Striated myogenesis and peristalsis in the fetal murine esophagus occur without cell migration or interstitial cells of Cajal

Bi-layer silk fibroin grafts support functional tissue regeneration in a porcine model of onlay esophagoplasty

Partial circumferential, full thickness defects of the esophagus can occur as a result of organ perforation or tumour resection, or during surgical reconstruction of strictured segments. Complications associated with autologous tissue flaps conventionally utilized for defect repair necessitate the development of new graft options. In this study, bi-layer silk fibroin (BLSF) scaffolds were investigated for their potential to support functional restoration of partial circumferential defects in a porcine model of esophageal repair. Onlay thoracic esophagoplasty with BLSF matrices (~3 x 1.5 cm) was performed in adult swine (N = 6) for 3 months of implantation. All animals receiving BLSF grafts survived with no complications and were capable of solid food consumption. Radiographic esophagrams revealed preservation of organ continuity with no evidence of contrast extravasation or strictures. Fluoroscopic analysis demonstrated peristaltic contractions. Ex vivo tissue bath studies displayed contractile responses to carbachol, electric field stimulation, and KCl while isoproterenol produced tissue relaxation. Histological and immunohistochemical evaluations of neotissues showed a stratified, squamous epithelium, a muscularis mucosa composed of smooth muscle bundles, and a muscularis externa organized into circular and longitudinal layers, with a mix of striated skeletal muscle fascicles interspersed with smooth muscle. De novo innervation and vascularization were observed throughout the graft sites and consisted of synaptophysin-positive neuronal boutons and vessels lined with CD31-positive endothelial cells. The results of this study demonstrate that BLSF scaffolds can facilitate constructive remodeling of partial circumferential, full thickness esophageal defects in a large animal model. Copyright © 2017 John Wiley & Sons, Ltd.

Oesophageal and sternohyal muscle fibres are novel Pax3-dependent migratory somite derivatives essential for ingestion

Striated muscles that enable mouth opening and swallowing during feeding are essential for efficient energy acquisition, and are likely to have played a fundamental role in the success of early jawed vertebrates. The developmental origins and genetic requirements of these muscles are uncertain. Here, we determine by indelible lineage tracing in mouse that fibres of sternohyoid muscle (SHM), which is essential for mouth opening during feeding, and oesophageal striated muscle (OSM), which is crucial for voluntary swallowing, arise from Pax3-expressing somite cells. In vivo Kaede lineage tracing in zebrafish reveals the migratory route of cells from the anteriormost somites to OSM and SHM destinations. Expression of pax3b, a zebrafish duplicate of Pax3, is restricted to the hypaxial region of anterior somites that generate migratory muscle precursors (MMPs), suggesting that Pax3b plays a role in generating OSM and SHM. Indeed, loss of pax3b function led to defective MMP migration and OSM formation, disorganised SHM differentiation, and inefficient ingestion and swallowing of microspheres. Together, our data demonstrate Pax3-expressing somite cells as a source of OSM and SHM fibres, and highlight a conserved role of Pax3 genes in the genesis of these feeding muscles of vertebrates.

Late embryonic and postnatal development of interstitial cells of cajal in mouse esophagus: distribution, proliferation and kit dependence

This paper investigates alterations in interstitial cells of Cajal (ICC) in the esophagus of mice from embryonic day 13.5 (E13.5) to 36 days postpartum (P0-P36) using immunohistochemistry. At E13.5, Kit+ cells presented in clusters and differentiated into spindle-like cells with biopolar processes within the outer (longitudinal) and inner (circular) muscle layers at E17.5. These Kit+ ICC with long processes were also Ano1+ and prominent at birth. The density of ICC gradually decreased, and at P36 it became about one twentieth of that at birth. Kit ligand (stem cell factor) expression is lower in striated muscle cells than that in smooth muscle cells. The ICC number was higher in the distal (close to the cardia) than in the proximal esophagus (close to the pharynx). Some Kit+/Ki67+ and Kit+/bromodeoxyuridine+ cells were observed within the muscle layers, and proliferation persisted from birth through adulthood (P28) with a gradually decreasing cell number. At 24 h, Kit+ ICC were dramatically decreased and almost missing 48 h after administration of imatinib (a Kit inhibitor). Our results indicate that ICC proliferation is age dependent and persists throughout the postnatal period. There is a dramatic decrease in the ICC number from P0 to adult life. The Kit signal is essential for the postnatal development of ICC in the esophagus.

Morphology of the developing muscularis externa in the mouse esophagus

Muscularis externa of mouse esophagus is composed of two skeletal muscle layers in the adult. But less attention is paid to the histogenesis of the muscularis externa of the esophagus, and controversies still exist about the developmental process and the spatio-temporal expression characteristics of muscle-specific proteins during the development of esophageal muscularis externa. To further probe into the developmental pattern of muscularis externa of the mouse esophagus and the expression characteristics of different muscle-specific proteins, immunohistochemical and terminal deoxyribonucleotidyl transferase-mediated deoxyuridine triphosphate (dUTP)-digoxigenin nick-end labeling apoptotic staining methods are used to investigate the expression patterns of different muscle-specific proteins and to elucidate the relationship of these protein expressions with the development of muscularis externa of the mouse esophagus. Thus, an understanding of the developing esophageal muscularis externa may be important for developing therapeutic strategies for the treatment of human esophagus diseases. Serial sections of mouse embryos from embryonic day (ED) 12 to ED18, and full-length esophagi from postnatal first to 5th day were stained with monoclonal antibodies against α-smooth muscle actin (α-SMA), α-sarcomerical actin (α-SCA), desmin, and monoclonal anti-skeletal myosin (MHC), while apoptosis was determined using the terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick-end labeling assay. The expression of α-SMA was started at ED12. During the development of ED14-ED15, α-SMA positive cells were seen extending from the walls of left three, four, and six arch arteries toward the dorsal wall of esophagus. Stronger expression of α-SCA and desmin could be detected at ED14 and ED15, expression intensity in caudal segment and inner layer was stained stronger than that of cranial segment and outer layer, but after ED16, strong expression of α-SCA and desmin was found in the outer layer of muscularis externa. Expression of MHC was first detected in the outer layer of cranial segment of muscularis externa at ED17. At ED18, MHC had extended to the level of thyroid gland, staining intensity in the outer layer and cranial segment was stronger than that of inner layer and caudal segment. One to five days after birth, the thickness of the esophageal muscle layer was obviously increased. Most of the muscle cells in the cranial segment of esophagus showed strong expression of α-SCA and clear cross striations at higher magnification. With progression toward the caudal segment, expression intensity of α-SCA became weaker, but the expression intensity of desmin was the same at different levels of esophagus. The muscle fibers were arranged densely with high expression of MHC in the cranial segment. During the development of esophageal muscularis externa, few apoptotic cells were observed. α-SMA, α-SCA, desmin, and MHC show different expression patterns. The differentiation of outer layer of esophageal muscularis externa is quicker than that of inner layer, and the caudal segment is quicker than that of the cranial segment. Besides, apoptosis may not participate in the development of esophageal muscularis externa. The smooth muscle cells from arch arteries may participate in the development of esophageal muscularis externa.

Retinoic acid rescues deficient airway innervation and peristalsis of hypoplastic rat lung explants

BACKGROUND

Bronchial peristalsis modulates lung growth and is deficient in hypoplastic nitrofen-exposed rat lung explants. Retinoic acid (RA) rescues lung hypoplasia. This study examines whether decreased bronchial innervation contributes to this developmental deficiency and if RA is able to recover bronchial innervation and motility.

MATERIAL AND METHODS

After IRB approval, pregnant rats received either 100 mg nitrofen or vehicle on gestational day 9.5 (E9.5). Embryonic lung primordia harvested on E13 were cultured for 72 h and RA was added daily to the medium when appropriate. Lung growth was assessed by counting the number of terminal buds and measuring explant surface, total DNA and protein in control, control + RA, nitrofen and nitrofen + RA groups. Peristaltic contractions were recorded for 10 min under an inverted microscope. Lung explants stained for anti-protein gene product 9.5 (PGP 9.5) and smooth muscle α-actin were examined under a confocal microscope for depicting the specific relationship between neural and smooth muscle cells. PGP 9.5 and smooth muscle α-actin levels were quantified by Western blot analysis for assessing the neural and muscle cell expressions. Comparisons between groups were made with non-parametric tests.

RESULTS

The number of terminal buds, the explants' surface and the DNA and protein contents were significantly decreased in nitrofen-exposed lungs in comparison with controls. In contrast, these measurements were normal in explants exposed to both nitrofen and RA. Bronchial peristalsis (contractions/min) was significantly decreased in nitrofen-exposed lungs in comparison with controls; in contrast, in nitrofen + RA lungs it was similar to controls. In all study groups, the airways were surrounded by smooth muscle and ensheathed in a plexus of nerve fibers containing ganglia. PGP 9.5 protein levels were decreased in nitrofen-exposed lungs, but they normalized when RA was added. No differences were found in α-actin protein levels. Explants exposed only to RA were similar to control.

CONCLUSIONS

Lung growth, bronchial innervation and peristalsis are decreased in nitrofen-exposed lung explants and are rescued by RA. If deficient airway innervation contributing to dysmotility and pulmonary hypoplasia can be pharmacologically rescued, new relatively simple prenatal interventions could be envisioned.

Molecular aspects of esophageal development

The following on molecular aspects of esophageal development contains commentaries on esophageal striated myogenesis and transdifferentiation; conversion from columnar into stratified squamous epithelium in the mouse esophagus; the roles for BMP signaling in the developing esophagus and forestomach; and evidence of a direct conversion from columnar to stratified squamous cells in the developing esophagus.

The expression of nestin delineates skeletal muscle differentiation in the developing rat esophagus

The muscularis externa of the developing rodent esophagus is initially composed of smooth muscle, and later replaced by skeletal muscle in a craniocaudal progression. There is growing evidence of distinct developmental origins for esophageal smooth and skeletal muscles. However, the identification of skeletal muscle progenitor cells is controversial, and the detailed cell lineage of their descendants remains elusive. In the current study, we carried out multiple labeling immunofluorescence microscopy of nestin and muscle type-specific markers to characterize the dynamic process of rat esophageal myogenesis. The results showed that nestin was transiently expressed in immature esophageal smooth muscle cells in early developing stages. After nestin was downregulated in smooth muscle cells, a distinct population of nestin-positive cells emerged as skeletal muscle precursors. They were mitotically active, and subsequently co-expressed MyoD, followed by the embryonic and later the fast type of skeletal muscle myosin heavy chain. Thus, the cell lineage of esophageal skeletal muscle differentiation was established by an immunotyping approach, which revealed that skeletal myocytes arise from a distinct lineage rather than through transdifferentiation of smooth muscle cells during rat esophageal myogenesis.