16 thoughts on “The gift from mom that keeps on giving”

  1. … who got it from one of his old dept’s former grad students (and who my last two publications may wind up being with), now a postdoc on Prince Edw Island, who got it from one of her friends…

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  2. And if the so-called “three-person pregnancies” are ever allowed, Hallmark will have to dream up a whole new holiday for the requisite cards. Happy Mitochondrial Mother’s Day.

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  3. I’ve wondered, if the mitochondria are captured once free living cells, has anyone tried to find our closest cousins among the bacteria?
    Should I try to friend them on Facebook?

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        1. Yes, thanks Mark! Glad you asked, kevin!

          Just one intriguing paragraph there:

          For years, they have known it was likely an Alphaproteobacterium, and that the mitochondria are closely allied with the Rickettsiales, a group of largely parasitic intracellular bacteria that include organisms that cause typhus and Rocky Mountain Spotted Fever. That would make sense: both mitochondria and intracellular parasites obviously have lots of adaptations that make them good at living inside other cells.

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          1. Diane, your intriguing paragraph may still be morally correct. The latest phylogeny safely (?) places the mitochondrion within Rickettsiales, close to Wohlbachia in fact, and in a parasitic clade. The way they do so is to enhance the phylogenetic resolution, besides more sequences, by adding a node for the pre-mitochondrion (the shared ancestor to Alphaproteobacteria) instead of just resolving the proto-mitochondrion (the original endo-whatever).

            The pre-mitochondrion looks to have been an ATP-stealing parasite (had an ATP-importer), before it evolved into an ATP-giving symbiont. This should be a more likely state, as it obviates the need for immediate mutual benefit. “Therefore we argue that the benefits proposed by various hypotheses (e.g., oxygen scavenger hypothesis and hydrogen hypothesis) are irrelevant in explaining the establishment of the initial symbiosis.” [ http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0110685 ]

            Now that the eukaryote ancestor looks to have been endowed with an active actine skeleton and other paraphernalia for phagocytosis, it seems like all constraints for the mitochondrion endosymbiosis are fulfilled. I feel obligated to post this fresh result, since the lead author is at my alma mater and the paper got an enthusiastic editorial in Nature!

            “Here we describe the discovery of ‘Lokiarchaeota’, a novel candidate archaeal phylum, which forms a monophyletic group with eukaryotes in phylogenomic analyses, and whose genomes encode an expanded repertoire of eukaryotic signature proteins that are suggestive of sophisticated membrane remodelling capabilities. … Indeed, based upon our results it seems plausible that the archaeal ancestor of eukaryotes had a dynamic actin cytoskeleton and potentially endo- and/or phagocytic capabilities, which would have facilitated the invagination of the mitochondrial progenitor.” [“Complex archaea that bridge the gap between prokaryotes and eukaryotes”, Anja Spang et al, Nature]

            [Note that they still want to sequence more archaea to try to confirm this. The crucial grouping Lokiarchaeota-Eukarya had a ML bootstrap of 80, which is “moderate” support I think, not being an expert. What sold me is that they get the actins as near the actin root, et cetera. Plus the key eukaryote gene gain is evenly distributed between Archaea-Lokiarchaeota respectively Lokiarchaeota-Eukarya, which makes the new clade truly transitional, even if it is just a cousin to our ancestor.]

            “This technically outstanding paper has far-reaching implications for how we view early eukaryotic evolution, including our own deep ancestry.” [“Steps on the road to eukaryotes”, Embley & Williams, Nature]

            To add some personal speculation, the Lokiarchaeota and its close relatives were found by environmental sequencing in sediments a few km from the vent Loki’s Catsle that it gets its name from.

            [“The proposed naming of the Eukarya-affiliated candidate phylum Lokiarchaeota and the Lokiarchaeum lineage is made in reference to the sampling location, Loki’s Castle29, which in turn was named after the Norse mythology’s shape-shifting deity Loki. Loki has been described as ‘‘a staggeringly complex, confusing, and ambivalent figure who has been the catalyst of countless unresolved scholarly controversies’’34, in analogy to the ongoing debates on the origin of eukaryotes.”]

            Archaea are low energy specialists, so the deep sea environment should be a nice fit. As I understand the evolutionary tendencies in such nutrient sparse environments the organisms tend to evolve capacities to harvest larger than usual food sources that they happen by. Perhaps that was a driver for evolving invagination.

          3. More oy ouch, “Loki’s Castle”.

            And to think I just now noticed “shape-shifting”, they did a lulz! It would be nice to get hold of the actual organism, and see what it can do. I know that archaea (and bacteria) can shapeshift in response to pH et cetera. But this could be more … invaginative … shape-shifting. [/less reading, more coffee]

          4. Torbjörn, thanks! I think I grasped enough of that to understand how exciting this work is! Talk about your missing link! 😀

            And I love the name choice and why they chose it–who says scientists aren’t romanticists as well?

            And by the way…by calling my excerpt “just one intriguing paragraph there,” I meant to imply, “just one of the many intriguing paragraphs there.” I see now I should have spelled that out.

            Thanks again, very cool science!

  4. Over the last 5 years, there has been considerable debate as to whether there is recombination in human mitochondrial DNA (mtDNA) (for references, see Piganeau and Eyre-Walker, 2004). That debate appears to have finally come to an end with the publication of some direct evidence of recombination. Schwartz and Vissing (2002), 2 years ago, presented the case of a 28-year-old man who had both maternal and paternally derived mtDNA in his muscle tissue – in all his other tissues he had only maternally derived mtDNA. It was the first time that paternal leakage and, consequently, heteroplasmy was observed in human mtDNA. In a recent paper, Kraytsberg et al (2004) take this observation one step further, and claim to show that there has been recombination between the maternal and paternal mtDNA in this individual.

    Ladoukakis ED, Eyre-Walker A (October 2004). “Evolutionary genetics: direct evidence of recombination in human mitochondrial DNA”. Heredity 93 (4): 321

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    1. Interesting! And either they were incredibly lucky to stumble upon that particular guy, or it’s more common than one would have thought.

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