Polyglutamylation of tubulin's C-terminal tail controls pausing and motility of kinesin-3 family member KIF1A.

The kinesin-3 family member KIF1A plays a critical role in site-specific neuronal cargo delivery during axonal transport. KIF1A cargo is mislocalized in many neurodegenerative diseases, indicating that KIF1A's highly efficient, superprocessive motility along axonal microtubules needs to be tightly regulated. One potential regulatory mechanism may be through posttranslational modifications (PTMs) of axonal microtubules. These PTMs often occur on the C-terminal tails of the microtubule tracks, act as molecular "traffic signals" helping to direct kinesin motor cargo delivery, and include C-terminal tail polyglutamylation important for KIF1A cargo transport. KIF1A initially interacts with microtubule C-terminal tails through its K-loop, a positively charged surface loop of the KIF1A motor domain. However, the role of the K-loop in KIF1A motility and response to perturbations in C-terminal tail polyglutamylation is underexplored. Using single-molecule imaging, we present evidence that KIF1A pauses on different microtubule lattice structures, linking multiple processive segments together and contributing to KIF1A's characteristic superprocessive run length. Furthermore, modifications of the KIF1A K-loop or tubulin C-terminal tail polyglutamylation reduced KIF1A pausing and overall run length. These results suggest a new mechanism to regulate KIF1A motility via pauses mediated by K-loop/polyglutamylated C-terminal tail interactions, providing further insight into KIF1A's role in axonal transport.

An allelic series of spontaneous Rorb mutant mice exhibit a gait phenotype, changes in retina morphology and behavior, and gene expression signatures associated with the unfolded protein response.

The Retinoid-related orphan receptor beta (RORß) gene encodes a developmental transcription factor and has 2 predominant isoforms created through alternative first exon usage; one specific to the retina and another present more broadly in the central nervous system, particularly regions involved in sensory processing. RORß belongs to the nuclear receptor family and plays important roles in cell fate specification in the retina and cortical layer formation. In mice, loss of RORß causes disorganized retina layers, postnatal degeneration, and production of immature cone photoreceptors. Hyperflexion or "high-stepping" of rear limbs caused by reduced presynaptic inhibition by Rorb-expressing inhibitory interneurons of the spinal cord is evident in RORß-deficient mice. RORß variants in patients are associated with susceptibility to various neurodevelopmental conditions, primarily generalized epilepsies, but including intellectual disability, bipolar, and autism spectrum disorders. The mechanisms by which RORß variants confer susceptibility to these neurodevelopmental disorders are unknown but may involve aberrant neural circuit formation and hyperexcitability during development. Here we report an allelic series in 5 strains of spontaneous Rorb mutant mice with a high-stepping gait phenotype. We show retinal abnormalities in a subset of these mutants and demonstrate significant differences in various behavioral phenotypes related to cognition. Gene expression analyses in all 5 mutants reveal a shared over-representation of the unfolded protein response and pathways related to endoplasmic reticulum stress, suggesting a possible mechanism of susceptibility relevant to patients.

The Genome of C57BL/6J "Eve", the Mother of the Laboratory Mouse Genome Reference Strain.

Isogenic laboratory mouse strains enhance reproducibility because individual animals are genetically identical. For the most widely used isogenic strain, C57BL/6, there exists a wealth of genetic, phenotypic, and genomic data, including a high-quality reference genome (GRCm38.p6). Now 20 years after the first release of the mouse reference genome, C57BL/6J mice are at least 26 inbreeding generations removed from GRCm38 and the strain is now maintained with periodic reintroduction of cryorecovered mice derived from a single breeder pair, aptly named Adam and Eve. To provide an update to the mouse reference genome that more accurately represents the genome of today's C57BL/6J mice, we took advantage of long read, short read, and optical mapping technologies to generate a de novo assembly of the C57BL/6J Eve genome (B6Eve). Using these data, we have addressed recurring variants observed in previous mouse genomic studies. We have also identified structural variations, closed gaps in the mouse reference assembly, and revealed previously unannotated coding sequences. This B6Eve assembly explains discrepant observations that have been associated with GRCm38-based analyses, and will inform a reference genome that is more representative of the C57BL/6J mice that are in use today.