Freethought & Rationalism Archive

MrDarwin · 12-12-2002, 12:43 PM

This is pretty exciting news, since sea squirts represent a "transitional form" between invertebrates and vertebrates:

<a href="http://www.washingtonpost.com/wp-dyn/articles/A46388-2002Dec12.html" target="_blank">Scientists Pin Down Sea Squirt Genetics</a>

scigirl · 12-12-2002, 02:37 PM

Quote:

"The sea squirt enjoys a special place in the hearts of biologists because it provides the first evolutionary connection between invertebrates and vertebrates," Levine said. "You look at the adult and you think it is one simple creature, but if you look at the embryo, you see a clear connection to higher animals. This is our ancient, ancient cousin."

Very nice! Embryo studies always reconvince me of evolution.

scigirl

Darwin's Finch · 12-12-2002, 02:51 PM

According to the article, the sea squirt is the seventh animal to be sequenced. Does anyone know if there is some kind of agreed-upon grand plan for the order in which animals will be sequenced, or are there just a number of independent research groups pursuing their own interests and presenting findings as they become available? I would think that there must be some broad consensus as to priorities, given the limited amount of money available, but I don't recall ever reading anything about it.

**Just saw the rat genome thread, which helped answer my question**

[ December 12, 2002: Message edited by: Darwin's Finch ]</p>

lpetrich · 12-12-2002, 03:13 PM

There is no evidence of any absolute master plan; different groups sequence whatever organisms they find interesting, which is nowadays relatively easy for prokaryotes (the large majority of sequenced organisms).

However, the National Human Genome Research Institute does maintain a <a href="http://www.genome.gov/page.cfm?pageID=10002154" target="_blank">list of priority species</a>, and some of these will likely be sequenced as the existing human, mouse, and rat efforts wind down. This list is

Chimp
Dog
Cow
Chicken
Sea Urchin Strongylocentrotus purpuratus
Honeybee
15 species of fungi
Ciliates Oxytricha trifallax and Tetrahymena thermophila

With a lower priority for

Rhesus monkey
Primitive metazoan Trichoplax adhaerens

NHGRI decides on a set of priority organisms every 4 months, taking about 3 months after each proposal deadline. The most recent one was in October, meaning that we can expect the next decisions to be made next month.

lpetrich · 12-12-2002, 03:22 PM

The animal species with reasonably-complete sequences are, according to the article,

Human
Mouse
Pufferfish
Fruit Fly Drosophila melanogaster
Malaria Mosquito Anopheles gambiae
Nematode Caenorhabditis elegans

To which

Rat
Sea Squirt Ciona intestinalis

have just been added

pz · 12-12-2002, 03:28 PM

Quote:

Originally posted by MrDarwin:
<strong>This is pretty exciting news, since sea squirts represent a "transitional form" between invertebrates and vertebrates:

<a href="http://www.washingtonpost.com/wp-dyn/articles/A46388-2002Dec12.html" target="_blank">Scientists Pin Down Sea Squirt Genetics</a></strong>

No way! Ciona is an invertebrate, so it can't be a transitional to a vertebrate.

Besides, if it were transitional, since we have lots of vertebrates living today, why would we have any living sea squirts?

Zadok001 · 12-12-2002, 04:26 PM

It took me a minute to catch that rather brutal sarcasm. *sigh* I feel mentally insufficient.

MrDarwin · 12-13-2002, 06:54 AM

From Sciencedaily.com:

<a href="http://www.sciencedaily.com/releases/2002/12/021213063004.htm" target="_blank">Sea Squirt DNA Sheds Light On Vertebrate Evolution</a>

and the original press release:

<a href="http://www.jgi.doe.gov/News/news_12_12_02.html" target="_blank">Sea Squirt DNA Sheds Light on Vertebrate Evolution</a>

S2Focus · 12-13-2002, 11:19 AM

Quote:

"The sea squirt enjoys a special place in the hearts of biologists because it provides the first evolutionary connection between invertebrates and vertebrates,.....

Actually, the sea squirt enjoys a special place in the hearts of biologists (actually, scientists in general) because its life-cycle so resembles that of a tenured professor. Here's Daniel Dennett's take:

"The juvenile sea squirt wanders through the sea searching for a suitable rock or hunk of coral to cling to and make its home for life. For this task, it has a rudimentary nervous system. When it finds its spot and takes root, it doesn't need its brain anymore so it eats it! (It's rather like getting tenure.)"

[ December 13, 2002: Message edited by: S2Focus ]</p>

lpetrich · 12-14-2002, 07:38 AM

That's cute.

But judging from other examples of disappearing body parts, what likely happens is that many of the growing sea squirt's neurons commit cellular hara-kiri -- Apoptosis or Programmed Cell Death, the subject of this year's Nobel Prize in Medicine and Physiology.

More seriously, the sea-squirt tadpole phrase is much like what an early chordate is expected to look like; it has a notochord and a spinal cord, and evidence of early versions of some vertebrate endocrine glands, like the thyroid gland.

Although it has simple eyespots instead of full-scale eyes, the internal signaling of those eyespots' light-receptor cells works much like those of vertebrates, instead of like those of most invertebrates.

However, its blood oxygen carrier is not hemoglobin, but hemocyanin, which is common in invertebrates.

And while it has an innate immune system, like most of the rest of the animal kingdom, it does not a trace of the jawed-vertebrate adaptive immune system.

12-12-2002, 12:43 PM	#1
MrDarwin Veteran Member Join Date: May 2001 Location: Washington, DC Posts: 4,140	Scientists Pin Down Sea Squirt Genetics This is pretty exciting news, since sea squirts represent a "transitional form" between invertebrates and vertebrates: <a href="http://www.washingtonpost.com/wp-dyn/articles/A46388-2002Dec12.html" target="_blank">Scientists Pin Down Sea Squirt Genetics</a>

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12-12-2002, 02:51 PM	#3
Darwin's Finch Senior Member Join Date: Sep 2001 Location: Gardnerville, NV Posts: 666	According to the article, the sea squirt is the seventh animal to be sequenced. Does anyone know if there is some kind of agreed-upon grand plan for the order in which animals will be sequenced, or are there just a number of independent research groups pursuing their own interests and presenting findings as they become available? I would think that there must be some broad consensus as to priorities, given the limited amount of money available, but I don't recall ever reading anything about it. Just saw the rat genome thread, which helped answer my question [ December 12, 2002: Message edited by: Darwin's Finch ]</p>

12-12-2002, 03:13 PM	#4
lpetrich Contributor Join Date: Jul 2000 Location: Lebanon, OR, USA Posts: 16,829	There is no evidence of any absolute master plan; different groups sequence whatever organisms they find interesting, which is nowadays relatively easy for prokaryotes (the large majority of sequenced organisms). However, the National Human Genome Research Institute does maintain a <a href="http://www.genome.gov/page.cfm?pageID=10002154" target="_blank">list of priority species</a>, and some of these will likely be sequenced as the existing human, mouse, and rat efforts wind down. This list is Chimp Dog Cow Chicken Sea Urchin Strongylocentrotus purpuratus Honeybee 15 species of fungi Ciliates Oxytricha trifallax and Tetrahymena thermophila With a lower priority for Rhesus monkey Primitive metazoan Trichoplax adhaerens NHGRI decides on a set of priority organisms every 4 months, taking about 3 months after each proposal deadline. The most recent one was in October, meaning that we can expect the next decisions to be made next month.

12-12-2002, 03:22 PM	#5
lpetrich Contributor Join Date: Jul 2000 Location: Lebanon, OR, USA Posts: 16,829	The animal species with reasonably-complete sequences are, according to the article, Human Mouse Pufferfish Fruit Fly Drosophila melanogaster Malaria Mosquito Anopheles gambiae Nematode Caenorhabditis elegans To which Rat Sea Squirt Ciona intestinalis have just been added

12-12-2002, 04:26 PM	#7
Zadok001 Veteran Member Join Date: Nov 2002 Location: Two Steps Ahead Posts: 1,124	It took me a minute to catch that rather brutal sarcasm. sigh I feel mentally insufficient.

12-13-2002, 06:54 AM	#8
MrDarwin Veteran Member Join Date: May 2001 Location: Washington, DC Posts: 4,140	From Sciencedaily.com: <a href="http://www.sciencedaily.com/releases/2002/12/021213063004.htm" target="_blank">Sea Squirt DNA Sheds Light On Vertebrate Evolution</a> and the original press release: <a href="http://www.jgi.doe.gov/News/news_12_12_02.html" target="_blank">Sea Squirt DNA Sheds Light on Vertebrate Evolution</a>

12-14-2002, 07:38 AM	#10
lpetrich Contributor Join Date: Jul 2000 Location: Lebanon, OR, USA Posts: 16,829	That's cute. But judging from other examples of disappearing body parts, what likely happens is that many of the growing sea squirt's neurons commit cellular hara-kiri -- Apoptosis or Programmed Cell Death, the subject of this year's Nobel Prize in Medicine and Physiology. More seriously, the sea-squirt tadpole phrase is much like what an early chordate is expected to look like; it has a notochord and a spinal cord, and evidence of early versions of some vertebrate endocrine glands, like the thyroid gland. Although it has simple eyespots instead of full-scale eyes, the internal signaling of those eyespots' light-receptor cells works much like those of vertebrates, instead of like those of most invertebrates. However, its blood oxygen carrier is not hemoglobin, but hemocyanin, which is common in invertebrates. And while it has an innate immune system, like most of the rest of the animal kingdom, it does not a trace of the jawed-vertebrate adaptive immune system.

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