Microtubule termination patterns in mammalian sperm flagella

Detailed reconstructions of the flagellar tip (end-piece) in rodent spermatozoa have shown patterns of displacement between the termination points of the axonemal doublets (judging the terminations by the loss of electron density from the A-tubule). The patterns are in good agreement with those derived from sliding microtubule theory. In the hamster at least, the axis of major displacement passes approximately through doublet 1 and between doublets 5 and 6, though there may be some skewness in the clockwise direction. Microtubules derived from the plane at right angles to this (the central pair and presumably one or both of doublets 3 and 8) continue beyond the rest to the extreme tip, where they appear to be linked together at the cell membrane. This arrangement suggests that the tapering form of the end-piece, and of flagellar terminal filaments and ciliary tips in general, may be an adaptation to contain the sliding microtubules and prevent them impinging on the membrane overlying the tip.     

Regulation of some nitrogen catabolizing enzyme levels in chick liver.

Xanthine dehydrogenase, purine nucleoside phosphorylase, and tyrosine aminotransferase are all increased sharply in liver of chicks by dietary protein. Results in this paper show that most amino acids have this effect, with methionine and tryptophan being more effective than the remainder. This suggested that any source of amino nitrogen could cause a build-up of a nitrogenous intermedate(s) necessary for enzyme accumulation. The above hypothesis was tested by blocking the breakdown of amino acids using various antimetabolites. Results were uniformly successful in raising enzyme levels, and furthermore it was found that antimetabolites and amino acids are not additive, suggesting that they act by a similar mechanism.     

END‐OF‐LIFE CARE IN THE 21st CENTURY: ADVANCE DIRECTIVES IN UNIVERSAL RIGHTS DISCOURSE

This article explores universal normative bases that could help to shape a workable legal construct that would facilitate a global use of advance directives. Although I believe that advance directives are of universal character, my primary aim in approaching this issue is to remain realistic. I will make three claims. First, I will argue that the principles of autonomy, dignity and informed consent, embodied in the Oviedo Convention and the UNESCO Declaration on Bioethics and Human Rights, could arguably be regarded as universal bases for the global use of advance directives. Second, I will demonstrate that, despite the apparent consensus of ethical authorities in support of their global use, it is unlikely, for the time being, that such consensus could lead to unqualified legal recognition of advance directives, because of different understandings of the nature of the international rules, meanings of autonomy and dignity which are context‐specific and culture‐specific, and existing imperfections that make advance directives either unworkable or hardly applicable in practice. The third claim suggests that the fact that the concept of the advance directive is not universally shared does not mean that it should not become so, but never as the only option in managing incompetent patients. A way to proceed is to prioritize work on developing higher standards in managing incompetent patients and on progressing towards the realization of universal human rights in the sphere of bioethics, by advocating a universal, legally binding international convention that would outlaw human rights violations in end‐of‐life decision‐making.     

Crayfish,catfish and snails: the perils of uncontrolled biological control

A recent proposal that the Australian redclaw crayfish Cherax quadricarinatus and hybrid catfish could potentially control the snail hosts of schistosomiasis has been criticised on the grounds that crayfish pose a severe threat to aquatic ecosystems into which it might be introduced. This note examines the issue further, pointing out that both lack the host-specificity requirement to be a successful biological control agent. The catfish Clarias gariepinus is an omnivore and snails form only a small proportion of its diet; there is no evidence to suggest that it controls snail populations anywhere in Africa. The same applies to other species that have been proposed as biological control agents. Simple laboratory experiments are not an adequate guide to the efficiency of an animal as a biological control agent and detailed ecological investigations would usually demonstrate that few African fish species have this capability.     

An incremental approach to automated protein localisation

Background  

The subcellular localisation of proteins in intact living cells is an important means for gaining information about protein functions. Even dynamic processes can be captured, which can barely be predicted based on amino acid sequences. Besides increasing our knowledge about intracellular processes, this information facilitates the development of innovative therapies and new diagnostic methods. In order to perform such a localisation, the proteins under analysis are usually fused with a fluorescent protein. So, they can be observed by means of a fluorescence microscope and analysed. In recent years, several automated methods have been proposed for performing such analyses. Here, two different types of approaches can be distinguished: techniques which enable the recognition of a fixed set of protein locations and methods that identify new ones. To our knowledge, a combination of both approaches – i.e. a technique, which enables supervised learning using a known set of protein locations and is able to identify and incorporate new protein locations afterwards – has not been presented yet. Furthermore, associated problems, e.g. the recognition of cells to be analysed, have usually been neglected.     

Rigidity,Secondary Structure,and the Universality of the Boson Peak in Proteins

Complementary neutron- and light-scattering results on nine proteins and amino acids reveal the role of rigidity and secondary structure in determining the time- and lengthscales of low-frequency collective vibrational dynamics in proteins. These dynamics manifest in a spectral feature, known as the boson peak (BP), which is common to all disordered materials. We demonstrate that BP position scales systematically with structural motifs, reflecting local rigidity: disordered proteins appear softer than α-helical proteins; which are softer than β-sheet proteins. Our analysis also reveals a universal spectral shape of the BP in proteins and amino acid mixtures; superimposable on the shape observed in typical glasses. Uniformity in the underlying physical mechanism, independent of the specific chemical composition, connects the BP vibrations to nanometer-scale heterogeneities, providing an experimental benchmark for coarse-grained simulations, structure/rigidity relationships, and engineering of proteins for novel applications.