The rise and fall of photomutagenesis

UV is the most abundant human carcinogen, and protection from extensive exposure to it is a widespread human health issue. The use of chemicals (sunscreens) for protection is intuitive and efficacious. However, these chemicals may become activated to reactive intermediates when absorbing energy from UV, thus producing damage themselves, which may manifest itself in phototoxic, photoallergenic or photocarcinogenic reactions in humans. The development of safe sunscreens for humans is of high interest. Similar issues have been observed for some therapeutically used principles such as PUVA therapy for psoriasis or porphyrins for phototherapy of human cancers. Photoactivation has also been reported as a side effect of various pharmaceuticals such as the antibacterial fluoroquinolones. In this context, the authors have been involved over more than 20 years in the development and refinement of assays to test for photomutagenicity as an unwanted side effect of UV-mediated activation of such chemicals for cosmetic or pharmaceutical use. The initial years of great hopes for simple mammalian cell-based assays for photomutagenicity to screen out substances of concern for human use were followed by many years of collaborative trials to achieve standardization. However, it is now realized that this topic, albeit of human safety relevance, is highly complex and subject to many artificial modifiers, especially in vitro in mammalian cell culture. Thus, it is not really suitable for being engineered into a general testing framework within cosmetic or pharmaceutical testing guidelines. Much knowledge has been generated over the years to arrive at the conclusion that yes, photomutagenicity does exist with the use of chemicals, but how to best test for it will require a sophisticated case-by-case approach. Moreover, in comparison to the properties and risks of exposure to UV itself, it remains a comparatively minor human safety risk to address. In considering risks and benefits, we should also acknowledge beneficial effects of UV on human health, including an essential role in the production of Vitamin D. Thus, the interrelationships between UV, chemicals and human health remain a fascinating topic of research.     

The rise and fall of SRY

Comparisons between species reveal when and how SRY, the testis-determining gene, evolved. SRY is younger than the Y chromosome, and so was probably not the original mammal sex-determining gene that defined the Y. SRY is typical of genes on the Y chromosome. It arose from a gene on the proto-sex chromosome pair with a function (possibly brain-determination) in both sexes. It has been buffeted in evolution, and shows variation in copy number, structure and expression. And it is dispensable, having been lost at least twice independently in different rodent lineages. At the observed rate of attrition, the human Y chromosome will be gone in 5-10 million years. This could lead to the extinction of our species or to a burst of hominid speciation.     

Dynamic neuronal-glial interactions: an overview 20 years later

After commenting on some perceived reasons why our review may have been relatively frequently cited, a brief overview is presented that first summarizes what we knew 25 years ago about the dynamic neuronal-astroglial interactions that occur in response to changes in the physiological state of the animal. The brain system in which these dynamic interactions were studied was the magnocellular hypothalamo-neurohypophysial system (mHNS) of the rat. The mHNS developed as and continues to be the model system yielding the most coherent picture of dynamic morphological changes and insights into their functional consequences. Many other brain areas, however, have more recently come under scrutiny in the search for glial-neuronal dynamisms. Outlined next are some of the questions concerning this phenomenon that led to the research efforts immediately following the initial discoveries, along with the answers, both complete and incomplete, obtained to those research questions. The basis for this first wave of follow-up research can be characterized by the phrase "what we knew we didn't know at that time." The final section is an update and brief overview of highlights of both "what we know now" and "what we now know that we don't know" about dynamic neuronal-astroglial interactions in the mHNS.     

The fall and rise of apical dominance

The plant hormone auxin, synthesised in the shoot apex, moves down the stem and inhibits lateral branching. Auxin does not travel upward into the branches, so it must act indirectly; for example, through a second messenger. However, recent work on auxin transport suggests a possible additional mechanism whereby auxin transport in the stem prevents the establishment of auxin transport out of the branches, inhibiting their growth.     

The rise and fall of mutator bacteria

Bacteria with elevated mutation rates are frequently found among natural isolates. This is probably because of their ability to generate genetic variability, the substrate for natural selection. However, such high mutation rates can lead to the loss of vital functions. The evolution of bacterial populations may happen through alternating periods of high and low mutation rates. The cost and benefits of high mutation rates in the course of bacterial adaptive evolution are reviewed.     

The rise and fall of forensic hypnosis

This paper examines the fortunes of the controversial use of hypnosis to ‘enhance’ autobiographical memories in postwar America. From the 1950s through the early 1980s, hypnosis became increasingly popular as a means to exhume information thought to be buried within the mind. This practice was encouraged by lay understandings of memory drawn from a material culture full of new recording devices (motion pictures, tape and then video recorders); and during the years when the practice was becoming most popular and accepted, academic psychologists developed a contrary, reconstructive, account of memory that was put to use in a series of battles meant to put an end to hypnotic recall. But popular commitment to the idea of permanent memory ‘recordings’ sustained the practice and the assumptions about memory and self that were associated with it, and in the face of a culture of academic psychology fully committed to the idea of ‘reconstructive’, malleable memory, a tidal wave of ‘enhanced’ memories swept America in the late 1980s and 1990s, in the so-called ‘memory wars’. These, in turn, provoked academic psychologists to research the claims and counter claims central to the memory wars. The paper will also make an argument about the importance of lay knowledge in the psychological sciences explored in this paper: that popular psychological beliefs played a significant, even formative role in defining the nature of forensic psychological expertise, and also the framing of elite academic psychological research.     

The rise and fall of handicap principle: a commentary on the “Modelling and the fall and rise of the handicap principle”

The honesty of animal communication is in the spot lights in the last 30 years. During most of this time the field was dominated by one explanation: Zahavi’s handicap principle (Zahavi, J Theor Biol 67:603–605, 1975; Grafen, J Theor Biol 144:517–546, 1990). Grose (Biol Philos 2011) embarks to explain both the success of the theory and the empirical difficulties that exist despite this success. While I wholeheartedly agree with the criticism offered by Grose and with almost all the claims he makes, the treatment of the issue is far from complete and it still leaves much to be explained. Accordingly, my commentary consist of six sections: in the first section I clear up some technical issues left unexposed, most importantly the role of strategic cost in handicap signalling; in the second section I relate this to empirical testing; in the next section I comment on the historical development of the handicap principle; in the fourth section I review the biological models that came up with conclusions that contradict the handicap principle; in the fifth section I discuss the reasons behind the success of the handicap theory; finally, in the last section I discuss the application of the handicap theory to anthropology and human sciences.     

The rise and fall of the RNA world.

It is generally believed that there was a time when life on earth was based on RNA rather than on DNA and protein. Considering the relevant evidence from geophysics, geology, paleobiology, and molecular biology, it is possible to set the time frame for the existence of RNA-based life to a 400 million year interval beginning 4.0 to 4.2 billion years ago and ending 3.6 to 3.8 billion years ago. The minimum level of biochemical complexity that existed during this time consists of those functions necessary for the establishment and maintenance of an RNA-based evolving system, namely, an RNA unwinding activity, an RNA replicase activity, and a primitive biosynthetic apparatus leading to enrichment of the local environment with activated D mononucleotides.     

The rise and fall of bacterial clones: Streptococcus pneumoniae

Globally spreading bacterial strains belong to clonal types that have the capacity to colonize, spread and cause disease in the community. Recent comparative genomic analyses of well-defined clinical isolates have led to the identification of bacterial properties that are required for the successful spread of bacterial clones. In this Review, we discuss the evolution of bacterial clones, the importance of recombination versus mutations for evolution of clones, common methods used to study clonal relationships among bacteria, factors that may contribute to the clonal spread of bacteria and the potential relevance of bacterial clones to clinical disease. We focus on the common pathogen Streptococcus pneumoniae, although other bacteria are also briefly discussed, such as Helicobacter pylori, Staphylococcus aureus and Mycobacterium tuberculosis.