Characterization of previously described intraflagellar transport (IFT) mouse mutants has led to the proposition that normal primary cilia are required for mammalian cells to respond to the sonic hedgehog (SHH) signal. Here we describe an N-ethyl-N-nitrosourea–induced mutant mouse, alien (aln), which has abnormal primary cilia and shows overactivation of the SHH pathway. The aln locus encodes a novel protein, THM1 (tetratricopeptide repeat–containing hedgehog modulator-1), which localizes to cilia. aln-mutant cilia have bulb-like structures at their tips in which IFT proteins (such as IFT88) are sequestered, characteristic of Chlamydomonas reinhardtii and Caenorhabditis elegans retrograde IFT mutants. RNA-interference knockdown of Ttc21b (which we call Thm1 and which encodes THM1) in mouse inner medullary collecting duct cells expressing an IFT88–enhanced yellow fluorescent protein fusion recapitulated the aln-mutant cilial phenotype, and live imaging of these cells revealed impaired retrograde IFT. In contrast to previously described IFT mutants, Smoothened and full-length glioblastoma (GLI) proteins localize to aln-mutant cilia. We hypothesize that the aln retrograde IFT defect causes sequestration of IFT proteins in aln-mutant cilia and leads to the overactivated SHH signaling phenotype. Specifically, the aln mutation uncouples the roles of anterograde and retrograde transport in SHH signaling, suggesting that anterograde IFT is required for GLI activation and that retrograde IFT modulates this event.

THM1 negatively modulates mouse sonic hedgehog signal transduction and affects retrograde intraflagellar transport in cilia

Competing E3 Ubiquitin Ligases Govern Circadian Periodicity by Degradation of CRY in Nucleus and Cytoplasm

Mammalian Sonic hedgehog (Shh) signaling is essential for embryonic development and stem cell maintenance and has critical roles in tumorigenesis. Although core components of the Shh pathway are conserved in evolution, important aspects of mammalian Shh signaling are not shared with the Drosophila pathway. Perhaps the most dramatic difference between the Drosophila and mammalian pathways is that Shh signaling in the mouse requires a microtubule-based organelle, the primary cilium. Proteins that are required for the response to Shh are enriched in the cilium, but it is not clear why the cilium provides an appropriate venue for signal transduction. Here, we demonstrate that Kif7, a mammalian homologue of Drosophila Costal2 (Cos2), is a cilia-associated protein that regulates signaling from the membrane protein Smoothened (Smo) to Gli transcription factors. By using a Kif7 mutant allele identified in a reporter-based genetic screen, we show that, similar to Drosophila and zebrafish Cos2, mouse Kif7 acts downstream of Smo and upstream of Gli2 and has both negative and positive roles in Shh signal transduction. Mouse Kif7 activity depends on the presence of cilia and Kif7-eGFP localizes to base of the primary cilium in the absence of Shh. Activation of the Shh pathway promotes trafficking of Kif7-eGFP from the base to the tip of the cilium, and localization to the tip of the cilium is disrupted in a motor domain mutant. We conclude that Kif7 is a core regulator of Shh signaling that may also act as a ciliary motor.

https://www.pnas.org/content/pnas/106/32/13377.full.pdf

Mouse Kif7/Costal2 is a cilia-associated protein that regulates Sonic hedgehog signaling

High-resolution genetic maps are required for mapping complex traits and for the study of recombination. We report the highest density genetic map yet created for any organism, except humans. Using more than 10,000 single nucleotide polymorphisms evenly spaced across the mouse genome, we have constructed genetic maps for both outbred and inbred mice, and separately for males and females. Recombination rates are highly correlated in outbred and inbred mice, but show relatively low correlation between males and females. Differences between male and female recombination maps and the sequence features associated with recombination are strikingly similar to those observed in humans. Genetic maps are available from http://gscan.well.ox.ac.uk/#genetic_map and as supporting information to this publication.

/pdf/a-high-resolution-single-nucleotide-polymorphism-genetic-map-2rl7ssk0kz.pdf

A High-Resolution Single Nucleotide Polymorphism Genetic Map of the Mouse Genome

Two intraflagellar transport (IFT) complexes, IFT-A and IFT-B, build and maintain primary cilia and are required for activity of the Sonic hedgehog (Shh) pathway. A weak allele of the IFT-A gene, Ift144, caused subtle defects in cilia structure and ectopic activation of the Shh pathway. In contrast, strong loss of IFT-A, caused by either absence of Ift144 or mutations in two IFT-A genes, blocked normal ciliogenesis and decreased Shh signaling. In strong IFT-A mutants, the Shh pathway proteins Gli2, Sufu, and Kif7 localized correctly to cilia tips, suggesting that these pathway components were trafficked by IFT-B. In contrast, the membrane proteins Arl13b, ACIII, and Smo failed to localize to primary cilia in the absence of IFT-A. We propose that the increased Shh activity seen in partial loss-of-function IFT-A mutants may be a result of decreased ciliary ACIII and that the loss of Shh activity in the absence of IFT-A is a result of severe disruptions of cilia structure and membrane protein trafficking.

/pdf/the-ift-a-complex-regulates-shh-signaling-through-cilia-4nbmepemap.pdf

The IFT-A Complex Regulates Shh Signaling through Cilia Structure and Membrane Protein Trafficking

Phenotype-driven genetics can be used to create mouse models of human disease and birth defects. However, the utility of these mutant models is limited without identification of the causal gene. To facilitate genetic mapping, we developed a fixed single nucleotide polymorphism (SNP) panel of 394 SNPs as an alternative to analyses using simple sequence length polymorphism (SSLP) marker mapping. With the SNP panel, chromosomal locations for 22 monogenic mutants were identified. The average number of affected progeny genotyped for mapped monogenic mutations is nine. Map locations for several mutants have been obtained with as few as four affected progeny. The average size of genetic intervals obtained for these mutants is 43 Mb, with a range of 17-83 Mb. Thus, our SNP panel allows for identification of moderate resolution map position with small numbers of mice in a high-throughput manner. Importantly, the panel is suitable for mapping crosses from many inbred and wild-derived inbred strain combinations. The chromosomal localizations obtained with the SNP panel allow one to quickly distinguish between potentially novel loci or remutations in known genes, and facilitates fine mapping and positional cloning. By using this approach, we identified DNA sequence changes in two ethylnitrosourea-induced mutants.

/pdf/utilization-of-a-whole-genome-snp-panel-for-efficient-vemdg1k7qr.pdf

Utilization of a whole genome SNP panel for efficient genetic mapping in the mouse

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Utilization of a whole genome SNP panel for efficient genetic mapping in the mouse