Zebrafish expression reporters and mutants reveal that the IgSF cell adhesion molecule Dscamb is required for feeding and survival.

Down syndrome cell adhesion molecules (DSCAMs) are broadly expressed in nervous systems and play conserved roles in programmed cell death, neuronal migration, axon guidance, neurite branching and spacing, and synaptic targeting. However, DSCAMs appear to have distinct functions in different vertebrate animals, and little is known about their functions outside the retina. We leveraged the genetic tractability and optical accessibility of larval zebrafish to investigate the expression and function of a DSCAM family member, dscamb. Using targeted genome editing to create transgenic reporters and loss-of-function mutant alleles, we discovered that dscamb is expressed broadly throughout the brain, spinal cord, and peripheral nervous system, but is not required for overall structural organization of the brain. Despite the absence of obvious anatomical defects, homozygous dscamb mutants were deficient in their ability to ingest food and rarely survived to adulthood. Thus, we have discovered a novel function for dscamb in feeding behavior. The mutant and transgenic lines generated in these studies will provide valuable tools for identifying the molecular and cellular bases of these behaviors.

Serotonin neuromodulation directs optic nerve regeneration.

Optic nerve (ON) regeneration in mammalian systems is limited by an overshadowing dominance of inhibitory factors. This has severely hampered the identification of pro-regenerative pathways. Here, we take advantage of the regenerative capacity of larval zebrafish to identify pathways that promote ON regeneration. From a small molecule screen, we identified modulators of serotonin (5-HT) signaling that inhibit ON regeneration. We find several serotonin type-1 receptor genes are expressed in RGC neurons during regeneration and that inhibiting 5-HT1 receptors or components of the 5-HT pathway selectively impedes ON regeneration. We show that 5-HT1 receptor signaling is dispensable during ON development yet is critical for regenerating axons to emerge from the injury site. Blocking 5-HT receptors once ON axons have crossed the chiasm does not inhibit regeneration, suggesting a selective role for 5-HT receptor signaling early during ON regeneration. Finally, we show that agonist-mediated activation of 5-HT1 receptors leads to enhanced and ectopic axonal regrowth. Combined, our results provide evidence for mechanisms through which serotonin-dependent neuromodulation directs ON regeneration in vivo.

The mucosal barrier and anti-viral immune responses can eliminate portions of the viral population during transmission and early viral growth.

Little is known about how specific individual viral lineages replicating systemically during acute Human Immunodeficiency Virus or Simian Immunodeficiency Virus (HIV/SIV) infection persist into chronic infection. In this study, we use molecularly barcoded SIV (SIVmac239M) to track distinct viral lineages for 12 weeks after intravenous (IV) or intrarectal (IR) challenge in macaques. Two Mafa-A1*063+ cynomolgus macaques (Macaca fascicularis, CM) were challenged IV, and two Mamu-A1*001+ rhesus macaques (Macaca mulatta, RM) were challenged IR with 200,000 Infectious Units (IU) of SIVmac239M. We sequenced the molecular barcode of SIVmac239M from all animals over the 12 weeks of the study to characterize the diversity and persistence of virus lineages. During the first three weeks post-infection, we found ~70-560 times more unique viral lineages circulating in the animals challenged IV compared to those challenged IR, which is consistent with the hypothesis that the challenge route is the primary driver restricting the transmission of individual viral lineages. We also characterized the sequences of T cell epitopes targeted during acute SIV infection, and found that the emergence of escape variants in acutely targeted epitopes can occur on multiple virus templates simultaneously, but that elimination of some of these templates is likely a consequence of additional host factors. These data imply that virus lineages present during acute infection can still be eliminated from the systemic virus population even after initial selection.

Pregnancy-associated plasma protein-aa supports hair cell survival by regulating mitochondrial function.

To support cell survival, mitochondria must balance energy production with oxidative stress. Inner ear hair cells are particularly vulnerable to oxidative stress; thus require tight mitochondrial regulation. We identified a novel molecular regulator of the hair cells' mitochondria and survival: Pregnancy-associated plasma protein-aa (Pappaa). Hair cells in zebrafish pappaa mutants exhibit mitochondrial defects, including elevated mitochondrial calcium, transmembrane potential, and reactive oxygen species (ROS) production and reduced antioxidant expression. In pappaa mutants, hair cell death is enhanced by stimulation of mitochondrial calcium or ROS production and suppressed by a mitochondrial ROS scavenger. As a secreted metalloprotease, Pappaa stimulates extracellular insulin-like growth factor 1 (IGF1) bioavailability. We found that the pappaa mutants' enhanced hair cell loss can be suppressed by stimulation of IGF1 availability and that Pappaa-IGF1 signaling acts post-developmentally to support hair cell survival. These results reveal Pappaa as an extracellular regulator of hair cell survival and essential mitochondrial function.