Title Author Date

Substitution of Argument Musgrave, Ian Apr 24, 2005

[continued]

Neither are challenges to evolution, both can be assembled by the known
mechanisms of evolution. Adding a simple protein "globbing" system to a
haemocyte patch is well with the capabilities of evolution, this can then
be elaborated on later by gene duplication and so on.

>The jump from simple Chordata with 0 genes of BCS to fishes with 28 genes
within alleged
>50 millions years, while being practically intact within half a billion
succeding years is not >explainable with "shuffle and test" hypothesis.

Amphioxus does have at least a thrombin. Ascidians don't have clotting
genes, but they DO have some complement genes (several of which are
trypsin-derived proteases), and the closest relative of the clotting system
is, interestingly enough, the proteases of the complement system (the MASPS
especially). The complement system is involved in immobilizing and lysing
invading microorganisms. This is relevant because in invertebrates with a
clotting system, they have a single enzyme, coagulase, which converts
coagulin to an insoluble form which tangles up the haemocytes. Coagulin
also is used to immobilise bacteria as part of the host defense. Fibrin is
also used to immobilise invading bacteria, and thrombin feeds into the
complement system, helping to activate complement C3.

While thrombin can activate the complement system, MASPS on the other hand
cleave fibrinogen to fibrin and activate Factor XIII, as well as being
inhibited by some of the thrombin inhibitors. Furthermore MASP binds to
(but does not cleave) a fibrinogen-like peptide in the Ascidian complement
system. It requires no stretch of the imagination to see how duplication of
the MASP arm of the simple ascidian complement system could result in a
primitive haemocyte globing system (as is seen in arthropod coagulin
systems) which is then refined by selection and elaborated by repeated
rounds of gene duplication, given that most of the clotting system is
basically duplicates of itself (there were at least two who genome
duplication evens between the protochordates and jawed vertebrates).

All this is quite simple, and given that gene duplication occurs rapidly,
could easily be accomplished in under 50 million years.

>Any system has some sort of irreducible complexity. It infers from the
very notion of a
>system. The ado about IC means that reductionists turn blind eyes to a
problem. I can see
>either some kind of saltation or a creation to yield such intricate
systems like hemostasis.

Take a closer look; most of the intricacy comes from repeated rounds of
duplication.

>Talking about amphioxis' clotting as a ancestor of the modern BCS and
descending of platelets from haemocyte

[continued]

Related Articles: Clotted rot for rotten clots

Title Author Date

Substitution of Argument Musgrave, Ian Apr 24, 2005

This sentence is unfinished. But from what we know of ascidian and
amphioxus clotting, as well of the haemocyte-only and haemocyte/coagulin
systems of simple and advanced non-chordate invertebrates, the sequence of
events suggested is plausible. Especially with the functional and
structural homology of thrombin and MASP, and thrombin/fibrinogen playing
dual and complementary roles in the complement and clotting systems. I
previously used the example of the calcium activated trypsin in amphioxus
as a model for the start of a simple clotting system (and thrombin is also
calcium activated). The MASP system already exists in ascidians, and can
easily be modified to provide a protoglobing system for amphioxus, which
can be elaborated in agnathans until we have the complete system in jawed
vertebrates (see especially the references in my original post which go
into some detail about how this may be accomplished).

Cheers! Ian

Related Articles: Clotted rot for rotten clots