Quantitative genetic analysis of life-history traits of Caenorhabditis elegans in stressful environments

In Figure 1 of [Harvey et al (Evolutionary Biology 2008, 8:15)] the plotted data were inverted. The correct Figure is shown below. The text and statistical analyses in [Harvey et al (Evolutionary Biology 2008, 8:15)] are correct.     

Structure of the cyanobacterial Magnesium Chelatase H subunit determined by single particle reconstruction and small-angle X-ray scattering

The biosynthesis of chlorophyll, an essential cofactor for photosynthesis, requires the ATP-dependent insertion of Mg²⁺ into protoporphyrin IX catalyzed by the multisubunit enzyme magnesium chelatase. This enzyme complex consists of the I subunit, an ATPase that forms a complex with the D subunit, and an H subunit that binds both the protoporphyrin substrate and the magnesium protoporphyrin product. In this study we used electron microscopy and small-angle x-ray scattering to investigate the structure of the magnesium chelatase H subunit, ChlH, from the thermophilic cyanobacterium Thermosynechococcus elongatus. Single particle reconstruction of negatively stained apo-ChlH and Chl-porphyrin proteins was used to reconstitute three-dimensional structures to a resolution of ∼30 Å. ChlH is a large, 148-kDa protein of 1326 residues, forming a cage-like assembly comprising the majority of the structure, attached to a globular N-terminal domain of ∼16 kDa by a narrow linker region. This N-terminal domain is adjacent to a 5 nm-diameter opening in the structure that allows access to a cavity. Small-angle x-ray scattering analysis of ChlH, performed on soluble, catalytically active ChlH, verifies the presence of two domains and their relative sizes. Our results provide a basis for the multiple regulatory and catalytic functions of ChlH of oxygenic photosynthetic organisms and for a chaperoning function that sequesters the enzyme-bound magnesium protoporphyrin product prior to its delivery to the next enzyme in the chlorophyll biosynthetic pathway, magnesium protoporphyrin methyltransferase.     

Costing Alternative Birth Settings for Women at Low Risk of Complications: A Systematic Review

Background

There is demand from women for alternatives to giving birth in a standard hospital setting however access to these services is limited. This systematic review examines the literature relating to the economic evaluations of birth setting for women at low risk of complications.

Methods

Searches of the literature to identify economic evaluations of different birth settings of the following electronic databases: MEDLINE, CINAHL, EconLit, Business Source Complete and Maternity and Infant care. Relevant English language publications were chosen using keywords and MeSH terms between 1995 and 2015. Inclusion criteria included studies focussing on the comparison of birth setting. Data were extracted with respect to study design, perspective, PICO principles, and resource use and cost data.

Results

Eleven studies were included from Australia, Canada, the Netherlands, Norway, the USA, and the UK. Four studies compared costs between homebirth and the hospital setting and the remaining seven focussed on the cost of birth centre care and the hospital setting. Six studies used a cost-effectiveness analysis and the remaining five studies used cost analysis and cost comparison methods. Eight of the 11 studies found a cost saving in the alternative settings. Two found no difference in the cost of the alternative settings and one found an increase in birth centre care.

Conclusions

There are few studies that compare the cost of birth setting. The variation in the results may be attributable to the cost data collection processes, difference in health systems and differences in which costs were included. A better understanding of the cost of birth setting is needed to inform policy makers and service providers.     

Exploiting the life cycle of Strongyloides ratii.

The nematode Strongyloides ratti has a remarkable life cycle, which has both a parasitic and a free-living phase. The free-living phase includes a choice between two developmental routes. Here, Mark Viney discusses recent advances in understanding the biology of this developmental switch and shows how the life cycle of this nematode can be used to explore the lifestyle transitions common to all parasitic nematodes, as well as to address other basic biological questions.     

Extraordinary plasticity in aging in Strongyloides ratti implies a gene-regulatory mechanism of lifespan evolution

Aging evolves as the result of weakened selection against late-acting deleterious alleles due, for example, to extrinsic mortality. Comparative studies of aging support this evolutionary theory, but details of the genetic mechanisms by which lifespan evolves remain unclear. We have studied aging in an unusual nematode, Strongyloides ratti, to gain insight into the nature of these mechanisms, in this first detailed examination of aging in a parasitic nematode. S. ratti has distinct parasitic and free-living adults, living in the rat small intestine and the soil, respectively. We have observed reproductive and demographic aging in parasitic adults, with a maximum lifespan of 403 days. By contrast the maximum lifespan of free-living adults is only 5 days. Thus, the two adults of S. ratti have evolved strikingly different rates of aging. Parasitic nematode species are frequently longer-lived than free-living species, presumably reflecting different extrinsic mortality rates in their respective niches. Parasitic and free-living female S. ratti are morphologically different, yet genetically identical. Thus, the 80-fold difference in their lifespans, the greatest plasticity in aging yet reported, must largely reflect evolved differences in gene expression. This suggests that interspecific differences in lifespan may evolve via similar mechanisms.     

Pesticide exposure: the hormonal function of the female reproductive system disrupted?

Some pesticides may interfere with the female hormonal function, which may lead to negative effects on the reproductive system through disruption of the hormonal balance necessary for proper functioning. Previous studies primarily focused on interference with the estrogen and/or androgen receptor, but the hormonal function may be disrupted in many more ways through pesticide exposure. The aim of this review is to give an overview of the various ways in which pesticides may disrupt the hormonal function of the female reproductive system and in particular the ovarian cycle. Disruption can occur in all stages of hormonal regulation: 1. hormone synthesis; 2. hormone release and storage; 3. hormone transport and clearance; 4. hormone receptor recognition and binding; 5. hormone postreceptor activation; 6. the thyroid function; and 7. the central nervous system. These mechanisms are described for effects of pesticide exposure in vitro and on experimental animals in vivo. For the latter, potential effects of endocrine disrupting pesticides on the female reproductive system, i.e. modulation of hormone concentrations, ovarian cycle irregularities, and impaired fertility, are also reviewed. In epidemiological studies, exposure to pesticides has been associated with menstrual cycle disturbances, reduced fertility, prolonged time-to-pregnancy, spontaneous abortion, stillbirths, and developmental defects, which may or may not be due to disruption of the female hormonal function. Because pesticides comprise a large number of distinct substances with dissimilar structures and diverse toxicity, it is most likely that several of the above-mentioned mechanisms are involved in the pathophysiological pathways explaining the role of pesticide exposure in ovarian cycle disturbances, ultimately leading to fertility problems and other reproductive effects. In future research, information on the ways in which pesticides may disrupt the hormonal function as described in this review, can be used to generate specific hypotheses for studies on the effects of pesticides on the ovarian cycle, both in toxicological and epidemiological settings.     

Mucus liquid crystallinity: is function related to microstructural domain size?

The size of liquid crystalline domains formed in partially dried giraffe saliva is found to be an order of magnitude greater than that previously documented for slug pedal mucus. A correlation between (a) intrinsic liquid crystalline domain size and (b) the scale of surface topography over which the mucus is required to provide lubrication is postulated. The scale of mucus microstructure can be related, via a simple model, to two significant material constants: the elastic constant K for distortion of molecular alignment in the liquid crystalline state, and the anchoring energy I at the liquid crystal/substrate interface. In turn, the quantity K is expected to depend on fundamental molecular characteristics of the constituent mucin, such as molecular weight and degree of glycosylation. The possibility that observations of mucus microstructure might serve as a diagnostic tool for mucus defects at the molecular level is suggested.