Cell Specialization

[Xittenn]

If most/all of the organelles between cells of a species are the same, what then determines how a cell specializes? I know that the end effect is to be able to excrete various proteins, but what signal pathways ensure that a cell is secreting the proteins relevant to its specialization? How are stem/meristem cells differentiated to have a specialization, and what do stem/meristem cells have that specialized cells do not?

[immortal]

If most/all of the organelles between cells of a species are the same, what then determines how a cell specializes?

 

The genes that are always expressed in all the cells of the body are called as Housekeeping genes and they are necessary for the cell to perform the basic functions to sustain itself like ribosomes, Krebs cycle enzymes, oxidative phosphorylation enzymes, cytochrome, ATP synthase etc.

 

There are other genes which are expressed only in some cells like hemoglobin in erythrocytes, actin and myosin in muscle fibres etc. It is determined by gene regulation.

 

I know that the end effect is to be able to excrete various proteins, but what signal pathways ensure that a cell is secreting the proteins relevant to its specialization?

 

There are cytoplasm determinants(co-factors and repressors) which induce stable permanent changes in cell types by controlled gene expression. The cells undergo programmed cell death called as Apoptosis to maintain the structure and number of cells that is required to form tissues and organs. The Homeo box genes are expressed during differentiation of body parts.

 

Also there are small interference RNA's which control gene regulation.

 

How are stem/meristem cells differentiated to have a specialization, and what do stem/meristem cells have that specialized cells do not?

 

Meristem cells have a capacity called as cellular totipotency that they can didifferentiate again into a form of callus and regenerate a whole plant from a part of a plant which is highly differentiated.

 

Redifferentiation can be induced by cytokinins, auxins, gibberellins and other sugar molecules to differentiate the vascular tissues of xylem and phloem and also the differentiation of buds and other organs.

[Xittenn]

Hey thanks! : D

[CharonY]

Cell differentiation is a complex topic, but the key as already mentioned, are regulatory responses, as well as gradients of signal molecules. Cells communicate with each other and differentiation is guided by gradients of certain signals that allow the cells to coordinate and form distinct tissues, for instance. You may want to read up on morphogens.

[Xittenn]

Cell differentiation is a complex topic, but the key as already mentioned, are regulatory responses, as well as gradients of signal molecules. Cells communicate with each other and differentiation is guided by gradients of certain signals that allow the cells to coordinate and form distinct tissues, for instance. You may want to read up on morphogens.

 

Thank you sir, will do!

[nealsdomain]

I am pretty sure we don't fully understand the mechanisms of cellular differentiation. A lot of computer scientists are researching this in a field called Amorphous Computing. While it is in basic stages, amorphous computing believes heavily cells in gathering signals from neighbors in order to direct their own behavior. Starting from the single cellular zygote to a multicellular colony of identical cells in the blastula undergoing cleavage, they are all getting signals from their neighbors to see "what everyone else is doing." As immortal discussed, the signalling that I am talking about is actually genetic regulation using molecules such as the autoinducers that bacteria use for quorum sensing.

[immortal]

It would be not right to compare the signalling mechanisms of quorum sensing used in bio-films which constitutes different prokaryotic single cellular organisms and organize themselves to form colonies with the signalling mechanisms used in multicellular tissues.

 

In multicellular organisms cell-to-cell interactions takes place through gap junctions whose basic unit is called as connexons or pores which aid in regulated transport of ions, micro-molecules and metabolites and the macromolecules stay with in the cells which makes those cells tissue specific or defines what a tissue is.

 

There are also Cell adhesion proteins and carbohydrate complexes which aid in cell adhesion and all this help in the differentiation of the embryo from its initial stages to the final stage of a fully developed organism.

 

So basically Cellular interactions and Cell adhesions are the key to embryonic development.

 

Biofilms and quorum sensing backgrounder

[CharonY]

My bad, carry on. missed a post.

It is true that on the physical level we do not know all of the details (or even of all the players). There are similaritities to quorum sensing in as much as signal gradients trigger specific cellular responses. Obviously the stratification within biofilm is much looser than in actual tissues. Direct cell-cell interactions play roles in both systems, however. Obviously, in most cases direct neighboring communication is insufficient as it does not integrate enough data to create a larger tissue or form tissue boundaries (though boundary conditions can be conveniently assumed in models).

Edited February 17, 2012 by CharonY

[nealsdomain]

Alright well, I stand corrected