Prothoracic Gland or PTC
Prothoracic gland (PTC) or moulting gland and ecdysone or moulting hormone
The 3rd endocrine gland-prothoracic gland- is an irregular branching mass of glandular cells situated in the prothorax (segment of the thorax which bears the anterior most of its three pairs of legs), in close association along with the tracheal lubes and secretes the hormone ecdysone that has been isolated and crystallized in pure form from Calliphora and from pupa of a silkworm. It is a unique water soluble steroid and is associated closely to cholesterol. Recent studies though show that all an ecdysone is converted into P ecdysone (ecdysterone) after liberation into the haemolymph and that ecdysterone is the active moulting hormone.
Ecdysterone exerts its effect directly on those cells concerned in growth and moulting; it activates them and stimulates them to renew protein synthesis. It is believed that it acts directly on those loci in the chromosomes that are concerned with growth. It induces characteristic puffing in the giant polytene chromosomes of Diptera. These puffs are referred to be the sites for the formation of the messenger R N A required for protein synthesis.