| Summary: | 博士 === 國立中興大學 === 生物科技學研究所 === 99 === Growth in vertebrates involves complex interactions of genes, metabolism, nutrition and hormones. In fish and other higher vertebrates, the growth hormone (GH) regulated insulin-like growth factor I (IGF-I) that produced from liver is a major mean of body growth control. However, based on the knockout studies in mouse, it is obvious that the body growth is controlled not only by the GH and IGF-I source, but also by a non IGF-I and GH source. Progranulin (PGRN) is a multi-functional growth factor that involved in tumorigenesis and wound healing. In the first part of present study, I identified and characterized pgrn cDNA in tilapia. Administration of a single dose (500 ng/g body weight) of recombinant seabream growth hormone (rbGH) by intraperitoneal (ip) injection into one-month-old tilapia resulted in significantly increased expression of IGF-I and PGRN. The co-induction of IGF-I and PGRN following GH treatment may suggest the involvement of PGRN in GH regulated growth in tilapia.
Further, I used zebrafish model organism and studied the role of PGRN in embryonic liver development. In our study, the knockdown of Progranulin A (GrnA), an orthologue of mammalian PGRN, using antisense morpholinos resulted in impaired liver morphogenesis in zebrafish (Danio rerio). In addition, a GrnA deficiency was also found to be associated with the deregulation of MET-related genes in the neonatal liver using a microarray analysis. In contrast, the decrease in liver size that was observed in grnA morphants was avoided when ectopic MET expression was produced by co- injecting met mRNA and grnA MO. This phenomenon suggests that GrnA might play a role in liver growth regulation via MET signaling. Our data have indicated that GrnA plays a vital role in embryonic liver morphogenesis in zebrafish. As a result, a novel link between PGRN and MET signaling is proposed.
In the last part of my study, we studied the genetic requirements of PGRN in the postnatal myogenesis. The Pax7-positive adult myogenic progenitor cells, known as satellite cells, contribute to postnatal muscle growth through hypertrophy and hyperplasia. We knocked down zebrafish GrnA resulting in impaired muscle growth at 6 days post fertilization (dpf). Immunohistochemistry analysis and the gene expression profile of muscle growth-related genes further demonstrated that the impaired muscle growth was the result of a reduction in the number of mitotic satellite cells. In contrast, the decrease in the number of Pax7-positive satellite cells was rescued by ectopic MET expression achieved through co-injecting met mRNA or grnA MOs. We also examined the effect of grnA gain-of-function on postnatal myogenesis by establishing the muscle- specific expression of grnA transgenic zebrafish, Tg(mlc2:grnA), which bypass early embryonic myogenesis. Overexpression of GrnA resulted in enhanced muscle growth with hypertrophy and hyperplasia and improved satellite cell proliferation in Tg(mlc2:grnA) larvae. In conclusion, we demonstrate a critical role for GrnA in promoting satellite cell proliferation and propose that GrnA mediates MET signaling in postnatal myogenesis.
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