Miguel Almeida is a postdoctoral researcher at the Gurdon Institute/University of Cambridge, UK where he recently joined the lab of Eric Miska. Prior to this, he pursued his PhD in the lab of René Ketting at the Institute of Molecular Biology in Mainz.
We asked Miguel about his latest publication on bioRxiv:
The double-stranded DNA-binding proteins TEBP-1 and TEBP-2 form a telomeric complex with POT-1
Sabrina Dietz, Miguel Vasconcelos Almeida et al. (2020)
Could you explain the main findings of your work?
In our new preprint we have found two factors that bind to the double-stranded telomere in the nematode model organism, the one and only, Caenorhabditis elegans. Telomeres are repetitive sequences at the ends of linear chromosomes that provide a couple of challenges to eukaryotic cells. Dedicated proteins, or protein complexes, have evolved to solve these challenges and maintain telomere homeostasis. The first challenge is inefficient replication at chromosome ends, the so-called end-replication problem. Telomeres shorten with every cell division, which means telomeres become increasingly short with age and this has been associated with cellular senescence. Telomerase, for example, solves this problem by actively elongating telomeres. The second challenge, the end-protection problem, is that telomeres can be “interpreted” by the cells as DNA damage, which may lead to incorrect repair and chromosome fusions. Protein complexes, like mammalian shelterin, effectively protect telomeres from this. Since telomere deregulation is a hallmark of cancer, the study of animal telomeres is very relevant for human health. Telomeres are intensively studied in cancer cell lines, but animal models, especially with telomere repeats similar to vertebrates, to study telomere biology in vivo under homeostasis are lacking.
Enter C. elegans! We believe this nematode could be a great model to study telomere biology due to the similarity of its telomere repeat sequence to that of human telomeres (TTAGGC vs TTAGGG), many available genetic tools, compartmentalized post-mitotic soma vs dividing germline, and fast generation time. POT-1/2 and MRT-1 are known to bind the single-stranded part of telomeres in C. elegans, but it remains unknown whether these interact with each other in the context of a complex. We designed a quantitative proteomics screen with the aim of acquiring a comprehensive perspective of the proteins associated to C. elegans telomeres. Besides the previously known telomere-binders POT-1/2 and MRT-1, we found two novel factors. We confirmed that these uncharacterized proteins (that turn out to be paralogs) bind to double-stranded telomere sequences in vitro and colocalize to telomeres in the germline. Thus, we named them telomere binding proteins 1 and 2 (TEBP-1/2). To our surprise, tebp-1 and tebp-2 mutants display opposed telomere lengths despite sharing a common origin by gene duplication. Although the single mutants show no fertility defects, at higher temperatures tebp-2 mutants have a mortal germline, and tebp-1; tebp-2 double mutants have synthetic sterility. Although we still do not know how this happens, germline development seems to go very wrong in these animals. We further show that TEBP-1 and TEBP-2 interact with each other and with POT-1/2 and MRT-1. Yeast two-hybrid experiments and quantitative proteomics support a direct interaction between TEBP-1 and TEBP-2 with POT-1. We think POT-1 is connecting the double-strand binders TEBP-1 and TEBP-2 with the single-strand binders POT-2 and MRT-1. This is just a working model that hopefully will help us frame more and more testable hypotheses. With this work we have provided a broader perspective on the organization and function of C. elegans telomeres. We hope that our preprint and the tools we have developed will create some interest in adopting C. elegans as a telomere model.
I’ve also summarised these findings in my first attempt at a #SciTwitter #tweetstorm (available here in case you want to take a look and spread the word around).
Why did you decide to post your work on bioRxiv?
It has not been my “first rodeo” posting on bioRxiv and it will not be the last. Overall, as an author, I can highly recommend posting your work on bioRxiv, to get it “out there” as soon as possible. To me, this benefits not only scientific and lay audiences (which in most cases pay the taxes that fund your research), who can quickly and freely discover the results of your research, but also gives the authors some peace of mind: your work will be already accessible while you and your paper navigate the muddy waters of peer-review.
Besides those more philosophical reasons, two important practical factors also weighed-in. This preprint is the result of many years of hard work by many people (https://twitter.com/migueldvalmeida/status/1296125530920583168). Having the preprint out in August allowed first author Sabrina Dietz (now a Dr!) to have a preprint with the bulk of her PhD work publicly available before her PhD defense. In my case, this preprint will strengthen my CV for ongoing/upcoming postdoctoral fellowship applications. As many funding organizations do not accept publication entries in CVs referring to unpublished papers (the quasi-mythical “in preparation”, “submitted”, “in revision”, or “in press”), but do accept preprints, posting our work on bioRxiv will potentially help out my career development before its final peer-reviewed version is out.