Flipping through the Guardian today I came across an interesting article about genetics: How humans share a common genetic link with your everyday snail! Intrigued I read on.

Humans are odd and biologically complex in the extreme like most living creatures. On the outside we are resolutely symmetrical, mirror image; two arms, two legs, two eyes, two ears. One on the left hand side of our bodies and one on the right. Inside however we are vastly asymmetrical.

The heart is split in two, left and right, the left side is larger and more muscular, the liver favours the right side, spleen on the left, stomach to the left, gallbladder on the right and the intestines weave in an asymmetrical fashion in the rest of the space provided. Aside from a very few, rare, medical exceptions our insides are consistantly skewed in a particular fashion which is decided by a specific gene called Nodal.

This Nodal gene is switched on early in the development of an embryo and tells cells whether they are to form on the right or the left. This pattern is recurring in all animals with a spines; mammals, birds, fish and reptiles the gene is similarly used.

Accoring to Mr. Myres of The Guardian’s findings, it was thought until recently that insects and molluscs used a different mechanism  – until some further research was carried out on the obviously asymmetrical garden snail.* Yip, you guessed it, the snail has the Nodal gene with a shell on it’s back where some species it coils left and others to the right.

“Here we report the first evidence for a nodal orthologue in a non-deuterostome group. We isolated nodal and Pitx (one of the targets of Nodal signalling) in two species of snails and found that the side of the embryo that expresses nodal and Pitx is related to body chirality: both genes are expressed on the right side of the embryo in the dextral (right-handed) species Lottia gigantea and on the left side in the sinistral (left-handed) species Biomphalaria glabrata.“- IWJS*

Snails in the experiment were given drugs to inhibit the Nodal pathway which yeilded interesting results where the snails had straight, smooth shells of a different shape rather than rounded spirals.

The gene isn’t exactly the same. The snail’s gene is activated on the right rather than left and uses a different trigger but evolution possibly having taken it’s toll, the similarity is striking. So far apart in evolution yet the same genes are present in early development at such a basic level. One gene may seem insignificant, but it’s more evidence to suggest that all living things are interconnected.

Mr. Myres says:-

“A snail is a strange-looking beast, at least to us, but right down at the core of its biology it is built with the same toolbox of genes that we use, and we share a common ancestry with it. A very distant ancestry, for sure — our last common ancestor lived over 600,000,000 years ago — but it should at least give you pause as you’re exterminating the little pests in your garden this summer.”

I’ve always rather liked snails.

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*   Link – International Weekly Journal of Science. – http://www.nature.com/nature/journal/v457/n7232/full/nature07603.html

Link – The Guardian article. – http://www.guardian.co.uk/science/2009/apr/15/genetics-embryos-and-stem-cells

Visualisation and Quantification of Morphogen Gradient Formation in the Zebrafish

Harvey SA, Smith JC (2009)

PLoS Biol 7(5): e1000101 doi:10.1371/journal.pbio.1000101

During embryonic development, signalling molecules known as morphogens act in a concentration-dependent manner to provide positional information to responding tissues. In the early zebrafish embryo, graded signalling by members of the nodal family induces the formation of mesoderm and endoderm, thereby patterning the embryo into three germ layers. Nodal signalling has also been implicated in the establishment of the dorso-ventral axis of the embryo. Although one can infer the existence of nodal gradients by comparing gene expression patterns in wild-type embryos and embryos in which nodal signalling is diminished or augmented, real understanding can only come from directly observing the gradients. One approach is to determine local ligand concentrations in the embryo, but this is technically challenging, and the presence of inhibitors might cause the effective concentration of a ligand to differ from its actual concentration. We have therefore taken two approaches to visualise a direct response to nodal signalling. In the first, we have used transgenic embryos to study the nuclear accumulation of a Smad2-Venus fusion protein, and in the second we have used bimolecular fluorescence complementation to visualise the formation of a complex between Smad2 and Smad4. This has allowed us to visualise, in living embryos, the formation of a graded distribution of nodal signalling activity. We have quantified the formation of the gradient in time and space, and our results not only confirm that nodal signalling patterns the embryo into three germ layers, but also shed light on its role in patterning the dorso-ventral axis and highlight unexpected complexities of mesodermal patterning.

One of the earliest events in vertebrate embryonic development is the patterning of the embryo into three germ layers: the ectoderm, mesoderm, and endoderm. Morphogens are signalling molecules that act in a concentration-dependent manner to induce the formation of different cell types. Members of the nodal family are thought to form a morphogen gradient in the developing zebrafish embryo and to be essential for pattern formation. Mesoderm and endoderm are believed to develop due to high levels of nodal signalling, while cells experiencing the lowest concentrations of nodal signalling become ectoderm. Although this idea is widely accepted, the formation of a nodal morphogen gradient has never been observed directly, and we have therefore used two different approaches to visualise the intensity of nodal signalling within individual cells. Our approaches have allowed us to visualise a gradient of nodal signalling activity in the developing zebrafish embryo. Quantification of the levels of nodal signalling experienced by individual cells confirms that nodal signalling patterns the animal-vegetal axis of the zebrafish embryo and, in contrast to previous studies, also suggests that it plays a role in patterning the dorso-ventral axis of the zebrafish embryo.

Secretly I’m a bit of a science geek under my literary vestments.

I’ve just learnt that we, as in Homo sapiens, are related to the common snail. New research has just found out that snails have the same nodal as humans. We are all completely asymmetrical inside the body, unlike the outside, and it’s the nodal that decides whether, say, the heart is bigger on the left than on the right. And now it appears that the spirals on snails’ shells use the same molecule as we do.

I’ll never put salt on a snail again.

P. Z. Myers, the beloved (and also despiséd) author of the popular science blog Pharyngula, has started producing a column on the Guardian website.  His first column is on asymmetry in animals — in particular the gene nodal, which sets up directional (left-right) asymmetries in animals.  P. Z. points out recent research (reference below) showing that snails, who have directionally coiled shells, lose the directionality when nodal is inactivated.   The asymmetry of the human body is also generated in ways similar to that of snails, and again nodal plays a key role.  The gene is somehow involved in determining the directionality of the way cilia (small hairs) beat in the early embryo, which sets up a concentration gradient that can make an embryo left- or right-handed.

I’ve always been fascinated by directional asymmetries — those traits that occur on a consistent side (right or left) in a species.  These include the side of the body that harbors the narwhal’s tusk. and our own internal organs. Other such traits include the direction in which the ears of an owl are turned, and what side of its body a flounder comes to rest on when it changes into a bottom-dweller.  Directional asymmetries are not rare in animals. But how are they formed? How does a gene “know” it’s on the right or the left?  The finding that the direction of cilia movement can tell a gene which side it’s on goes a long way to solving this question, but still leaves open the final question:  why do cilia spin in a given direction? How do they know whether to go clockwise or counterclockwise?  This may, ultimately, reside in the asymmetry of molecules that make up cilia.

At any rate, P. Z.’s column is good, but his explanation of nodal on Pharyngula is even better.  P. Z. has a real talent for explaining science clearly and engagingly, and too often this is overlooked by the hordes of people who visit his blog for the controversy, atheism, and trenchant attacks on religion.  (One thing I’ve found from writing this blog is that visits are much more numerous when I’m attacking something than when I’m talking about science, a fact that’s a little bit sad.)
But the point I wanted to make relates to an earlier post I made about what counts as evidence for evolution.  P. Z.’s  elegant description of how nodal works was hijacked by the Guardian editors by putting it under the title:

Reference: Grande, C., and N. H. Patel. 2009. Nodal signalling is involved in left–right asymmetry in snails. Nature 457:1008-1011.

Identification of common and unique modifiers of zebrafish midline bifurcation and cyclopia

Wuhong Pei and Benjamin Feldman

Developmental Biology Volume 326, Issue 1, 1 February 2009, Pages 201-211 doi:10.1016/j.ydbio.2008.11.008

Loss of the zebrafish Nodal-related protein Squint causes a spectrum of phenotypes including cyclopia and midline bifurcations (MB). Here we examine MBs and their relation to cyclopia in maternal-zygotic squint (MZsqt) mutants. There is a concordance of MB with cyclopia in MZsqt embryos. Heat treatment and depletion of Hsp90a are “common” risk factors, each of which increases the incidence of both phenotypes. Midline identity is specified on both sides of MBs, and deep-layer cells are initially lacking within bifurcations, whereas enveloping layer cells are intact. Bifurcations do not appear until the completion of gastrulation and are preceded by gaps in the expression of wnt5b, an essential regulator of dorsal convergence. The incidence of early MBs and wnt5b expression defects in heated MZsqt embryos is high, but there is also substantial recovery. Wnt5b depletion increases the incidence of MB, but not cyclopia, and as such Wnt5b is a “unique” risk factor for MB. Reciprocally, depletion of Wnt11 or Hsp90b increases cyclopia only. In summary, we find that MB arises after gastrulation in regions that fail to express wnt5b, and we show that two complex dysmorphologies – MB and cyclopia – can be promoted by either common or unique risk factors.

Possibly the nicest beach on the planet, clear water, squeeky white sand…wicked. 5D, 50mm, F11, 1/15sec, ND4 filter, Nodal Ninja

Mullaloo Point Rocks

Mullaloo Point rocks, about a month ago. They are all covered with sand now till winter. 10 frames, 50mm, F16, Canon 5D.

“Surf Club”

Sorrento SLSC last Sunday night

Comments welcome…

Ketika anda melakukan input data pada software sap2000, maka anda akan mendapatkan istilah nodal yang merupakan bagian dari modelisasi struktur itu sendiri. Bagaimanaka menurut anda pengertian nodal itu? Apakah manfaatnya? Apa kegunaannya? Ikuti pengertian lebih lanjut dari tulisan ini di Nodal SAP2000

Haemodynamics determined by a genetic programme govern asymmetric development of the aortic arch

Kenta Yashiro, Hidetaka Shiratori & Hiroshi Hamada

Nature Vol 450 | 8 November 2007 | doi:10.1038/nature06254

Laterality of the internal organs of vertebrates is determined by asymmetric Nodal signalling in the lateral plate mesoderm. A deficiency of such signalling results in heterotaxia syndrome, characterized by anomalous laterality of visceral organs and complex congenital heart conditions1. Pitx2, the transcription factor induced by the Nodal signal, regulates left–right asymmetric morphogenesis. The cellular and molecular bases of asymmetric morphogenesis remain largely unknown, however. Here we show that ablation of unilateral Pitx2 expression in mice impairs asymmetric remodelling of the branchial arch artery (BAA) system, resulting in randomized laterality of the aortic arch. Pitx2-positive cells were found not to contribute to asymmetrically remodelled arteries. Instead, Pitx2 functions in the secondary heart field and induces a dynamic morphological change in the outflow tract of the heart, which results in the provision of an asymmetric blood supply to the sixth BAA. This uneven distribution of blood flow results in differential signalling by both the platelet-derived growth factor receptor and vascular endothelial growth factor receptor 2. The consequent stabilization of the left sixth BAA and regression of its right counterpart underlie left-sided formation of the aortic arch. Our results therefore indicate that haemodynamics, generated by a Pitx2-induced morphological change in the outflow tract, is responsible for the asymmetric remodelling of the great arteries.

Okay, so today begins the attempt at 30 days.  It didn’t work.  I was going to explain the world in 30 days or something, but as I recall there were some valuable points and I’m at the house-cleaning point.  Justify yourself for a blog or else fly on over to the trash can.

Rose is angry because I joked “You should try living with yourself for 30 days.”

She not only gets angry, as I recall, she has problems on who’s going.  As in do I get kicked out.  I suppose it’s the time of the month; toward the first of it, rent just got paid so I should get kicked out.  Or something.

Presumably this is some sort of role-reversal bit.  It would rather go with her need to imitate me.  The indication seems to be that any “personal relationship” is either “fulfilling and makes one grow”–for both, mind you–or a weighted relationship with a limited number of modes of communication and by nature little in shared values.  That’s this culture’s model.

To confuse recollection with its representation is to ensure error.

In any relationship involving representation (which is necessary unless the “thought” is somehow the things themselves) [that is, a relationship involving an ordered set used to represent a set which is presemably ordered within the ordered set (the representative set)] there will exists relationships and almost certainly events–which don’t exist in the set being represented.

That is, you have to have a language of some sort to talk about the world.  The language has to have order–the purpose of the language is to communicate, which means a shared pattern.  This means that there are “interior” rules of the set used for representation–the language–that only have to do with it and the purpose it serves [presumably for a society but that's yet another pathway along which to wander and not yet thanks].  It doesn’t have anything to do with the outside world, the thing ostensibly being represented.  It has to do with what is seen as necessity for communication and for the ability to perceive the real.

And let us say before closing that there are all sorts of rules involved.  Many of them are quite necessary.  Rules are after all what define a society, and the over-riding need for confirmed identity is the main support of society as we know it.

Finally I will be getting a panoramic tripod head thanks to Jim, who I spoke with at length with earlier today. Jim was very informative and we ended up having a long conversion about his product. If your on the fence about a tripod head give Jim a call / email he will explain it all to you and you’ll also be helping out a fellow aussie business. I ended up getting the NN5L

www.nodalninja.com.au

Spool