Highlights d Chemogenetic and/or optogenetic activation of primary cilia alters axonal behavior d Ciliary activity modulates axonal growth cones and filopodiallamellipodial balance d Arl13b-Inpp5e activity in cilia facilitates axonal tract formation and targeting d Disrupted ciliary signaling contributes to axonal tract malformations in JSRD

Sonic hedgehog (Shh) signal transduction specifies ventral cell fates in the neural tube and is mediated by the Gli transcription factors that play both activator (GliA) and repressor (GliR) roles. Cilia are essential for Shh signal transduction and the ciliary phosphatidylinositol phosphatase, Inpp5e, is linked to Shh regulation. In the course of a forward genetic screen for recessive mouse mutants, we identified a functional null allele of Inpp5e, ridge top (rdg), with expanded ventral neural cell fates at E10.5. By E12.5, Inpp5erdg/rdg embryos displayed normal neural patterning and this correction over time required Gli3, the predominant repressor in neural patterning. Inpp5erdg function largely depended on the presence of cilia and on Smoothened, the obligate transducer of Shh signaling, indicating Inpp5e functions within the cilium to regulate the pathway. These data indicate that Inpp5e plays a more complicated role in Shh signaling than previously appreciated. We propose that Inpp5e attenuates Shh signaling in the neural tube through regulation of the relative timing of GliA and GliR production, which is important in understanding how duration of Shh signaling regulates neural tube patterning.

O-linked β-N-acetylglucosamine (O-GlcNAc) is a single sugar modification found on many different classes of nuclear and cytoplasmic proteins. Addition of this modification, by the enzyme O-linked N-acetylglucosamine transferase (OGT), is dynamic and inducible. One major class of proteins modified by O-GlcNAc is transcription factors. O-GlcNAc regulates transcription factor properties through a variety of different mechanisms including localization, stability and transcriptional activation. Maintenance of embryonic stem (ES) cell pluripotency requires tight regulation of several key transcription factors, many of which are modified by O-GlcNAc. Octamer-binding protein 4 (Oct4) is one of the key transcription factors required for pluripotency of ES cells and more recently, the generation of induced pluripotent stem (iPS) cells. The action of Oct4 is modulated by the addition of several post-translational modifications, including O-GlcNAc. Previous studies in mice found a single site of O-GlcNAc addition responsible for transcriptional regulation. This study was designed to determine if this mechanism is conserved in humans. We mapped 10 novel sites of O-GlcNAc attachment on human Oct4, and confirmed a role for OGT in transcriptional activation of Oct4 at a site distinct from that found in mouse that allows distinction between different Oct4 target promoters. Additionally, we uncovered a potential new role for OGT that does not include its catalytic function. These results confirm that human Oct4 activity is being regulated by OGT by a mechanism that is distinct from mouse Oct4.

Highlights d Arl13b null mutant mice display commissural axon guidance defects d Arl13b is required for Shh-mediated growth cone attraction d Cilia-deficient Arl13b is sufficient for its role in axon guidance

1 Inpp5e attenuates Sonic hedgehog signal transduction through a combination of positive and 2 negative regulatory roles that likely control the relative timing of Gli processing. 3 4 Abstract 5 6 Sonic hedgehog (Shh) signal transduction specifies ventral cell fates in the neural tube7 and is mediated by the Gli transcription factors that play both activator (GliA) and repressor 8 (GliR) roles. Cilia are essential for Shh signal transduction and the ciliary phosphatidylinositol 9 phosphatase, Inpp5e, is linked to Shh regulation. In the course of a forward genetic screen for 10 recessive mouse mutants, we identified a functional null allele of Inpp5e, ridge top (rdg), with 11 expanded ventral neural cell fates at E10.5. By E12.5, Inpp5e rdg/rdg embryos displayed normal 12 neural patterning and this correction over time required Gli3, the predominant repressor in 13 neural patterning. Inpp5e rdg function largely depended on the presence of cilia and on 14 Smoothened, the obligate transducer of Shh signaling, indicating Inpp5e functions within the 15 cilium to regulate the pathway. These data indicate that Inpp5e plays a more complicated role in 16 Shh signaling than previously appreciated. We propose that Inpp5e attenuates Shh signaling in 17

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