Pregnancy in the mature adult mouse does not alter the proportion of mammary epithelial stem/progenitor cells

Introduction In humans, an early full-term pregnancy reduces lifetime breast cancer risk by up to 50% whereas a later pregnancy (>35 years old) can increase lifetime risk. Several mechanisms have been suggested, including changes in levels of circulating hormones, changes in the way the breast responds to these hormones, changes in gene expression programmes which may alter susceptibility to transformation and changes to mammary stem cell numbers or behaviour. Previous studies have shown that the mammary tissue isolated from both virgin and parous mice has the ability to repopulate a cleared mammary fat pad in transplant experiments. Limited dilution transplant assays have demonstrated that early pregnancy (at 5 weeks of age) reduces stem/progenitor cell numbers in the mouse mammary epithelium by twofold. However, the effects on stem/progenitor cell numbers in the mammary epithelium of a pregnancy in older animals have not yet been tested. Methods Mice were put through a full-term pregnancy at 9 weeks of age, when the mammary epithelium is mature. The total mammary epithelium was purified from parous 7-week post-lactation and age-matched virgin mice and analysed by flow cytometry and limiting dilution cleared fat pad transplants. Results There were no significant differences in the proportions of different mammary epithelial cell populations or numbers of CD24+/Low Sca-1- CD49fHigh cells (stem cell enriched basal mammary epithelial compartment). There was no significant difference in stem/progenitor cell frequency based on limiting dilution transplants between the parous and age-matched virgin epithelium. Conclusions Although differences between parous and virgin mammary epithelium at later time points post lactation or following multiple pregnancies cannot be ruled out, there are no differences in stem/progenitor cell numbers between mammary epithelium isolated from parous animals which were mated at 9 weeks old and virgin animals. However, a recent report has suggested that animals that were mated at 5 weeks old have a twofold reduction in stem/progenitor cell numbers. This is of interest given the association between early, but not late, pregnancy and breast cancer risk reduction in humans. However, a mechanistic connection between stem cell numbers and breast cancer risk remains to be established

From Romantic Gothic to Victorian Medievalism: 1817 and 1877

"The Cambridge History of the Gothic was conceived in 2015, when Linda Bree, then Editorial Director at Cambridge University Press, first suggested the idea to us

Foodweb Kerplunk

This educational game produced by the Yale Center for Computational Ecology offers a highly interactive and engaging way to get a feel for the complex interrelationships of food webs. In Foodweb Kerplunk, the user plays the part of a town council member in suburban California, trying to protect native chaparral wildlife against the pressures of urban sprawl. Although Foodweb Kerplunk is designed for adult students, it could also serve as a valuable addition to advanced ecology-related courses at the high school level. The Web site includes detailed instructions and a brief introduction to the chaparral ecosystem

BacSim, a simulator for individual-based modelling of bacterial colony growth

This paper introduces spatially explicit individual-based modelling (IbM) to microbial ecology. The great potential of IbM lies in addressing 0002-2653 # 1998 SGM 3275 J.-U. KREFT,G.BOOTH and J. W.T.WIMPENN

Consequences of body size variation among herbivores on the strength of plant-herbivore interactions in a seasonal environment

Individual-based model Food web interactions Frequency-dependence Non-linearity Body size variation a b s t r a c t Classical theory in community ecology assumes that smaller-scale details such as individual traits can be abstracted safely and that community dynamics can be simply characterized in terms of net changes in population densities. Here we use a mechanistic simulation model of a three-level food web to explore the effect of initial body size variation among herbivores on final plant abundance resulting from a non-linear relationship between population demography and body size. We show that initial herbivore body size variation has a negative effect on their survival and consequently a positive effect on the final plant biomass. We then use trait distribution, in combination with body size-survival and body size-fitness curves estimated through simulations, to generate predictions for comparison with observed food web effects. We show that, owing to frequency-dependence, our ability to predict herbivore population dynamics is limited. However, at the community-level, this frequency-dependence, as well as changes in herbivore population size, can be abstracted safely and the strength of plant-herbivore interactions can be simply predicted from initial body size distribution in combination with the survival curve. Our findings suggest a need to revisit classical theory in community ecology. Doing so will require the mechanistic study of population demography and experimental testing of the effect of trait variation on community dynamics. © 2007 Elsevier B.V. All rights reserved. Introduction The way in which different organizational levels (e.g., individual, population, community) combine to influence population and community dynamics remains a fundamental research question in ecolog