A colored scanning electron micrograph of hematopoietic stem cells. Cannon and colleagues report efficient genome editing in human hematopoietic stem and progenitor cells using zinc finger nuclease mRNA and AAV6 donor DNA (p 1256). Credit: SPL/Science Source

Microscopic image of microfluidic droplets. Rotem et al. (p 1165) use microfluidics in combination with DNA barcoding and sequencing to collect data on the location of histone modifications from thousands of single cells. Credit: Assaf Rotem

Artist's rendition of an optogenetically controlled Ca2+ channel. Kyung et al. present OptoSTIM1, an optogenetic tool for manipulating intracellular Ca2+ levels by activating endogenous Ca2+ channels. Credit: Won Do Heo

Zuhua He and colleagues (p 996) find that overexpression of the ERECTA gene in rice (and tomato) increases heat tolerance. Rice fields at sunset. Photographer: Philip Wallick. © Corbis

Deep learning of protein-DNA-binding specificities seen through an artist's eyes. Alipanahi et al. show that deep learning techniques can be used to ascertain the binding sequences of proteins on RNA and DNA from experimental data (p 831). Credit: Graham Johnson

A representation of a heart stimulated by light pulses delivered at two sites. Nussinovitch and Gepstein pace the rat heart using viral delivery of a channelrhodopsin-2 transgene and optical activation (p 750). Credit: Elizabeth McDonald.

Artist's rendition of the chromosomes in a male human cell, with maternally and paternally inherited chromosomes shown in different colors. Cao et al. assemble a haplotype-resolved human genome without using a reference sequence (p 617). Credit: Chris Hammang

Upland cotton (Gossypium hirsutum) planted in the Xinjiang Uygur Autonomous Region of China. Two draft genome sequences of G. hirsutum, the most widely cultivated cotton species, provide insights into cotton evolution and fiber biology (pp 524, 531). Credit: Tianzhen Zhang, Nanjing Agricultural University, China

Artist's representation of nucleosomes showing various measured (dark blue) and predicted (light blue) epigenetic modifications. Ernst and Kellis present a method for imputing the locations of epigenetic marks from experimental data on other marks (p 364). Credit: Chris Hammang

A macroscopic fiber capable of transmitting electrical signal, light and drugs is pulled to create brain probes with a diameter <50 μm. Canales et al. demonstrate the utility of the probes for studying neural function in freely moving animals for extended periods of time (p 277).

Aerial photograph showing 30 million hectares of small farms in northern China that include fields planted with insecticidal transgenic Bt cotton and natural refuges of other crops that do not make Bt toxins. Wu et al. show that natural refuges have helped to delay evolution of Bt resistance in cotton bollworm. One alternative for delaying resistance to Bt crops is engineering them to produce two or more toxins that kill the same pest, which is analyzed by Carriére et al. (p 169; p 161) Credit: Ming Zhang, Microfotos

Scanning electron microscope image of an inorganic scaffold that can be used to boost vaccine efficacy (p 64; p 44) Credit: Aileen Li, Jaeyun Kim and James C Weaver