Segmentation (biology)

This article focuses on the segmentation of animal body plans, specifically using the examples of the taxa Arthropoda, Chordata, and Annelida.

While all three have a generally segmented body plan and use a growth zone, they use different mechanisms for generating this patterning.

Many taxa (for example the molluscs) have some form of serial repetition in their units but are not conventionally thought of as segmented.

[1] Segmentation in animals typically falls into three types, characteristic of different arthropods, vertebrates, and annelids.

Arthropods such as the fruit fly form segments from a field of equivalent cells based on transcription factor gradients.

[3] To properly segment the Drosophila embryo, the anterior-posterior axis is defined by maternally supplied transcripts giving rise to gradients of these proteins.

[2] Segmentation appears to be regulated by the gene Hedgehog, suggesting its common evolutionary origin in the ancestor of arthropods and annelids.

[1] Although perhaps not as well understood as Drosophila, the embryological process of segmentation has been studied in many vertebrate groups, such as fish (Zebrafish, Medaka), reptiles (Corn Snake), birds (Chicken), and mammals (Mouse).

The "wavefront" is where clock oscillations arrest, initiating gene expression that leads to the patterning of somite boundaries.

[7][8] The interaction of other signaling molecules, such as myogenic regulatory factors, with this gradient promotes the development of other structures, such as muscles, across the basic segments.