ACTN3 genotype influences masseter muscle characteristics and self-reported bruxism

OBJECTIVES

Main aim of the study was to explore the association between genetic polymorphisms in ACTN3 and bruxism. Secondary objectives included masseter muscle phenotypes assessment between bruxers and non-bruxers and according to genetic polymorphisms in ACTN3.

MATERIALS AND METHODS

Fifty-four patients undergoing orthognathic surgery for correction of their malocclusion were enrolled. Self-reported bruxism and temporomandibular disorders status were preoperatively recorded. Saliva samples were used for ACTN3 genotyping. Masseter muscle samples were collected bilaterally at the time of orthognathic surgery to explore the muscle fiber characteristics.

RESULTS

There were significant differences in genotypes for rs1815739 (R577X nonsense) (p = 0.001), rs1671064 (Q523R missense) (p = 0.005), and rs678397 (intronic variant) (p = 0.001) between bruxers and non-bruxers. Patients with self-reported bruxism presented a larger mean fiber area for types IIA (p = 0.035). The mean fiber areas in individuals with the wild-type CC genotype for rs1815739 (R577X) were significantly larger for type IIA fibers (1394.33 μm² [572.77 μm² ]) than in those with the TC and TT genotypes (832.61 μm² [602.43 μm² ] and 526.58 μm² [432.21 μm² ] [p = 0.014]). Similar results for Q523R missense and intronic variants.

CONCLUSIONS

ACTN3 genotypes influence self-reported bruxism in patients with dentofacial deformity through specific masseter muscle fiber characteristics.

A longitudinal assessment of sex differences in the growth of the mandibular retromolar space

OBJECTIVE

To assess longitudinal variation in patterns of retromolar space growth, with regard to sex and cervical vertebrae maturation.

DESIGN

We utilized serial lateral cephalograms from three craniofacial growth studies (Denver, Iowa, Oregon), measuring retromolar space and cervical vertebrae maturation in 99 subjects (56% male) from 8 to 18 years of age for each subject. Repeated measures ANOVA and a linear mixed effects model were used to assess retromolar space growth through time.

RESULTS

Our analyses revealed an average increase in retromolar space of 8.73 mm from 8 to 18 years. While t-tests failed to find differences in retromolar space growth between males and females at the measured age points, repeated measures ANOVA and linear mixed effects models revealed modest differences in growth trends between sexes, with females having more growth earlier but a younger age of deceleration of growth (between 12 and 14 years of age).

CONCLUSIONS

Our results confirm large increases in retromolar space through growth, reaching an average of 1.38 mm/year around puberty. Importantly, we add to the conversation regarding sex differences, showing differences in timing of growth. This highlights the importance of using longitudinal data and analytical approaches to address questions of this nature.

Condyle modeling stability, craniofacial asymmetry and ACTN3 genotypes: Contribution to TMD prevalence in a cohort of dentofacial deformities

Craniofacial asymmetry, mandibular condylar modeling and temporomandibular joint disorders are common comorbidities of skeletally disproportionate malocclusions, but etiology of occurrence together is poorly understood. We compared asymmetry, condyle modeling stability and temporomandibular health in a cohort of 128 patients having orthodontics and orthognathic surgery to correct dentofacial deformity malocclusions. We also compared ACTN3 and ENPP1 genotypes for association to clinical conditions. Pre-surgical posterior-anterior cephalometric and panometric radiographic analyses; jaw pain and function questionnaire and clinical examination of TMD; and SNP-genotype analysis from saliva samples were compared to assess interrelationships. Almost half had asymmetries in need of surgical correction, which could be subdivided into four distinct morphological patterns. Asymmetric condyle modeling between sides was significantly greater in craniofacial asymmetry, but most commonly had an unanticipated pattern. Often, longer or larger condyles occurred on the shorter mandibular ramus side. Subjects with longer ramus but dimensionally smaller condyles were more likely to have self-reported TMD symptoms (p = 0.023) and significantly greater clinical diagnosis of TMD (p = 0 .000001), with masticatory myalgia most prominent. Genotyping found two significant genotype associations for ACTN3 rs1671064 (Q523R missense) p = 0.02; rs678397 (intronic SNP) p = 0.04 and one significant allele association rs1815739 (R577X nonsense) p = 0.00. Skeletal asymmetry, unusual condyle modeling and TMD are common and interrelated components of many dentofacial deformities. Imbalanced musculoskeletal functional adaptations and genetic or epigenetic influences contribute to the etiology, and require further investigation.

TMJ related short-term outcomes comparing two different osteosynthesis techniques for bilateral sagittal split osteotomy

OBJECTIVES

Bilateral sagittal split osteotomy (BSSO) is a morpho-functional surgery and post-surgical osteosynthesis may influence temporomandibular joint (TMJ) health. Our objective was to evaluate temporomandibular disorders (TMD) and TMJ symptoms after orthognathic surgery according to the type of osteosynthesis used in a population of patients with dentofacial deformities.

MATERIALS AND METHODS

One hundred and eighty-three consecutive patients undergoing orthodontic and maxillofacial surgery treatment for correction of their malocclusion were recruited for a two-year period at Lille University Hospital. All patients had at least a mandibular BSSO using Epker's technique. Each patient was examined before and one year after orthognathic surgery. We compared osteosynthesis by miniplates fixed with monocortical screws (n=42) and the hybrid fixation with bicortical retro-molar screws used with miniplates (n=141). TMJ health was assessed by monitoring TMD signs and symptoms according to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) and scores obtained from the "Jaw Pain Function" questionnaire.

RESULTS

There was no significant difference in pre-operative and one year post-operative RDC/TMD assessments (p≥0.91) or JPF score (p≥0.29) between the two types of osteosynthesis.

CONCLUSION

There was no difference in TMJ health between the two techniques of osteosynthesis after BSSO.

CLINICAL RELEVANCE

In our experience the hybrid technique fixation affords many advantages and does not influence postoperative TMD compared with osteosynthesis by miniplates.

Pre-operative parafunctional or dysfunctional oral habits are associated with the temporomandibular disorders after orthognathic surgery: An observational cohort study

BACKGROUND

Temporomandibular disorders (TMDs) are frequent and disabling, and hence, preventing them is an important health issue. Combining orthodontic and surgical treatments for malocclusions has been shown to affect temporomandibular joint (TMJ) health. However, publications regarding the risk factors that predict negative TMJ outcomes after orthognathic surgery are scarce.

OBJECTIVE

Present prospective cohort study was conducted to identify an association between pre-operative dysfunctional/parafunctional oral habits and the presence of TMD symptoms after orthognathic surgery.

METHOD

We included 237 patients undergoing orthodontics and surgical treatment for malocclusions associated with dentofacial deformities within the Department of Oral and Maxillofacial Surgery of the University of Lille. Their parafunctional and dysfunctional oral habits were recorded through clinical examination along with the presence of TMD symptoms before and after the surgery. According to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) classification, the TMD symptoms studied were myalgia, arthralgia, disc displacement with or without reduction.

RESULTS

Multivariate analysis revealed significant associations among bruxism (odds ratio [OR] 3.17 [1.066; 9.432]), lingual interposition (OR 4.241 [1.351; 13.313]), as well as primary swallowing (OR 3.54 [1.225; 10.234]) and the presence of postoperative symptoms of myalgia. Moreover, a significant association was observed between the presence of any dysfunctional oral habit and postoperative disc displacement with reduction (OR 4.611 [1.249; 17.021]).

CONCLUSION

Bruxism and dysfunctional oral habits were shown to be risk factors for the presence of TMD symptoms also after combined orthodontic and surgical treatment. Treating such habits before orthognathic surgery should help prevent TMD.

ENPP1 and ESR1 genotypes associated with subclassifications of craniofacial asymmetry and severity of temporomandibular disorders

INTRODUCTION

We investigated whether ACTN3, ENPP1, ESR1, PITX1, and PITX2 genes which contribute to sagittal and vertical malocclusions also contribute to facial asymmetries and temporomandibular disorders (TMD) before and after orthodontic and orthognathic surgery treatment.

METHODS

One hundred seventy-four patients with a dentofacial deformity were diagnosed as symmetric or subdivided into 4 asymmetric groups according to posteroanterior cephalometric measurements. TMD examination diagnosis and jaw pain and function (JPF) questionnaires assessed the presence and severity of TMD.

RESULTS

Fifty-two percent of the patients were symmetric, and 48% were asymmetric. The asymmetry classification demonstrated significant cephalometric differences between the symmetric and asymmetric groups, and across the 4 asymmetric subtypes: group 1, mandibular body asymmetry; group 2, ramus asymmetry; group 3, atypical asymmetry; and group 4, C-shaped asymmetry. ENPP1 SNP-rs6569759 was associated with group 1 (P = 0.004), and rs858339 was associated with group 3 (P = 0.002). ESR1 SNP-rs164321 was associated with group 4 (P = 0.019). These results were confirmed by principal component analysis that showed 3 principal components explaining almost 80% of the variations in the studied groups. Principal components 1 and 2 were associated with ESR1 SNP-rs3020318 (P <0.05). Diagnoses of disc displacement with reduction, masticatory muscle myalgia, and arthralgia were highly prevalent in the asymmetry groups, and all had strong statistical associations with ENPP1 rs858339. The average JPF scores for asymmetric subjects before surgery (JPF, 7) were significantly higher than for symmetric subjects (JPF, 2). Patients in group 3 had the highest preoperative JPF scores, and groups 2 and 3 were most likely to be cured of TMD 1 year after treatment.

CONCLUSIONS

Posteroanterior cephalometrics can classify asymmetry into distinct groups and identify the probability of TMD and genotype associations. Orthodontic and orthognathic treatments of facial asymmetry are effective at eliminating TMD in most patients.

Condylar geometry variation is associated with ENPP1 variant in a population of patients with dento-facial deformities

PURPOSE

Bone remodeling is essential in maintaining bone health. Considering that ENPP1 contributes to bone geometry and bone mineralization, the aim of our study was to analyze the association between single-nucleotide polymorphisms (SNPs) of ENPP1 and condylar remodeling.

MATERIALS AND METHODS

A total of 156 patients undergoing orthodontic and maxillofacial surgery treatment for correction of malocclusion were included in this prospective study. Saliva samples from all subjects were used for DNA extraction and genotyping. Four ENPP1 SNPs were selected and tested to determine whether specific allelic variants are correlated with condylar remodeling. The criteria of condylar remodeling chosen were the ratio between each side of condylar height or surface differences on a dental panoramic of each patient. A diagnostic threshold was set at 15% difference between both sides.

RESULTS

The ENPP1 SNP rs9373000 showed a statistically significant association with condylar height ratio >15% (p = 0.012). The GG genotype was found to be a protective factor against condylar height decrease (p = 0.003).

CONCLUSION

This study identifies the genetic variant rs9373000 as a potentially causal variant for mandibular condyle geometry variation for patients presenting with dento-facial deformities.

ENPP1 and ESR1 genotypes influence temporomandibular disorders development and surgical treatment response in dentofacial deformities

Dentofacial deformities are dys-morpho-functional disorders involving the temporomandibular joints (TMJ). Many authors have reported a TMJ improvement in dysfunctional subjects with malocclusion after orthodontic or combined orthodontic and surgical treatment particularly for the relief of pain. In particular, few studies have highlighted the demographic and clinical predictors of response to surgical treatment. To date, no genetic factor has yet been identified as a predictor of response to surgical treatment. The aim of this cohort study is therefore to identify single-nucleotide polymorphisms associated with postoperative temporomandibular disorders (TMD) or with TMJ symptoms after orthognathic surgery. Here, we found the AA genotype of SNP rs1643821 (ESR1 gene) as a risk factor for dysfunctional worsening after orthognathic surgery. In addition, we have identified TT genotype of SNP rs858339 (ENPP1 gene) as a protective factor against TMD in a population of patients with dentofacial deformities. Conversely, the heterozygous genotype AT was identified as a risk factor of TMD with respect to the rest of our population. All these elements are particularly important to bring new screening strategies and tailor future treatment.

PERSPECTIVE

This study allows us to identify sub-populations at high risk of developing postoperative temporomandibular disorders after orthognathic surgery procedures. Many other genes of interest could be potential factors influencing the dysfunctional response to orthognathic surgery, particularly genes of the Opera cohort.

Nodal pathway genes are down-regulated in facial asymmetry

PURPOSE

Facial asymmetry is a common comorbid condition in patients with jaw deformation malocclusion. Heritability of malocclusion is advancing rapidly, but very little is known regarding genetic contributions to asymmetry. This study identifies differences in expression of key asymmetry-producing genes that are down-regulated in patients with facial asymmetry.

METHODS

Masseter muscle samples were collected during bilateral sagittal split osteotomy orthognathic surgery to correct skeletal-based malocclusion. Patients were classified as class II or III and open or deep bite malocclusion with or without facial asymmetry. Muscle samples were analyzed for gene expression differences on Affymetrix HT2.0 microarray global expression chips.

RESULTS

Overall gene expression was different for asymmetric patients compared with other malocclusion classifications by principal component analysis (P < 0.05). We identified differences in the nodal signaling pathway, which promotes development of mesoderm and endoderm and left-right patterning during embryogenesis. Nodal and Lefty expression was 1.39- to 1.84-fold greater (P < 3.41 × 10), whereas integral membrane Nodal modulators Nomo1,2,3 were -5.63 to -5.81 (P < 3.05 × 10) less in asymmetry subjects. Fold differences among intracellular pathway members were negative in the range of -7.02 to -2.47 (P < 0.003). Finally Pitx2, an upstream effector of Nodal known to influence the size of type II skeletal muscle fibers was also significantly decreased in facial asymmetry (P < 0.05).

CONCLUSIONS

When facial asymmetry is part of skeletal malocclusion, there are decreases in nodal signaling pathway genes in masseter muscle. This data suggest that the nodal signaling pathway is down-regulated to help promote development of asymmetry. Pitx2 expression differences also contributed to both skeletal and muscle development in this condition.

ACTN3 R577X genotypes associate with Class II and deepbite malocclusions

INTRODUCTION

α-Actinins are myofibril anchor proteins that influence the contractile properties of skeletal muscles. ACTN2 is expressed in slow type I and fast type II fibers, whereas ACTN3 is expressed only in fast fibers. ACTN3 homozygosity for the 577X stop codon (ie, changing 577RR to 577XX, the R577X polymorphism) results in the absence of α-actinin-3 in about 18% of Europeans, diminishes fast contractile ability, enhances endurance performance, and reduces bone mass or bone mineral density. We have examined ACTN3 expression and genetic variation in the masseter muscle of orthognathic surgery patients to determine the genotype associations with malocclusion.

METHODS

Clinical information, masseter muscle biopsies, and saliva samples were obtained from 60 subjects. Genotyping for ACTN3 single nucleotide polymorphisms, real-time polymerase chain reaction quantitation of muscle gene message, and muscle morphometric fiber type properties were compared to determine statistical differences between genotype and phenotype.

RESULTS

Muscle mRNA expression level was significantly different for ACTN3 single nucleotide polymorphism genotypes (P <0.01). The frequency of ACTN3 genotypes was significantly different for the sagittal and vertical classifications of malocclusion, with the clearest association being elevated 577XX genotype in skeletal Class II malocclusion (P = 0.003). This genotype also resulted in significantly smaller diameters of fast type II fibers in masseter muscles (P = 0.002).

CONCLUSION

ACTN3 577XX is overrepresented in subjects with skeletal Class II malocclusion, suggesting a biologic influence during bone growth. ACTN3 577XX is underrepresented in subjects with deepbite malocclusion, suggesting that muscle differences contribute to variations in vertical facial dimensions.

Molecular motor MYO1C, acetyltransferase KAT6B and osteogenetic transcription factor RUNX2 expression in human masseter muscle contributes to development of malocclusion

OBJECTIVE

Type I myosins are molecular motors necessary for glucose transport in the cytoplasm and initiation of transcription in the nucleus. Two of these, MYO1H and MYO1C, are paralogs which may be important in the development of malocclusion. The objective of this study was to investigate their gene expression in the masseter muscle of malocclusion subjects. Two functionally related proteins known to contribute to malocclusion were also investigated: KAT6B (a chromatin remodelling epigenetic enzyme which is activated by MYO1C) and RUNX2 (a transcription factor regulating osteogenesis which is activated by KAT6B).

DESIGN

Masseter muscle samples and malocclusion classifications were obtained from orthognathic surgery subjects. Muscle was sectioned and immunostained to determine fibre type properties. RNA was isolated from the remaining sample to determine expression levels for the four genes by TaqMan(®) RT-PCR. Fibre type properties, gene expression quantities and malocclusion classification were compared.

RESULTS

There were very significant associations (P<0.0000001) between MYO1C and KAT6B expressions. There were also significant associations (P<0.005) between RUNX2 expression and masseter muscle type II fibre properties. Very few significant associations were identified between MYO1C and masseter muscle fibre type properties.

CONCLUSIONS

The relationship between MYO1C and KAT6B suggests that the two are interacting in chromatin remodelling for gene expression. This is the nuclear myosin1 (NM1) function of MYO1C. A surprising finding is the relationship between RUNX2 and type II masseter muscle fibres, since RUNX2 expression in mature muscle was previously unknown. Further investigations are necessary to elucidate the role of RUNX2 in adult masseter muscle.

Epigenetic influence of KAT6B and HDAC4 in the development of skeletal malocclusion

INTRODUCTION

Genetic influences on the development of malocclusion include heritable effects on both masticatory muscles and jaw skeletal morphology. Beyond genetic variations, however, the characteristics of muscle and bone are also influenced by epigenetic mechanisms that produce differences in gene expression. We studied 2 enzymes known to change gene expressions through histone modifications, chromatin-modifying histone acetyltransferase KAT6B and deacetylase HDAC4, to determine their associations with musculoskeletal variations in jaw deformation malocclusions.

METHODS

Samples of masseter muscle were obtained from subjects undergoing orthognathic surgery from 6 malocclusion classes based on skeletal sagittal and vertical dysplasia. The muscles were characterized for fiber type properties by immunohistochemistry, and their total RNA was isolated for gene expression studies by microarray analysis and quantitative real-time polymerase chain reaction.

RESULTS

Gene expressions for fast isoforms of myosins and contractile regulatory proteins and for KAT6B and HDAC4 were severalfold greater in masseter muscles from a patient with a deepbite compared with one with an open bite, and genes related to exercise and activity did not differ substantially. In the total population, expressions of HDAC4 (P = 0.03) and KAT6B (P = 0.004) were significantly greater in subjects with sagittal Class III than in Class II malocclusion, whereas HDAC4 tended to correlate negatively with slow myosin type I and positively with fast myosin gene, especially type IIX.

CONCLUSIONS

These data support other published reports of epigenetic regulation in the determination of skeletal muscle fiber phenotypes and bone growth. Further investigations are needed to elucidate how this regulatory model might apply to musculoskeletal development and malocclusion.

Masseter function and skeletal malocclusion

The aim of this work is to review the relationship between the function of the masseter muscle and the occurrence of malocclusions. An analysis was made of the masseter muscle samples from subjects who underwent mandibular osteotomies. The size and proportion of type-II fibers (fast) decreases as facial height increases. Patients with mandibular asymmetry have more type-II fibers on the side of their deviation. The insulin-like growth factor and myostatin are expressed differently depending on the sex and fiber diameter. These differences in the distribution of fiber types and gene expression of this growth factor may be involved in long-term postoperative stability and require additional investigations. Muscle strength and bone length are two genetically determined factors in facial growth. Myosin 1H (MYOH1) is associated with prognathia in Caucasians. As future objectives, we propose to characterize genetic variations using "Genome Wide Association Studies" data and their relationships with malocclusions.

In vivo oxygen consumption and hemoglobin levels in human thyroarytenoid muscle

OBJECTIVES/HYPOTHESIS

Visible light spectroscopy (VLS) is the technology behind the Food and Drug Administration-approved TSTAT device that is used to monitor tissue oxygen (StO(2)) and relative total hemoglobin (rtHb) levels by measuring reflected visible light. The purpose of this novel, pilot study was to determine if VLS is a reliable and valid method of measuring StO(2) and rtHb levels in the human thyroarytenoid/lateral cricoarytenoid (TA-LCA) muscle complex, thus providing information about vocal fold muscle physiology.

STUDY DESIGN

Pre-test/post-test with mulitple baselines and two conditions.

METHODS

VLS measurements were taken at baseline, during exercise, and following recovery on six subjects using both noncontact channel-port endoscope (endo-probe) and laryngeal electromyography (LEMG) needle-guided techniques.

RESULTS

The average baseline StO(2) was 69% (standard deviation [SD] = 3.6%) for the LEMG-guided probe and was 71.5% (SD = 2.8%) for the endo-probe. During phonation, the StO(2) for the LEMG-guided probe dropped to 59% (SD = 7%; P = .04). Mean rtHb measured by the LEMG probe rose from a baseline of 144 μM (SD = 165 μM) to 214 μM (SD = 166 μM, P = .34) during phonation and back to 149 μM (SD = 139 μM, P = .85) after recovery. Mean rtHb as measured using the endo-probe at baseline and after recovery was 104 μM (SD = 30 μM, P = .76).

CONCLUSIONS

VLS can be used to measure changes in StO(2) and rtHb levels pre- and postexercise in the human TA-LCA muscle complex.

Cytochrome c oxidase deficiency in human posterior cricoarytenoid muscle

BACKGROUND

Mitochondrial alterations occur in skeletal muscle fibers throughout the normal aging process, resulting from increased accumulation of reactive oxide species (ROS). These result in respiratory chain abnormalities, which decrease the oxidative capacity of muscle fibers, leading to decreased contractile force, sarcopenia, or fiber necrosis. Intrinsic laryngeal muscles are a cranial muscle group that possesses some distinctive genotypic, phenotypic, and physiologic properties. Their susceptibility to mitochondrial alterations resulting from biological processes that increase levels of oxidative stress may be one of these distinctive characteristics.

OBJECTIVES

The incidence of cytochrome c oxidase (COX) deficiency (COX(-)) was determined in human posterior cricoarytenoid (PCA) muscle when compared with the human thyrohyoid (TH) muscle, an extrinsic laryngeal muscle that served as "control" muscle. Ten PCA and 10 TH muscles were harvested postlaryngectomy from 10 subjects ranging in age from 55 to 86 years. Differences in COX(-) were compared within and between muscle types using tissue section staining and standard morphometric analysis.

RESULTS AND CONCLUSIONS

COX(-) fibers were identified in both the PCA and TH muscles. The PCA muscle had 10 times as may affected fibers as the TH muscle, with significant differences in COX(-) found between muscle type and fiber type (P=0.003). Almost all of this effect was the result of elevated levels of COX(-) in type I fibers from the PCA muscle (P=0.002) that showed a strong positive correlation with increased age. These results suggest that increased mitochondrial alterations may occur in the PCA muscle during normal aging.

Masticatory hypermuscularity is not related to reduced cranial volume in myostatin-knockout mice

It has been suggested recently that masticatory muscle size reduction in humans resulted in greater encephalization through decreased compressive forces on the cranial vault. Following this logic, if masticatory muscle size were increased, then a reduction in brain growth should also occur. This study was designed to test this hypothesis using a myostatin (GDF-8) knockout mouse model. Myostatin is a negative regulator of skeletal muscle growth, and individuals lacking this gene show significant hypermuscularity. Sixty-two [32 wild-type (WT) and 30 GDF-8 -/- knockout], 1, 28, 56, and 180-day-old CD-1 mice were used. Body and masseter muscle weights were collected following dissection and standardized lateral and dorsoventral cephalographs were obtained. Cephalometric landmarks were identified on the radiographs and cranial volume was calculated. Mean differences were assessed using a two-way ANOVA. KO mice had significantly greater body and masseter weights beginning at 28 days compared with WT controls. No significant differences in cranial volumes were noted between KO and WT. Muscle weight was not significantly correlated with cranial volume in 1, 28, or 180-day-old mice. Muscle weights exhibited a positive correlation with cranial volume at 56 days. Results demonstrate that masticatory hypermuscularity is not associated with reduced cranial volume. In contrast, there is abundant data demonstrating the opposite, brain growth determines cranial vault growth and masticatory apparatus only affects ectocranial morphology. The results presented here do not support the hypothesis that a reduction in masticatory musculature relaxed compressive forces on the cranial vault allowing for greater encephalization.

Age-related changes in craniofacial morphology in GDF-8 (myostatin)-deficient mice

It is well recognized that masticatory muscle function helps determine morphology, although the extent of function on final form is still debated. GDF-8 (myostatin), a transcription factor is a negative regulator of skeletal muscle growth. A recent study has shown that mice homozygous for the myostatin mutation had increased muscle mass and craniofacial dysmorphology in adulthood. However, it is unclear whether such dysmorphology is present at birth. This study examines the onset and relationship between hypermuscularity and craniofacial morphology in neonatal and adult mice with GDF-8 deficiency. Fifteen (8 wild-type and 7 GDF-8 -/-), 1-day-old and 16 (9 wt and 7 GDF-8 -/-), 180-day-old male CD-1 mice were used. Standardized radiographs were taken of each head, scanned, traced, and cephalometric landmarks identified. Significant mean differences were assessed using a group x age, two-way ANOVA. Myostatin-deficient mice had significantly (P < 0.01) smaller body and masseter muscle weights and craniofacial skeletons at 1 day of age and significantly greater body and masseter muscle weights at 180 days of age compared to controls. Myostatin-deficient mice showed significantly (P < 0.001) longer and "rocker-shaped" mandibles and shorter and wider crania compared to controls at 180 days. Significant correlations were noted between masseter muscle weight and all cephalometric measurements in 180-day-old Myostatin-deficient mice. Results suggest that in this mouse model, there may be both early systemic skeletal growth deficiencies and later compensatory changes from hypermuscularity. These findings reiterate the role that masticatory muscle function plays on the ontogeny of the cranial vault, base, and most notably the mandible.

Craniosacral therapy: the effects of cranial manipulation on intracranial pressure and cranial bone movement

STUDY DESIGN

Quasi-experimental design.

OBJECTIVES

To determine if physical manipulation of the cranial vault sutures will result in changes of the intracranial pressure (ICP) along with movement at the coronal suture.

BACKGROUND

Craniosacral therapy is used to treat conditions ranging from headache pain to developmental disabilities. However, the biological premise for this technique has been theorized but not substantiated in the literature.

METHODS

Thirteen adult New Zealand white rabbits (oryctolagus cuniculus) were anesthetized and microplates were attached on either side of the coronal suture. Epidural ICP measurements were made using a NeuroMonitor transducer. Distractive loads of 5, 10, 15, and 20 g (simulating a craniosacral frontal lift technique) were applied sequentially across the coronal suture. Baseline and distraction radiographs and ICP were obtained. One animal underwent additional distractive loads between 100 and 10,000 g. Plate separation was measured using a digital caliper from the radiographs. Two-way analysis of variance was used to assess significant differences in ICP and suture movement.

RESULTS

No significant differences were noted between baseline and distraction suture separation (F = 0.045; P>.05) and between baseline and distraction ICP (F = 0.279; P>.05) at any load. In the single animal that underwent additional distractive forces, movement across the coronal suture was not seen until the 500-g force, which produced 0.30 mm of separation but no corresponding ICP changes.

CONCLUSION

Low loads of force, similar to those used clinically when performing a craniosacral frontal lift technique, resulted in no significant changes in coronal suture movement or ICP in rabbits. These results suggest that a different biological basis for craniosacral therapy should be explored.

Fiber-type differences in masseter muscle associated with different facial morphologies

BACKGROUND

The influence of muscle forces and associated physiologic behaviors on dental and skeletal development is well recognized but difficult to quantify because of the limited understanding of the interrelationships between physiologic and other mechanisms during growth.

METHODS

The purpose of this study was to characterize fiber-type composition of masseter muscle in 44 subjects during surgical correction of malocclusion. Four fiber types were identified after immunostaining of biopsy sections with myosin heavy chain-specific antibodies, and the average fiber diameter and percentage of muscle occupancy of the fiber types were determined in each of 6 subject groups (Class II or Class III and open bite, normal bite, or deepbite). A 2 x 3 x 4 analysis of variance was used to determine significant differences between mean areas for fiber types, vertical relationships, and sagittal relationships.

RESULTS

There were significant differences in percentage of occupancy of fiber types in masseter muscle in bite groups with different vertical dimensions. Type I fiber occupancy increased in open bites, and conversely, type II fiber occupancy increased in deepbites. The association between sagittal jaw relationships and mean fiber area was less strong, but, in the Class III group, the average fiber area was significantly different between the open bite, normal bite, and deepbite subjects. In the Class III subjects, type I and I/II hybrid fiber areas were greatly increased in subjects with deepbite.

CONCLUSIONS

Given the variation between subjects in fiber areas and fiber numbers, larger subject populations will be needed to demonstrate more significant associations between sagittal relationships and muscle composition. However, the robust influence of jaw-closing muscles on vertical dimension allowed us to conclude that vertical bite characteristics vary according to the fiber type composition of masseter muscle.

Transforming growth factor-beta isoform expression in the perisutural tissues of craniosynostotic rabbits

OBJECTIVE

To describe the expression patterns of the various transforming growth factor-beta (Tgf-beta) isoforms, known to be involved in suture development, in the perisutural tissues of rabbits with naturally occurring craniosynostosis and relate such differential expression to the pathogenesis of premature suture fusion.

METHOD

Twenty-one coronal sutures were harvested from six wild-type control New Zealand White rabbits and five rabbits with familial coronal suture synostosis at 25 days of age for histomorphometric and immunohistochemical analyses. Tgf-beta isoform immunoreactivity was assessed using indirect immunoperoxidase procedures with specific antibodies.

RESULTS

Synostosed sutures had significantly (p <.01) greater bone area and relatively more osteoblasts and osteocytes in the osteogenic fronts, compared with wild-type sutures. Tgf-beta isoform immunoreactivity showed differential staining patterns between wild-type and synostosed perisutural tissues. In wild-type sutures, Tgf-beta1 and Tgf-beta3 immunoreactivity was significantly (p <.001) greater than Tgf-beta2 staining in all perisutural tissues. In synostosed sutures, the opposite pattern was observed, with Tgf-beta2 immunoreactivity significantly (p <.001) greater than Tgf-beta1 and Tgf-beta3 in the osteogenic fronts, dura mater, and periosteum.

CONCLUSIONS

Findings from this study suggest that an overexpression of Tgf-beta2, either in isolation or in association with an underexpression of Tgf-beta1 and Tgf-beta3, may be related to premature suture fusion (craniosynostosis) in this pathological rabbit model. These abnormal expression patterns may be involved in premature suture fusion either through increased cell proliferation, decreased apoptosis of the osteoblasts or both at the osteogenic fronts.

Anatomy and fiber type composition of human interarytenoid muscle

Intrinsic laryngeal muscle investigations, especially those of the interarytenoid (IA) muscle, have been primarily teleologically based. We determined IA muscle anatomy and histochemical and immunohistochemical classification of extrafusal and intrafusal (muscle spindle) fibers in 5 patients. Extrafusal fibers were oxidative type I and glycolytic types IIA and IIX. Intrafusal fibers of muscle spindles were identified by the presence of tonic and neonatal myosin. The results demonstrate that the IA muscle has a phenotype similar to that of limb skeletal muscle. Myosin coexpression, the absence of intrafusal fibers, and fiber type grouping were unusual features found previously in the thyroarytenoid and posterior cricoarytenoid muscles, but they were not present in the IA muscle. These findings lead to the conclusion that the IA muscle has functional significance beyond its assumed importance in maintaining vocal fold position during phonation. The presence of spindles demonstrates differences in motor control as compared to the thyroarytenoid and posterior cricoarytenoid muscles. Further, extrafusal fiber characteristics implicate IA muscle involvement in muscle tension dysphonia and adductor spasmodic dysphonia. Given the unique physiologic characteristics of the human IA muscle, further research into the role of the IA muscle in voice disorders is warranted.

Segregation analysis of mandibular prognathism in Libya

The etiology of mandibular prognathism has been attributed to various genetic inheritance patterns and some environmental factors. The variation in inheritance patterns can be partly due to the use of different statistical approaches in the respective studies. The objective of this study was to investigate the role of genetic influences in the etiology of this trait. We performed segregation analysis on 37 families of patients currently being treated for mandibular prognathism. Mandibular prognathism was treated as a qualitative trait, with cephalometric radiographs, dental models, and photographs used to verify diagnosis. Segregation analysis of a prognathic mandible in the entire dataset supported a transmissible Mendelian major effect, with a dominant mode of inheritance determined to be the most parsimonious.

Staining of human thyroarytenoid muscle with myosin antibodies reveals some unique extrafusal fibers, but no muscle spindles

This study describes the myosin composition of extrafusal and intrafusal muscle fibers found in the human thyroarytenoid (TA) and sternohyoid (control) muscles. We sought to determine the presence of muscle spindles in the TA muscle, and to identify unusual extrafusal fiber types, using the commonly accepted approach of tissue staining with myosin isoform specific antibodies. Extrafusal fibers are organized into motor units, which subsequently produce muscle movement, whereas intrafusal fibers compose muscle spindles, the primary stretch receptor that provides afferent (feed back) information to the nervous system for regulation of motor unit length and tonicity. Immunohistochemical identification of muscle spindles was confirmed in sternohyoid, but not in TA samples; however, some extrafusal fibers contained tonic myosin. These results indicate that human TA muscle functions similar to some mammalian extraocular muscle, performing unloaded (non-weight bearing) contractions without afferent information from native muscle spindles.

Muscle fiber type composition and effects of vocal fold immobilization on the two compartments of the human posterior cricoarytenoid: a case study of four patients

The human posterior cricoarytenoid (PCA) muscle is divided into two compartments, the vertical and horizontal bellies, which contain differences in their myosin heavy chain (MyHC) composition. Using immunohistochemical techniques on whole PCA samples, this study provides a more thorough description of the fiber type composition of entire bellies of the PCA. Four patients provided complete PCA samples containing both compartments of their right and left sides; two with unilaterally immobilized vocal folds. The horizontal belly had 80% slow (type I) fibers and 20% fast (type II) fibers. The vertical belly contained equal amounts of slow and fast fibers (approximately 55%:45%); clearly distinguishing between two compartments. Atrophy of muscle fibers and fiber type grouping were also present in both normal and affected subjects; providing no clear confirmation of the clinical findings of vocal fold immobilization. Further study of the PCA muscle from patients with unilaterally immobilized vocal folds is needed.

Comparison of skeletal and dental changes between 2-point and 4-point rapid palatal expanders

Rapid palatal expansion has been a clinically accepted technique used by orthodontists for over 100 years. Its primary goal is to maximize orthopedic and minimize orthodontic movements of teeth. Historically, this was best accomplished by including 4 teeth in the appliance. However, including more teeth makes construction and insertion more difficult. The appliance also is less comfortable for patients and hinders oral hygiene. The 4-point hyrax expander can be modified by removing the 2 anterior wires, creating a 2-point expander between the first molars only. The purpose of this study was to determine the difference, if any, between midpalatal suture separation and dental expansion produced between 2-point and 4-point palatal expanders. Thirty subjects between the ages of 6 and 16 years were randomly assigned to either the 2-point (n = 15) or the 4-point group (n = 15). The groups were compared on dental and radiographic landmarks. The groups showed no statistical differences in total molar cusp width, molar gingival width, canine cusp width, canine gingival width, or diastema width. There were slight differences in arch perimeter and midpalatal suture separation. The results of this study showed that the 2-point appliance produced similar effects on the midpalatal suture and the dentition as did the 4-point appliance. It might therefore be considered instead of the 4-point appliance to successfully produce adequate skeletal and dental expansion.

Specialized cranial muscles: how different are they from limb and abdominal muscles?

Mammalian skeletal muscle fibers can be classified into functional types by the heavy chain (MyHC) and light chain (MyLC) isoforms of myosin (the primary motor protein) that they contain. Most human skeletal muscle contains fiber types and myosin isoforms I, IIA and IIX. Some highly specialized muscle fibers in human extraocular and jaw-closing muscles express either novel myosins or unusual combinations of isoforms of unknown functional significance. Extrinsic laryngeal muscles may express the extraocular MyHC isoform for rapid contraction and a tonic MyHC isoform for slow tonic contractions. In jaw-closing muscles, fiber phenotypes and myosin expression have been characterized as highly unusual. The jaw-closing muscles of most carnivores and primates have tissue-specific expression of the type IIM or 'type II masticatory' MyHC. Human jaw-closing muscles, however, do not contain IIM myosin. Rather, they express myosins typical of developing or cardiac muscle in addition to type I, IIA and IIX myosins, and many of their fibers are hybrids, expressing two or more isoforms. Fiber morphology is also unusual in that the type II fibers are mostly of smaller diameter than type I. By combining physiological and biochemical techniques it is possible to determine the maximum velocity of unloaded shortening (V(o)) of an individual skeletal muscle fiber and subsequently determine the type and amount of myosin isoform. When analyzed, some laryngeal fibers shorten at much faster rates than type II fibers from limb and abdominal muscle. Yet some type I fibers in masseter show an opposite trend towards speeds 10-fold slower than type I fibers of limb muscle. These unusual shortening velocities are most probably regulated by MyHC isoforms in laryngeal fibers and by MyLC isoforms in masseter. For the jaw-closing muscles, this finding represents the first case in human muscle of physiological regulation of kinetics by light chains. Together, these results demonstrate that, compared to other skeletal muscles, cranial muscles have a wider repertoire of contractile protein expression and function. Molecular techniques for reverse transcription of mRNA and amplification by polymerase chain reaction have been applied to typing of single fibers isolated from limb muscles, successfully identifying pure type I, IIA and IIX and hybrid type I/IIA and IIA/IIX fibers. This demonstrates the potential for future studies of the regulation of gene expression in jaw-closing and laryngeal muscles, which have such a variety of complex fiber types fitting them for their roles in vivo.

Tooth agenesis and craniofacial morphology in an orthodontic population

Previous reports have produced conflicting conclusions regarding the relationship among tooth agenesis, the congenital absence of teeth, and variations in craniofacial morphology. Traditional cephalometric assessment and computer-assisted morphometric analysis of jaw size were used to reexamine this relationship in a white orthodontic population. A positive diagnosis of tooth agenesis (including third molar determination) was made in 89 subjects of mixed age and sex who previously had orthodontic treatment but who were not determined to have a recognized syndrome or a craniofacial anomaly. Cephalograms for these subjects were compared with control data from subjects reported in Bolton Standards of Dentofacial Developmental Growth. Missing teeth and their locations were correlated with changes in selected linear and angular measurements of the Bolton cephalometric analysis. Area measurements of the jaw size of the subjects grouped by age were compared with Bolton cephalometric templates. Relatively little correlation was found between missing teeth and changes in cephalometric measurements. Where identified, a decreased maxillary jaw size and maxillary tooth agenesis were generally associated. Two-dimensional area measurements showed that most age groups had significant decreases in maxillary jaw size associated with tooth agenesis. Relatively few groups had significant changes in mandibular size associated with tooth agenesis.

Unloaded shortening velocity and myosin heavy chain variations in human laryngeal muscle fibers

Myosin description in human laryngeal muscles is incomplete, but evidence suggests the presence of type I, IIA, IIX, and tonic myosin heavy chain (MHC) fibers. This study describes the unloaded shortening velocity (V0) of chemically skinned laryngeal muscle fibers measured by the slack test method in relation to MHC content. Skeletal fibers from human laryngeal and limb muscle biopsy specimens were obtained for determination of V0, and subsequently, glycerol-sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used to determine the MHC isoform content. The fibers from human limb muscle had shortening speeds similar to those in previous reports on human skeletal fibers. Type I, IIA, and IIX fibers of laryngeal muscle had shortening speeds similar to those of fibers from limb muscle, but laryngeal fibers with heterogeneous MHC expression had a wide range of shortening speeds, some being nearly twice as fast as limb fibers. In addition, MHC isoform bands from human extraocular muscle comigrated with some bands from laryngeal muscle--a finding suggesting that extraocular myosin may also be expressed.

Cranial base growth and morphology in second-trimester normal human fetuses and fetuses with cleft lip

OBJECTIVE

The present radiographic study describes the size and shape of the cranial base from the sagittal aspect for a sample of 77 second-trimester "normal" control fetuses (n = 61) and fetuses (n = 16) exhibiting isolated, unilateral clefts of the lip (CL), ranging in fertilization age from 10 to 22 weeks.

METHODS

Fetuses were placed in a cephalostat, and standardized, lateral head radiographs were taken. The radiographs were traced, and 15 cephalometric landmarks were identified and digitized for analysis. Growth curves for cranial base lengths, angles, and areas were compared between control and CL groups. Also, cranial base triangles were constructed and shape comparisons were made using tensor biometric analysis.

RESULTS

No significant differences (p >.05) in regression line slopes were noted for any comparisons between the control and CL samples. Tensor biometric analysis also revealed no significant differences in the shapes of various cranial base triangles between the control and CL samples.

CONCLUSION

This report presents second-trimester baseline growth curves for various cranial base components in CL human fetal specimens, and these data suggest that CL fetuses may also be used as an appropriate control sample for prenatal growth comparison studies of cleft lip and palate and cleft palate.

Abundant expression of myosin heavy-chain IIB RNA in a subset of human masseter muscle fibres

Type IIB fast fibres are typically demonstrated in human skeletal muscle by histochemical staining for the ATPase activity of myosin heavy-chain (MyHC) isoforms. However, the monoclonal antibody specific for the mammalian IIB isoform does not detect MyHC IIB protein in man and MyHC IIX RNA is found in histochemically identified IIB fibres, suggesting that the IIB protein isoform may not be present in man; if this is not so, jaw-closing muscles, which express a diversity of isoforms, are likely candidates for their presence. ATPase histochemistry, immunohistochemistry polyacrylamide gel electrophoresis and in situ hybridization, which included a MyHC IIB-specific mRNA riboprobe, were used to compare the composition and RNA expression of MyHC isoforms in a human jaw-closing muscle, the masseter, an upper limb muscle, the triceps, an abdominal muscle, the external oblique, and a lower limb muscle, the gastrocnemius. The external oblique contained a mixture of histochemically defined type I, IIA and IIB fibres distributed in a mosaic pattern, while the triceps and gastrocnemius contained only type I and IIA fibres. Typical of limb muscle fibres, the MyHC I-specific mRNA probes hybridized with histochemically defined type I fibres, the IIA-specific probes with type IIA fibres and the IIX-specific probes with type IIB fibres. The MyHC IIB mRNA probe hybridized only with a few histochemically defined type I fibres in the sample from the external oblique; in addition to this IIB message, these fibres also expressed RNAs for MyHC I, IIA and IIX. MyHC IIB RNA was abundantly expressed in histochemical and immunohistochemical type IIA fibres of the masseter, together with transcripts for IIA and in some cases IIX. No MyHC IIB protein was detected in fibres and extracts of either the external oblique or masseter by immunohistochemistry, immunoblotting and electrophoresis. Thus, IIB RNA, but not protein, was found in the fibres of two different human skeletal muscles. It is believed this is the first report of the substantial expression of IIB mRNA in man as demonstrated in a subset of masseter fibres, but rarely in limb muscle, and in only a few fibres of the external oblique. These findings provide further evidence for the complexity of myosin gene expression, especially in jaw-closing muscles.

Differential effects of diminished oestrogen and androgen levels on development of skeletal muscle fibres in hypogonadal mice

Androgen and oestrogen hormones influence skeletal muscle size and the characteristics of skeletal muscle fibre types. These effects have typically been assessed by producing acute shortages (castration/ovariectomy) or by hormone supplementation. Little evidence exists, however, on how sex hormone shortages affect muscle development from early stages through to adulthood. Using the hypogonadal mouse model (hpg) we examined the effects of diminished androgen and oestrogen upon muscle size and fibre type composition in murine gastrocnemius and soleus muscles. Hypogonadal male soleus muscle was significantly smaller than normal males, and approximated the normal and hypogonadal females weight and fibre type characteristics. The hypogonadal male gastrocnemius muscle, however, was significantly small in comparison with normal and hypogonadal female gastrocnemius muscles, with the type IIB fibre diameters decreased most markedly. The hypogonadal female soleus muscle approximated the normal female phenotype, but the gastrocnemius muscle was larger than the normal female, approximating the size of the normal male gastrocnemius muscle. Here too, the type IIB fibres showed the most alteration, with greatly increased fibre diameters. Appropriate amounts of androgens were necessary for gender-specific patterns of growth in male muscles, whilst similar amounts of oestrogen were necessary for female gastrocnemius muscle growth, but not for female soleus muscle. Hypogonadism in this murine model generally retards muscle development in males, but has no apparent influence or enhances muscle development in females. Type IIB fibres are most dependent upon sex hormones for appropriate development, but this relationship is muscle-specific.

Skeletal muscle function and fibre types: the relationship between occlusal function and the phenotype of jaw-closing muscles in human

Mammalian skeletal muscle cells are composed of repeated sarcomeric units containing thick and thin filaments of myosin and actin, respectively. Excitation of the myosin ATPase enzyme is possible only with presence of Mg-ATP and Ca(2+). Skeletal muscle fibres may be classified into several types according to the isoform of myosin they contain. Nine isoforms of myosin heavy chain are known to exist in mammalian skeletal muscle including type I, IIA, IIB, IIX, IIM, alpha, neonatal, embryonic, and extra-ocular. Healthy adult human limb skeletal muscle contains type I, IIA, IIB, and IIX myosin heavy chains. The jaw-closing muscles of most carnivores and primates have tissue-specific expression of the type IIM or 'type II masticatory' myosin heavy chain. Adult human jaw-closing muscles, however, do not contain IIM myosin. Rather, they express type I, IIA, IIX (as in human limb muscle), and myosins typically expressed in developing or cardiac muscle. The morphology of human jaw-closing muscle fibres is also unusual in that the type II fibres are of smaller diameter that type I fibres, except in cases of increased function and hypertrophy. This paper describes the relationship of fibre types and motor unit function to changes in human occlusion and masticatory activity. Refereed Scientific Paper

A unique form of mental retardation with a distinctive phenotype maps to Xq26-q27

We report a novel X-linked mental retardation (XLMR) syndrome, with characteristic facial dysmorphic features, segregating in a large North Carolina family. Only males are affected, over four generations. Clinical findings in the seven living affected males include a moderate degree of mental retardation (MR), coarse facies, puffy eyelids, narrow palpebral fissures, prominent supraorbital ridges, a bulbous nose, a prominent lower lip, large ears, obesity, and large testicles. Cephalometric measurements suggest that the affected males have a distinctive craniofacial skeletal structure, when compared with normative measures. Obligate-carrier females are unaffected with MR, but the results of cephalometric skeletal analysis suggest craniofacial dysmorphisms intermediate between affected males and normative control individuals. Unaffected male relatives show no clinical or cephalometric resemblance to affected males. The blood-lymphocyte karyotype and the results of DNA analysis for fragile-X syndrome and of other routine investigations are normal. Linkage analysis for polymorphic DNA markers spanning the X chromosome established linkage to Xq26-q27. Maximum LOD scores were obtained at marker DXS1047 (maximum LOD score = 3.1 at recombination fraction 0). By use of haplotype analysis, we have localized the gene for this condition to an 18-cM genetic interval flanked by ATA59C05 and GATA31E08. On the basis of both the clinical phenotype and the mapping data, we were able to exclude other reported XLMR conditions. Therefore, we believe that a unique recessive XLMR syndrome with a distinctive and recognizable phenotype is represented in this family.

Skeletal fiber types and spindle distribution in limb and jaw muscles of the adult and neonatal opossum, Monodelphis domestica

The South American opossum, Monodelphis domestica, is very immature at birth, and we wished to assess its potential for studies of jaw muscle development. Given the lack of prior information about any Monodelphis fiber types or spindles, our study aimed to identify for the first time fiber types in both adult and neonatal muscles and the location of spindles in the jaw muscles. Fiber types were identified in frozen sections of adult and 6-day-old jaw and limb muscles by using myosin ATPase and metabolic enzyme histochemistry and by immunostaining for myosin isoforms. The distribution of fiber types and muscle spindles throughout the jaw-closer muscles was identified by immunostaining of sections of methacarnoy-fixed, wax-embedded heads. Most muscles contained one slow (type I) and two fast fiber types (equivalent to types IIA and IIX), which were similar to those in eutherian muscle, and an additional (non-IIB) fast type. In jaw-closer muscles, the main extrafusal fiber type was IIM (characteristic of these muscles in some eutherians), and almost all spindles were concentrated in four restricted areas: one in masseter and three in temporalis. Six-day neonatal muscles were very immature, but future spindle-rich areas were revealed by immunostaining and corresponded in position to the adult areas. Extrafusal and spindle fiber types in Monodelphis share many similarities with eutherian mammalian muscle. This finding, along with the immaturity of myosin isoform expression observed 6 days postnatally, indicates that Monodelphis could provide a valuable model for studying early developmental events in the jaw-closer muscles and their spindles.

Changes in myosin expression in denervated laryngeal muscle

The effects of chronic denervation on the myosin heavy chain (MyHC) content and muscle fiber type composition of rat laryngeal muscles are described. The posterior cricoarytenoid (PCA) and thyroarytenoid (TA) muscles were removed 3 weeks, 3 months, and 6 months after recurrent laryngeal nerve sectioning. Myofibrillar adenosine triphosphatase staining of cryostat sections was performed, and fiber type percentages were determined. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used to separate MyHC isoforms, and densitometry was subsequently used for quantitative analysis. Unoperated animals served as controls. In the PCA muscle, denervation resulted in a progressive reduction in type I MyHC (the slow-contracting isoform) to an almost complete loss at 6 months, with a concomitant increase in type II MyHCs (fast-contracting isoforms, excluding type IIL). Type IIL MyHC (laryngeal-specific isoform) remained relatively constant up to 6 months after denervation. The myosin expression in the TA muscle, which contained only type II MyHCs, remained relatively constant with denervation. Changes in fiber type composition of the muscles described from tissue staining correlated with MyHC content. These findings in laryngeal muscle confirm the dependence of type I MyHC expression upon neural input, as has been found previously in limb skeletal muscles. Since the expression of all MyHCs except the IIL was modified after denervation in the PCA muscle, it is possible that the IIL isoform is maintained by factors that differ from those in the other skeletal myosins.

Unloaded shortening velocities of rabbit masseter muscle fibres expressing skeletal or alpha-cardiac myosin heavy chains

1. Some rabbit masseter fibres express the alpha-cardiac myosin heavy chain (MHC). To compare the biochemical and physiological properties of these fibres with other skeletal fibre types, we examined the histochemical and immunohistochemical staining characteristics, maximum velocity of shortening (V(zero)) and MHC isoform content of fibres from rabbit masseter and soleus muscles. 2. The fibre-type composition of muscle sections was determined with MHC antibodies and myofibrillar ATPase histochemistry. Fibres we designated 'type alpha-cardiac' were different from type I and type II fibres in that they stained positively with the alpha-cardiac MHC antibody and they maintained. ATPase reactivity after acid and alkali pre-incubations. Samples of superficial masseter contained a few type I fibres, with the majority of fibres classified as either type IIA or type alpha-cardiac. Soleus samples contained type I, IIA and IIC fibres. 3. The V(zero) of chemically skinned fibres was determined by the slack-test method. Each fibre was subsequently characterized as type I, IIA, IIC or alpha-cardiac from MHC identification using gel electrophoresis (SDS-PAGE). In masseter fibres the V(zero) values were (in muscle lengths s-1): type I, 0.54 +/- 0.05 (mean +/- S.D., n = 3); type IIA, 1.23 +/- 0.34 (n = 27); type alpha-cardiac, 0.78 +/- 0.08 (n = 9). In soleus fibres V(zero) values were: type I, 0.55 +/- 0.06 (n = 14); type IIA, 0.89 +/- 0.04 (n = 8); type IIC, 0.73 (n = 2). 4. We conclude that the rabbit masseter muscle contains an 'alpha-cardiac' fibre type that is distinct from other skeletal fibres. This fibre type expresses only the alpha-cardiac MHC, has unusual myofibrillar ATPase reactivity and has a V(zero) intermediate between type I and type II fibres.

Myosin expression in the jaw-closing muscles of the domestic cat and American opossum

Sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE), glycerol SDS-PAGE, two-dimensional electrophoresis, and protein immunoblotting techniques were used to identify myosin heavy chain (MHC) and light chain (MLC) isoforms in limb and masticatory muscles of the cat and American opossum. The fibre types in which these isoforms are expressed were identified by histochemistry and immunohistochemistry. Antibodies specific for the type IIM MHC isoform characteristic of cat jaw-closing muscles and the type I MHC isoform were produced and characterized. The IIM antibody stained the majority of fibres found in the jaw-closing muscles of both species. These IIM-containing fibres characteristically had a histochemical ATPase that remained active after both acid and alkali pre-incubations. A minority of type I fibres was also present in cat jaw-closing muscles, and these reacted positively with antibody specific for type I MHC. It was confirmed that the vast majority of fibres in the cat jaw-closing muscles contained only the characteristic masticatory MHC (IIM) and masticatory MLCs (LC1m and LC2m). These muscles did not contain either the type II fibre isoforms of limb muscles or the atrial cardiac (alpha-cardiac) MHC. The type IIM MHC could also be identified in jaw-closing muscles of the opossum. Two-dimensional gel electrophoresis was used to identify the MLC composition of single, histochemically defined, type I fibres in the cat soleus and deep masseter. The type I fibres of limb muscle contained the usual slow MLCs, but type I fibres from the jaw-closing muscles contained only the masticatory light chains.

Atypical myosin heavy chain in rat laryngeal muscle

The myosin content of rat posterior cricoarytenoid and thyroarytenoid muscles was described by means of histochemical, immunohistochemical, and electrophoretic techniques. Laryngeal muscles were dissected and frozen, together with other muscles (extraocular, diaphragm, extensor digitorum longus, and soleus) for comparative purposes, then sectioned serially and stained: 1) histochemically for myofibrillar adenosine triphosphatase reactivity and 2) immunohistochemically for myosin heavy chain (MHC) content with six different antibodies. Other portions of the muscle samples were electrophoresed by a glycerol sodium dodecyl sulfate-polyacrylamide gel electrophoresis technique that separates the MHC protein into its specific isoforms. In electrophoretic comparison to limb muscles, the laryngeal muscles contained an additional MHC band we designated as type IIL (type II laryngeal) MHC. On histochemical and immunohistochemical staining, no fibers from the thyroarytenoid muscle and few fibers from the posterior cricoarytenoid muscle could be classified according to the standard fiber type categories established for limb muscles (types I, IIA, IIB, and IIX). These laryngeal muscle fibers appear to represent an atypical fiber type.

Fibre type classification and myosin isoforms in the human masseter muscle

Human masseter muscle is highly unusual since it contains relatively large numbers of fibres with variable myofibrillar ATPase staining as well as fibres that express neonatal and alpha-cardiac myosin heavy chain (MHC). These findings however, have not been organised together into a fibre type classification scheme. Biopsies from the anterior superficial area of masseter were collected from a large sample of healthy young adults. Biopsies were sectioned and stained for myofibrillar ATPase reactivity and the presence of MHC isoforms as detected by a series of antibodies. The MHC composition of the same biopsies was also analysed using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). A series of rectus abdominis muscle biopsies were analysed similarly to serve as a control for type I, IIA and IIB fibres and isoforms. From the histochemical, immunohistochemical and biochemical experiments we found the masseter to contain type I, IM, IIC, IIA and IIB fibres as previously classified, but in addition there were type neonatal, alpha-cardiac, and 'other' (three or more myosins including neonatal and alpha-cardiac). The percentage of each fibre type was highly variable in masseter biopsies, but generally type I fibres were most common, and the proportion of IIB, neonatal, alpha-cardiac and 'other' fibres was low. Even in biopsies that contained relatively large amounts of these last three fibre types, the amount of neonatal and/or alpha-cardiac MHC detected on SDS-PAGE was limited, suggesting that these MHCs are a minor component in the fibres in which they are expressed.

Fibre type distribution in the muscle spindles of cat jaw-elevator muscles

Small samples of the masseter and temporalis muscles of six adult male cats were dissected free, snap-frozen and cryosectioned. Serial sections from areas with muscle spindles were histochemically stained for myofibrillar ATPase after incubation in acid and alkali buffer, and for reactivity to two different myosin isoform-specific antibodies. Differential reactivity to these four stains identified bag1, bag2 and chain intrafusal fibre types. The most typical distribution of fibres within the spindle was 1 bag1, 1 bag2 and 3-4 chains. Although a few spindles were found in the anterior area of the temporalis that attaches to the coronoid process of the mandible and in the anterior area of the superficial masseter, the vast majority were found in the deepest portion of the masseter. Here spindles were characteristically with a number of simple spindles fused together into complex units.