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Our study investigating an enigmatic chromosome in zebra finches is now published in @NatureComms! This has been a massive team effort: @fjruizruano @AnneMarie_DC @AlexJCharles @TI_Gossmann_EVO @denniskappei @HemmingsNicola1 @MirreSimons @alexander_suh. Thread follows...
But first just a quick link to the study ;) https://www.nature.com/articles/s41467-019-13427-4
This all started for me when I followed a tip and wrote to @alexander_suh looking for a lab to carry out my MSc project in. It later emerged that Alex had only had his lab website up for a few days when I contacted him, and when I arrived his lab group increased 100% in size.
Alex is full of great ideas for projects, and after our first discussion, I was left to choose between three. One stood out for me though: a gigantic chromosome (>10% of the genome) that is only found in the germline cells of the zebra finch, but never in the somatic cells.
The project would be to find out what this thing did. Even though it was found over 20 years ago ( http://tiny.cc/u2k1gz ), in 2017 nothing was known about its potential function. In the last two years a great international team has come together to answer just that question.
Our paper in @NatureComms reveals that the zebra finch germline restricted chromosome (GRC) is packed full of genes, sequestered over millions of years from the somatic genome, and active both transcriptionally and translationally.
The GRC has never failed to amaze us - some of its genes are copied hundreds of times, whereas the somatic genome has a single pair of alleles. The GRC is only passed on in one copy, unlike most typical chromosomes in animals which are passed on in two (1 from each parent).
This means it doesn't have a homologous chromosome to recombine with, and we think it must get copied early in development in order to partner up during cell division. We can think of it as a clone, and this may explain why it evolves so rapidly (harder to fix mistakes).
We think the GRC has become stably inherited because it gained a vital role: its genes are likely important for early development of embryos. So it turns out this enigmatic blob in the karyotype is probably responsible for fundamental finch biology.
By analysing the GRC genes, we could show that it is truly ancient, and in fact is likely to be found in all songbirds - that's half of all living birds! If it has similar behaviour in other songbirds, then this chromosome may have played a massive role in songbird evolution.
The idea that the GRC is actually widespread among birds is also supported by a great recent study by Anna Torgasheva and colleagues, who used cytogenetic methods and observed an incredibly diverse size among GRCs in different birds: ( https://www.pnas.org/content/116/24/11845)
I'll close there, and self-plagiarise my earlier tweet from the GRC bioRxiv submission:
The zebra finch germline chromosome,
makes use of a true mobile home,
in testes and ova,
you'll find this wild rover,
sometimes in a pair or alone!
Thanks for your trust @alexander_suh!
The zebra finch germline chromosome,
makes use of a true mobile home,
in testes and ova,
you'll find this wild rover,
sometimes in a pair or alone!
Thanks for your trust @alexander_suh!
