Abstract
Juvenile hormone (JH) is a unique sesquiterpenoid hormone which regulates both insect metamorphosis and insect reproduction. It also may be utilized by some insects to mediate polyphenisms and other life history events that are environmentally regulated. This article details the history of the research on this versatile hormone that began with studies by V. B. Wigglesworth on the “kissing bug” Rhodnius prolixus in 1934, through the discovery of a natural source of JH in the abdomen of male Hyalophora cecropia moths by C. M. Williams that allowed its isolation (“golden oil”) and identification, to the recent research on its receptor, termed Methoprene-tolerant (Met). Our present knowledge of cellular actions of JH in metamorphosis springs primarily from studies on Rhodnius and the tobacco hornworm Manduca sexta, with recent studies on the flour beetle Tribolium castaneum, the silkworm Bombyx mori, and the fruit fly Drosophila melanogaster contributing to the molecular understanding of these actions. Many questions still need to be resolved including the molecular basis of competence to metamorphose, differential tissue responses to JH, and the interaction of nutrition and other environmental signals regulating JH synthesis and degradation.
Highlights
Serendipity is often the key to novel and fundamental discoveries
All these findings showed that endocrine organ extracts contained substances that when injected into the blood could act on particular target organ(s); these substances were named “hormones” (Starling, 1905)
Stefan Kopecworking in Cracow, Poland between 1908 and 1912 was the first to show that in insects, unlike in birds and mammals, the secondary sex characteristics were not dependent on gonadal hormones (Cymborowski, 1981). He went on to demonstrate in the gypsy moth, Lymantria dispar, that the brain secreted a hormone that was necessary for metamorphosis (Kopec, 1917, 1922)
Summary
Serendipity is often the key to novel and fundamental discoveries. Physiologists early on are taught the August Krogh Principle: “For a large number of problems there will be some animal of choice or a few such animals on which it can be most conveniently studied” (Krogh, 1929). Experimental endocrinology began with Berthold who in 1849 transplanted testes into castrated roosters and showed that they caused the return of the normal secondary sex characteristics (enlarged combs and wattles) (Soma, 2006). The first work on hormonal control of metamorphosis was that of Gudernatsch (1912) who found that extracts of mammalian thyroid were sufficient to cause precocious metamorphosis of frog tadpoles, indicating a universality of function of these extracts. All these findings showed that endocrine organ extracts contained substances that when injected into the blood could act on particular target organ(s); these substances were named “hormones” (Starling, 1905)
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