COVER The axolotl, represented here by the Mexican axolotl Ambystoma mexicanum, has the ability to regenerate its brain. In this issue, a group of four papers profiles amphibian and reptile brain neurons with single-cell transcriptomics. Analyses lend insight into why the axolotl brain retains regenerative capability that the mammalian brain has lost as well as how structural brain innovations arose during evolution. See pages 1043, eabp8202, eabp9262, eabp9444, and eabp9186.

Photo: Avalon.red/Alamy Stock Photo

ONLINE COVER Elkhorn coral (Acropora palmata) in silhouette, East End, Grand Cayman, Cayman Islands. A. palmata’s reproductive genesis enabled Vasquez Kuntz et al. to study how somatic mutations (DNA alterations to non-germline cells after conception) transfer to offspring. They found that progeny harbor 50% of the 268 somatic mutations found in their parent. The authors suggest that somatic mutations may play a key role in adaptation to environmental changes over time.

ONLINE COVER Waves of IgA Regulate the Intestinal Microbiota. This month’s cover depicts the dynamic interplay between immunoglobulin A (IgA) and the commensal microbiota in the intestinal lumen. Penny and Domingues et al. report that secretory IgA exhibits daily rhythms in its release from lamina propria plasma cells into the intestinal tract, which are controlled by signals provided by food and the circadian clock. These “waves” of IgA regulate the daily oscillations in the relative abundance of commensal gut microbes to help maintain gut homeostasis.

ONLINE COVER Flexing Biomolecular Muscle. Actuation of soft microrobots can be achieved through the application of miniature motors, such as artificial muscles. However, the integration of such actuators within soft microrobots requires assembly processes that are often slow and require multiple steps. Wang et al. have developed a rapid and cost-effective in situ fabrication process that integrates artificial muscles composed of molecular motors in a variety of microrobots. This month’s cover shows a microrobot manipulating a ball; its arms are sequentially controlled by light-responsive artificial muscles.

ONLINE COVER This week, Kurimchak et al. show that the drug efflux pump MDR1 mediates the resistance of cancers to PROTACs, a class of drugs that induce the degradation of a target protein. This resistance can be overcome through combination treatment with the small-molecule drug lapatinib. The image shows a molecular model of a proteasome degrading a protein.

ONLINE COVER Transplant Taxonomy. This illustration depicts the altered taxa in the gut microbiomes of recipients after liver (orange dots) or kidney (blue dots) transplantation as compared to healthy controls (white dots); green dots represent taxa altered in both types of graft recipients. The outermost circle represents increased (blue) or decreased (red) abundance of bacterial species. Here, Swarte et al. found that the gut microbiomes in recipients of liver or renal transplants were substantially altered from healthy individuals. Antibiotics and immunosuppressive drugs contributed to development of this dysbiosis, and increased dysbiosis after transplant was associated with increased mortality. These findings suggest that microbiome-targeted interventions merit investigation to improve outcomes in transplant recipients.