Midichlorians, midichloria, and mitochondria

Nathan Lo is an evolutionary biologist interested in creepy crawlies, i.e. arthropods. Well, he’s Australian, so I guess that comes with the territory (see what I did there?). While postdoc’ing, he and his colleagues published a paper (Sassera et al., 2006) that would seem boring for anybody without an interest in taxonomy, a truly under-appreciated field.

The paper describes a bacterium that is a parasite for the mitochondria of a tick species called Ixodes ricinus, the nasty bugger responsible for Lyme disease. The authors obtained a female tick from Berlin, Germany and let it feed on a hamster until it laid eggs. By using genetic sequencing (you can use kits these days to extract the DNA, do PCR, gels and cloning, pretty much everything), electron microscopy (real powerful microscopes) and phylogenetic analysis (using computer softwares to see how closely related some species are) the authors came to the conclusion that this parasite they were working on is a new species. So they named it. And below is the full account of the naming, from the horse’s mouth, as it were:

“In accordance with the guidelines of the International Committee of Systematic Bacteriology, unculturable bacteria should be classified as Candidatus (Murray & Stackebrandt, 1995). Thus we propose the name ‘Candidatus Midichloria mitochondrii’ for the novel bacterium. The genus name Midichloria (mi.di.chlo′ria. N.L. fem. n.) is derived from the midichlorians, organisms within the fictional Star Wars universe. Midichlorians are microscopic symbionts that reside within the cells of living things and ‘‘communicate with the Force’’. Star Wars creator George Lucas stated that the idea of the midichlorians is based on endosymbiotic theory. The word ‘midichlorian’ appears to be a blend of the words mitochondrion and chloroplast. The specific epithet, mitochondrii (mi.to′chon.drii. N.L. n. mitochondrium -i a mitochondrion; N.L. gen. n. mitochondrii of a mitochondrion), refers to the unique intramitochondrial lifestyle of this bacterium. ‘Candidatus M. mitochondrii’ belongs to the phylum Proteobacteria, to the class Alphaproteobacteria and to the order Rickettsiales. ‘Candidatus M. mitochondrii’ is assigned on the basis of the 16S rRNA (AJ566640) and gyrB gene sequences (AM159536)” (p. 2539).

George Lucas gave his blessing to the Christening (of course he did).

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Acknowledgements: Thanks go to Ms. BBD who prevented me from making a fool of myself – this time – on the social media by pointing out to me that midichloria are real and that they are a mitochondrial parasite.

REFERENCE: Sassera D, Beninati T, Bandi C, Bouman EA, Sacchi L, Fabbi M, Lo N. (Nov. 2006). ‘Candidatus Midichloria mitochondrii’, an endosymbiont of the tick Ixodes ricinus with a unique intramitochondrial lifestyle. International Journal of Systematic and Evolutionary Microbiology, 56(Pt 11): 2535-2540. PMID: 17082386, DOI: 10.1099/ijs.0.64386-0. ABSTRACT | FREE FULLTEXT PDF 

By Neuronicus, 29 July 2017

Pesticides reduce pollination

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Close-up of a bee with pollen flying by a flower. Credit: Jon Sullivan. License: PD

Bees have difficult times these days, what with that mysterious colony collapse disorder on top of various viral, bacterial and parasitical diseases. Of course, the widespread use of pesticides did not help the thriving of the hive, as many pesticides have various deleterious effects on the bees, from poor foraging or less reproduction to even death.

The relatively new (’90s) class of insecticide – the neonicotinoids – has been met with great hope because has low toxic effects on birds and mammals, as opposed to the organophosphates, for example. Why that should be the case, is a mystery for me, because the neonicotinoids bind to the nicotinic receptors present in both peripheral and central nervous system in an irreversible manner, which does not put the neonicotinoids in a favorable light.

Now Stanley et al. (2015) have found that exposure to the neonicotinoid thiamethoxam reduces the pollination provided by the bumblebees to apples. They checked it using 24 bumblebee colonies and the exposure was at low levels over 13 days, trying to mimic realistic in-field exposure. The apples visited by the bumblebees exposed to insecticide had 36% reduction in apple seeds.

Almost 90% of the flowering plants need pollination to reproduce, so any threat to pollination can cause serious problems. Over the paste few years, virtually all USA corn had been treated with neonicotinoids; EU banned the thiamethoxam use in 2013. And, to make matters worse, neonicotinoids are but only one class of the many toxins affecting the bees.

Related post: Golf & Grapes OR Grandkids (but not both!)

Reference: Stanley DA, Garratt MP, Wickens JB, Wickens VJ, Potts SG, & Raine NE. (Epub 18 Nov 2015). Neonicotinoid pesticide exposure impairs crop pollination services provided by bumblebees. Nature, doi: 10.1038/nature16167. Article

By Neuronicus, 21 November 2015

Kinesin in axon regeneration

Fig. 8 from Lu, Lakonishok, & Gelfand (2015). License: Creative Commons 2.
Fig. 8 from Lu, Lakonishok, & Gelfand (2015). License: Creative Commons 2.

The longest neuron that a human has is from the spinal cord to the tip of the toes. As a cell, it needs various proteins in various places. How is this transport done? Surely not by diffusion, the proteins would degrade or would arrive at inopportune membrane-moments (I just coined that). Molecular motors, on the other hand, are toiling proteins which haul huge cargoes for the benefit of the cell in an incredibly ingenious manner (they have feet and sticky soles and gears and so on). Notable motors are kinesin and dynein, the former brings stuff to the terminal buttons of the axon, the latter goes in the opposite direction, to the soma. They walk on a railway-like scaffold in a very funny manner, if you are to believe the simulations. Go on, I dare you, search kinesin or dynein animation on Google or YouTube and tell me then that biology is not funny.

And because no self-respectable scientist can work with the molecular motors without adding his/her contribution to the above-mentioned wealth of animations, the paper below comes with no less than 9 movies (as online supplemental material)! Lu et al. (2015) focused their attention on the role of kinesin in injured neurons. The authors dyed several types of proteins in fly neurons and then cultured the cells in a Petri dish. And then cut their axons with a glass needle. After that, they used a really fancy microscope (and a good microscopist, you should look at their pictures) to look at what happens. Which is this: the cut activates a c-Jun N-terminal kinase cascade (the cell’s response to stress), which leads to sliding of microtubules (part of cell’s cytoskeleton), which is com­pletely dependent on kinesin-1 heavy chain. This sliding initiates axonal regeneration (see picture).

I believe the kinesins and dyneins are the most charming, funny, and endearing proteins out there. Yes, I’m anthropomorphizing clumps of amino acids. I know, I’m a geek.

Reference: Lu W, Lakonishok M, & Gelfand VI (1 Apr 2015, Epub 5 Feb 2015). Kinesin-1–powered microtubule sliding initiates axonal regeneration in Drosophila cultured neurons. Molecular Biology of the Cell, 26(7):1296-307. doi: 10.1091/mbc.E14-10-1423. Article | FREE FULLTEXT PDF | Supplemental movies

Some youtube videos I mentioned before, quite accurate, too: best in show

by Neuronicus, 12 November 2015

The song of a fly… the courtship of another

Drosophila melanogaster image illustrating sexual dimorphism and mating behavior. Credit: TheAlphaWolf (Wikimedia Commons)
Drosophila melanogaster image illustrating sexual dimorphism and mating behavior. Credit: TheAlphaWolf (Wikimedia Commons)

Did you know that flies sing? True to the dictum that I just made up – ‘where is song, there is lust’ – it turns out not only that flies can sing, but they even have courtship songs! Granted, since they don’t have a larynx, the male flies sing by vibrating their wings in a certain way, which is unique to each fly species, and females listen with the feather-looking bit on top of their antennae, called arista. The behavior has generated enough research that a fairly hefty review about it has been published two years ago in Nature Reviews Neuroscience, pointing to a gene central to the male courtship circuitry and expressed only in the fly’s neurons, the fru gene (I bet it was called that way because when you make mutants you get fru/fru …).

Zhou et al. (2015) used a series of complicated experiments to successively activate or inhibit the neurons which express the fru gene, in order to identify the neural circuitry underlying hearing and processing the courtship songs. This circuitry is different in males and females, which makes sense since the serenading male expects different behaviors from his audience, depending on their sex; the listening males hurry to compete for the intended female and the females slow down and… listen carefully. Mind wondering: if I was the one serenading, wouldn’t I want to drive away the competitors, instead of drawing them in towards the object of my desire? Perhaps I want the competitors to also engage in courtship behavior so I can show off my wing vibrating prowess… Anyway, digression aside, in addition to figuring out which neuron does what, the authors managed to elicit courtship behavior in the listening males by optogenetically stimulating the 3rd and 4th order neurons in the newly identified circuit.

Besides being strangely interesting in itself, the research fills a gap in the understanding how courtship behavior is recognized, at least in fruit flies, which may be very useful information for other species as well, humans included.

Reference: Zhou, C., Franconville, R., Vaughan, A. G., Robinett, C. C., Jayaraman, V., & Baker, B. S. (21 September 2015). Central neural circuitry mediating courtship song perception in male Drosophila. Elife, 4:1-15. doi: 10.7554/eLife.08477. Article + FREE PDF

For the interested specialist, the MATLAB source code for analyzing calcium-imaging data can be found here.

By Neuronicus, 24 September 2015