Abstract
Proper cell-cell adhesion and communication are essential during development. Both are heavily maintained and regulated by the content present in the extracellular matrix (ECM), which composes the tough exoskeleton called the cuticle. An enzyme called Chitin synthase (CS) provides the exoskeleton with much of its strength and stability through the production of chitin. Chitin, a polymer of N-acetyl-ß-D-glucosamine, is an important element in the exoskeleton of invertebrates and functions much like cellulose in plants and keratin in vertebrates, that is, to provide hardness, strength, and protection against the external environment. The underlying component for both chitin and cuticle formation is CS, which is found across several different species. It is now known that nearly 5-6 different copies of CS in yeast and fungi have been condensed into only two copies in insects. During insect development, one of the two copies is involved in formation of the gut lining while the other is involved in epidermal tissue development, helping to produce the tracheal lining as well as the exoskeleton. The gene that encodes for the chitin synthase involved in the epidermal tissue in D. melanogaster is called krotzkof verkehrt (kkv); we are specifically interested in its involvement in the formation of the exoskeleton. kkv is an important gene during development as it is involved in production of chitin by CS, which is then used to synthesize the cuticle found in the ECM. Mutant kkv results in detachment of the cuticle from the apical end of the cellular body, which then dilates and results in a lethal, curved, short embryo with a scrambled head that is unable to hatch. Not only does kkv need to function properly but CS must also be localized to the appropriate region in order to synthesize chitin. There are currently two hypotheses as to how that may occur: (1) CS rests on the apical membrane, and secrets chitin into the ECM, which is then guided to the proper location, and a cuticle is formed or (2) CS is carried around in vesicles termed chitosomes, which localize kkv to the right region while chitin synthesis is initiated inside. Upon proper localization, chitin is finally released. Recent discoveries in CRISPR/Cas9 have been used to facilitate understanding of this predicament.
