The juvenile hormones: historical facts and speculations on future research directions.

Publisher Summary
This chapter briefly discusses hormonal control of diapause. Diapause is an arrest in development accompanied by a major shutdown in metabolic activity. The evolution of diapause is arguably one of the most critical events bolstering the success of insects. The capacity to periodically shut down development has enabled insects and their arthropod relatives to invade environments that are seasonally hostile. Indeed, very few environments permit continuous insect development. Even in the tropics, where temperatures throughout the year may be compatible with ectotherm development, seasonal patterns of rainfall drive cycles of plant growth that favor insects with the ability to periodically become dormant. Unlike a simple quiescence that is an immediate response to an unfavorable environmental condition, diapause is a genetically programmed response that occurs at a specific stage for each species. Sometimes, the insect will enter diapause at this particular stage in each generation regardless of the environmental conditions it receives—a developmental program referred to as obligatory diapause. Much more frequently, the decision to enter diapause is determined by environmental factors, usually day length, received by that individual or its mother at an earlier developmental stage. This is referred to as facultative diapause.

10 – Hormonal Control of Diapause

The hypothesis that physiological and developmental regulatory mechanisms are similar has been presented. Well-known developmental systems chosen illustrate the capability of the model to suggest a simple mechanism underlying the effects on development of a diverse group of chemicals. This hypothesis might be applied to other systems including the induction of the lens, limb regeneration, and the induction of the head of hydra (124). 

I have proposed this hypothesis not only because it permits consideration of a complex and varied array of experimental observations as reflections of a simple basic biochemical mechanism, but because recent technical advances in instrumentation and methods allow it to be directly tested. The fluorescent antibody method for the cytochemical measurement of cyclic nucleotides provides a means for investigating changes in the concentrations of cyclic nucleotides in developing cells and could also be used to detect neurotransmitters in developing cells. Similarly, the scanning electron microscope in the emitted x-ray mode provides a method for measuring changes in the content and distribution of cations within developing cells. 

The hypothesis presented here suggests pleasing asceticism on the part of eukaryotes. It suggests that simple derivatives of metabolites, including neurotransmitters and cyclic nucleotides, are linked together as regulatory molecules throughout the eukaryotes. The neurotransmitters are suggested to have a more general role in information transmission in eukaryotes than is generally accepted. They are hypothesized to have progressed during evolution from being intracellular messengers to a role as intercellular messengers for the relatively slow communication of developmental informaton; and, finally, this process has culminated with their participation in the rapid intercellular communication mediated by nerves. The thought that the complex pictures of physiological regulation and of the construction of a complex multicellular organism like man might be painted with so few colors is quite satisfying.

https://science.sciencemag.org/content/sci/185/4156/1012.full.pdf

Chemical messengers in development: a hypothesis.

Cyclic Nucleotide Phosphodiesterases: Properties, Activators, Inhibitors, Structure–Activity Relationships, and Possible Role in Drug Development

Publisher Summary
This chapter reviews the influence that endocrine hormones have on the growth and development of insects. The mechanism of action of none of the insect hormones is known with certainty, and it is postulated that they may act at several of the many possible control points. As several orders of insects are separated widely in evolutionary time, it might be that growth hormones do not act uniformly in all insects. The classical scheme of endocrine control of molting and metamorphosis in holometabolous insects has been plagued by questions raised as a result of contemporary investigations in the functioning of insect hormones. An exception to the classical scheme is the finding that renewed secretion by the brain is not always needed for each molt. Insect neurosecretory cells appear to play important roles in many other physiological processes. One important question that needs answering relates to the regulation and mechanism of synthesis and release of neurosecretion in insect cells. The activity of α-ecdysone—arthropod hormones that are produced by the prothoracic gland in insects and that trigger molting and metamorphosis and are synthesized from chiolestrol—and various side chain deoxyecdysones is partially because of their metabolism to β-ecdysone.

Shalom W. Applebaum

Papers

Stimulation of adenyl cyclase in pupal wing epidermis by β-ecdysone☆

Cyclic AMP phosphodiesterase activity in the midgut of Manduca sexta.