reviewed to confirm the distance of obstructing lesion from central incisors. A previously described anatomical classification of oesophagus was used to define the level of obstruction to be upper, middle or lower oesophagus and this was compared with patient perceived level.

RESULTS

Three thousand six hundred and sixty-eight patients were included, 42.0% of who were female, mean age 70.7 ± 12.8 years old. Of those with obstructing lesions, 726 gave a perceived level of dysphagia: 37.2% had oesophageal cancer, 36.0% peptic stricture, 13.1% pharyngeal pouches, 10.3% Schatzki rings and 3.3% achalasia. Twenty-seven point five percent of patients reported pharyngeal level (upper) dysphagia, 36.9% mid sternal dysphagia and 25.9% lower sternal dysphagia (9.5% reported multiple levels). The level of obstructing lesion seen on diagnostic testing was upper (17.2%), mid (19.4%) or lower (62.9%) or combined (0.3%). When patients localised their level of dysphagia to a single level, the kappa statistic was 0.245 (P < 0.001), indicating fair agreement. 48% of patients reporting a single level of dysphagia were accurate in localising the obstructing pathology. With respect to pathology, patients with pharyngeal pouches were most accurate localising their level of dysphagia (P < 0.001). With respect to level of dysphagia, those with pharyngeal level lesions were best able to identify the level of dysphagia accurately (P < 0.001). No association (P > 0.05) was found between gender, patient age or clinical symptoms with their ability to detect the level of dysphagia.

CONCLUSION

Patient perceived level of dysphagia is unreliable in determining actual level of obstructing pathology and should not be used to tailor investigations.

Branchial cleft anomalies: a pictorial review of embryological development and spectrum of imaging findings

Abstract

The branchial arches are the embryological precursors of the face, neck and pharynx. Anomalies of the branchial arches are the second most common congenital lesions of the head and neck in children, with second branchial arch anomalies by far the most common. Clinically, these congenital anomalies may present as cysts, sinus tracts, fistulae or cartilaginous remnants with typical clinical and radiological findings. We review the normal embryological development of the branchial arches and the anatomical structures of the head and neck that derive from each arch. The typical clinical and radiological appearances of both common and uncommon branchial arch abnormalities are discussed with an emphasis on branchial cleft anomalies.

Key points

• Anomalies of the branchial arches usually present as cysts, sinuses or fistulae.

• Second branchial arch anomalies account for approximately 95 % of cases.

• There are no pathognomonic imaging features so diagnosis depends on a high index of suspicion and knowledge of typical locations.

• Persistent cysts, fistulae or recurrent localised infection may be due to branchial arch anomalies.

• Surgical excision of the cyst or tract is the most common curative option.

Switching of the Laryngeal Cavity From the Respiratory Diverticulum to the Vestibular Recess: A Study Using Serial Sagittal Sections of Human Embryos and Fetuses

A cecum-like protrusion of the pharynx (the laryngeal cecum or vestibular recess [VR]) develops immediately anterior to the laryngeal part of the respiratory diverticulum. An expansion of the VR has been well described, whereas the fate of the diverticulum is still obscure, although its pharyngeal opening corresponds to the glottis. We observed sagittal sections of 10 embryos (five specimens at 5-6 weeks and another five at 7-8 weeks) and eight fetuses at 25-30 weeks. At 5-6 weeks, a lumen of the laryngeal part of the respiratory diverticulum appeared, and subsequently, the VR opened into the epithelial lamina. Because of this discrete separation, it seemed unlikely that the pharyngeal pouches contributed to the laryngeal epithelium. At 6-7 weeks, the VR exhibited a high boot-shaped lumen with canalization to the diverticular lumen at the level of the cricoid cartilage. Thus, in a midline area between the bilateral arytenoid cartilages, double laryngeal lumina were evident, separated by the thick midline epithelial lamina. At 25-30 weeks, the inferior part of the VR lumen had become enlarged because of the destruction of the epithelial lamina along the arytenoid and corniculate cartilages. In contrast, candidates for the initial diverticular lumen remained as epithelial slits in the anterosuperior side of the transverse arytenoid muscle. Therefore, the final anterior and lateral laryngeal walls seemed to originate from the VR with canalization, in contrast to the part of the posterior wall derived from the initial diverticular wall.