Ahmed, Reda

I am PhD student working on chitinases in Drosophila in the Cuticle Biology Group.



Insects inhabit a large diversity of ecosystems, have very different life styles and are very speciose. One hypothesis to explain this evolutionary success is related to the various forms the insect cuticle can take. The cuticle is an armour and anti-desiccation coat composed of the polysaccharide chitin, proteins, and lipids that interact together and are distributed in distinct horizontal layers. Chitin, a polymer of N-acetyl-b-D-glucosamine, is the major component of insect’s procuticle and it functions as a scaffolding material supporting the cuticles of the epidermis and the tracheae.

During development, insects run through several moulting cycles (visualised in Fig. 1). During these cycles, they produce chitinolytic enzymes for degradation of the old cuticle giving the space for the newly synthesized cuticle. Chitinolytic enzymes include chitinases {poly[1,4-(Nacetyl-b-D-glucosaminide)] glycanohydrolase; EC} and b-N-acetylglucosaminidases (b-N-acetyl-b-Dhexosaminide N-acetylhexosaminohydrolase; EC Both degrade chitin to low molecular weight, soluble and insoluble oligosaccharides.

Fig. 1. Larval stages L1, L2, and L3 in D. melanogaster. The enlarged anterior parts of each larvae show how different the anterior hooks look like after each moult.

Moreover, chitin modification during cuticle formation requires the activity of chitin deacetylases. Upon full deacetylation, chitin is modified into a new form called chitosan. Chitosan is known as an important biomaterial, which has a lot of beneficial applicability. In the insect cuticle, however, chitin is only partially converted to chitosan. This raises the question of whether chitinases have the ability to degrade the so called ”partially deacetylated form of chitin and/or semi chitosan” during moulting or not.

In my project, I am interested in variou sorganisational levels of chitin degradation:

1. Chts expression profiling in melanogaster (Fig. 2)

Fig. 2. Expression profile of one of the Chitinases in different developmental stages of D. melanogaster. eP, mP and lP means early, middle and late pupal stage.




2. Distribution of Chts over the fly body (Chts-GFP flies) – the cellular level

3. Specificity of Chts in development and moulting – the morphological level)

4. Hydrolytic activities of Chts on chitin and chitosan – the biochemical level)

Taken together, this project aims at providing molecular, genetic and biochemical background for further research in chitin and chitosan degradation both in medical and agricultural sciences.