The 4th European Meeting on Planarian Biology was held in the charming Spanish town of Sant Feliu de Guixols, overlooking the azure waters of the Costa Brava. The 3-day conference (25-27th September) provided an opportunity to share recent advances in flatworm biology and regeneration, and served to strengthen the links and collaborations between the labs working with this relatively young model organism. The meeting proved to be fun and worthwhile, not least because it brought together holistic and reductionist approaches to understanding flatworm and stem cell biology. The content of the meeting was varied and talks were broadly separated into themes that included: the fundamental characteristics of neoblasts, neurogenesis in planarians, growth control, -omics, environmental signals, and evolutionary and phylogenetic perspectives on flatworm biology. It is difficult to condense all the work mentioned in the conference in this blog post, but I will focus on some personal highlights that illustrate the breadth of the topics covered.
Norito Shibita, an invited speaker, summarized his recent published work on DjPiwiB, which showed that this protein suppresses transposons in the neoblasts and is also active during the differentiation process to maintain genome stability. Moreover, preliminary evidence was given to suggest that following knockdown of DjPiwiB in Dugesia Japonica, three genes (gH4, MCM2, and Calumelin) are upregulated compared to control worms. Consequently, DjPiwiB may also coordinate gene expression during differentiation alongside its role in TE suppression.
Pascual-Carreras, Eudald, a PhD student from Teresa Adell’s group, presented data concerning a novel peptide found in planarians, Blitzschnell (Smed-bs), which when inhibited by RNAi produces an acceleration of the regenerative response. Intriguingly, this same protein plays a role in regulating cell number when animals are in starved conditions, as Smed-bs RNAi results in an increase in the total cell number in homeostatic starved planarians compared to control worms. Interestingly, the increase in cell number in starved worms does not result in an increase in overall worm size, but instead results in a reduction in cell size, that in turn leads to an increase in cell density and eventually to overgrowths.
Jordi Solana presented work, recently published in Elife, to show that the MBNL proteins reduce the expression of stem cell-related gene isoforms in S. mediterranea, whilst another protein called CELF counteracts MBNL proteins by helping to express gene isoforms that are active in stem cells. They were able to show that two different exons exist for the enzymatic core of the histone methyltransferase DOT1L, which mediates the methylation of H3 at Lysine 79, one of which is found in stem cells (X1 specific) and the other in differentiated cells (Xins specific). Future downstream analysis will highlight whether the alternative splicing of DOT1L controlled by the CELF/MBNL factors has a differential effect on the epigenetic environment of stem cells compared to differentiating/differentiated cells.
Jochen Rink presented a PacBio assembly of the Schmidtea mediterranea (sexual) genome, which seems to be a substantial improvement on the previous publicly available genome. This assembly has generated genome scaffolds of several megabases in length (N50 = 3.8Mbp), allowing for a better resolution of repetitive areas compared to the previous (N50 = 80,000bp). Indeed, the PacBio assembly was able to resolve particularly large transposable elements – with one Gypsy/M1 being found to be over 30kb in length!
One highlight of the conference was that Prasad (a post-doc in the Aboobaker lab) won best poster prize for his project investigating the migratory behaviour of stem cells using a high-throughput shielded irradiation assay. This assay has revealed some exciting new phenomena about stem cells during migration including that cells migrate specifically in an anterior direction which requires the polarity determinant notum, and that the morphology and distribution of migratory cells implicates them in the epithelial to mesenchymal transition (EMT). (You can read a little bit more on this project here: http://biorxiv.org/content/early/2016/10/14/080853)
I presented a poster on my first year DPhil work concerning the role of the Tudor-domain containing proteins (TDRDs) and its role in maintaining stemness in planaria via an involvement in the PIWI-piRNA pathway. It was good to receive some feedback from fellow planarian enthusiasts and experts, and the conference gave me the opportunity to defend and discuss my work outside the lab. Moreover, Sounak (a 3rd year DPhil student) gave a short talk introducing planaria as an emerging model system to study DNA damage in the context of adult stem cells. Using an RNAi screen, he showed that different DNA repair pathways are critical for allowing stem cells to survive following 15Gy irradiation (a dose that is not normally lethal to planarians, so the stem cells must have robust recovery mechanisms).
Overall, the planarian meeting proved to be thoroughly enjoyable. The conference provided an unrivalled opportunity to share recent findings and discuss outstanding questions concerning planarian biology (i.e. why is planarian transgenesis so difficult?) with PIs and students from other planarian labs around the world. I am looking forward to the next meeting in 2018!.