Exxon still loves Volvox

I hope Exxon’s scientists know more more algal taxonomy than their ad team. We’ve seen before that they don’t know the difference between Chlorophyte green algae and cyanobacteria (Exxon loves Volvox). Some of the things they’ve lumped together in that video are more distantly related than humans are to mushrooms.

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MicroRNAs in Chlamydomonas

One of the biggest changes in evolutionary theory in the late 20th century was the growing appreciation for the central role of changes in gene expression in macroevolution. Developmental genes, especially Hox genes, turned out to be remarkably conserved across lineages that diverged over half a billion years ago. The subsequent huge changes in morphology were more often due to changes in when and where those genes were expressed than to changes in the coding sequences of the genes themselves.

Even more recently, an entire new class of regulatory mechanisms was discovered and found to be important in developmental processes. MicroRNAs (miRNAs) are short (21-24 nucleotides) sequences of RNA that reduce gene expression by promoting the breakdown of messenger RNAs (mRNAs) and by repressing translation of mRNAs into proteins. We have only known that microRNAs even existed since the early 1990’s, and their importance in gene regulation and development wasn’t appreciated until the 2000’s.

Although they are structurally similar, plant and animal microRNAs repress gene expression through very different mechanisms. A new paper by Betty Y-W. Chung and colleagues in Nature Plants shows that the regulatory mechanisms of Chlamydomonas microRNAs have both striking similarities and important differences with animal miRNAs:

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Non-model model organisms

Jim Umen, the lead organizer of the upcoming Volvox meeting, has written a section for a new paper in BMC Biology, “Non-model model organisms.” Like all of the BMC journals, BMC Biology is open access, so you can check out the original.

The article surveys organisms that, while not among the traditional model systems, have been developed as model systems for studying particular biological questions. The paper has an unusual format, with a discrete section devoted to each species, each written by one or two of the authors. Aside from Volvox, there are sections on diatoms, the ciliates Stentor and Oxytricha, the amoeba Naeglaria, fission yeast, the filamentous fungus Ashbya, the moss Physcomitrella, the cnidarian Nematostella, tardigrades, axolotls, killifish, R bodies (a bacterial toxin delivery system), and cerebral organoids (a kind of lab-grown micro-brain).

Dr. Umen presents Volvox and its relatives as a model system for understand the evolution of traits related to the evolution of multicellularity:

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Ehrenberg on Eudorina

Eudorina elegans, from Ehrenberg 1832.

Eudorina elegans, from Ehrenberg 1832.

Eudorina elegans was described by the German biologist Christian Gottfried Ehrenberg in his Lectures at the Academy of Sciences in Berlin in the years 18301836 (Vorträge in der Akademie der Wissenschaften zu Berlin im Jahre 1830-1836). With the help of Google Translate, here’s what he had to say about it (page 17):

I have also found an eye-shaped form in the family of the epigones, or of the mucous, intestinal infusoria, which have a hairy body. This form of infusoria is also undefined, but it is confused by me, and probably by all previous observers, with Pandorina Morum (Volvox Morum Müller); Less accurate observers also thought they were probably Volvox Globator. I found them in the basin of the animal garden in the spring of this year between conferences. It is quite consistent with the same form, as I see from my drawing made in the Ural, that the animal which I, as Pandorina Morum, from Kyschtym, have doubtless listed in my list of the Russian Infusoria, and I am of the opinion that I had at that time only overlooked the unsuspected eye. The body consists of a gelatinous, globule-shaped sphere, in which a certain number of spherical, green-colored animals are enclosed, each showing a beautiful red, round but small eye, and a simple, long, whirling, or supporting eyelash through the water. The whirling is seen very clearly as soon as a fine, turbid substance is added to the water. To this animal, which is one of the most beautiful infusoria, I have given the generic name Eudorina, in consideration of the closely related eyeless genus Pandorina. The only known species I have called Eudorina argus (beautiful green eye ball).

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New review of green algal sex

Hiroyuki Sekimoto from Japan Women’s University has published a review of sexual reproduction in the volvocine algae and in the Charophyte Closterium in the Journal of Plant Research. In addition to a brief description of the Chlamydomonas sexual cycle, it includes a succinct review of the genetics of sex and sex determination. Unfortunately, the article is paywalled, and my inquiry to the author has so far gone unanswered.

Figure 1 from Sekimoto 2017. The life cycle of Chlamydomonas reinhardtii. Vegetative cells (V) di erentiate into mt+ and mt− gametes (G) during nitrogen starvation (−N). Mating types are restricted by mating-type loci (+ and −). When gametes are mixed, the plus and minus agglutinin mol- ecules on their agellar surfaces adhere to each other, and this adhe- sion results in increased intracellular cAMP levels. The signal trig- gers gamete cell wall release and mating-structure activation. Cells then fuse to form binucleate quadri agellated cells. Zygotes with thick cell walls germinate in response to light and nitrogen supple- mentation, and undergo meiosis to release four haploid vegetative cells

Figure 1 from Sekimoto 2017. The life cycle of Chlamydomonas reinhardtii. Vegetative cells (V) differentiate into mt+ and mt− gametes (G) during nitrogen starvation (−N). Mating types are restricted by mating-type loci (+ and −). When gametes are mixed, the plus and minus agglutinin molecules on their flagellar surfaces adhere to each other, and this adhesion results in increased intracellular cAMP levels. The signal triggers gamete cell wall release and mating-structure activation. Cells then fuse to form binucleate quadriflagellated cells. Zygotes with thick cell walls germinate in response to light and nitrogen supplementation, and undergo meiosis to release four haploid vegetative cells.

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Algae porn

I track the #Volvox hashtag on Twitter, which is how I find out about a lot of the off-label uses of the name Volvox, like DJ VolvoxVolvox the ship, and Volvox the art gallery. Every now and then, it even turns up something related to Volvox the little rolling algae. The other day, @QuintaSwinger tweeted the following video with #Volvox:

The Twitter handle is about just what you think it is; apparently volvocine sex puts someone in mind of polyamory. I suppose I can see that: when a sperm packet enters a colony, it gets busy with all the ova. The video was uploaded to YouTube by Dr. Donald Ott from the University of Akron.

I think the algae in the video are not actually Volvox, though. Certainly the still photo at the beginning is Volvox. Probably not section Volvox (too few cells), and probably not Developmental Program 2 (germ cells too small in the one on the lower right). If I had to guess, I’d say V. aureus, but that’s largely a Bayesian bet because they’re so common. Maybe Alexey Desnitskiy or Hisayoshi Nozaki can comment.

The colonies in the video, though, look more like Pleodorina to me. Not P. sphaerica, since the somatic cells are all in the front, but without more information I can’t narrow it down more than that.

Invasive Pleodorina indica in Poland

Figure 3 B-I from Knysak and Żelazna-Wieczorek 2017. Pleodorina indica (Iyengar) H. Nozaki 400x.

Figure 3 B-I from Knysak and Żelazna-Wieczorek 2017. Pleodorina indica (Iyengar) H. Nozaki 400x.

A new paper in Oceanological and Hydrobiological Studies reports a massive bloom of Pleodorina indica in a reservoir in central Poland. Piotr Knysak and Joanna Żelazna-Wieczorek sampled the reservoir on the Olechówka River in Łódź during the summer of 2015 and found that P. indica made up ~95% of the algae collected.

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