Well, it has been a long time, but I thought it was about time I posted a serious post again.
Segmentation is an interesting development process. It is extremely important for generating a multicellular organism. In us vertebrates it is for instance obvious during somitogenesis. This will for instance lead to these nice segmental objects in your spine better known as vertebrae.
In insects the segmentation is even more obvious. Just look at the outside of one and you will see a distince head segment, thorax segment and abdomen segment. Moreover the extremities of the insect are clearly segmented. Each pair looks different depending on their position on the body axis.
And if you look at annelids, for instance the common earth worm, you see the importance of segmentiation immediately.
Now, the common perception was that this segmentation probably developed independently during evolution in different phyla, because Insects and Vertebrates use different Gene networks to establish segmentation, and they use different methods. For instance in vertebrates the Notch signalling pathway is very important, and they use 'segmentation clock' method.
In drosophila (fruit fly) notch is not used at all, but there is a hierarchical set of genes whose interactions lead to segmentation along the anterior posterior axis.
Last June a group published a paper on the function of Notch during the segmentation of not an insect, but a spider. Clearly spiders and insects are both arthropods and therefore more closely related than for instance spiders and vertebrates, such as the mouse or the zebrafish.
And guess what? The spider segmentation is not only dependent on similar genes in the fruitfly, but it is also dependent on notch signalling. Moreover, the process of segmentation is highly similar to the 'segmentation clock' model of the vertebrates. There is a posterior growth zone in which there is dynamic expression of notch signalling genes which leads to the formation of stripes of notch and delta expression that correspond with segments.
Knocking out notch and delta expression with dsRNAi injection showed severe defects in segmentation, effecting genes that are used also in the segmentation of drosophila.
In conclusion there might be a common origin of segmentation in all phyla, but there have been modifications in some group, leading to quite different systems nowadays.
ref
Stollewerk et al., 'Involvement of Notch and Delta genes in spider segmentation' (2003) Nature vol 423, p 863-865
Segmentation is an interesting development process. It is extremely important for generating a multicellular organism. In us vertebrates it is for instance obvious during somitogenesis. This will for instance lead to these nice segmental objects in your spine better known as vertebrae.
In insects the segmentation is even more obvious. Just look at the outside of one and you will see a distince head segment, thorax segment and abdomen segment. Moreover the extremities of the insect are clearly segmented. Each pair looks different depending on their position on the body axis.
And if you look at annelids, for instance the common earth worm, you see the importance of segmentiation immediately.
Now, the common perception was that this segmentation probably developed independently during evolution in different phyla, because Insects and Vertebrates use different Gene networks to establish segmentation, and they use different methods. For instance in vertebrates the Notch signalling pathway is very important, and they use 'segmentation clock' method.
In drosophila (fruit fly) notch is not used at all, but there is a hierarchical set of genes whose interactions lead to segmentation along the anterior posterior axis.
Last June a group published a paper on the function of Notch during the segmentation of not an insect, but a spider. Clearly spiders and insects are both arthropods and therefore more closely related than for instance spiders and vertebrates, such as the mouse or the zebrafish.
And guess what? The spider segmentation is not only dependent on similar genes in the fruitfly, but it is also dependent on notch signalling. Moreover, the process of segmentation is highly similar to the 'segmentation clock' model of the vertebrates. There is a posterior growth zone in which there is dynamic expression of notch signalling genes which leads to the formation of stripes of notch and delta expression that correspond with segments.
Knocking out notch and delta expression with dsRNAi injection showed severe defects in segmentation, effecting genes that are used also in the segmentation of drosophila.
In conclusion there might be a common origin of segmentation in all phyla, but there have been modifications in some group, leading to quite different systems nowadays.
ref
Stollewerk et al., 'Involvement of Notch and Delta genes in spider segmentation' (2003) Nature vol 423, p 863-865