The genome of Schmidtea mediterranea and the evolution of core cellular mechanisms

Abstract

SummaryThe planarian Schmidtea mediterranea is an important model for stem cell research and regeneration. We report the first highly contiguous genome assembly of Schmidtea mediterranea, using long-read sequencing and a de novo assembler (MARVEL) enhanced for low complexity reads. The S. mediterranea genome is highly polymorphic and repetitive genome, and harbors a novel class of giant Gypsy retroelements. Further, the genome assembly lacks a number of highly conserved genes, including critical components of the mitotic spindle assembly checkpoint, yet planarians maintain checkpoint function. Our genome assembly provides a key model system resource that will be useful for studying regeneration and the evolutionary plasticity of cell biological core mechanisms.

Efficient mitotic checkpoint signaling depends on integrated activities of Bub1 and the RZZ complex

“…The RZZ complex is able to polymerize, hereby generating the outer corona of the kinetochore which recruits checkpoint proteins and proteins regulating microtubule attachment (Pereira et al, 2018;Rodriguez-Rodriguez et al, 2018;Sacristan et al, 2018). Furthermore, the RZZ complex could have additional functions in the checkpoint beyond Mad1 recruitment (Grohme et al, 2018). However, an accurate quantitative characterization is still missing and the limited effect of Rod removal in non-transformed cells suggests a minor role of the complex in checkpoint signaling (Silió et al, 2015).…”

Diversification and biogeographic history of the Western Palearctic freshwater flatworm genusSchmidtea(Tricladida: Dugesiidae), with a redescription ofSchmidtea nova

“…It should be noted that occurrence of S. polychroa in North America is the result of human‐mediated dispersal (Ball, ; Benazzi & Benazzi‐Lentati, ). The species S. mediterranea is a model organism in regeneration research (Reddien & Alvarado, ; Rink, ) with a fully sequenced genome (Robb, Ross, & Alvarado, ; Grohme et al, ), while S. polychroa has been used as a model organism in studies on embryogenesis (Cardona, Hartenstein, & Romero, ; Monjo & Romero, ) and reproduction (D'Souza & Michiels, ; Pongratz, Storhas, Carranza, & Michiels, ). In comparison with these two model species, S. lugubris and S. nova are poorly studied.…”

Regeneration writ large

“…Our knowledge of the biology of dormant residual disease is cripplingly limited. Writing in the New England Journal of Medicine, Pan et al 1 examine rates of metastatic cancer spread in 62,923 women treated for breast cancer and given adjuvant therapy. The authors' findings provide a window on dormancy in this disease.…”

“…A meta-analysis shows that these individuals are still at risk of relapse. 1 report that women who take drugs for five years after their primary breast cancer has been removed are still at risk of a late relapse, because of tumour cells that have migrated to a secondary site such as the bone and adopted a dormant state. a, Tumour-cell dormancy can involve many factors, including: poor blood-vessel supply, which means that there is insufficient oxygen and nutrients for proliferation; ongoing surveillance by immune cells that kill some dormant tumour cells; and signals, both tumour-cell-intrinsic and from cells in the surrounding bone niche, that inhibit proliferation (dashed curly arrow).…”

“…For centuries, researchers have sought to understand these abilities, the instructions for which are encoded in DNA. In two papers in Nature, Grohme et al 1 and Nowoshilow et al 2 respectively report the genomes of a planarian (Schmidtea mediterranea) and a salamander, the axolotl (Ambystoma mexicanum). These studies mark a crucial step towards understanding regeneration.…”