No description available.

Thesis (M Dent (Orthodontics)) -- University of Limpopo, 2011 / Introduction: Flexion of the cranial base plays a very crucial role in the study of the craniofacial complex, particularly with the development of skeletal jaw relationships. An understanding of growth of the cranial base has come to assume great importance in orthodontics, and successful treatment of skeletal jaw malrelationships depends largely on the growth and flexion of the patients' cranial base. The aim of this study was to determine the relationship between cranial base flexion and skeletal jaw relationships in a sample of Black South Africans. Materials and method: The sample comprised of 300 pre-treatment lateral cephalograms of Black South Africans which was equally divided into Class I, Class . II and Class III skeletal jaw relationships according to the cephalometric tracing and analysis, and each class of skeletal jaw relationship had an equal number of male and female subjects. A digital cephalometric analysis software program (Orthview<ID, Netherlands) was used to trace and analyse the selected lateral cephalograms. The sample was first analysed to determine if gender differences existed for the mean cranial base flexion value in all three classes of skeletal jaw relationships. , , Comparisons among Class I, II and III mean cranial base flexton values using an independent t-test were made. The averag~ cranial base 'flexion value of the Black South Africans in this study was also compared with the average cranial base flexion value of Black and Caucasian South Africans from the previous studies for significance using an independent t-test. Results: Age distribution showed no statistically significant differences in all the three classes of skeletal jaw relationship (p > 0.05). There were no statistically significant differences between the mean cranial base flexion values of the male and female subjects in all the three classes of skeletal jaw relationships (p > 0.05). The results of this study demonstrated a significantly larger mean cranial base flexion value in the Class II skeletal jaw relationship sample when it was compared with the mean cranial base flexion values of Class I and Class III skeletal jaw relationship samples respectively (p < 0.05). There was no statistically significant difference between Class I and Class III skeletal jaw relationship samples with regards to the cranial base flexion (p> 0.05). The results of this study also showed no statistically . significant difference between the average cranial base flexion values of Black South Africans of the present study as well as Black and Caucasian South Africans of the previous study (p > 0.05). Conclusion: It was concluded that, in this sample, a larger cranial base flexion value is a feature of Class II skeletal jaw relationship and a smaller cranial base flexion value is a feature of both Class I and Class 11\ skeletal jaw relationships. Keywords: cranial base flexion, skeletal classification, skeletal jaw malrelationship

Understanding the regulatory mechanisms controlling utrophin A expression at the sarcolemma of dystrophic muscles will facilitate the development of therapeutic strategies to ameliorate the pathophysiological features of Duchenne Muscular Dystrophy (DMD). The main goal of this study was to characterize the regulation of utrophin A IRES activity using a transgenic mouse model expressing the utrophin A 5’UTR bicistronic reporter and to identify trans-acting factors that could mediate IRES activity and endogenous expression of utrophin A. We found that utrophin A IRES activity is specifically expressed in skeletal muscles. Moreover, we identified eEF1A2 as a muscle-specific trans-acting factor that can interact with utrophin A and mediate IRES-dependent translation of utrophin A. Finally, we showed that eEF1A2 mediates endogenous utrophin A expression and localization in skeletal muscle. Identifying pharmacological compounds that would specifically target eEF1A2 and increase endogenous levels of utrophin A expression could serve as a drug-based therapy to treat DMD.

Understanding the regulatory mechanisms controlling utrophin A expression at the sarcolemma of dystrophic muscles will facilitate the development of therapeutic strategies to ameliorate the pathophysiological features of Duchenne Muscular Dystrophy (DMD). The main goal of this study was to characterize the regulation of utrophin A IRES activity using a transgenic mouse model expressing the utrophin A 5’UTR bicistronic reporter and to identify trans-acting factors that could mediate IRES activity and endogenous expression of utrophin A. We found that utrophin A IRES activity is specifically expressed in skeletal muscles. Moreover, we identified eEF1A2 as a muscle-specific trans-acting factor that can interact with utrophin A and mediate IRES-dependent translation of utrophin A. Finally, we showed that eEF1A2 mediates endogenous utrophin A expression and localization in skeletal muscle. Identifying pharmacological compounds that would specifically target eEF1A2 and increase endogenous levels of utrophin A expression could serve as a drug-based therapy to treat DMD.

Altered apoptotic signaling in skeletal muscle has been observed in a number of disease states associated with skeletal muscle atrophy. Therefore, understanding the mechanisms that lead to increased skeletal muscle apoptosis may help to prevent the atrophy associated with various diseases. Apoptosis repressor with caspase recruitment domain (ARC) is a potent anti-apoptotic protein that is able to inhibit apoptosis mediated by both the death-receptor and mitochondrial pathways. In addition, ARC has a unique distribution pattern and is highly expressed in terminally differentiated tissue such as skeletal muscle. To characterize the role of ARC in skeletal muscle morphology and apoptosis, soleus and plantaris muscles of 18 week-old ARC-deficient mice were excised and compared to those of age-matched wild-type littermates. While no differences were seen in muscle weights between genotypes, in the ARC KO animals, the cross-sectional area (CSA) of the soleus was smaller, while the CSA of the plantaris was larger. With respect to fiber type distribution, both muscles demonstrated a shift towards a faster myosin heavy chain expression pattern. For example, soleus muscles of ARC KO animals had significantly less type I fibers and more IIa fibers, while plantaris muscles had significantly less type IIa fibers, and more IIb fibers. In ARC KO animals, type I and IIa fibers were significantly smaller in the soleus, while type IIb fibers were larger in the plantaris. DNA fragmentation (a hallmark of apoptosis) was increased in the soleus, but not plantaris muscles of ARC KO animals. Surprisingly, activity of the proteolytic enzymes caspase-2, -3, -8, and -9, as well as calpains, was not different in either soleus or plantaris muscles. To determine whether a lack of ARC protein affects apoptotic signaling in skeletal muscle, the total expression of pro- and anti-apoptotic proteins were also assessed. In the soleus, no changes were observed in whole tissue AIF, cytochrome c, EndoG, and Smac. In the plantaris, there was no change in total muscle AIF; however, there were trends towards decreased cytochrome c, and increased Smac, as well as a significant decrease in EndoG ARC KO animals. No changes were observed in Bcl-2 and XIAP in the soleus; however, there were significant reductions in FLIP(s) and HSP70 content. In the plantaris, no changes were observed in anti-apoptotic protein content. Subcellular fractionation of red quadriceps for ARC KO mice revealed an increased Bax:Bcl-2 ratio in the isolated mitochondrial fractions. Furthermore, in cytosolic fractions of red quadriceps, AIF protein content was significantly increased in ARC KO animals. Conversely, no changes in apoptotic-related protein content were observed in any fractions from white quadriceps between groups. In agreement with these findings, isolated mitochondria from ARC-deficient animals were more susceptible to calcium induced swelling, as well as membrane potential loss compared to controls. Taken together, these results suggest that in slow-oxidative skeletal muscle of ARC-deficient mice there is increased apoptosis due to caspase-independent, mitochondrial-mediated apoptotic signaling. Furthermore, this study is the first to show ARC plays an important role in skeletal muscle morphology, as ARC KO mice have an altered skeletal muscle phenotype and morphology.

No description available.

<i>Trichinella spiralis</i> is a parasitic nematode of mammalian skeletal muscle.  Its life cycle includes two stages where developmental progression appears to be inhibited until a specific host niche is encountered.  The newborn larva, released within the host intestine depends upon entry to skeletal muscle for continued development.  The muscle larva encapsulates within skeletal muscle and further reproductive development is dependent upon ingestion by a new host.  Developmental arrest has been extensively characterised in <i>Caenorhabditis</i> <i>elegans</i>, where an alternative L3 larva, the dauer larva, is formed in response to environmental conditions refractive to continued reproductive development.  Using the wealth of genetic information regarding <i>C. elegans</i> dauer formation, putative periods of arrest were examined in <i>T. spiralis.</i> TGF-<span lang=EN-GB style='font-family:Symbol'>b-like and insulin-like signalling pathways are critical mediators of <i>C. elegans </i>dauer formation.  A <i>T. spiralis</i> TGF-<span lang=EN-GB style='font-family: Symbol'>b-ligand was identified and designated <i>ts-tll-1</i>.  Sequencing and analysis revealed <i>ts-tll-1</i> to be similar to vertebrate bone morphogenetic proteins and <i>C. elegans </i>DBL-1, is involved in body size regulation.  EST mining identified putative type I and II TGF-<span lang=EN-GB style='font-family:Symbol'>b receptors and a subtilsin-like proprotein convertase, suggesting conservation of TGF-<span lang=EN-GB style='font-family:Symbol'>b-like signalling in <i>T. spiralis.  </i>A partial <i>Trichinella </i>gene encoding an orthologue of the <i>C. elegans</i> insulin-like, tyrosine kinase receptor, DAF-2, was identified by degenerate PCR and designated <i>ts-tkr.  ts-tkr</i> is most similar to <i>C. elegans daf-2</i> within the highly conserved tyrosine kinase domain.  Two alternative transcripts of <i>ts-tkr</i> were identified by 3’ RACE, which differed in their 3’ UTRs.  Semi-quantitative RT-PCR analysis suggested <i>ts-tkr </i>expression was greatest in adult worms, implying a role in promoting reproductive development. Semi-quantitative RT-PCR was also to assess the expression of selected housekeeping and ES protein encoding genes during the <i>T. spiralis </i>life cycle.  While transcription in the <i>C. elegans</i> dauer is depressed, there was no obvious transcriptional repression in <i>Trichinella</i> newborn or muscle larva.

Although much work has been carried out to identify the mechanisms by which muscle is formed, many of the regulatory pathways involved have yet to be fully elucidated. In creating perturbations during the embryonic period, either nutritionally (with a marginal vitamin A deficiency model) or pharmacologically (with the b₂-adrenerguic agonist clenbuterol), a comparison with 'normal' muscle development may be attained. Differences in the temporal expression of specific regulatory proteins may then enhance the existing knowledge of their function in regulating muscle development. Prior to studying changes in muscle regulatory proteins due to perturbations, it was first necessary to illustrate their temporal pattern in "normal" muscle development. The results indicated that a complex regulatory system operates in myogenesis with a number of proteins appearing to be involved in the process of muscle development. A marginal vitamin A deficiency model was established in which maternal retinol levels were clearly reduced in treatment animals in comparison with controls. This resulted in offspring that showed clearly symptoms of marginal vitamin A deficiency. Changes in the abundance of five proteins were observed in response to marginal vitamin A deficiency. Overall, these changes suggested a potential reduction in secondary myogenesis, based on reduced levels of MHCfast, associated with secondary fibres, following birth. Analysis of RNA, DNA and protein values suggested that neonates from clenbuterol fed dams may have reduced hyperplasia and/or increased hypertrophy. Biochemical analysis revealed that proteins such as GATA-2, PKC and Shh, which have previously been associated with hypertrophy, were altered in response to clenbuterol. Further evidence in support of hypertrophy was indicated in an apparent increase in fibre size of neonates detected by MHC immunolocalisation. In conclusion, it has been demonstrated that both nutritional and pharmacological manipulations throughout are gestation capable of altering myogeneiss <i>in utero</i> by two different mechanisms.

Understanding the regulatory mechanisms controlling utrophin A expression at the sarcolemma of dystrophic muscles will facilitate the development of therapeutic strategies to ameliorate the pathophysiological features of Duchenne Muscular Dystrophy (DMD). The main goal of this study was to characterize the regulation of utrophin A IRES activity using a transgenic mouse model expressing the utrophin A 5’UTR bicistronic reporter and to identify trans-acting factors that could mediate IRES activity and endogenous expression of utrophin A. We found that utrophin A IRES activity is specifically expressed in skeletal muscles. Moreover, we identified eEF1A2 as a muscle-specific trans-acting factor that can interact with utrophin A and mediate IRES-dependent translation of utrophin A. Finally, we showed that eEF1A2 mediates endogenous utrophin A expression and localization in skeletal muscle. Identifying pharmacological compounds that would specifically target eEF1A2 and increase endogenous levels of utrophin A expression could serve as a drug-based therapy to treat DMD.

Altered apoptotic signaling in skeletal muscle has been observed in a number of disease states associated with skeletal muscle atrophy. Therefore, understanding the mechanisms that lead to increased skeletal muscle apoptosis may help to prevent the atrophy associated with various diseases. Apoptosis repressor with caspase recruitment domain (ARC) is a potent anti-apoptotic protein that is able to inhibit apoptosis mediated by both the death-receptor and mitochondrial pathways. In addition, ARC has a unique distribution pattern and is highly expressed in terminally differentiated tissue such as skeletal muscle. To characterize the role of ARC in skeletal muscle morphology and apoptosis, soleus and plantaris muscles of 18 week-old ARC-deficient mice were excised and compared to those of age-matched wild-type littermates. While no differences were seen in muscle weights between genotypes, in the ARC KO animals, the cross-sectional area (CSA) of the soleus was smaller, while the CSA of the plantaris was larger. With respect to fiber type distribution, both muscles demonstrated a shift towards a faster myosin heavy chain expression pattern. For example, soleus muscles of ARC KO animals had significantly less type I fibers and more IIa fibers, while plantaris muscles had significantly less type IIa fibers, and more IIb fibers. In ARC KO animals, type I and IIa fibers were significantly smaller in the soleus, while type IIb fibers were larger in the plantaris. DNA fragmentation (a hallmark of apoptosis) was increased in the soleus, but not plantaris muscles of ARC KO animals. Surprisingly, activity of the proteolytic enzymes caspase-2, -3, -8, and -9, as well as calpains, was not different in either soleus or plantaris muscles. To determine whether a lack of ARC protein affects apoptotic signaling in skeletal muscle, the total expression of pro- and anti-apoptotic proteins were also assessed. In the soleus, no changes were observed in whole tissue AIF, cytochrome c, EndoG, and Smac. In the plantaris, there was no change in total muscle AIF; however, there were trends towards decreased cytochrome c, and increased Smac, as well as a significant decrease in EndoG ARC KO animals. No changes were observed in Bcl-2 and XIAP in the soleus; however, there were significant reductions in FLIP(s) and HSP70 content. In the plantaris, no changes were observed in anti-apoptotic protein content. Subcellular fractionation of red quadriceps for ARC KO mice revealed an increased Bax:Bcl-2 ratio in the isolated mitochondrial fractions. Furthermore, in cytosolic fractions of red quadriceps, AIF protein content was significantly increased in ARC KO animals. Conversely, no changes in apoptotic-related protein content were observed in any fractions from white quadriceps between groups. In agreement with these findings, isolated mitochondria from ARC-deficient animals were more susceptible to calcium induced swelling, as well as membrane potential loss compared to controls. Taken together, these results suggest that in slow-oxidative skeletal muscle of ARC-deficient mice there is increased apoptosis due to caspase-independent, mitochondrial-mediated apoptotic signaling. Furthermore, this study is the first to show ARC plays an important role in skeletal muscle morphology, as ARC KO mice have an altered skeletal muscle phenotype and morphology.