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.

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.

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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.

19To support cell survival, mitochondria must balance energy production with oxidative stress. Inner 20 ear hair cells are particularly vulnerable to oxidative stress; thus require tight mitochondrial regulation. 21 We identified a novel molecular regulator of the hair cells' mitochondria and survival: Pregnancy-22 associated plasma protein-aa (Pappaa). Hair cells in zebrafish pappaa mutants exhibit mitochondrial 23 defects, including elevated mitochondrial calcium, transmembrane potential, and reactive oxygen 24 species (ROS) production and reduced antioxidant expression. In pappaa mutants, hair cell death is 25 enhanced by stimulation of mitochondrial calcium or ROS production and suppressed by a 26 mitochondrial ROS scavenger. As a secreted metalloprotease, Pappaa stimulates extracellular insulin-27 like growth factor 1 (IGF1) bioavailability. We found that the pappaa mutants' enhanced hair cell loss 28 can be suppressed by stimulation of IGF1 availability and that Pappaa-IGF1 signaling acts post-29 developmentally to support hair cell survival. These results reveal Pappaa as an extracellular regulator 30 of hair cell survival and essential mitochondrial function. 31 32Without a sufficient regenerative capacity, a nervous system's form and function critically depends 33 on the molecular and cellular mechanisms that support its cells' longevity. Neural cell survival is 34 inherently challenged by the nervous system's high energy demand, which is required to support basic 35 functions, including maintaining membrane potential, propagating electrical signals, and coordinating 36 the release and uptake of neurotransmitters (Halliwell, 2006; Kann and Kovács, 2007; Howarth et al., 37 2012). Metabolic energy is primarily supplied by mitochondrial oxidative phosphorylation (Kann and 38 Kovács, 2007). Although this process is essential to cell survival, a cytotoxic consequence is the 39 generation of reactive oxygen species (ROS). Oxidative stress caused by ROS accumulation damages 40 vital cell components including DNA, proteins, and lipids (Schieber and Chandel, 2014). Neural cells 41 are particularly vulnerable to oxidative stress due not only to their energy demand and thereby ROS 42 production, but also to their relatively insufficient antioxidant capacity (Halliwell, 1992). This 43 heightened susceptibility to oxidative stress-mediated cell death is believed to underlie aging and 44 neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), and 45 Amyotrophic lateral sclerosis (ALS) (Perry et al., 2002; Barber et al., 2006; Mattson and Magnus, 46 2006; Blesa et al., 2015). 47 Hair cells of the inner ear are a population of neural cells that are particularly susceptible to 48 oxidative stress-induced death (Gonzalez-Gonzalez, 2017) These specialized sensory cells relay sound 49 and balance information to the central nervous system. Hair cell death or damage, which is irreversible 50 in mammals, is the primary cause of hearing loss, and is exacerbated by ag...