Fetal and adult hematopoietic stem cells give rise to distinct T cell lineages in humans

Although the mammalian immune system is generally thought to develop in a linear fashion, findings in avian and murine species argue instead for the developmentally ordered appearance (or "layering") of distinct hematopoietic stem cells (HSCs) that give rise to distinct lymphocyte lineages at different stages of development. Here we provide evidence of an analogous layered immune system in humans. Our results suggest that fetal and adult T cells are distinct populations that arise from different populations of HSCs that are present at different stages of development. We also provide evidence that the fetal T cell lineage is biased toward immune tolerance. These observations offer a mechanistic explanation for the tolerogenic properties of the developing fetus and for variable degrees of immune responsiveness at birth.     

A molecular elevator

We report the incrementally staged design, synthesis, characterization, and operation of a molecular machine that behaves like a nanoscale elevator. The operation of this device, which is made of a platformlike component interlocked with a trifurcated riglike component and is only 3.5 nanometers by 2.5 nanometers in size, relies on the integration of several structural and functional molecular subunits. This molecular elevator is considerably more complex and better organized than previously reported artificial molecular machines. It exhibits a clear-cut on-off reversible behavior, and it could develop forces up to around 200 piconewtons.     

THE EFFECT OF THE TIMING OF AMMONIUM NITRATE DRESSINGS ON THE HEADING OF S48 TIMOTHY (PHLEUM PRATENSE L.)

The response of single plants of Aberystwyth S48 timothy ( Phleum pratense L.) to increasing rates of ammonium nitrate applied in the spring and autumn is described.
All spring treatments markedly increased the number of heads, as well as the total head-length per plant, but autumn dressings had no significant effect. Percentage head-length distribution was also greatly influenced by applications of nitrogenous fertilizer in the spring. Each higher rate of application gave a proportionate increase in the number of heads over 9 cm. in length, and a corresponding reduction in the frequency of those of 4 cm. or less. There was a positive correlation between head-length and number of florets per unit length.
The results are discussed in terms of their relationship to current practices in managing timothy crops for seed.     

AN INEXPENSIVE SEED CLEANER FOR USE WITH SINGLE HEADS OF TIMOTHY

Constructional details are given of an inexpensive seed cleaner capable of handling material from single heads of timothy, yielding cleaned seed of over 98% purity by weight. The conditions within the cleaner are reproducible and running costs negligible.