Change in corpus allatum function during metamorphosis of the tobacco hornworm Manduca sexta: Regulation at the terminal step in juvenile hormone biosynthesis

Changes in activity of the corpora allata (CA) during larval-pupal-adult development of the tobacco hornworm Manduca sexta were studied by transplantation assays, measurements of in vitro juvenile hormone (JH) and JH acid synthesis, and determination of JH acid methyltransferase (JHAMT) and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activities. The data from these assays demonstrate that the CA cease to secrete JH by day 4 of the last larval instar (wandering stage). With regard to JH synthesis, they remain inactive throughout the prepupal, pupal, and most of the pharate adult periods. CA of females, but not of males, resume JH synthesis shortly before eclosion. The biochemical basis of the inactivation process is the loss of JHAMT activity. However, prepupal CA produce JH acids, as shown by enzyme and in vitro assays. Pupal and pharate adult CA do not synthesize JH acids although levels of HMG-CoA reductase activity seem to remain relatively high. Radiolabeled JH was recovered from hemolymph of allatectomized prepupae that had been injected with radiolabeled JH acid. These results provide further evidence that certain peripheral tissues (eg, imaginal discs) convert JH acid secreted by the prepupal CA to JH and, thus, that JH acid is a prohormone in the prepupal period. The CA change from hormone secretion to prohormone secretion during larval-prepupal transformation, a unique functional alteration in an endocrine gland.     

How We Forgot Who Discovered DNA: Why It Matters How You Communicate Your Results

One hundred and fifty years ago, a hopeful young researcher reported a recent discovery he had made. Working in the bowels of a medieval castle in the German city of Tübingen, he had isolated a then entirely new type of molecule. This was the birth of a field that would fundamentally change the course of biology, medicine, and beyond. His discovery: DNA. His name: Friedrich Miescher. In this article, the authors try to find answers to the question why—despite the fact that virtually everyone nowadays knows DNA—hardly anyone remembers the man who discovered it. In the history of science, the discovery of DNA was a seminal moment. Why then did it not enter into public memory? Ground‐breaking discoveries can occur in a historical context that is not ready to appreciate them. But that's not all that decides who is remembered and who is forgotten. Scientific pioneers sometimes fail to publicize their findings in a way that ensures that they receive the attention they merit. As discussed here, their personalities and habits may cause discoveries to be “overwritten” by more recent researchers, resulting in distorted cultural memories no longer reflecting the initial event.     

Studies on the hammerhead RNA self-cleaving domain

Nine different hammerhead RNA self-cleaving domains consistent with the consensus secondary structure proposed by Keese and Symons (1987) were prepared and tested for cleavage. Each hammerhead was constructed from two oligoribonucleotides in two different configurations. Although cleavage was observed in all nine cases, the rates of cleavage varied by more than a thousand fold. The presence of RNA secondary structure incompatible with hammerhead formation in the individual oligos may be responsible for the large rate differences. We have also examined the degree of participation of a proposed dimer hammerhead intermediate in one case and conclude that, while such a four-stranded structure can form, it is not the preferred reaction intermediate.     

Distinct roles for adhesion molecules during innervation of embryonic chick muscle

In vitro studies have suggested that the cell adhesion molecules NCAM and G4/L1 contribute to a variety of events during neural development. We have directly tested the role played by these molecules in the process of initial nerve ingrowth and ramification in the embryonic chick iliofibularis muscle by in ovo injections of specific adhesion-blocking antibodies and analysis of the resultant nerve branching pattern in muscle whole mounts. Antibodies against both molecules produced axonal defasciculation, which resulted in an enhanced transverse projection to the fast region of the muscle. In the case of anti-G4/L1, we also observed a large increase in the number of side branches that form from nerve trunks in the slow region and an enhancement of nerve branching in the fast region. Conversely, anti-NCAM produced a striking decrease in both the number and length of side branches in the slow region, and a reduction in nerve branching in the fast region. A similar reduction of nerve branching was obtained following injection of an endosialidase, which removes sialic acid from NCAM, and which was observed to enhance fiber-fiber apposition, presumably by increasing cell adhesion. Based on their biochemical properties in vitro and their in vivo distribution, both NCAM and G4/L1 are in a position to contribute to axon-axon adhesive interactions, whereas NCAM would be expected to also promote axon-myotube interactions. Our observations in fact indicate that these two adhesion molecules play different but complementary roles during muscle innervation and, specifically, that axon-axon fasciculation is influenced by both NCAM and G4/L1 in an anatomically distinct manner to regulate the overall pattern of nerve branching and that NCAM-mediated axon-myotube interactions are necessary for the attainment of the normal stereotyped pattern of nerve branching in both fast and slow regions of this muscle.