Biology subjects

Nagai, M. H.

Publications and source records attributed to Nagai, M. H..

3 recordsLinked to original sources

bioRxiv2021

Encoding of odors by mammalian olfactory receptors

O_LIIdentified ligands for > 500 mouse ORs C_LIO_LIORs are specifically tuned towards individual odorants and their molecular properties C_LIO_LIOdor molecular properties are informative of odor responses C_LIO_LIPredictive modeling and convergent evolution analyses suggest specific residues within a canonical location for odorant binding C_LI Olfactory receptors (ORs) constitute the largest multi-gene family in the mammalian genome, with hundreds to thousands of loci in humans and mice respectively1. The rapid expansion of this massive family of genes has been generated by numerous duplication and diversification events throughout evolutionary history. This size, similarity, and diversity has made it challenging to define the principles by which ORs encode olfactory stimuli. Here, we performed a broad surveying of OR responses, using an in vivo strategy, against a diverse panel of odorants. We then used the resulting interaction profiles to uncover relationships between OR responses, odorants, odor molecular properties, and OR sequences. Our data and analyses revealed that ORs generally exhibited sparse tuning towards odorants and their molecular properties. Odor molecular property similarity between pairs of odorants was informative of odor response similarity. Finally, ORs sharing response to an odorant possessed amino acids at poorly conserved sites that exhibited both, predictive power towards odorant selectivity and convergent evolution. The localization of these residues occurred primarily at the interface of the upper halves of the transmembrane domains, implying that canonical positions govern odor selectivity across ORs. Altogether, our results provide a basis for translating odorants into receptor neuron responses for the unraveling of mammalian odor coding.

neuroscience↗

bioRxiv2021

Decoding the olfactory map: targeted transcriptomics link olfactory sensory neurons to glomeruli

Sensory processing in vertebrate olfactory systems is organized across olfactory bulb glomeruli, wherein axons of peripheral sensory neurons expressing the same olfactory receptor co-terminate to transmit receptor-specific activity to central neurons. Understanding how receptors map to glomeruli is therefore critical to understanding olfaction. High-throughput spatial transcriptomics is a rapidly advancing field, but low-abundance olfactory receptor expression within glomeruli has previously precluded high-throughput mapping of receptors to glomeruli. Here we combined spatial sectioning along the anteroposterior, dorsoventral, and mediolateral axes with target capture enrichment sequencing to overcome low-abundance target expression. This strategy allowed us to spatially map 86% of olfactory receptors across the olfactory bulb and uncover a relationship between OR sequence and glomerular position. ONE SENTENCE SUMMARYTargeted enrichment of olfactory receptor mRNA in olfactory bulb sections determines spatial positions for murine glomeruli.

neuroscience↗

bioRxiv2019

Depletion of Ric-8B leads to reduced mTORC2 activity

mTOR, a serine/threonine protein kinase that is involved in a series of critical cellular processes, can be found in two functionally distinct complexes, mTORC1 and mTORC2. In contrast to mTORC1, little is known about the mechanisms that regulate mTORC2. Here we show that mTORC2 activity is reduced in mice with a hypomorphic mutation of the Ric-8B gene. Ric-8B is a highly conserved protein that acts as a non-canonical guanine nucleotide exchange factor (GEF) for heterotrimeric Gs/olf type subunits. We found that Ric-8B hypomorph embryos are smaller than their wild type littermates, fail to close the neural tube in the cephalic region and die during mid-embryogenesis. Comparative transcriptome analysis revealed that signaling pathways involving GPCRs and G proteins are dysregulated in the Ric-8B mutant embryos. Interestingly, this analysis also revealed an unexpected impairment of the mTOR signaling pathway.\n\nPhosphorylation of Akt at Ser 473 is downregulated in the Ric-8B mutant embryos, indicating a decreased activity of mTORC2. In contrast, phosphorylation of S6, a downstream target of mTORC1, is unaltered. Knockdown of the endogenous Ric-8B gene in HEK293T cells leads to reduced phosphorylation levels of Akt at Ser 473, but not of S6, further supporting the selective involvement of Ric-8B in mTORC2 activity. Our results reveal a crucial role for Ric-8B in development and provide novel insights into the signals that regulate mTORC2 activity.\n\nAuthor SummaryGene inactivation in mice can be used to identify genes that are involved in important biological processes and that may contribute to disease. By using this approach, we found that the Ric-8B gene is essential for embryogenesis and for the normal development of the nervous system. Ric-8B mutant mouse embryos are smaller than their wild type littermates and show neural tube defects at the cranial region. This approach also allowed us to identify the biological pathways that are involved in the observed phenotypes, the G protein and mTORC2 signaling pathways. mTORC2 plays particular important roles also in the adult brain, and has been implicated in neurological disorders. Ric-8B is highly conserved in mammals, including humans. Our mutant mice provide a model to study the complex molecular and cellular processes underlying the interplay between Ric-8B and mTORC2 in neuronal function.

molecular biology↗