Cytoplasmic determinants are special molecules which play a very important role during
oocyte maturation
Oogenesis, ovogenesis, or oögenesis is the differentiation of the ovum (egg cell) into a cell competent to further develop when fertilized. It is developed from the primary oocyte by maturation. Oogenesis is initiated in the embryonic stage.
O ...
, in the female's
ovary
The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. ...
. During this period of time, some regions of the
cytoplasm accumulate some of these cytoplasmic determinants, whose distribution is thus very heterogenic. They play a major role in the development of the embryo's organs. Each type of cell is determined by a particular determinant or group of determinants. Thus, all the organs of the future embryo are distributed and operating well thanks to the right position of the cytoplasmic determinants. The action of the determinants on the
blastomeres is one of the most important ones. During the
segmentation, cytoplasmic determinants are distributed among the
blastomeres, at different times depending on the species and on the type of determinant. Therefore, the daughter cells resulting from the first divisions are totipotent : they can, independently, lead to a complete individual. That is not possible after the cytoplasmic determinants have been distributed in the differentiated blastomeres.
Mosaic development
During the mosaic development, the future embryo contains all the distinct cytoplasmic determinants that are distributed in distinct cells. Regions of the organism differentiate very quickly if each cell contains specific cytoplasmic determinants since the first divisions : then the cell divides to give all the other cell of its type, and the same process happens in all types of cells in the organism.
As a result, in the case of the mosaic development, cell
totipotence disappears very quickly during
segmentation. Indeed, each new created cell determines a new region of the future organism, and it is independent from the other ones : thus development is independent from interaction between cells. It is most of all known in certain animals as nematodes ''
C. elegans
''Caenorhabditis elegans'' () is a free-living transparent nematode about 1 mm in length that lives in temperate soil environments. It is the type species of its genus. The name is a blend of the Greek ''caeno-'' (recent), ''rhabditis'' ( ...
'', or
ascidians (marine animals).
Regulation development
Other animals show regulation development; their cells show totipotence for a longer time. In these animals, cytoplasmic determinants are more rapidly distributed between newly created cells.
are an example of animals that undergo regulation development.
Presumptive territories map
The
zygote already contains the future organization of the embryo, through cytoplasmic determinants distribution. Presumptive Territories Maps could be established simply by coloring particular regions of the zygote's
cytoplasm.
References
{{reflist
Biology website, embryogenesis part : http://www.botanic06.com/site/EvolVie/physio/embryo5.htm
Cell biology