Basics: Neurulation

When we had last seen our basic embryo, it had gone through gastrulation — a process in which cells of a two-layered sheet had moved inward, setting up the three germ layers (endoderm, mesoderm, and ectoderm) of the early embryo. In particular, cells at the organizer, a tissue that induces or organizes migrating cells, had rolled inwards to set up specific axial mesoderm structures: the prechordal plate, which will underlie cranial structures, and the notochord, which resides under the future hindbrain and spinal cord. At this point, the embryo has an outer layer of ectoderm, and lying under part of it, a band of prechordal mesoderm and notochord. In addition, the ectoderm is loaded with a molecule called BMP-4, a member of the TGF-β family of signaling molecules, and under its influence will go on to make skin, not nervous system. So what next?

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The lovely stalk-eyed fly

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Sphyrocephala beccarii

Here is a spectacularly pretty and weird animal: stalk-eyed flies of the family Diopsidae. There are about 160 species in this group that exhibit this extreme morphology, with the eyes and the antennae displaced laterally on stalks. They often (but not always) are sexually dimorphic, with males having more exaggerated stalks—the longer stalks also make them clumsy in flight, so this is a pattern with considerable cost, and is thought to be the product of sexual selection. The Sphyrocephala to the right is not even an extreme example. Read on to see some genuinely bizarre flies and a little bit about the development of this structure.

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The Strange Case of the Woman with a Breast on her Foot

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Stevie C sent along this article on
An unusual presentation of supernumerary breast tissue (just what were you googling for, Stevie?), in which a woman reports an annoying growth on her foot, and when examined, is discovered to have a breast growing there, complete with nipple and fatty tissue (but in this case, no glandular tissue).

It’s in the Dermatology Online Journal, not the Onion.

I hadn’t heard of this before myself, but it’s fascinating. These supernumerary breasts can pop up all over the place, including the face, back, and thigh (and foot, obviously). They can be functionally complete, and can even lactate. The authors report some weak and sometimes contradicted associations with other oddities, but no causal mechanism is known. These cases of autonomous self-organization and recruitment of organs are extremely interesting—it suggests that a breast would be a fairly easy tissue to grow in a dish. I’d love to know what the molecular signal for initiating differentiation—I suspect it’s something simple and common.

Evolution of the jaw

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What do you know…just last week, I posted an article dismissing a creationist’s misconceptions about pharyngeal organization and development, in which he asks about the evidence for similarities between agnathan and gnathostome jaws, and what comes along but a new paper on the molecular evidence for the origin of the jaw, which describes gene expression in the lamprey pharynx. How timely! And as a plus, it contains several very clear summary diagrams to show how all the bits and pieces and molecules relate to one another.

The short summary is that there is a suite of genes (the Hox and Dlx genes, which define a cartesian coordinate system for the branchial arch elements, Fgf8/Dlx1 genes that establish proximal jaw elements, and Bmp4/Msx1 genes that demarcate more distal elements) that are found in both lampreys and vertebrates in similar patterns and roles, and that vertebrate upper and lower jaws are homologous to the upper and lower “lips” of the lamprey oral supporting apparatus.

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The manimal will have a British accent

Well, not really—but the UK government will tolerate and support research into human-animal hybrids. No one is interested in raising a half-pig/half-man creature to adulthood, but instead this work is all about understanding basic mechanisms of development and human disease.

Scientists want to create the hybrid embryos to study the subtle molecular glitches that give rise to intractable diseases such as Parkinson’s, Alzheimer’s and cystic fibrosis. The researchers would take a cell from a patient and insert it into a hollowed out animal egg to make an embryo, which would be 99.9% human and 0.1% animal. Embryonic stem cells extracted from the week-old embryo would then be grown into nerves and other tissues, giving scientists unprecedented insight into how the disease develops in the body. Under existing laws, the embryos must be destroyed no later than 14 days after being created and cannot be implanted.

(I don’t care for how they phrased it: these will be a collection of animal-derived cells that contain human nuclear DNA. They will not be human.)

This is precisely the kind of useful biomedical research our American president called one of the “most egregious abuses of medical research” in his state of the union speech last year. Essentially, the only people who oppose it are confused wackos with delusions about the ‘sanctity’ of human life who think a few cells in a dish should have more rights and privileges than an adult woman—a substantial chunk of the Republican base.

We see once again where the so-far eminently successful American scientific machine is stymied by the religious twits who have looked at the possibilities of 21st century biology, and turned away, allowing other countries the opportunity to pass us by.

I should have included a link to this other article, in which government ministers declare that they will no longer oppose the research.

Basics: Gastrulation, invertebrate style

The article about gastrulation from the other day was dreadfully vertebrate-centric, so let me correct that with a little addendum that mentions a few invertebrate patterns of gastrulation—and you’ll see that the story hasn’t changed.

Remember, this is the definition of gastrulation that I explained with some vertebrate examples:

The process in animal embryos in which endoderm and mesoderm move from the outer surface of the embryo to the inside, where they give rise to internal organs.

I described frogs and birds and mammals the other day, so lets take a look at sea urchins and fruit flies.

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Basics: Gastrulation

That guy, John Wilkins, has been keeping a list of presentations of basic concepts in science, and he told me I’m supposed to do one on gastrulation. First I thought, no way—that’s way too hard, and I thought this was all supposed to be about basic stuff. But then I figured that it can’t be too hard, after all, all you readers went through it successfully, and you even managed to do it before you developed a brain. So, sure, let’s rattle this one off.

In the simplest terms, gastrulation is a stage in early development; in human beings it occurs between two and three weeks after fertilization. It is that stage when a two-layered cell mass undergoes a set of specific movements and interactions that establish the three germ layers of the embryo (endoderm, mesoderm, and ectoderm) and the beginnings of a three-dimensional structure. The end result doesn’t look like much of an animal, but it has set up pools of cells that will contribute to specific future cell types, and has laid down the rough outline of tissues along the body axis.

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Ducks with 6 limbs are not caused by genetic changes!

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Cool: here’s a duck with four hindlimbs.

I have to gripe about the description, though:

A rare mutation has left eight-day-old Stumpy with two extra legs behind the two he moves around on. … The mutation is rare but cases have been recorded across the world.

No, no, no. This is almost certainly not the result of a mutation, and it’s one of my pet peeves when the media makes this wrong assumption, that every change in a newborn is the product of a genetic change. This is the result of a developmental error, not a genetic one, most likely caused by a fusion of two embryos in a single egg.

(via Apostropher)