title: Role of growth factors in the regulation of skeletal muscle mass, fibre type and fibre size

authors: Martyn, Julie Anne Kerr

abstract: Growth factors play an important role in the regulation of the growth and development of many tissues including muscle. Muscle is derived from somitic cells that differentiate to form myoblasts. These myoblasts then fuse to form myofibres. As these myofibres mature they take on the morphological, biochemical and physiological properties of mature muscle fibres. It is the plasticity of muscle fibres with respect to these properties that gives skeletal muscle its remarkable ability to adapt to different conditions of loading and usage. The aim of this thesis was to determine the role of growth factors in regulating muscle fibre type and fibre size in two different models of altered muscle mass.

Bovine muscle development was examined in normal foetuses (NM) and in double-muscled Belgian Blue foetuses (DM) carrying a mutation in the gene for myostatin. Muscle fibre type and fibre size were characterised using semi-automated computer-assisted image analysis after myofibrillar ATPase histochemical staining. Plasma IGF levels were measured, IGF-1 mRNA was measured using in situ hybridisation and IGF receptor binding was analysed by receptor autoradiography. Myostatin mRNA was analysed using semi-quantitative RT-PCR.

Skeletal muscle hypertrophy and atrophy were induced m adult rabbits by immobilisation of the hind limb with muscles in a lengthened and shortened position respectively. Fibre type and fibre size changes were analysed as described above and myostatin mRNA expression levels were measured using Northern blot analysis and semi-quantitative RT-PCR.

Results showed there was a biphasic change in the percentage of type 1 muscle fibres in both NM and DM, with the percentage initially declining, then increasing again. The percentage of type 1 fibres was consistently lower in DM. Circulating levels of IGF-1 increased with gestational age and levels of IGF-1 and IGF-2 were not different between NM and DM. IGF-1 mRNA expression in skeletal muscle declined with age in a pattern that was unrelated to changes in fibre type. Levels of IGF-1 mRNA were lower in DM during late gestation and this decrease was temporally linked to a reduced area of type 1 fibres in DM at this stage of development. Myostatin mRNA declined with gestational age, and levels of the mutant mRNA were higher in DM.

In induced hypertrophy, myostatin mRNA expression was lower than in controls and in atrophy, myostatin mRNA was elevated at 2 days but not at 6 days. There were no changes in fibre type or fibre size over the treatment period. Myostatin protein was evenly localised to all muscle fibre types.

In conclusion, IGF-1 appears to be unrelated to changes in fibre type during bovine muscle development, but may play a role in the regulation of fibre size. The DM condition is associated with a change in fibre type, but the role of myostatin in mediating this change remains unknown. Changes in myostatin mRNA in response to induced hypertrophy and atrophy strongly suggest an important role for myostatin as a negative regulator of skeletal muscle mass in postnatal animals.

text: Role of growth factors in the regulation of skeletal muscle mass, fibre type and fibre size Growth factors play an important role in the regulation of the growth and development of many tissues including muscle. Muscle is derived from somitic cells that differentiate to form myoblasts. These myoblasts then fuse to form myofibres. As these myofibres mature they take on the morphological, biochemical and physiological properties of mature muscle fibres. It is the plasticity of muscle fibres with respect to these properties that gives skeletal muscle its remarkable ability to adapt to different conditions of loading and usage. The aim of this thesis was to determine the role of growth factors in regulating muscle fibre type and fibre size in two different models of altered muscle mass.

Bovine muscle development was examined in normal foetuses (NM) and in double-muscled Belgian Blue foetuses (DM) carrying a mutation in the gene for myostatin. Muscle fibre type and fibre size were characterised using semi-automated computer-assisted image analysis after myofibrillar ATPase histochemical staining. Plasma IGF levels were measured, IGF-1 mRNA was measured using in situ hybridisation and IGF receptor binding was analysed by receptor autoradiography. Myostatin mRNA was analysed using semi-quantitative RT-PCR.

Skeletal muscle hypertrophy and atrophy were induced m adult rabbits by immobilisation of the hind limb with muscles in a lengthened and shortened position respectively. Fibre type and fibre size changes were analysed as described above and myostatin mRNA expression levels were measured using Northern blot analysis and semi-quantitative RT-PCR.

Results showed there was a biphasic change in the percentage of type 1 muscle fibres in both NM and DM, with the percentage initially declining, then increasing again. The percentage of type 1 fibres was consistently lower in DM. Circulating levels of IGF-1 increased with gestational age and levels of IGF-1 and IGF-2 were not different between NM and DM. IGF-1 mRNA expression in skeletal muscle declined with age in a pattern that was unrelated to changes in fibre type. Levels of IGF-1 mRNA were lower in DM during late gestation and this decrease was temporally linked to a reduced area of type 1 fibres in DM at this stage of development. Myostatin mRNA declined with gestational age, and levels of the mutant mRNA were higher in DM.

In induced hypertrophy, myostatin mRNA expression was lower than in controls and in atrophy, myostatin mRNA was elevated at 2 days but not at 6 days. There were no changes in fibre type or fibre size over the treatment period. Myostatin protein was evenly localised to all muscle fibre types.

In conclusion, IGF-1 appears to be unrelated to changes in fibre type during bovine muscle development, but may play a role in the regulation of fibre size. The DM condition is associated with a change in fibre type, but the role of myostatin in mediating this change remains unknown. Changes in myostatin mRNA in response to induced hypertrophy and atrophy strongly suggest an important role for myostatin as a negative regulator of skeletal muscle mass in postnatal animals.

year: 1999

title: Elucidating the sugar import pathway into developing kiwifruit berries (Actinidia deliciosa)

authors: Gould, Nick

subjects: carbon-14

abstract: The aim of this work was to investigate the roles of the apoplasmic and symplasmic pathways in the delivery of solutes to the outer pericarp of developing green-fleshed kiwifruit berries (Actinidia deliciosa [A. Chev.] C. F. Liang et A. R. Ferguson var. deliciosa ‘Hayward’). Experiments with the symplasmic tracer 5(6)-carboxyfluorescein (CF) showed symplasmic movement of dye during the initial rapid growth stage of the fruit, but as fruit growth slowed and starch content increased, a reduction in symplasmic spread of CF was observed (+126 DAA [days after anthesis]). Measurements of sugar uptake rates from the apoplasm were sufficient to account for the dry matter accumulation in growing fruit at each stage of fruit growth, and could potentially operate alongside a symplasmic pathway for post-phloem unloading of sugars during the rapid growth period. Energy requirements driving uptake from the apoplasm appear to depend on the sugar concentration gradients across the cell membrane throughout fruit development. Together, these data suggest: 1) the post-phloem symplasmic pathway is important during the fruit rapid growth stage, 2) the uptake of sugars from the apoplasm has a role in the transport of carbohydrates in the fruit, especially later in fruit development when the symplasmic pathway is reduced, and 3) apoplasmic sugar has an important role in the flow of water into the apoplasm of the fruit, providing a mechanism to maintain hydrostatic pressure gradients along the phloem supplying the fruit.

text: Elucidating the sugar import pathway into developing kiwifruit berries (Actinidia deliciosa) The aim of this work was to investigate the roles of the apoplasmic and symplasmic pathways in the delivery of solutes to the outer pericarp of developing green-fleshed kiwifruit berries (Actinidia deliciosa [A. Chev.] C. F. Liang et A. R. Ferguson var. deliciosa ‘Hayward’). Experiments with the symplasmic tracer 5(6)-carboxyfluorescein (CF) showed symplasmic movement of dye during the initial rapid growth stage of the fruit, but as fruit growth slowed and starch content increased, a reduction in symplasmic spread of CF was observed (+126 DAA [days after anthesis]). Measurements of sugar uptake rates from the apoplasm were sufficient to account for the dry matter accumulation in growing fruit at each stage of fruit growth, and could potentially operate alongside a symplasmic pathway for post-phloem unloading of sugars during the rapid growth period. Energy requirements driving uptake from the apoplasm appear to depend on the sugar concentration gradients across the cell membrane throughout fruit development. Together, these data suggest: 1) the post-phloem symplasmic pathway is important during the fruit rapid growth stage, 2) the uptake of sugars from the apoplasm has a role in the transport of carbohydrates in the fruit, especially later in fruit development when the symplasmic pathway is reduced, and 3) apoplasmic sugar has an important role in the flow of water into the apoplasm of the fruit, providing a mechanism to maintain hydrostatic pressure gradients along the phloem supplying the fruit.

year: 2013

title: Te ahi tawhito, te ahi tipua, te ahi nā Mahuika: Re-igniting native women’s ceremony

authors: Murphy, Ngahuia Aroha Grace

subjects: Native women's ceremony

abstract: This research examines the multiple ways in which Māori, and Hawai’ian and Native American women, are re-activating feminine ceremonial forms and recovering sacred relationships with customary feminine deities. Attention is focused on the creation of personal ritual practices that respond to contemporary decolonising and ecological contexts.
A mana wahine theoretical and methodological framework motivated by emancipatory agendas that seek to facilitate transformation is used. Key to mana wahine projects is the creation of space for Native women to define themselves and their own stories and knowledges. This is important because Native women’s voices, knowledge and ritual histories continue to be marginalised. Furthermore, debased colonial renditions of femininity, which have been reproduced, perpetuate patriarchal and colonial politics that engender discord in Native communities today.  
The study used a suite of complimentary methods to engage 45 Native women and men. Interviews and kōrero (discussion), ceremony, mana wahine wānanga (women’s sacred learning space), Native sacred site visits, solicited journals, collaboration in ritual theatre productions, and analysis of mana wahine artworks as discursive texts were employed to gather stories of spiritual continuation that are unique and largely unchartered in academia. 
The empirical material is organised around four themes in four different chapters. The first of these empirical chapters re-interprets colonial ethnographic material alongside karakia (incantations), mōteatea (songs), cosmological and tribal stories, to reveal bold examples of Māori female ritual leadership. The second empirical chapter comprises an analysis of key colonial processes that have attempted to erase Native women’s ritual ontologies and the strident expressions of Native women’s resistance to colonial imperatives. The third empirical chapter investigates the multiple channels through which Native women are restoring their ceremonial lives. The fourth chapter investigates rerenga atua (menstruation) rituals that celebrate the Native feminine body as a cosmological site of communion with feminine deities. 
The rich weave of Native women’s stories of ceremony, old and new, threads into decolonising Indigenous scholarship around the world that also seeks to recover the sacred feminine as a key site of Native sovereignty. These discussions reveal a self-renewing Native belief system based on vibrant and evolving rituals that respond directly to current socio-political, spiritual and ecological realities.

text: Te ahi tawhito, te ahi tipua, te ahi nā Mahuika: Re-igniting native women’s ceremony This research examines the multiple ways in which Māori, and Hawai’ian and Native American women, are re-activating feminine ceremonial forms and recovering sacred relationships with customary feminine deities. Attention is focused on the creation of personal ritual practices that respond to contemporary decolonising and ecological contexts.
A mana wahine theoretical and methodological framework motivated by emancipatory agendas that seek to facilitate transformation is used. Key to mana wahine projects is the creation of space for Native women to define themselves and their own stories and knowledges. This is important because Native women’s voices, knowledge and ritual histories continue to be marginalised. Furthermore, debased colonial renditions of femininity, which have been reproduced, perpetuate patriarchal and colonial politics that engender discord in Native communities today.  
The study used a suite of complimentary methods to engage 45 Native women and men. Interviews and kōrero (discussion), ceremony, mana wahine wānanga (women’s sacred learning space), Native sacred site visits, solicited journals, collaboration in ritual theatre productions, and analysis of mana wahine artworks as discursive texts were employed to gather stories of spiritual continuation that are unique and largely unchartered in academia. 
The empirical material is organised around four themes in four different chapters. The first of these empirical chapters re-interprets colonial ethnographic material alongside karakia (incantations), mōteatea (songs), cosmological and tribal stories, to reveal bold examples of Māori female ritual leadership. The second empirical chapter comprises an analysis of key colonial processes that have attempted to erase Native women’s ritual ontologies and the strident expressions of Native women’s resistance to colonial imperatives. The third empirical chapter investigates the multiple channels through which Native women are restoring their ceremonial lives. The fourth chapter investigates rerenga atua (menstruation) rituals that celebrate the Native feminine body as a cosmological site of communion with feminine deities. 
The rich weave of Native women’s stories of ceremony, old and new, threads into decolonising Indigenous scholarship around the world that also seeks to recover the sacred feminine as a key site of Native sovereignty. These discussions reveal a self-renewing Native belief system based on vibrant and evolving rituals that respond directly to current socio-political, spiritual and ecological realities.

year: 2019