Molecular epidemiology of TB: challenging dogmas and asking new questions

Traditional epidemiological methods provide insight into the dynamics of diseases such as tuberculosis. These traditional techniques have limitations and rely on a number of assumptions. The application of molecular techniques to the study of epidemiology has allowed us to gain new insights into the biology of the organism Mycobacterium tuberculosis and the dynamics of the disease. We have been enabled to push the limits of understanding of the epidemiology of this disease, allowing us to challenge the old clinical dogmas, ask new questions, design new strategies, and measure the efficacy of such new interventions to combat this age-old scourge. Among the dogmas challenged are that infection outside the home is commonplace, so-called relapse cases may in fact be largely reinfection, and active transmission may be more common than previously thought and reactivation disease relatively uncommon. These findings alone demand urgent attention and the design of optimal intervention strategies to reduce the burden of disease.     

The four questions of ethology

Ethology is the biological study of behaviour and concerns itself with questions about the causes, functions, evolution and development of aspects of behaviour. These different questions are illustrated with examples from the study of bird song. This subject has had most impact on understanding of developmental issues, showing the intricate interplay between genes and environment during ontogeny. Work on the evolution of song has involved comparison between closely related species to see how their songs have changed since separation, but also the shorter term cultural evolution that occurs when song is passed from one animal to another by learning. Studies of function, while fraught with difficulties, have revealed that song can have a variety of advantages. As far as causes are concerned, some impressive discoveries have recently been made on the neural basis of song. The need for such work to be complemented by studies of behaviour at the level of the whole animal is stressed, and studies of song sequencing are used to illustrate this.     

Lifestyle assessment: just asking makes a difference.

A 10 minute assessment of 180 family practice patients showed that 11% indicated a problem with drinking alcohol, 20% with cigarette smoking, 36% with consumption of coffee or tea, and 3% with non-medical drug use, while 11% wanted to discuss their use of medications. Moreover, being asked questions resulted in a twofold or threefold increase in the patients'' intentions of discussing such a problem with their doctor. Although there was good overall agreement in recognising a problem between the patient and doctor, in roughly 40% of instances where the patient indicated a problem the doctor was unaware of it. These patients tended to be young, well educated, and employed in professional occupations, and were on their first visit to the doctor. Such brief assessments of lifestyle should be routinely conducted in family practice for both case finding and prevention.     

The clade Ecdysozoa, perplexities and questions

A relatively new clade, the Ecdysozoa [Aguinaldo et al., 1997. Nature 387, 489-493] was raised based on the 18S ribosomal DNA sequences that indicate a close relationship between the moulting phyla (Arthropoda, Tardigrada, Onychophora, Nematoda, Nematomorpha, Kinorhyncha, Lorificera and Priapula), from which the Annelida, with other phyla, are excluded.However, the authors here expressed puzzlement about this conclusion. In particular they stressed that: (a) ecdysis might not be an autapomorphy for the Ecdysozoa; (b) some Ecdysozoa phyla are unrelated from one another with regard to morphology and embryogeny; (c) the annelids have a body architecture that is more similar to arthropods than some of the Ecdysozoa; (d) the annelids are moulting animals; (e) some phyla excluded from the new clade (e.g. the gastrotrichs), probably carry out a gradual ecdysis by flaking similar to that of the polychaetes.The authors concluded that the clade Ecdysozoa appears to be phylogenetically unconvincing.     

The Martian atmosphere: Some unanswered questions

Summary The study of the Martian atmosphere and its significance for the possible origin of life on Mars is still very incomplete. Further investigations are needed to define the total volatile inventory, the early history of the atmosphere, and the relationship of the atmosphere to the question of indigenous life. In addition, studies of Venus, comets, and the Jupiter system will add significantly to our abilities to understand the early history of Mars.     

The structure of the phloem--still more questions than answers

Long-distance assimilate distribution in higher plants takes place in the enucleate sieve-tube system of the phloem. It is generally accepted that flow of assimilates is driven by an osmotically generated pressure differential, as proposed by Ernst Münch more than 80?years ago. In the period between 1960 and 1980, the pressure flow hypothesis was challenged when electron microscopic images suggested that sieve tubes contain obstructions that would prevent passive flow. This led to the proposal of alternative translocation mechanisms. However, most investigators came to the conclusion that obstructions in the sieve-tube path were due to preparation artifacts. New developments in bioimaging have vastly enhanced our ability to study the phloem. Unexpectedly, in vivo studies challenge the pressure-flow hypothesis once again. In this review we summarize current investigations of phloem structure and function and discuss their impact on our understanding of long-distance transport in the phloem.     

The paraflagellar rod of kinetoplastida: solved and unsolved questions

The flagellum of almost every member of the Kinetoplastida contains, next to its canonical 'nine-plus-two' axoneme, structure, a unique, complex and highly organized lattice-like structure called the paraflagellar rod or paraxial rod. Here, Philippe Bastin, Keith Matthews and Keith Gull summarize the latest findings on its structure, the nature of its protein components and their corresponding genes. They also consider the possible functions of this intriguing organelle.     

Crystal studies of B-DNA: The answers and the questions

The history of DNA crystallography is reviewed and is followed by discussion of the methods used for structure determination. The features of B-DNA molecular and crystal structures are described. © 1997 John Wiley & Sons, Inc. Biopoly 44: 23–44, 1997