The Mas-related genes (Mrgs) comprise a family of >50 G proteincoupled receptors (GPCRs), many of which are expressed in specific subsets of nociceptive sensory neurons in mice. In contrast, humans contain a related but nonorthologous family of genes, called MrgXs or sensory neuron-specific receptors, of which many fewer appear to be expressed in sensory neurons. To determine whether the diversity of murine Mrgs is generic to rodents or is an atypical feature of mice, we characterized MrgA, MrgB, MrgC, and MrgD subfamilies in rat and gerbil. Surprisingly, although mice have Ϸ22 MrgA and Ϸ14 MrgC genes, rats and gerbils have just a single MrgA and MrgC gene. This murine-specific expansion likely reflects recent retrotransposon-mediated unequal crossover events. The expression of Mrgs in rat sensory ganglia suggests that the extensive cellular diversity in mice can be simplified to a core subset of approximately four different genes (MrgA, MrgB, MrgC, and MrgD), defining a similar number of neuronal subpopulations. Our results suggest more generally that mouse-human genomic comparisons may sometimes reveal differences atypical of rodents. I n many sensory systems, including taste, olfaction, and vision, primary sensory neurons express diverse families of seven transmembrane domain G protein-coupled receptors (GPCRs) to detect and discriminate among various chemical and visual stimuli (1-3). The expansion of diverse GPCR families is enabled by the fact that functional receptors and their transcriptional controls often reside within small (Ϸ10-kb) segments of DNA present in tandem arrays (4-6). The success of this molecular unit is reflected in the fact that GPCRs constitute the largest single gene family in all metazoan genomes (7-10).Recent studies have identified a novel family of GPCRs specifically expressed in primary nociceptive sensory neurons in mice and humans (11,12). In vitro studies suggest that some of these receptors can be activated by neuropeptides that contain C-terminal -RF(Y)amide or -RF(Y)G motifs (11-13). Members of this family have been referred to as Mas-related genes (Mrgs) (11,14,15). Alternatively, in humans they have been called sensory neuron-specific receptors (SNSRs) (12). In mice, the Mrg family is comprised of six single-copy genes (MrgD, MrgE, MrgF͞RTA, MrgG, MrgH͞GPR90, and MAS1), as well as three large clades or subfamilies (MrgA, MrgB, and MrgC) that together comprise Ϸ50 distinct sequences. The differential expression of various mouse (m)Mrgs defines a surprisingly diverse axis of cellular heterogeneity among murine nociceptive sensory neurons, the functional significance of which is currently unclear (11).In contrast to the extensive sequence diversity exhibited by mMrgA, mMrgB, and mMrgC subfamilies, in humans there are only four functional hMrgX͞SNSR genes. Although some of these genes are specifically expressed in nociceptive sensory neurons like their murine counterparts, none of the human and mouse genes are strictly orthologous (11). This difference raises the question of...

Huntington disease (HD) is an autosomal dominant neurodegenerative disorder caused by CAG-expansion in the huntingtin gene (HTT) that results in a toxic gain of function in the mutant huntingtin protein (mHTT). Reducing the expression of mHTT is therefore an attractive therapy for HD. However, wild-type HTT protein is essential for development and has critical roles in maintaining neuronal health. Therapies for HD that reduce wild-type HTT may therefore generate unintended negative consequences. We have identified single-nucleotide polymorphism (SNP) targets in the human HD population for the disease-specific targeting of the HTT gene. Using primary cells from patients with HD and the transgenic YAC18 and BACHD mouse lines, we developed antisense oligonucleotide (ASO) molecules that potently and selectively silence mHTT at both exonic and intronic SNP sites. Modification of these ASOs with S-constrained-ethyl (cET) motifs significantly improves potency while maintaining allele selectively in vitro. The developed ASO is potent and selective for mHTT in vivo after delivery to the mouse brain. We demonstrate that potent and selective allele-specific knockdown of the mHTT protein can be achieved at therapeutically relevant SNP sites using ASOs in vitro and in vivo.

Brain injury, genetic manipulations, and pharmacological treatments can result in alterations of motor skills in mice. Fine motor coordination and balance can be assessed by the beam walking assay. The goal of this test is for the mouse to stay upright and walk across an elevated narrow beam to a safe platform. This test takes place over 3 consecutive days: 2 days of training and 1 day of testing. Performance on the beam is quantified by measuring the time it takes for the mouse to traverse the beam and the number of paw slips that occur in the process. Here we report the protocol used in our laboratory, and representative results from a cohort of C57BL/6 mice. This task is particularly useful for detecting subtle deficits in motor skills and balance that may not be detected by other motor tests, such as the Rotarod.