László ORBÁN, Ph.D, Senior Principal Investigator

László Orbán obtained his university diploma (1981) and doctoral degree (1983) at József Attila University (now Szeged University) in Hungary. He received postdoctoral training in the laboratory of János Nemcsók (JAU; ’83-86) and Andreas Chrambach (NIH; 86-89), respectively. In 1989, he established the first fish molecular biology lab of Hungary at the Agricultural Biotechnology Center (Gödöllő) and led it for ten years. 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. Over the past two decades, he has been the lead PI of several large-scale projects on aquaculture-related R&D, including - most recently - an NRF-sponsored CRP project on a selection program to produce elite lines of food fishes. Together with his colleagues, Dr. Orbán published over 90 peer-reviewed publications in international journals and four book chapters. Earlier, he has been a member of the Editorial Advisory Board of Aquaculture and an Academic Editor of PLoS ONE. Recently, he became a member of the joint Editorial Board of Journal of Endocrinology and Journal of Molecular Endocrinology. He is an Adjunct Professor of Murdoch University (Australia) and the Georgikon Faculty of the University of Pannonia (Keszthely, Hungary) as well as an Honorary Professor of Szent István University (Gödöllő, Hungary).

You may wish to contact Prof László ORBÁN at: Tel: (65) 6872 7000, 6872 7413 (DID) or 6872 7414 (lab) Email: laszlo@tll.org.sg

For information on PhD studies at TLL, click HERE

Research Interests

The main interests of our team are to: (i) help fish production through the use of cutting edge aqua-genomics R&D; (ii) learn more about the structural and functional secrets of fish genomes; and (iii) 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 physiology by using the tools of molecular biology, genetics and functional genomics.

Our main research projects are the following:

1) Structural and functional analyses of fish genomes and transcriptomes: Fishes form the biggest group of vertebrates with over 34 thousand species. Their genomes tend to be more complex than those of other vertebrates, due to an ancient teleost-specific genome duplication (TGSD) event that took place following the separation of their common ancestor from that of land vertebrates and produced an additional set of paralogs. Despite increasing efforts during the last two decades, our knowledge about fish genomes is still limited.

As part of our research project funded by the Singapore National Research Foundation (NRF) since 2012, we have formed the Asian Seabass Genome Consortium that contains over a dozen research teams from ten countries. In collaboration with these partners, we have sequenced, assembled and annotated the genome of the Asian seabass (Vij et al. 2016). Utilization of long-read sequencing technology and multi-step scaffolding has resulted in the best metrics (Fig. 1) among the de novo assembled fish genomes published so far.

Figure 1: The Asian seabass has the best metrics among the de novo assembled fish genomes till date.

With a contig N50 of 1.06Mb, the Asian seabass genome has made it into the 1Mb Contig Club ( #1MbCtgClub) and the first 50 fish genomes to be published ( #50FishGmes, Fig. 2). The genome assembly and annotation datasets can be downloaded at http://laszlo.tll.org.sg/asb_genome/.

Figure 2: Snapshot of published genomes; click HERE to see full list.

Earlier, we have obtained a comprehensive transcriptome of Asian seabass encompassing >80% of the expected protein-coding loci (Thevasagayam et al. 2015). This served as an important resource for genome annotation. In addition, the availability of genome sequence information has provided an opportunity to study the biology of the fish. The Asian seabass is a catadromous fish, spending most of its life in fresh water and migrating to the sea to breed. We aim to compare the transcriptomes of the osmoregulatory organs of fishes grown in fresh and seawater in order to understand the basis of euryhalinity.

We have also been working on producing a transcriptome and draft genome sequence for the Mozambique tilapia.

In collaboration with Qian Hu Corporation Ltd., we have constructed the first genetic linkage map for the highly priced ornamental fish, Asian arowana (Shen et al. 2014). Later, we have been invited to participate into the BGI-led Asian arowana Genome Project that has produced a high-quality reference genome assembly for the golden variety of the species and draft sequences for the red and green varieties. Our data indicate that the species has a ZW/ZZ-type sex chromosomal system (Bian et al. 2016).

We have been studying zebrafish ( Danio rerio) for over 1.5 decades and generated several tools for the analysis of its transcriptome and genome. Earlier, we have produced 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).

The genome and transcriptome information obtained from the above projects will serve as platforms for the development of molecular tools for better understanding the biology and for genetic/genomic selection towards increased productivity and quality of the above fish species and possibly even their close relatives.

2) Molecular aquaculture and fish biology: Aquaculture is the fastest growing animal food sector and will soon overtake wild fisheries in total global catch. 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 help the production increase 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.

With the funding awarded by NRF, we started a transition from marker-assisted selection towards more advanced genomic selection with the same partners. We are working on the production of fast-growing Asian seabass lines that are also more resistant to diseases as well as Mozambique tilapia that grow well in brackish or even full seawater. An important aspect of this work is deepening of our understanding of the host-pathogen interactions through lab-based (Jiang et al. 2014) and farm-based challenges and analysis of molecular responses to vaccination in the fishes (Fig. 3). We are also performing 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 (Ngoh et al. 2015) and feed additives.

Figure 3: The early transcriptomes of head kidneys from vaccinated Asian seabass showed distinct differences from those of controls.

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 indicated that sex determination is polygenic in domesticated lines of this species (Liew et al. 2012, Liew and Orban 2014), whereas others have shown that wild type individuals collected from the natural waters show signs of a sex chromosomal system.

We have been studying the molecular regulation of gonad differentiation of zebrafish for over one and a half decades. We have characterized several candidate genes with sex-related functions, analyzed the gonad transformation process and detected the involvement of major signaling pathways [[(Wang et al. 2007), for reviews see (Orban et al. 2009) (Liew and Orban 2014)] (Fig. 4). Recently, we have published a story in collaboration with Japanese researchers on the role of the primordial germ cell (PGC) count in the gonadal transformation of zebrafish (Tzung et al. 2015).

Figure 4: Shifts in the balance of pro-male and pro-female pathways determine the direction of gonadal differentiation in zebrafish. For details see: (Wang and Orban 2007) (Wang et al. 2007) (Pradhan et al. 2012) (Sreenivasan et al. 2014) (Wang et al. 2007)

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.

4) Additional projects: In addition to the above, we have also been studying the genetic regulation of scale pattern formation in cyprinids (Rohner et al. 2009, Casas et al. 2013) and have performed small-scale projects on other commercial food fish species, including scorpionfishes (Saju et al. 2014) and turbot (Casas et al. 2011). Furthermore, we used key mitochondrial markers to aid in barcoding of Asian seabass and obtained evidence for a species-split across its geographic spread (Vij et al. 2014). We plan to extend our capability of species identification to ascertain the identity of other fish species as well.</p%