Is sex necessary?

Fungal sexual reproductive modes have markedly high diversity and plasticity, and asexual species have been hypothesized to arise frequently from sexual fungal species. A recent study on the red yeasts provides further support for the notion that sexual ancestors may give rise to shorter-lived asexual species. However, presumed asexual species may also be cryptically sexual, as revealed by other recent studies.See research article: http://www.biomedcentral.com/1471-2148/11/249     

Is a virtual trajectory necessary in reaching movements?

The mass-spring model of limb control was extended to two-joint arm movements in the horizontal plane and tested against kinematic data from human subjects. Two versions of the model were compared in order to test the idea that the equilibrium position of the hand moves along a virtual trajectory as demonstrated in single-joint arm movements (Bizzi et al. 1982, 1984; Latash and Gottlieb 1991). In the peripheral version, the equilibrium position was shifted abruptly, while the torques generated at the joints are gated by rise-time functions. In the central version, the equilibrium position was updated gradually according to a predefined trajectory. The paths and tangential velocity profiles of the hand generated by these two versions were compared to Morasso's (1981) experimental data. The central version generally performed better throughout the workspace except in certain special directions. Moreover, its paths exhibited more stability as the movement speed was varied.     

Is your initiator really necessary?

There is little hard evidence for the involvement of specific genotoxic initiators in the pathogenesis of the common carcinoma. Recent findings suggest that sporadic carcinogenesis is a dynamic and probabilistic process which requires a critical mass of abnormal cells for its expression, and that this requirement may distinguish the evolution of carcinomas from that of paediatric or haematologic malignancies. The proposal that specific carcinogens are neither necessary nor sufficient for tumourigenesis is consistent with the growing realization that aberrant expression of specific oncogenes is neither necessary nor sufficient for cellular transformation. These new perspectives have major implications for basic research strategy and public health policy.     

Influenza-virus-induced signaling cascades: targets for antiviral therapy?

Influenza viruses continue to pose a severe threat worldwide, causing thousands of deaths and an enormous economic loss every year. The major problem in fighting influenza is the high genetic variability of the virus, resulting in the rapid formation of variants that escape the acquired immunity against previous virus strains, or have resistance to antiviral agents. Every virus depends on its host cell and, hence, cellular functions that are essential for viral replication might be suitable targets for antiviral therapy. As a result, intracellular signaling cascades induced by the virus, in particular mitogen-activated protein kinase pathways, have recently come into focus.     

Is free halogen necessary for disinfection?

The principle of Le Chatelier was used in demonstrating that 3-chloro-4,4-dimethyl-2-oxazolidinone (compound 1) itself kills Staphylococcus aureus rather than the very small amount of free chlorine in hydrolysis equilibrium with compound 1. On the other hand, when the N-bromo analog of compound 1 (compound 1B) was used as the disinfectant, the mixture of combined compound 1B and free bromine formed in the hydrolysis equilibrium provided disinfection. When the hydrolysis equilibrium for 1B was suppressed to the level at which a negligible amount of free bromine remained in solution, combined compound 1B was much more efficacious than combined compound 1 at killing S. aureus.     

Is interleukin-6 the necessary pyrogenic cytokine?

(1) This paper analyses arguments suggesting a critical role for interleukin-6 (IL-6) in the manifestation of fever.

(2) Evidence supporting such a role for IL-6 derives from the excellent correlation between IL-6 in plasma and the accompanying fever, from neutralization experiments with anti-IL-6-antibodies, and from studies in IL-6-deficient mice.

(3) Peripherally administered IL-6 has rather poor pyrogenic properties and needs co-factors to elicit pronounced fever.

(4) Circumventricular organs, which lack a tight blood–brain barrier, have been identified as brain sites where circulating IL-6 causes a direct genomic activation of cellular elements in astrocytes and endothelial cells.

(5) Due to the fact that the onset of fever frequently preceeds the formation of sufficient amounts of IL-6 and the activation of brain cells by this cytokine, it is suggested that IL-6 contributes to the maintenance rather than to the induction of the initial phase of fever.

(6) During the time course of fever IL-6 seems to be involved in the induction of endogenous anti-inflammatory/antipyretic mediators and thus in the manifestation of defervescence.     

Is a decline in offspring quality a necessary consequence of maternal age?

Recent studies in two species of Drosophila have demonstrated a negative effect of parental age on offspring fitness, including a reduced hatch rate of eggs and larval-to-adult viability. This has led to a call to consider the decline of offspring quality as a function of parental age in theoretical considerations of the evolution of ageing. We have tested whether a decline in egg and larval quality of older mothers is a general feature of senescence by examining it in the cockroach Nauphoeta cinerea. We also tested whether maternal age affected the reproductive potential of daughters. Although maternal age at first reproduction profoundly affected maternal fitness, there was no difference in hatch rate or larval viability between the offspring of young and old mothers. Likewise, the reproductive potential of the daughters of young and old mothers was the same. Thus, while maternal age effects may be important aspects of ageing in some systems, the generality and overall importance for theories of ageing remain unclear.