Bursicon (from the Greekbursikos, pertaining to tanning) is an insecthormone which mediates tanning in the cuticle of adult flies.
Structure
The molecular structure of the hormone has been characterized rather recently. Bursicon is a 30 kDa neurohormoneheterodimericprotein which is encoded by CG13419 gene and made of two cysteine knot subunits, Burs-α and Burs-β.
Fraenkel G, Hsiao C, Seligman M (January 1966). “Properties of bursicon: an insect protein hormone that controls cuticular tanning”. Science. 151 (3706): 91–3. doi:10.1126/science.151.3706.91. PMID5908970. S2CID39062433.
Function
Bursicon plays a very important role in insect wing expansion during the last step of metamorphosis: maturation of the wing. At this time, the newly emerged adult removes dead cells of larval tissues. In Drosophila and Lucilia cuprina fly, the epidermis of wing is detached by extensive cell death apoptosis, at the time of wing spreading.
The cells that undergo death are removed from the wing cuticle and are absorbed into the thoracic cavity through wing veins. Subsequent wing maturation is disrupted if the process of cell death is inhibited or delayed somehow.
Bursicon is released just after eclosion and induces epidermis cell death. At the same time it hastens the tanning reaction, and hardens the newly expanded cuticle of the wing.
Bursicon is found in different insects and considered to be unspecific. It is produced by median neurosecretory cells in the brain, circulates in blood and stored in corpora cardiaca.
Firstly, mutants of Drosophila melanogaster that lack bursicon gene can not spread their wings after eclosion. Secondly, the elongated abdomen shape of a newly eclosed fly remains for a much longer period of time. In addition, the abdomen of a fly is less melanized.
The name “bursicon” is derived from the Latin word “bursa,” which means “purse” or “sac.” This name was chosen because bursicon is involved in the process of cuticle tanning and hardening, which can be thought of as “closing” or “sealing” the new exoskeleton after an insect molts. The hormone essentially helps to “seal the deal” on the new cuticle, ensuring it hardens properly and provides the necessary protection and structure for the insect.
While humans don’t have wings or an exoskeleton, there are some parallels in the way our bodies handle structural integrity and repair. Here are a few human processes that share similarities with the functions of bursicon in insects:
Human Parallels:
Collagen Production: Collagen is a protein that provides structure and strength to various tissues, including skin, bones, and tendons. The process of collagen synthesis and cross-linking is somewhat analogous to the cuticle tanning and hardening in insects.
Wound Healing: The human body’s wound healing process involves several stages, including clot formation, tissue regeneration, and remodeling. This process ensures that the skin and other tissues regain their integrity and strength after injury, similar to how bursicon helps harden and stabilize the insect cuticle after molting.
Bone Remodeling: Osteoblasts and osteoclasts are cells involved in the continuous process of bone formation and resorption. This dynamic remodeling ensures that bones maintain their strength and adapt to stress, akin to how bursicon ensures the proper hardening of the insect exoskeleton.
Hormonal Regulation:
Growth Factors: Various growth factors, such as transforming growth factor-beta (TGF-β) and fibroblast growth factor (FGF), play crucial roles in tissue repair and regeneration. These factors help coordinate the complex processes of cell proliferation, differentiation, and extracellular matrix production.
While these human processes are not direct equivalents to bursicon’s role in insects, they highlight the importance of structural integrity and repair mechanisms in both humans and insects.
The term “bursa” has given rise to several related biological terms, primarily associated with structures and conditions involving these fluid-filled sacs. Here are some key terms:
