Musculoskeletal patterning in the pharyngeal segments of the zebrafish embryo

The head skeleton and muscles of the zebrafish develop in a stereotyped pattern in the embryo, including seven pharyngeal arches and a basicranium underlying the brain and sense organs. To investigate how individual cartilages and muscles are specified and organized within each head segment, we have examined their early differentiation using Alcian labeling of cartilage and expression of several molecular markers of muscle cells. Zebrafish larvae begin feeding by four days after fertilization, but cartilage and muscle precursors develop in the pharyngeal arches up to 2 days earlier. These chondroblasts and myoblasts lie close together within each segment and differentiate in synchrony, perhaps reflecting the interdependent nature of their patterning. Initially, cells within a segment condense and gradually become subdivided into individual dorsal and ventral structures of the differentiated arch. Cartilages or muscles in one segment show similar patterns of condensation and differentiation as their homologues in another, but vary in size and shape in the most anterior (mandibular and hyoid) and posterior (tooth-bearing) arches, possibly as a consequence of changes in the timing of their development. Our results reveal a segmental scaffold of early cartilage and muscle precursors and suggest that interactions between them coordinate their patterning in the embryo. These data provide a descriptive basis for genetic analyses of craniofacial patterning.

FINE STRUCTURE OF CHLORIDE CELLS FROM THREE SPECIES OF FUNDULUS

A morphological basis for osmoregulation in the teleosts was studied by comparing the fine structure of chloride cells found in epithelia of the gills of three species of fish: Fundulus heteroclitus which can survive in a wide range of salinities, and F. similis and F. chrysotus which are usually restricted to salt water and fresh water environments, respectively. Gills were removed from F. heteroclitus which had been laboratory adapted to either sea water or pond water. For a comparison, gills were also removed from the marine F. similis and the fresh water F. chrysotus which had been adapted to their natural environments. Gill-filaments were fixed in Millonig's phosphate buffered (pH 7.4), 1 per cent osmium tetroxide and were embedded in Epon. Thin sections of filaments were stained with lead hydroxide. The cytoplasm of chloride cells of all three species of Fundulus is heavily populated with mitochondria and is filled with tubules of the agranular endoplasmic reticulum (ER). An orderly secretory cycle was indicated for chloride cells of salt water adapted F. heteroclitus and the marine F. similis. An amorphous material is observed in the agranular ER. Its density increases towards the apical end of the cell. In the apical cytoplasm, tubules of the agranular ER appear to converge and to discharge the amorphous material into an apical cavity. Except for the actual opening of the apical cavity, the distal end of salt water adapted chloride cells is characteristically shielded from the hypertonic environment by thin cytoplasmic flanges projecting from the neighboring epithelial cells. Chloride cells of the fresh water F. chrysotus resemble chloride cells of pond water adapted F. heteroclitus, in that these cells do not have apical cavities with the functional appearance of those in the sea water adapted forms. The distal end of fresh water adapted chloride cells is typically exposed to the free surface of the gill-filament. The possible function of the cell type is discussed.

Genetic aspects of the BOR syndrome--branchial fistulas, ear pits, hearing loss, and renal anomalies

A pedigree of branchio-oto-renal dysplasia (the BOR syndrome) is reported, including the documentation by serial audiometric studies of the onset and rapid progression of hearing loss in the twin sister of an affected child. The literature on this syndrome is analyzed to derive some figures for use in genetic counseling of such families. Branchio-oto-renal dysplasia is an autosomal dominant disorder in which affected individuals may have preauricular pits, lachrymal duct stenosis, hearing loss, branchial fistulas or cysts, structural defects of the outer, middle, and inner ear, and renal anomalies, which may range from mild hypoplasia to complete absence. Not all features of the syndrome are expressed in all carriers of the gene, but few carriers lack all the features, and the pits, branchial clefts, and hearing loss, are frequently expressed. Those offspring of affected persons who have pits or fistulas are likely (about 80%) to have hearing loss of varying degrees of severity. A minority of heterozygotes (about 7%) may have hearing loss without pits or fistulas. The risk of severe renal malformation is probably fairly low. Whether families that show dominant inheritance of pits, clefts, and deafness without renal anomalies represent variants of the BOR syndrome or a separate entity (the BO syndrome), is still not clear. At present, any individual with preauricular pits and branchial clefts deserves both otologic and renal investigation.

Familial branchio-oto-renal dysplasia: a new addition to the branchial arch syndromes

The present report concerns a two-generation family of nine individuals in which the father and three of the six living children all had: (1) a mixed hearing loss with a Mondini type cochlear malformation and stapes fixation; (2) cup-shaped, anteverted pinnae with bilateral prehelical pits: (3) bilateral branchial cleft fistulas; and (4) bilateral renal dysplasia and anomalies of the collecting system. The father and one affected son also had aplasia of the lacrimal ducts. A fourth child who died at 5 months of age was reported to have branchial cleft fistulas and bilateral polycystic kidneys at autopsy. In addition, the concept of noso-embryologic communities is presented. Such groups are composed of syndromes whose total phenotypic spectra not only overlap but also share common elements in embryogenesis. This concept is illustrated with a group of branchial arch syndromes that are related in this way.

First branchial cleft anomalies

Our experience with anomalies of the first branchial cleft is reviewed. This includes 38 cases, the largest series collected to date. A new classification is proposed based on the anatomic findings--whether cyst, sinus, or fistula is present. The embryology and pathology of first cleft anomalies are discussed and an approach to the diagnosis and management of these lesions is given. In addition, a patient with a branchial cleft defect involving the middle ear space is reported.

First fossil lamprey: a record from the Pennsylvanian of Illinois

A fossil record of lampreys has previously been unknown. A new genus demonstrates the presence of this group in the Pennsylvanian. The body outline, parts of the head skeleton, rasping tongue mechanism, gill basket, and other internal organs are preserved. The fossils are very similar in structure to modern forms. The absence of hagfish characters in the fossil supports the view that the common ancestor of lampreys and hagfishes lived prior to the Pennsylvanian.

Branchio-oto-renal syndrome: reduced penetrance and variable expressivity in four generations of a large kindred

The family on which this report is based is of interest because it contains individuals with the branchio-oto-renal (BOR) syndrome who have renal hypoplasia or malformations of the kidney or collecting system including duplication; only branchial and ear anomalies; and apparent nonpenetrance of the syndrome. This report provides evidence to support the hypothesis that in some families variable expressivity includes duplication of the urinary collecting system in individuals with other manifestations of the BOR syndrome as well as individuals with branchial and ear anomalies who have apparently normal kidneys.

Sports and peripheral nerve injury

Peripheral nerve injury is one of the serious complications of athletic injuries; however, they have rarely been reported. According to the report by Takazawa et al., there were only 28 cases of peripheral nerve injury among 9,550 cases of sports injuries which had been treated in the previous 5 years at the clinic of the Japanese Athletic Association. The authors have encountered 1,167 cases of peripheral nerve injury during the past 18 years. Sixty-six of these cases were related to sports (5.7%). The nerves most frequently involved were: brachial plexus, radial nerve, ulnar, peroneal, and axillary nerves (in their order of frequency). The most common causes of such injuries were mountain climbing, gymnastics, and baseball. More often, peripheral nerve injury seemed to be caused by continuous compression and repeated trauma to the involved nerve. Usually it appeared as an entrapment neuropathy and the symptoms could be improved by conservative treatment. Some of the cases were complicated by fractures and surgical exploration became necessary. Results of treatment produced excellent to good improvement in 87.9% of the cases. With regard to compartment syndrome, the authors stress the importance of early and precise diagnosis and a fasciotomy.

STUDIES ON CILIA. THE FIXATION OF THE METACHRONAL WAVE

Upon excision into spring water, the lateral cilia of the gill of the freshwater mussel Elliptio complanatus (Solander) stop beating, but 0.04 M potassium ion can activate the gill so that these cilia again beat with metachronal rhythm. One per cent osmium tetroxide quickly pipetted onto a fully activated gill fixes the lateral cilia in a pattern that preserves the form and arrangement of the metachronal wave, and permits the cilia to be studied with the electron microscope in all stages of their beat cycle. Changes are seen in the fixed active preparation that are not present in the inactive control, i.e., in the packing of the cilia, the position of the axis of the ciliary cross-section, and the diameter of the ring of peripheral filaments. Analysis of these parameters may lead to new correlations between ciliary fine structure and function.

Fgf8 expression in the Tbx1 domain causes skeletal abnormalities and modifies the aortic arch but not the outflow tract phenotype of Tbx1 mutants

Fgf8 and Tbx1 have been shown to interact in patterning the aortic arch, and both genes are required in formation and growth of the outflow tract of the heart. However, the nature of the interaction of the two genes is unclear. We have utilized a novel Tbx1(Fgf8) allele which drives Fgf8 expression in Tbx1-positive cells and an inducible Cre-LoxP recombination system to address the role of Fgf8 in Tbx1 positive cells in modulating cardiovascular development. Results support a requirement of Fgf8 in Tbx1 expressing cells to finely control patterning of the aortic arch and great arteries specifically during the pharyngeal arch artery remodeling process and indicate that the endoderm is the most likely site of this interaction. Furthermore, our data suggest that Fgf8 and Tbx1 play independent roles in regulating outflow tract development. This finding is clinically relevant since TBX1 is the candidate for DGS/VCFS, characterized clinically by variable expressivity and reduced penetrance of cardiovascular defects; Fgf8 gene variants may provide molecular clues to this variability.

Alteration of murine odontogenic patterning and prolongation of expression of epidermal growth factor mRNA by retinol in vitro

Retinoids alter the patterning of murine odontogenesis in vivo and stimulate epithelial proliferation. Because odontogenesis is dependent on proliferation of mandibular epithelium, the effects of retinol on the patterning of odontogenic epithelium were studied. These experiments control for developmental stage, applied retinoid concentration and duration of exposure. Explants exposed for 24 h to 0.1 micrograms/ml of retinol exhibited enhanced odontogenesis. Day-9 mandibles exposed to retinol at 1-5 micrograms/ml had altered epithelial patterns consistent with those in previous in vivo experiments, including supernumerary epithelial buds in regions associated with supernumerary incisors in vivo. These changes were associated with a dose-dependent increase in epithelial proliferation and a prolonged expression of epidermal growth factor (EGF) mRNA. Altered expression of EGF mRNA may be responsible for the disrupted pattern of the dental lamina. This is the first report of a retinoid-induced alteration in EGF mRNA expression.

Carcinoma arising in a branchial cleft cyst

A patient is presented who was found to have invasive squamous cell carcinoma arising in the epithelial lining of a lateral cervical cyst which had been present for more than 40 years. Radical neck dissection was performed, and metastases were found in a single cervical lymph node. A critical review of cases of branchiogenic carcinoma reported over the past quarter-century yielded no more than three others which meet the criteria for diagnosis of this entity established by Martin, Morfit, and Ehrlich in 1950.

First branchial cleft anomalies

A series of nine cases of first branchial cleft anomalies treated at Children's Hospital of Michigan from 1970-1978 is presented. A review of the literature and analysis of these cases reveals that the accepted criteria for classification of these anomalies are confusing and inadequate as they preclude the proper classification of a number of these cases. The embryogenesis of these anomalies is discussed with attention given to their relationship to the facial nerve. A proper classification is suggested.

Acute suppurative thyroiditis and the branchial apparatus

Acute suppurative thyroiditis and thyroid abscess are rare. The finding of a sinus tract arising from the pyriform sinus in some cases highlights the possibility of a branchial apparatus origin. We present three case histories that include a left-sided lesion and radiologic or surgical-anatomic evidence of an internal sinus tract. Our discussion focuses on two considerations: first, the exact branchial pouch from which this lesion arises, and second, a proposed protocol for the work-up and management of patients with the onset or recurrence of acute suppurative thyroiditis or thyroid abscess.

Neural crest and the origin of species-specific pattern

For well over half of the 150 years since the discovery of the neural crest, the special ability of these cells to function as a source of species-specific pattern has been clearly recognized. Initially, this observation arose in association with chimeric transplant experiments among differentially pigmented amphibians, where the neural crest origin for melanocytes had been duly noted. Shortly thereafter, the role of cranial neural crest cells in transmitting species-specific information on size and shape to the pharyngeal arch skeleton as well as in regulating the timing of its differentiation became readily apparent. Since then, what has emerged is a deeper understanding of how the neural crest accomplishes such a presumably difficult mission, and this includes a more complete picture of the molecular and cellular programs whereby neural crest shapes the face of each species. This review covers studies on a broad range of vertebrates and describes neural-crest-mediated mechanisms that endow the craniofacial complex with species-specific pattern. A major focus is on experiments in quail and duck embryos that reveal a hierarchy of cell-autonomous and non-autonomous signaling interactions through which neural crest generates species-specific pattern in the craniofacial integument, skeleton, and musculature. By controlling size and shape throughout the development of these systems, the neural crest underlies the structural and functional integration of the craniofacial complex during evolution.

VITO-1, a novel vestigial related protein is predominantly expressed in the skeletal muscle lineage

In order to identify novel genes expressed in skeletal muscle we performed a subtractive hybridization for genes expressed in human skeletal muscle but not in other tissues. We identified a novel scalloped interaction domain (SID) containing protein in humans and in the mouse, which we named VITO-1. Highest homology of VITO-1 was found with the Drosophila vestigial and the human TONDU proteins in the SID (54 and 40%, respectively). Using whole-mount hybridzation and Northern blot analysis, we showed that VITO-1 is expressed in the somitic myotome from E8.75 mouse embryos onwards and later on in skeletal muscle but not in the heart. Additional expression domains during development were detected in the pharyngeal pouches and clefts starting at E8.0 as well as in the cranial pharynx and in Rathkes pouch. By Northern blot analysis, we found VITO-1 to be up-regulated in C2C12 myotubes although some expression can be detected in proliferating C2C12 myoblasts. No expression was spotted in other adult mouse tissues. Likewise, expression of human Vito-1 during fetal and adult human development was found exclusively in skeletal muscle preferentially in fast skeletal muscles. These data suggest a role of VITO-1 for the development of skeletal muscles and of pharyngeal clefts/Rathkes' pouch derived structures.

Cysts, sinuses and fistulas of the neck arising from the first and second branchial clefts

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