Fachbereich Informatik

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Disputation Praveen Baskaran

am Mittwoch, 9. Mai 2018, um 13:00 Uhr in Raum A 301, Sand 1

Promotionsvortrag am
9. Mai 2018, 13:00
Gebäude: Sand 1, 72076 Tübingen Raum: A301

Praveen Baskaran

Titel des Vortrags

Comparative analysis of gene duplications and their impact on
expression levels in nematode genomes

Berichterstatter 1: Prof. Dr. Daniel Huson
Berichterstatter 2: Prof. Dr. Ralf J. Sommer

Kurze Zusammenfassung des Vortrags

Gene duplication is a major mechanism that plays a vital role in different evolutionary innovations,
ranging from generating novel traits to phenotypic plasticity. Evolutionary impact of gene duplication and the
fate of duplicated genes has been studied in detail. However, little is known about the impact of gene
duplication on gene expression with respect to different evolutionary time scales. Here, we study genomewide
patterns of gene duplications in nematodes and assess their effect on expression levels. This study
encompasses various macroevolutionary comparisons at different time scales and microevolutionary
comparisons within the species Pristionchus pacificus. At the macroevolutionary level, by comparing species
separated more than 280 million years ago, we found various lineage-specific expansions in multiple gene
families along the Pristionchus lineage. Moreover, we found that duplicated genes are highly enriched among
developmentally regulated genes. Interestingly, the results also show evidence for selection on duplication to
increases the gene expression levels in a developmental stage-specific manner.
To gain insights into the microevolution of gene expression levels after gene duplication, we
compared different strains of P. pacificus and found that an additional gene copy does usually not increase
gene expression levels in the different strains. Furthermore, we found a strong depletion of duplicated genes
in large parts of the P. pacificus genome indicating towards negative selection against gene duplication. This
shows that the impact on gene expression levels following gene dupli- cation differs dramatically, where a
selection for increased gene dosage dominates macroevolution and negative selection on gene duplication
dominates within species level. This led us to wonder what happens at the intermediate time scale. We
compared recent duplicates of P. pacificus with their single-copy orthologs in two closely related species and
found a pattern similar to the microevolutionary trend. Additionally, comparison of closely related species of
the Strongyloides genus and its developmental transcriptome also shows overall strong depletion of
duplicated genes, similar to the observation at the microevolutionary level. At the same time, a strong
enrichment of duplicated genes was found at a developmental stage associated with the parasitic activity of
the nematodes. Similar to the macroevolutionary picture of P. pacificus, we also found selection for higher
gene dosage in parasitism-associated gene families of S. papillosus, indicating the adaptive potential of
duplicated genes. Even though these studies show widespread selection against both duplication and
changes in gene expression, duplications are favoured in some conditions leading to adaptive changes in the
organism. Overall this indicates that the regulation of expression levels of duplicated genes was subjected to
different selection processes at different time scales, which represent a complex interplay between different
evolutionary processes like natural selection, population dynamics, and genetic drift.