Laszlo ORBAN, Ph.D, Director, SRP
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Laszlo Orban obtained his university diploma (1981) and doctoral degree (1983) at the Jozsef Attila University (now Szeged University) in Hungary. He spent his postdoc periods in the laboratories of Janos Nemcsok (JAU) and Andreas Chrambach (NIH), respectively. In 1989 he established the first fish molecular biology lab of Hungary at ABC (Godollo) and led it for ten years. In 1997 he received a Candidate of Biological Sciences degree from the Hungarian Academy of Sciences. From 1998 until 2002 he was a Principal Investigator at the Institute of Molecular Agrobiology, since then he has been leading the Reproductive Genomics Group at TLL. Dr. Orban is an Adjunct Professor of the Georgikon Faculty at the University of Pannonia (Keszthely, Hungary) and an Adjunct Associate Professor of the Department of Biological Sciences of the National University of Singapore. You may wish to contact Prof Laszlo ORBAN at: |
For information on PhD studies at TLL, click HERE Research Interests
The main interest of our team is to understand more about the genetic regulation of fish sex. Accordingly, most of our research projects are aiming to answer questions related to various aspects of teleost reproduction by using the tools of molecular biology, genetics and functional genomics.
Our main research projects are the following:
1) Molecular aquaculture and fish biology:
Aquaculture is the fastest growing animal food sector and will shortly overtake wild fisheries in total global catch. Despite having relatively small water space of its own, Singapore’s geographic location makes it an ideal hub for aquaculture R&D with over 80% of global seafood production originating from the surrounding Asian nations.
Through research-based aquaculture, our lab aims to dramatically advance the production of commercially important tropical fish species such as the Asian seabass (Lates calcarifer), Mozambique tilapia (Oreochromis mossambicus) and Asian arowana (Scleropages formosus). During the past 13 years, we have concentrated mostly on studies of teleost reproduction. In collaboration with the Yue group (TLL) and the Marine Aquaculture Center of the Agri-Food & Veterinary Authority of Singapore (MAC/AVA), we have been working on a marker-assisted selection program for producing Asian seabass with increased growth rate since 2004.
Figure 1: Tilapias at our facility ( Photo: Chin Heng Goh)
With recently awarded funding from the Singapore National Research Foundation (NRF), 2012 will mark our transition from the current approach to more advanced genomic selection with the same partners. We intend to produce fast-growing Asian seabass that is also more resistant to diseases as well as Mozambique tilapia that grow well in brackish or even full seawater. We will also perform nutrigenomic studies to find the feed type(s) best suited to our fish and to improve our understanding on the physiological response of Asian seabass to different types of feeds.
In addition to the above, we have also been studying the genetic regulation of scale pattern formation in cyprinids and performed small-scale projects on other commercial foodfish species, including scorpionfishes and turbot (Casas et al., 2011)*.
2) Structural and functional analyses of fish genomes:
Fishes form the biggest group of vertebrates with over 34 thousand species. Their genomes are more complex than those of other vertebrates, due to an ancient genome duplication event that took place following the separation of their common ancestor from that of land vertebrates. Despite increasing efforts during the last two decades, our knowledge about fish genomes is still limited.
We are currently embarking on an NRF-funded research project that aims to produce elite lines of Asian seabass and tilapia in order to increase local seafood production. We aim to sequence, assemble and characterize the genome of a double-haploid Asian seabass individual, produce a draft genome sequence for the Mozambique tilapia and determine the transcriptomes of both species. These goals will be achieved using a combination of cutting-edge tools, including next-generation sequencing technologies and microarrays. The genome and transcriptome information will serve as platforms for the development of molecular tools for genetic/genomic selection towards increased productivity and quality of these food fish species.
We have been studying zebrafish (Danio rerio) for over a decade and generated several tools for the analysis of its transcriptome and genome. Earlier, we have generated two gonadal cDNA arrays and used them to detect differences between the transcriptomes of testis and ovary (Li et al., 2004; Sreenivasan et. al., 2008). Recently we have created an expression microarray by custom designing an oligo array based on the latest zebrafish transcripts available in the public database (Zv9 genome assembly) and three CNV arrays with average probe spacing of 10, 1.7 and 0.5 kb, respectively, that would allow for comparative analysis of genomes of zebrafish varieties (Liew et al., in prep).
In collaboration with Qian Hu Corporation Ltd., we have constructed a first-generation genetic linkage map for the highly priced ornamental fish, Asian arowana (Shen et al., in prep.). This map will allow for comparative studies among teleosts and it will also serve as a tool for the future analysis of important phenotypic traits such as color and sex.
3) Reproductive biology:
The Asian seabass is a protandrous (i.e. male-first) sequential hermaphrodite. It typically matures as a male at 2-3 years of age and subsequently transforms into a fully mature female at 4-5 years of age. Due to this reproductive strategy, its breeding programs face the challenges of long generation time and variable sex ratios. In order to better understand and eventually control these processes, we are studying the molecular mechanisms behind gonad differentiation, maturation and transformation in the Asian seabass. This is aided by the information that we have obtained from years of studying the zebrafish model (see below). To this end, we have produced a custom expression microarray based on sequences obtained from next generation sequencing to profile the transcriptomes of various gonad types and other organs. We have also developed non-invasive methods for sexing based on quantification of hormonal levels in mature individuals.
We have analyzed the sex determination of zebrafish with several different tools, including CNV arrays and PCR-based assays. Our data indicate that sex determination is polygenic in this species (Liew et al., 2012). Our group also has been studying the molecular regulation of gonad differentiation of zebrafish for many years. We have characterized several candidate genes with sex-related functions, such as tbp2 (Bartfai et al., 2004), cyp11b2 (Wang and Orban, 2007) and ar (Hossain et al., 2008). We have analyzed the gonad transformation process by studying the histology, reporter expression (Wang et al., 2007) and transcriptome of transforming gonad, and detected the involvement of major signaling pathways. Using our new expression microarray (above) we have also performed a preliminary experiment by analyzing 28-105 dpf transgenic zebrafish sorted according to their gonadal Egfp expression into males and females. We were able to detect bifurcation of the gonadal transcriptome as early as 28 dpf (Fig 2.).
Fig 2: PCA plot of zebrafish gonadal transcriptomesbetween 28 and 105 dpf shows clear
differences between the two sexs
We have also obtained more information about the peculiar reproductive biology of a mouthbrooding osteoglossid, the Asian arowana. Through the use of polymorphic microsatellite markers, we have analyzed the breeding relationships of ponds and found both mono- and polygamous brooders. We have developed a molecular test for the identification of the mouthbrooding parent and we are in the process of describing the changes that happen in the body of that parent during the 1.5 month-long process.
* For the list of references please click HERE