Categoria: Cell biology

T cell activation and function require a structured engagement of antigen-presenting cells. These cell contacts are characterized by two distinct dynamics in vivo: transient contacts resulting from promigratory junctions called immunological kinapses or prolonged contacts from stable junctions called immunological synapses. Kinapses operate in the steady state to allow referencing to self-peptide-MHC (pMHC) and searching for pathogen-derived pMHC.

Synapses are induced by T cell receptor (TCR) interactions with agonist pMHC under specific conditions and correlate with robust immune responses that generate effector and memory T cells. High-resolution imaging has revealed that the synapse is highly coordinated, integrating cell adhesion, TCR recognition of pMHC complexes, and an array of activating and inhibitory ligands to promote or prevent T cell signaling. In this review, we examine the molecular components, geometry, and timing underlying kinapses and synapses.

We integrate recent molecular and physiological data to provide a synthesis and suggest ways forward.Technology can be complicated, but we’ve seen it all before and can help…

Optimal protein synthesis requires bases in transfer RNAs to be modified. A key modification has been shown to involve an unusual two-step mechanism that entails the sequential activities of two enzymes. 

A central dogma of molecular biology is that DNA and the corresponding RNA are complementary. But this complementarity is rewired by a process called RNA editing, which recodes genomic information by modifying, deleting or inserting nucleotides in RNA transcripts. RNA editing has wide-ranging roles in various cellular processes and has clear implications in human disease1. The molecular and biochemical mechanisms underlying RNA editing have proved a challenge to scientists since its discovery 30 years ago in trypanosomes, a type of protozoan2. On page 494, Rubio et al.3 now provide intriguing evidence that editing of transfer RNAs is an unconventional two-step process, thus reasserting a valuable mechanistic concept for the field

An evolutionarily well-conserved editing process called base deamination converts RNA components known as nucleosides into other nucleosides: more specifically, it converts cytidine (C) into uridine (U), and adenosine (A) into inosine (I). In tRNAs, such conversions generate ‘wobble’ base pairs that are crucial for proper translation of the genetic code, and that maintain tertiary structure5,6,7. The enzyme that edits tRNA in archaea7 (which, along with bacteria, constitute the microorganisms known as prokaryotes) has been identified, but its counterpart in eukaryotes (organisms that include plants, animals, fungi and protozoa) has remained elusive.

Cancer incidence and mortality statistics reported by the American Cancer Society¹ and other resources were used to create the list. To qualify as a common cancer for the list, the estimated annual incidence for 2019 had to be 40,000 cases or more.

The most common type of cancer on the list is breast cancer, with 271,270 new cases expected in the United States in 2019. The next most common cancers are lung cancer and prostate cancer. 

Because colon and rectal cancers are often referred to as “colorectal cancers,” these two cancer types are combined for the list. For 2019, the estimated number of new cases of colon cancer and rectal cancer are 101,420 and 44,180, respectively, adding to a total of 145,600 new cases of colorectal cancer.