Reproductive Genomics Group

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Life@TLL

Szeverenyi, I, R Ramamoorthy, ZW Teo, HF Luan, ZG Ma and S Ramachandran: Large scale systematic study on stability of Ds element and timing of transposition in rice. Plant and Cell Physiology. Fenner, BJ, R Thiagarajan, HK Chua and J Kwang: Betanodavirus B2 is an RNAi antagonist that facilitates intracellular viral RNA accumulation. Journal of Virology. Murata-Hori, M: Roles of microtubules in the regulation of cytokinesis in animal cells. In In Signal Transduction of Cell Division (ed. Toru Miki).

Bártfai, R., C. Balduf, T. Hilton, Y. Rathmann, Y. Hadzhiev, L. Tora, L. Orbán, and F. Müller. 2004. TBP2, a Vertebrate Specific Member of the TBP Family, Is Required in Embryonic Development of Zebrafish. Current Biology 14(7): 593-598.

Motegi F., M. Mishra, M.K. Balasubramanian and I. Mabuchi. 2004. Myosin-II Reorganization During Mitosis is Controlled Temporally by its Dephosphorylation and Spatially by Mid1 in Fission Yeast. The Journal of Cell Biology. 165: 685-695.

Shanthi Soundararajan,Gregory Jedd, Xiaolei Li, Marilou Ramos-Pamploña, Nam H.Chua, and Naweed I. Naqvi (2004) Woronin Body Function in Magnaporthe grisea Is Essential for Efficient Pathogenesis and for Survival during Nitrogen Starvation Stress. Plant Cell 16 (6): 1564-1574.

A/Prof Laszlo Orban, Principal Investigator

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 years in the laboratory of Janos Nemcsok (JAU) and Andreas Chrambach (NIH). In 1989 he established the first fish molecular biology lab of Hungary at ABC (Godollo) and led it for ten years. From 1998 until 2002 he was a principal investigator at IMA (Singapore), since then he has been leading the Reproductive Genomics Group at TLL.

You may wish to contact A/Prof Laszlo ORBAN 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 interest of our lab is to understand more about the genetic regulation of fish sex. Accordingly 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.

Research Projects

1) Testis differentiation in the zebrafish
	Zebrafish (Danio rerio, Cyprinidae) is a juvenile hermaphrodite, accordingly the males go through a “juvenile ovary stage” before their gonads start to transform into a functional testis. Our lab is studying testis differentiation in zebrafish by using a combination of tools, including histology, transgenic lines with sex- and developmental stage-specific reporter expression as well as a custom-made 6.5K “Gonad UniClone” cDNA microarray. We have shown that although zebrafish males develop “juvenile ovaries”, they differ vastly in the extent of their commitment toward femaleness during this stage before testis differentiation (Fig. 1.). Currently we are comparing the gene expression “profiles” of gonads at various different stages of their development in order to identify genes regulating the “juvenile ovary to testis” transformation process.
Figure 1: Detailed histological study on the gonad of developing zebrafish females (A-D) and three types of males (E-P) sorted according to the expression of vas::egfp reporter construct which expresses strongly in the ovary. Degenerating oocytes (do) can be clearly detected even in the gonad of type I males (N) in absence of visible gonadal EGFP expression (M), confirming that every zebrafish male goes through the “juvenile ovary to testis” transformation process.

2) Comparative genomic study of gonad differentiation in cyprinid teleost

In collaboration with Dr. Hans Komen (Wageningen University, The Netherlands) we are searching for genes with conserved regulatory roles in the gonad differentiation of common carp (Cyprinus carpio L., Cyprinidae) and zebrafish. By using testis samples from all-male common carp populations generated through androgenesis, we are performing cross-species hybridization experiments with the microarray described above.

3) Candidate genes with putative role in the gonad differentiation in teleosts

We are also working on the functional characterization of a number of candidate genes. Earlier we described a new transcription initiation factor, called TBP2, which is conserved in all vertebrates (Fig. 2.) and expressed differentially in the male and female gonad (see also Persengiev et al., PNAS 100: 14887-14891, 2003 and Jallow et al., PNAS 101: 13525-13530, 2004). Currently we are working on the identification of the partners of TBP2 in complexes formed in the ovary and during embryonic development.

Figure 2: Unrooted evolutionary distance tree generated with the Neighbouhood Join method showing the relationship of TBP, TBP2 and TRF1

4) The reproductive behavior of Asian arowana
	We have a pioneering research collaboration with Qian Hu Fish Farm on the reproductive biology of a primitive teleost called Asian arowana (Scleropages formosus, Osteoglossidae) or dragonfish. Asian arowanas are interesting for basic research due to their unusual reproductive strategy (a few eggs of huge size protected by mouthbrooding) and they command an extremely high price in the ornamental fish trade. We are studying the partner selection process by using genotyping with polymorphic DNA markers isolated in our lab and trying to develop methods to predict mate choice on the basis of genotypes. Our results - implemented into practice at the farm - are revolutionizing the breeding practice of the species.
Figure 3: Harvesting the offspring from the buccal cavity of an Asian arowana brooder

5) Molecular phylogenetics of bonytongues

The suborder of Osteoglossoidei contains eight different species. They are distributed throughout all the continents of the Southern Hemisphere, except Antarctica. As experimental data on their relationship are scarce and contradictory, we are studying the phylogenetics of the color varieties of Asian arowana and other osteoglossid species by using various kinds of polymorphic DNA markers (mostly described by our lab).

6) Genomic analysis of teleost sex chromosomes

The majority of the 24 thousand fish species do not seem to have highly differentiated sex chromosomes and those that do seem to show tremendous variability. We have been searching for differences among male and female genomes by PCR-based methods during the past ten years and have successfully isolated DNA markers associated with sex from three different teleost species (African catfish, Asian arowana and turbot). Sex-associated DNA markers might be used for increasing the density of genetic linkage map of sex chromosomes. The comparative analysis of sex chromosomes will help us to understand the secrets of their evolution. Sex-specific DNA markers allow us to develop “molecular sexing methods”, which are useful for improving the aquaculture production of farm fish species with differential growth rate and maturation time between the two sexes.