Another important gene, heat shock factor (MeHSF) was also cloned using homology based PCR because it was suggested to participate in the transcriptional regulation of many essential components of ovarian maturation including vitellogenin gene and several proteins for hormones metabolism. The complete cDNA sequence of MeHSF was 2211 bp in length, which encoded a 622 amino acid protein. The translated MeHSF protein shared high similarity with those of other species, especially in the N terminal region. RT-PCR showed that MeHSF was universally expressed in most of the female tissues investigated including ovary, central nervous system, heart, gill, gut and muscle. However, its expression was not detectable in eyestalk and hepatopancreas. MeHSF was highly expressed in immature ovaries, and decreased dramatically with the progress of ovarian maturation. Since the synthesis of vitellogenin in ovary showed an opposite trend, the result suggested that MeHSF probably functioned as a transcriptional repressor to vitellogenin. Four HSFs isoforms generated from alternative splicing were obtained in immature ovaries, suggesting a possible universal role of HSF in coordinating transcription of different target genes during shrimp ovarian maturation. / As an important component of enzymatic scavenger systems, glutathione peroxidases (GPx) play important roles in maintaining the balance between reactive oxygen species (ROS) production and cellular scavenging ability. In this research, a full length GPx gene (MeGPx) which had been identified using RAP-PCR previously was cloned and characterized. MeGPx might play a pivotal role in preventing oocytes from oxidative damage and balancing ROS production. The present data on shrimp GPx provides insights on the regulation of ROS in the ovarian maturation process. / Four candidate genes possibly participating in the regulation of ovarian maturation were obtained by random sequencing the libraries, including metallothionein, two zinc finger proteins and member 4 of wingless-type MMTV integration site family (WNT4). The zinc finger protein containing a plant homeodomain, was only expressed in the eyestalk of female with immature ovaries, but not that of female with early mature and mature ovaries. The full length cDNA sequence of shrimp WNT4 gene (MeWNT4) was obtained using RACE technique. RT-PCR showed that the expression of MeWNT4 in eyestalk decreased with the maturation of shrimp ovaries. Interestingly, MeWNT4 was strongly expressed in the central nervous system and gut of both female and male shrimp. It was suggested that WNT4 could antagonize the testis determining factor (SRY), and play an essential role in suppressing the formation of testis, and at the same time, controlling of female development. Thus, the identification WNT4 from crustacean would contribute to our understanding on the sex determination mechanism. / In this thesis, two genes, heat shock protein 90 and heat shock factor, possibly playing important roles in shrimp ovarian maturation were identified and characterized. / Shrimp farming plays an important economic role in Southeast Asian countries. Yet further development of this industry is seriously restricted by the environmental deterioration and the prevalence of fetal diseases. Moreover, the failure of sexual maturation of cultured female shrimp forms a bottleneck to the further development of shrimp aquaculture. With the aim to produce shrimp without totally depending on the wild stocks, many studies have been focused on the endocrine regulation of shrimp ovarian maturation. In order to enhance our understanding on the molecular events occurred during ovarian maturation, in this research, several candidate genes are identified, and their potential roles in ovarian maturation are studied in the shrimp Metapenaeus ensis. / Since heat shock protein 90 gene is one of the essential components of steroid hormone signal cascades in vertebrates, it was cloned and isolated by homology cloning strategy. The complete cDNA sequence of shrimp Hsp90 ( MeHsp90) was 2524 by in length, which encoded a 720 amino acid polypeptide. The MeHsp90 coding region was interrupted by four introns. MeHsp90 was differentially expressed in eyestalk, ovary and hepatopancreas at different ovarian maturation stages, and consistently expressed in other tissues including heart, gill, gut, muscle and central nervous system. In vitro ovary explant assay revealed that MeHsp90 expression in immature ovary could be induced by the addition of exogenous estradio1-17beta. MeHsp90 was highly expressed in pre-vitellogenic oocytes, and its expression decreased with the progress of maturation, and finally stopped in late-vitellogenic oocytes. The co-regulation of MeHsp90 and vitellogenin by estrogen hormone suggested a possible regulatory role of Hsp90 in vitellogenin synthesis of the shrimp. / Wu, Long Tao. / "May 2008." / Adviser: Chu Ka Hou. / Source: Dissertation Abstracts International, Volume: 70-03, Section: B, page: 1409. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (p. 92-113). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.