Cell specification, determination and morphogenesis

10 important questions on Cell specification, determination and morphogenesis

Explain the term 'cell specification'

During early development, an embryonic cell is set on a path of molecular changes. It becomes comitted to certain fates, and passes through the following stages: specification --> determination --> differentiation.
Cell specification is a term for the phenomenon of the embryonic cell being capable to differentiate autonomously when it is placed in a neutral environment. This means that there is something instinsic to the embryonal cell that makes sure it can specify.

What are the (3) modes of cell specification?

Automous, conditional and syncytial.

Explain the term 'autonomous specification (mosaic)'.

The blastomere inherits morphogenic determinants which will influence the cell's development. An isolated blastomere will produce the same cells what it would have made if it were still part of the embryo. Moreover, the embryo from which that cell is taken will lack only those cells that would have been produced by the missing blastomere.
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Explain the term 'conditional specification'.

The fate of a cell depends upon the conditions in which the cell finds itself. If such a blastomere is removed from an early embryo, the remaining embryo cells alter their fate so that the roles of the missing cells can be taken over. The isolated blastomere can also give rise to a wide variety of cells. Cells are able to be transplanted to other blastomeres and adapt to the environment, e.g dorsal cells become ventral when transplanted to host ventral regions.

Explain the term syncytial specification

Interaction do not only uccur between cells, but also between parts of one cell. This is mostly occuring in insects, like Drosophila.

What does the transplantation experiment of Spemann and Mangold show?

That dorsal lip cells (the organizer), the precursor cells to the notochord, are able to organise the host cells in a way that they can form a new body axis.

What is the difference between determination and specification?

In specification, the cells are predestined to develop in a certain direction, but are still susceptible to environmental factors. In determination the differentiation of the cells is terminally defined.

What is a fate map?

A map of an embryo showing the areas that are destined to develop into specific adult tissues and organs. In other words, it is a map of the developmental fate of a zygote or early embryo showing the adult organs that will develop from material at a given position on the zygote or early embryo.

In which ways can positions of cells change?

Convergence: cells go towards each other
Extension: cells move away from each other (and extend)
Intercalation: cells 'mix' with each other (radial and medio-lateral)

Which cell adhesion molecules are there and what do they attach?

Cadherines: calcium dependent cell-cell adhesion
CAMs: calcium independent cell-cell adhesion
Integrins: cell-ECM adhesion
Extracellular matrix molecules (collagen, fibronectin, laminin & tenascin): bind to integrins.

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