Where do the hagfish fit in?

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Hagfish are wonderful, beautiful, interesting animals. They are particularly attractive to evolutionary biologists because they have some very suggestive features that look primitive: they have no jaws, and they have no pectoral girdle or paired pectoral fins. They have very poorly developed eyes, no epiphysis, and only one semicircular canal; lampreys, while also lacking jaws, at least have good eyes and two semicircular canals. How hagfish fit into the evolutionary tree is still an open question, however.

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I want a heart in a jar

A lab at the University of Minnesota has done something cool: they’ve grown a functioning heart from stem cells. The problem with building complex organs in a lab is that their normal construction required an elaborate context in the developing embryo, something that is impossible to replicate, short of just growing the whole embryo. The Doris Taylor lab did something very clever: they took an adult rat or rabbit heart and stripped it of its cells, leaving behind a scaffold of nonliving connective tissue. Then they recellularized it with stem cells, and they differentiated appropriately to make a new, beating heart.

They’ve got a long way to go yet — the resynthesized hearts only beat with 2% of the strength of the normal adult heart — but it’s a good start.

You can watch a video describing the work. Warning: it does show one dead rat and a guy with a knife, and there are pulsing pink blobs of hearts in glass chambers, so it may not be for everyone.

Neurulation in zebrafish

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Neurulation is a series of cell movements and shape changes, inductive interactions, and changes in gene expression that partitions tissues into a discrete neural tube. It is one of those early and significant morphogenetic events that define an important tissue, in this case the nervous system, and it’s also an event that can easily go wrong, producing relatively common birth defects like holoprosencephaly and spina bifida. Neurulation has been a somewhat messy phenomenon for comparative embryology, too, because there are not only subtle differences between different vertebrate lineages in precisely how they segregate the neural tissue, but there are also differences along the rostrocaudal axis of an individual organism. A recent review by Lowery and Sive, though, tidies up the confusion and pulls disparate stories together.

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Evolution of vertebrate eyes

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A while back, I summarized a review of the evolution of eyes across the whole of the metazoa — it doesn’t matter whether we’re looking at flies or jellyfish or salmon or shrimp, when you get right down to the biochemistry and cell biology of photoreception, the common ancestry of the visual system is apparent. Vision evolved in the pre-Cambrian, and we have all inherited the same basic machinery — since then, we’ve mainly been elaborating, refining, and randomly varying the structures that add functionality to the eye.

Now there’s a new and wonderfully comprehensive review of the evolution of eyes in one specific lineage, the vertebrates. The message is that, once again, all the heavy lifting, the evolution of a muscled eyeball with a lens and retinal circuitry, was accomplished early, between 550 and 500 million years ago. Most of what biology has been doing since is tweaking — significant tweaking, I’m sure, but the differences between a lamprey eye and our eyes are in the details, not the overall structure.

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Drugs for brains

Here’s an interesting question: “if you could take a pill which enhanced attention and cognition with few or no side effects, would you?”

Shelley says yes. Janet says no. I say it depends on that qualifier, “few or no side effects” — if that were true, I’d say “Yes! Gimme more!” This is no dilemma at all.

Of course, that’s cheating. There’s no such thing as a drug that has no side effects. The real dilemma would crop up if a cognitive enhancer were available that did have problematic side effects — then my worry would be that pressure to succeed in my classes would be driving students to harm themselves in substantial ways. That happens already. Students take no-doz or skimp on sleep to do well, so there is some unavoidable harm from the stress of learning.

So that’s the information I need before I can make any decision — this is an issue that requires weighing costs and benefits, and telling me there is no cost simplifies it too much. For instance, caffeine has costs, but they’re low enough that my choice is to drink in moderation, but not to give it up altogether.

Load-bearing adaptation of women’s spines

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Blogging on Peer-Reviewed Research

Those of you who have been pregnant, or have been a partner to someone who has been pregnant, are familiar with one among many common consequences: lower back pain. It’s not surprising—pregnant women are carrying this low-slung 7kg (15lb) weight, and the closest we males can come to the experience would be pressing a bowling ball to our bellybutton and hauling it around with us everywhere we go. This is the kind of load that can put someone seriously out of balance, and one way we compensate for a forward-projecting load is to increase the curvature of our spines (especially the lumbar spine, or lower back), and throw our shoulders back to move our center of mass (COM) back.

Here’s the interesting part: women have changed the shape of individual vertebrae to better enable maintenance of this increased curvature, called lordosis, and fossil australopithecines show a similar variation.

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Bisexual flies and the neurochemistry of behavior

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On the one hand, this is a strange tale of mutant, bisexual, necrophiliac flies, and you’ve got to love it for the titillating nature of the experiments. But on the other, much more interesting hand, it’s a story about drilling down deeply into the causes of a complex behavior, and tracing it to a single gene product — and it also reveals much about the way the chemicals sloshing about in the brain can modulate responses to stimuli. Work by Grosjean and others on a simple Drosophila mutant, genderblind, which causes flies to be indiscriminate about gender in their courtship, opens up a window into how sexual responses are shaped and specified.

Think about human sexual responses. Some of us, when we see an attractive woman, are at least mildly aroused; others are have their sexual interest picqued when they see an attractive man; still others might feel sexual urges when they see a shoe, or a plush animal, or a pot of baked beans. No matter what the stimulus, these are all biological responses, with something in the environment matching some trigger in our brains and initiating a cascade of neural, neurochemical, and hormonal activity that leads to sexual behaviors. The question we want to address is what every step in the biology is doing; unfortunately, human behaviors are both too complex and not amenable to ethical experimentation, so we turn instead to simpler organisms that allow us to find simpler causes and carry out thorough experiments to probe the behavior.

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