Cell size is proportional to ploidy

[Monique]

It always amazed my how a mice is similar to a human, but all the systems are in miniature. Why doesn't a mouse grow as big as a human? What is the mechanism regulating the organ sized, a certain number of cells? A certain size? It actually turns out that somehow the physical size is known, not the number of cells. When one removes a portion of the liver, new cells will grow and restore the structure to its original size.

Now, I read about this salamander which exist in different ploidies. A ploidy means the number of copies of the genome that the cell carries, humans are diploid: of every gene we have two copies.

The salamander exist in haploid (11 chromosomes), diploid (22 chromosomes), and pentaploid (55 chromosomes) variations. Cell size in these salamanders increases with the ploidy!

But all these salamanders are all the same physical size, even though the cells of the latter are much larger than the former!

The haploid needs 5, the diploid 3 and the pentapoid 1 cell in order to make a kidney duct (circomference).

Apparently the size of an organism or organ is not controlled simply by counting cell divisions or cell numbers; total cell mass must somehow be regulated :)

 

[iansmith]

The only example where cell size is proportional to ploidy is in fruit producing plant. For example, wild strawberries are diploid (2n) and domesticated strain can be up to 10n. Wild strawberries produce a very little fruit and the domesticated strain can produce giangantic fruit. It been done in many plants to increase the fruit size.

Animals are a bit different but I think cell ploidy migth only affect organism or organs which have a set number of cells and it does not change.

 

[Monique]

Originally posted by iansmith
Animals are a bit different but I think cell ploidy migth only affect organism or organs which have a set number of cells and it does not change.

The example I gave is of an salamander.. how large are butterfly cells compared to other organisms? I seem to remember that they have an amazing amount of chromosomes..

I am not sure what you are saying, so if the ploidy of plants is artificially increases, the mass of the organism increases?

What I understood from the textbook example (the polyploidic salamander) is that the cell size might differ, but that the mass of the organism will remain the same. Concluding that organ size is not measured in the amount of cell, rather in the mass.

 

[iansmith]

Originally posted by Monique
The example I gave is of an salamander.. how large are butterfly cells compared to other organisms? I seem to remember that they have an amazing amount of chromosomes..?

# of chromosome vs. # base pair migth explain the difference. The butterfly migth have a smaller genome than salamander. The size of the cell of a given species is affected by the # of bp if I remember correctly.

Originally posted by Monique
I am not sure what you are saying, so if the ploidy of plants is artificially increases, the mass of the organism increases?

So crop have been breed to have an increase in ploidy and this artificial increase in ploidy results in an increase in the size of the fruit (at least) but I don't know about the the plant. The best examples are the strawberries, blueberries and other berries.

Originally posted by Monique
What I understood from the textbook example (the polyploidic salamander) is that the cell size might differ, but that the mass of the organism will remain the same. Concluding that organ size is not measured in the amount of cell, rather in the mass.

I cited an example where ploidy is increase artificial. I would have to look at my genetics book to find natural example of increase in ploidy due to mutation. Organ size is more or less regulated by mass rather than by cell number but sometimes the system goes a wired. I remember seen disease where the liver would always grow. These disease could offer explanation.

Also rotifer have a given # of cell at any times, increase ploidy could also give info about # of cell vs. total mass in respect to ploidy.

 

[Monique]

The only disease I know that increases liver size are lysosomal storage diseases.. these have a metabolic basis. There might be other ones though.

And you are talking about plants who evolved independently from animals into multicellular organisms, so I think we should leave them out.

The interesting thing about the salamander story was that all the structures were exactly the same size, with the number of cells adjusted to fit the dimensions.

So in animals cell size is proportional to ploidy, where the size of an organism is adjusted to spatial dimensions and not cell count. Agree?

 

[iansmith]

Originally posted by Monique
The only disease I know that increases liver size are lysosomal storage diseases.. these have a metabolic basis. There might be other ones though.

I migth be mistaken but cancer cell are not regulated by mass size. Could we study cancer cell and normal cell and see what is the diference in term of regulation of organ size/mass

Originally posted by Monique
And you are talking about plants who evolved independently from animals into multicellular organisms, so I think we should leave them out.

Agree but plant migth have elvolve parrallell mechanism that could be interresting to see if they could apply to animal.

Originally posted by Monique
So in animals cell size is proportional to ploidy, where the size of an organism is adjusted to spatial dimensions and not cell count. Agree? [/B]

Agree but cell count is important for C. elegant and Rotifers. What can we learn from them.

 

[Monique]

Originally posted by iansmith
Agree but cell count is important for C. elegant and Rotifers. What can we learn from them.

Is it? When you'd take away a few cells from C. elegans, will they regrow? If they do, it is not cell count that matters.

And what is Rotifers? A plant?

 

[iansmith]

Originally posted by Monique
Is it? When you'd take away a few cells from C. elegans, will they regrow? If they do, it is not cell count that matters.

This article (http://www.pubmedcentral.gov/articlerender.fcgi?tool=pmcentrez&rendertype=abstract&artid=33276 ) states that organ in C. elegans always have the same number of cell. What I was asking is if we change the ploidy in C. elegans will it affect the organ size and is there any difference in poidy in similar nematodes.

Originally posted by Monique
And what is Rotifers

It is a microscopic animals. It is in the same phylum as nematodes.

 

[azevedo]

Here are a couple of comments on the latest messages:

1. A zoological correction. Rotifers and nematodes are actually the names of different phyla. Although they look superficially similar, recent phylogenetic studies suggest that they are distant relatives in the animal kingdom: the phylum Rotifera are now thought to cluster close to the phyla Mollusca (such as squid and snails) and Annelida (such as earthworms), which all form a larger group known as the Lophotrochozoa, whereas the Nematoda are believed to group closer to the Arthropoda (such as flies, spiders and lobsters) and other molting animals, forming the larger group Ecdysozoa.

2. Your questions on the effects of polyploidy in C. elegans and other nematodes have been answered in detail in this paper by Flemming et al. (2000), and references therein. Briefly there are two main points to the story. First, tetraploid C. elegans are indeed larger by volume than wildtype worms, but not twice as large, presumably because other mechanisms regulate growth, or because tetraploidy is detrimental in other ways. Second, the size of nematodes in species closely related to C. elegans is largely determined by the amount of somatic polyploidization in the epidermis (and possibly the intestine): species with higher ploidy are larger, than the ones with lower ploidy.

 

[iansmith]

Originally posted by azevedo
1. A zoological correction. Rotifers and nematodes are actually the names of different phyla. Although they look superficially similar, recent phylogenetic studies suggest that they are distant relatives in the animal kingdom: the phylum Rotifera are now thought to cluster close to the phyla Mollusca (such as squid and snails) and Annelida (such as earthworms), which all form a larger group known as the Lophotrochozoa, whereas the Nematoda are believed to group closer to the Arthropoda (such as flies, spiders and lobsters) and other molting animals, forming the larger group Ecdysozoa.

That were my source of info. http://www.ncbi.nlm.nih.gov:80/Taxonomy/Browser/wwwtax.cgi?id=33217

You seem to be more up to date in term of the classification.

 

[azevedo]

Originally posted by iansmith
That were my source of info. http://www.ncbi.nlm.nih.gov:80/Taxonomy/Browser/wwwtax.cgi?id=33217

You seem to be more up to date in term of the classification.

I don't wish to be overly pedantic but it seems that you misread the link you cite. If you look carefully at the indentation you'll see that it correctly lists Nematoda and Rotifera as separate phyla, along with the more obscure Nematomorpha, Kinorhyncha, Gastrotricha, etc.

But you're correct that this is an old-fashioned classification. It used to be thought that there was a relatively basal group of animals (Metazoa) with a pseudocoelom that were related to each other (including the N and R we've been talking about). However, it is now believed that these Pseudocoelomata are polyphyletic (have multiple independent origins, not a single ancestor) and group with other Protostomes (which in that classification appeared as a subgroup of the Coelomata, one group up).

 

[iansmith]

Originally posted by azevedo
I don't wish to be overly pedantic but it seems that you misread the link you cite. If you look carefully at the indentation you'll see that it correctly lists Nematoda and Rotifera as separate phyla, along with the more obscure Nematomorpha, Kinorhyncha, Gastrotricha, etc.

I did not misread the link. I checked and Pseudocoelomata was labeled as phylum and Nematoda and Rotifera as classes. But Pseudocoelomata has been labeled as a section, a subkingdom and a grade and Nematoda and Rotifera were labeled as phylum.

 

[azevedo]

Originally posted by iansmith
I did not misread the link. I checked and Pseudocoelomata was labeled as phylum and Nematoda and Rotifera as classes. But Pseudocoelomata has been labeled as a section, a subkingdom and a grade and Nematoda and Rotifera were labeled as phylum.

It just shows that you shouldn't believe everything you read in the internet...

(And that those of us who endured descriptive zoology, phylum by phylum, class by class [zz)], need to inflict our pain on others.)

 

[Jikx]

Would doubling the amount of chromosomes inside a cell, double the rate of transcription of proteins? (assuming there are enough resources, and no regulatory inhibitors)

 

[nigeld]

A couple of references:

The original work showing that cell size relates to ploidyness is

Frankhauser, G. (1945). "The effects of changes in chromosome number on amphibian development." Quart. Rev. Biol 20: 20-78.

There has been a recent review covering this general topic, which is on the web

http://dev.biologists.org/cgi/reprint/127/14/2977.pdf

This gives some examples where cell size is not related to ploidyness. Nevertheless, I happen to think that there is something in the ploidyness relationship, but there are clearly other factors as well.