3)Post-transcriptional regulation

In eukaryotes, where export of RNA is required before translation is possible, nuclear export is thought to provide additional control over gene expression. All transport in and out of the nucleus is via the nuclear pore and transport is controlled by a wide range of importin and exportin proteins.

before translation, mRNA in eukariotyc cells should also be processed.

• Processing is a complex of different RNA modifications, such as splicing, capping and polyadenilation. Splicing is an intrinsic process of introne degradation. Intrones are non-coding sequences of DNA, whereas exons are coding ones. There are a lot of intrones and exons in one mRNA molecule, and a different proteins can be synthesized, depending on what intrones were degradated.

• Capping and polyadenilation stabilise an RNA molecule. In eukaryotic cells mRNA has to travel significant distances form nucleus, and should survive long enough to be translated. Without the 5' cap and poly-adenylated tail it will soon be destroyed by special factors.

17 Cellular Mechanisms of Development

1) Organisms in all three multicellular kingdoms—fungi,

plants, and animals—realize cell specialization by orchestrating

gene expression. That is, different cells express different

genes at different times. To understand development, we need to focus on how cells determine which genes to activate, and when.

Despite the many differences in developmental

paths of multicellular organisms, it is becoming

clear that most of them develop according

to molecular mechanisms that are very similar.

These mechanisms

evolved very early in the history of multicellular life. There are four important mechanisms we will focus on:

2) Cell movement & induction

Cell movement:

Cells migrate during many stages in animal development,

sometimes traveling great distances before reaching the site

where they are destined to develop. Even one tissue can contain cells, which originated from different parts of embryo. Two main ways of cell movement are known nowadays:

a) The first way for cell to move is to pull itself along using special cell adhesion molecules - cadherins. Two cadherins of the same type type can form a link between neighbour cells. Different set of cadherins on the cell surface determines the localization of this cell in mature organism.

b) Some cells use another type of CAMs - integrines. Those molecules also span plasma membrane and bind the cell to infracellular matrix: collagen, elastin, fibronectin and etc. Then the cell migrates along the ways, created with this matrix.

Induction: Induction takes place, when a cell switches from one path to another as a result of interaction

with an adjacent cell

For example, cells on a border between animal and vegetal pole blastomeres, develop as a mesoderm cells, but if we will separate animal and vegetal pole cells, none of them will develop features of mesoderm.

But how do cells induce developmental changes in neraby cells?

There are particular groups of cells called organizers, which

produce diffusible signal molecules that convey positional

information to other cells. The closer a particular cell is to an organizer, the higher

the concentration of the signal molecule, or morphogen, it

experiences. Morphogens alter transcription in developing cells and set a way of their development