Dynamics of Recent Thymic Emigrants in Young Adult Mice

The peripheral naive T-cell pool is generally thought to consist of a subpopulation of recent thymic emigrants (RTEs) and a subpopulation of mature naive (MN) T cells with different dynamics. Thymus transplantation and adoptive transfer studies in mice have provided contradicting results, with some studies suggesting that RTEs are relatively short-lived cells, while another study suggested that RTEs have a survival advantage. We here estimate the death rates of RTE and MN T cells by performing both thymus transplantations and deuterium labeling experiments in mice of at least 12 weeks old, an age at which the size of the T-cell pool has stabilized. For CD4⁺ T cells, we found the total loss rate from the RTE compartment (by death and maturation) to be fourfold faster than that of MN T cells. We estimate the death rate of CD4⁺ RTE to be 0.046 per day, which is threefold faster than the total loss rate from the MN T-cell compartment. For CD8⁺ T cells, we found no evidence for kinetic differences between RTE and MN T cells. Thus, our data support the notion that in young adult mice, CD4⁺ RTE are relatively short-lived cells within the naive CD4⁺ T-cell pool.

Pervasive gene expression responses to a fluctuating diet in Drosophila melanogaster: The importance of measuring multiple traits to decouple potential mediators of life span and reproduction

Phenotypic plasticity is an important concept in life-history evolution, and most organisms, including Drosophila melanogaster, show a plastic life-history response to diet. However, little is known about how these life-history responses are mediated. In this study, we compared adult female flies fed an alternating diet (yoyo flies) with flies fed a constant low (CL) or high (CH) diet and tested how whole genome expression was affected by these diet regimes and how the transcriptional responses related to different life-history traits. We showed that flies were able to respond quickly to diet fluctuations throughout life span by drastically changing their transcription. Importantly, by measuring the response of multiple life-history traits we were able to decouple groups of genes associated with life span or reproduction, life-history traits that often covary with a diet change. A coexpression network analysis uncovered which genes underpin the separate and shared regulation of these life-history traits. Our study provides essential insights to help unravel the genetic architecture mediating life-history responses to diet, and it shows that the flies' whole genome transcription response is highly plastic.