title: Chracterisation of Mighty during Skeletal Muscle Regeneration

authors: Dyer, Kelly Anne

subjects: skeletal muscle

abstract: Satellite cells are a distinct lineage of myogenic precursors that are responsible for the growth of muscle during post-natal life and for its repair after damage. During muscle growth and regeneration satellite cells are activated in response to growth signals from the environment, which induces the expression of one or both of the two MRFs, Myf-5 or MyoD. Activated satellite cells migrate to the site of injury and proliferate before these transcription factors go on to activate transcription of myogenic genes. The myoblasts can then adopt one of two fates. Some myoblasts initiate terminal differentiation and are able to either fuse into existing myofibres to repair them, or fuse with other myoblasts to form new fibres. Other myoblasts do not differentiate but instead return to quiescence and adopt a satellite cell position on repaired or newly formed fibres.

Mighty, a downstream target of myostatin that was discovered by the Functional Muscle Genomics Laboratory has recently been shown to induce cell hypertrophy in cell culture through enhanced differentiation and fusion of myoblasts. Myostatin-null mice have hypertrophic muscles and an improved muscle regeneration phenotype. These mice have also been shown to have higher basal levels of Mighty in skeletal muscle than wild-type mice. In this thesis the expression profile of Mighty during skeletal muscle regeneration was characterised in relation to MyoD. 

During regeneration Mighty gene expression was induced at day five post-injury in both wild-type and myostatin-null mice. In the myostatin-null mice Mighty gene expression remained elevated at day seven post injury in contrast to the levels in the wild-type, which had decreased at this time point. By day-14 and day-28 post-injury Mighty levels were decreased. The up-regulation of Mighty occurs at the time of peak myotube formation in regenerating skeletal muscle, consistent with a role for Mighty in enhancing differentiation and fusion of myoblasts. The extended up-regulation of Mighty in the myostatin-null muscle may be responsible for the enhanced regeneration phenotype of these mice.

Analysis of the myotube and reserve cell populations, which are an in vitro model of satellite cells, from both C2C12 cells and Mighty over-expressing clones (Clone 7 and Clone 11) showed that Mighty expression down-regulates two satellite cell markers, CD34 and Sca-1. Both these molecules have been recently shown to be involved in myoblast fusion and reserve cell specification, although their exact role in these processes is not yet known. Expression of Sca-1 is associated with a slowly proliferating non-dividing state while CD34 is associated with the population of reserve cells that do not fuse when notch signalling is inhibited. The results of this thesis indicate that Mighty over-expression may cause the enhanced fusion phenotype by regulating these two molecules.

In conclusion the data in this thesis supports a role for Mighty in the myotube formation phase of regeneration and may be able to enhance regeneration by recruiting more myoblasts to terminal differentiation by altering CD34 and    Sca-1 expression.

text: Chracterisation of Mighty during Skeletal Muscle Regeneration Satellite cells are a distinct lineage of myogenic precursors that are responsible for the growth of muscle during post-natal life and for its repair after damage. During muscle growth and regeneration satellite cells are activated in response to growth signals from the environment, which induces the expression of one or both of the two MRFs, Myf-5 or MyoD. Activated satellite cells migrate to the site of injury and proliferate before these transcription factors go on to activate transcription of myogenic genes. The myoblasts can then adopt one of two fates. Some myoblasts initiate terminal differentiation and are able to either fuse into existing myofibres to repair them, or fuse with other myoblasts to form new fibres. Other myoblasts do not differentiate but instead return to quiescence and adopt a satellite cell position on repaired or newly formed fibres.

Mighty, a downstream target of myostatin that was discovered by the Functional Muscle Genomics Laboratory has recently been shown to induce cell hypertrophy in cell culture through enhanced differentiation and fusion of myoblasts. Myostatin-null mice have hypertrophic muscles and an improved muscle regeneration phenotype. These mice have also been shown to have higher basal levels of Mighty in skeletal muscle than wild-type mice. In this thesis the expression profile of Mighty during skeletal muscle regeneration was characterised in relation to MyoD. 

During regeneration Mighty gene expression was induced at day five post-injury in both wild-type and myostatin-null mice. In the myostatin-null mice Mighty gene expression remained elevated at day seven post injury in contrast to the levels in the wild-type, which had decreased at this time point. By day-14 and day-28 post-injury Mighty levels were decreased. The up-regulation of Mighty occurs at the time of peak myotube formation in regenerating skeletal muscle, consistent with a role for Mighty in enhancing differentiation and fusion of myoblasts. The extended up-regulation of Mighty in the myostatin-null muscle may be responsible for the enhanced regeneration phenotype of these mice.

Analysis of the myotube and reserve cell populations, which are an in vitro model of satellite cells, from both C2C12 cells and Mighty over-expressing clones (Clone 7 and Clone 11) showed that Mighty expression down-regulates two satellite cell markers, CD34 and Sca-1. Both these molecules have been recently shown to be involved in myoblast fusion and reserve cell specification, although their exact role in these processes is not yet known. Expression of Sca-1 is associated with a slowly proliferating non-dividing state while CD34 is associated with the population of reserve cells that do not fuse when notch signalling is inhibited. The results of this thesis indicate that Mighty over-expression may cause the enhanced fusion phenotype by regulating these two molecules.

In conclusion the data in this thesis supports a role for Mighty in the myotube formation phase of regeneration and may be able to enhance regeneration by recruiting more myoblasts to terminal differentiation by altering CD34 and    Sca-1 expression.

year: 2006

title: The impact of reliance on incentive-based compensation schemes, information asymmetry and organisational commitment on managerial performance

authors: Chong, Vincent

subjects: reliance on incentive-based compensation schemes

abstract: This study examines the effects of information asymmetry and organisational commitment on the relation between the extent of reliance on incentive-based compensation schemes and managerial performance. The responses of 109 managers, drawn from a cross-section of Australian manufacturing companies, to a questionnaire survey, were analysed by using a multiple regression technique. The results provide evidence of higher managerial performance for managers with low organisational commitment and a high reliance on incentive-based compensation schemes in high information asymmetry situations. On the other hand, the results show that the performance level of managers with high organisational commitment is unaffected regardless of the degree of information asymmetry and the extent of reliance on incentive-based compensation schemes.

text: The impact of reliance on incentive-based compensation schemes, information asymmetry and organisational commitment on managerial performance This study examines the effects of information asymmetry and organisational commitment on the relation between the extent of reliance on incentive-based compensation schemes and managerial performance. The responses of 109 managers, drawn from a cross-section of Australian manufacturing companies, to a questionnaire survey, were analysed by using a multiple regression technique. The results provide evidence of higher managerial performance for managers with low organisational commitment and a high reliance on incentive-based compensation schemes in high information asymmetry situations. On the other hand, the results show that the performance level of managers with high organisational commitment is unaffected regardless of the degree of information asymmetry and the extent of reliance on incentive-based compensation schemes.

year: 2007

title: Enhancing well-being and social connectedness for Maori elders through a peer education (Tuakana-Teina) programme: A cross-sectional baseline study

authors: Oetzel, John G.

subjects: Science & Technology

abstract: Background: Māori kaumātua (elders) face stark health and social inequities compared to non-Māori New Zealanders. The tuakana-teina (older sibling-younger sibling) peer education programme is a strengths-based approach to enhance well-being and social connectedness. The purpose of this study is to present the baseline data from this programme and identify correlates of well-being outcomes.

Method: Participants included 128 kaumātua who completed a self-report survey about health-related quality of life, spirituality, social connection and loneliness, life satisfaction, cultural identity and connection, elder abuse, health service utilisation and demographics.

Findings: Multiple regression models illustrated the following correlates of outcomes: (a) self-rated health: needing more help with daily tasks (β = −0.36) and housing problems (β = –0.17); (b) health-related quality of life: needing more help with daily tasks (β = –0.31), housing problems (β = –0.21), and perceived autonomy (β = 0.19); (c) spiritual well-being: understanding of tikanga (cultural protocols) (β = 0.32) and perceived autonomy (β = 0.23); (d) life satisfaction: social support (β = 0.23), sense of purpose (β = 0.23), cultural identity (β = 0.24), trouble paying bills (β = –0.16), and housing problems (β = –0.16); (e) loneliness: elder abuse (β = 0.27), social support (β = –0.21), and missing pleasure of being with whānau (extended family) (β = 0.19).

Conclusions: Key correlates for outcomes centred on social support, housing problems, cultural connection and perceived autonomy. These correlates are largely addressed through the programme where tuakana/peer educators provide support and links to social and health services to teina/peer recipients in need. This study illustrates needs and challenges for kaumātua, whilst the larger programme represents a strengths-based and culturally-centred approach to address health issues related to ageing in an Indigenous population.

text: Enhancing well-being and social connectedness for Maori elders through a peer education (Tuakana-Teina) programme: A cross-sectional baseline study Background: Māori kaumātua (elders) face stark health and social inequities compared to non-Māori New Zealanders. The tuakana-teina (older sibling-younger sibling) peer education programme is a strengths-based approach to enhance well-being and social connectedness. The purpose of this study is to present the baseline data from this programme and identify correlates of well-being outcomes.

Method: Participants included 128 kaumātua who completed a self-report survey about health-related quality of life, spirituality, social connection and loneliness, life satisfaction, cultural identity and connection, elder abuse, health service utilisation and demographics.

Findings: Multiple regression models illustrated the following correlates of outcomes: (a) self-rated health: needing more help with daily tasks (β = −0.36) and housing problems (β = –0.17); (b) health-related quality of life: needing more help with daily tasks (β = –0.31), housing problems (β = –0.21), and perceived autonomy (β = 0.19); (c) spiritual well-being: understanding of tikanga (cultural protocols) (β = 0.32) and perceived autonomy (β = 0.23); (d) life satisfaction: social support (β = 0.23), sense of purpose (β = 0.23), cultural identity (β = 0.24), trouble paying bills (β = –0.16), and housing problems (β = –0.16); (e) loneliness: elder abuse (β = 0.27), social support (β = –0.21), and missing pleasure of being with whānau (extended family) (β = 0.19).

Conclusions: Key correlates for outcomes centred on social support, housing problems, cultural connection and perceived autonomy. These correlates are largely addressed through the programme where tuakana/peer educators provide support and links to social and health services to teina/peer recipients in need. This study illustrates needs and challenges for kaumātua, whilst the larger programme represents a strengths-based and culturally-centred approach to address health issues related to ageing in an Indigenous population.

year: 2021