Biology subjects

Alvarez-Buylla, A.

Publications and source records attributed to Alvarez-Buylla, A..

24 records · Page 2Linked to original sources

bioRxiv2021

Molecular diversity and lineage commitment of human interneuron progenitors

Cortical interneurons are indispensable for proper function of neocortical circuits. Changes in interneuron development and function are implicated in human disorders, such as autism spectrum disorder and epilepsy. In order to understand human-specific features of cortical development as well as the origins of neurodevelopmental disorders it is crucial to identify the molecular programs underlying human interneuron development and subtype specification. Recent studies have explored gene expression programs underlying mouse interneuron specification and maturation. We applied single-cell RNA sequencing to samples of second trimester human ganglionic eminence and developing cortex to identify molecularly defined subtypes of human interneuron progenitors and immature interneurons. In addition, we integrated this data from the developing human ganglionic eminences and neocortex with single-nucleus RNA-seq of adult cortical interneurons in order to elucidate dynamic molecular changes associated with commitment of progenitors and immature interneurons to mature interneuron subtypes. By comparing our data with published mouse single-cell genomic data, we discover a number of divergent gene expression programs that distinguish human interneuron progenitors from mouse. Moreover, we find that a number of transcription factors expressed during prenatal development become restricted to adult interneuron subtypes in the human but not the mouse, and these adult interneurons express species- and lineage-specific cell adhesion and synaptic genes. Therefore, our study highlights that despite the similarity of main principles of cortical interneuron development and lineage commitment between mouse and human, human interneuron genesis and subtype specification is guided by species-specific gene programs, contributing to human-specific features of cortical inhibitory interneurons.

neuroscience↗

bioRxiv2021

Single-cell analysis of the ventricular-subventricular zone reveals signatures of dorsal and ventral adult neurogenic lineages

The ventricular-subventricular zone (V-SVZ) is home to the largest neurogenic niche in the adult mouse brain. Previous work has demonstrated that resident stem cells in different locations within the V-SVZ produce different subtypes of new neurons for the olfactory bulb. While great progress has been made in understanding the differences in regional stem cell potential using viral and genetic lineage tracing strategies, the core molecular heterogeneity that underlies these regional differences is largely unknown. Here we present single whole-cell and single nucleus sequencing datasets of microdissected adult mouse V-SVZ, and evidence for the existence of two broad populations of adult neural stem cells. By using spatially resolved microdissections in the single nucleus sequencing dataset as a reference, and mapping marker gene expression in the V-SVZ, we find that these two populations reside in largely non-overlapping domains in either the dorsal or ventral V-SVZ. Furthermore, we identified two subpopulations of newly born neurons that have gene expression consistent with dorsal or ventral origins. Finally, we identify genes expressed by both stem cells and the neurons they generate that specifically mark either the dorsal or ventral adult neurogenic lineage. These datasets, methods and findings will facilitate the study of region-specific regulation of adult neurogenesis.

neuroscience↗

bioRxiv2020

Pumiliotoxin metabolism and molecular physiology in a poison frog

Poison frogs bioaccumulate alkaloids for chemical defense from their arthropod diet. Although many alkaloids are accumulated without modification, some poison frog species can metabolize pumiliotoxin (PTX 251D) into the more potent allopumiliotoxin (aPTX 267A). Despite extensive research characterizing the chemical arsenal of poison frogs, the physiological mechanisms involved in the sequestration and metabolism of individual alkaloids remain unclear. We first performed a feeding experiment with the Dyeing poison frog (Dendrobates tinctorius) to ask if this species can metabolize PTX 251D into aPTX 267A and what gene expression changes are associated with PTX 251D exposure in the intestines, liver, and skin. We found that D. tinctorius can metabolize PTX 251D into aPTX 267A, and that PTX 251D exposure changed the expression level of genes involved in immune system function and small molecule metabolism and transport. To better understand the functional significance of these changes in gene expression, we then conducted a series of high-throughput screens to determine the molecular targets of PTX 251D and identify potential proteins responsible for metabolism of PTX 251D into aPTX 267A. Although screens of PTX 251D binding human voltage-gated ion channels and G-protein coupled receptors were inconclusive, we identified human CYP2D6 as a rapid metabolizer of PTX 251D in a cytochrome P450 screen. Furthermore, a CYP2D6-like gene had increased expression in the intestines of animals fed PTX, suggesting this protein may be involved in PTX metabolism. These results show that individual alkaloids can modify gene expression across tissues, including genes involved in alkaloid metabolism. More broadly, this work suggests that specific alkaloid classes in wild diets may induce physiological changes for targeted accumulation and metabolism.

physiology↗

bioRxiv2020

Clustered γ-Protocadherins Regulate Cortical Interneuron Programmed Cell Death.

Cortical function critically depends on inhibitory/excitatory balance. GABAergic cortical inhibitory interneurons (cINs) are born in the ventral forebrain. After completing their migration into cortex, their final numbers are adjusted-during a period of postnatal development - by programmed cell death (PCD). The mechanisms that regulate cIN elimination remain controversial. Here we show that genes in the protocadherin (Pcdh)-{gamma} gene cluster, but not in the Pcdh- or Pcdh-{beta} clusters, are required for survival of cINs through a BAX-dependent mechanism. Surprisingly, the physiological and morphological properties of Pcdh-{gamma} deficient and wild type cINs during PCD were indistinguishable. Co-transplantation of wild type and Pcdh-{gamma} deficient interneuron precursor cells demonstrate that: 1) the number of mutant cINs eliminated was much higher than that of wild type cells, but the proportion of mutant or WT cells undergoing cell death was not affected by their density; 2) the presence of mutant cINs increases cell death among wild-type counterparts, and 3) cIN survival is dependent on the expression of Pcdh-{gamma} C3, C4, and C5. We conclude that Pcdh-{gamma}, and specifically {gamma}C3, {gamma}C4, and {gamma}C5, play a critical role in regulating cIN survival during the endogenous period of PCD. SignificanceGABAergic cortical inhibitory interneurons (cINs) in the cerebral cortex originate from the ventral embryonic forebrain. After a long migration, they come together with local excitatory neurons to form cortical circuits. These circuits are responsible for higher brain functions, and the improper balance of excitation/inhibition in the cortex can result in mental diseases. Therefore, an understanding of how the final number of cINs is determined is both biologically and, likely, therapeutically significant. Here we show that cell surface homophilic binding proteins belonging to the clustered protocadherin gene family, specifically three isoforms in the Pcdh-{gamma} cluster, play a key role in the regulation cIN programmed cell death. Co-transplantation of mutant and wild-type cINs shows that Pcdh-{gamma} genes have cell-autonomous and non-cell autonomous roles in the regulation of cIN cell death. This work will help identify the molecular mechanisms and cell-cell interactions that determine how the proper ratio of excitatory to inhibitory neurons is determined in the cerebral cortex.

neuroscience↗

bioRxiv2019

Transplanted cells are essential for the induction but not the expression of cortical plasticity

Transplantation of even a small number of embryonic inhibitory neurons from the medial ganglionic eminence (MGE) into postnatal visual cortex makes it lose responsiveness to an eye deprived of vision when the transplanted neurons reach the age of the normal critical period of activity-dependent ocular dominance (OD) plasticity. The transplant might induce OD plasticity in the host circuitry or might instead construct a parallel circuit of its own to suppress cortical responses to the deprived-eye. We transplanted MGE neurons expressing archaerhodopsin, closed one eyelid for 4-5 days, and, as expected, observed transplant-induced OD plasticity. This plasticity was evident even when the activity of the transplanted cells was suppressed optogenetically, demonstrating that the plasticity was produced by changes in the host visual cortex.\n\nSignificance StatementInterneuron transplantation into mouse V1 creates a window of heightened plasticity which is quantitatively and qualitatively similar to the normal critical period, i.e. short-term occlusion of either eye markedly changes ocular dominance. The underlying mechanism of this process is not known. Transplanted interneurons might either form a separate circuit to maintain the ocular dominance shift or might instead trigger changes in the host circuity. We designed experiments to distinguish the two hypotheses. Our findings suggest that while inhibition produced by the transplanted cells triggers this form of plasticity, the host circuity is entirely responsible for maintaining the ocular dominance shift.\n\nOne Sentence SummaryNeuronal transplants do not just grow and connect--they induce plasticity in the adult brain.

neuroscience↗

bioRxiv2019

Molecular physiology of chemical defenses in a poison frog

Poison frogs sequester small molecule lipophilic alkaloids from their diet of leaf litter arthropods for use as chemical defenses against predation. Although the dietary acquisition of chemical defenses in poison frogs is well-documented, the physiological mechanisms of alkaloid sequestration has not been investigated. Here, we used RNA sequencing and proteomics to determine how alkaloids impact mRNA or protein abundance in the Little Devil Frog (Oophaga sylvatica) and compared wild caught chemically defended frogs to laboratory frogs raised on an alkaloid-free diet. To understand how poison frogs move alkaloids from their diet to their skin granular glands, we focused on measuring gene expression in the intestines, skin, and liver. Across these tissues, we found many differentially expressed transcripts involved in small molecule transport and metabolism, as well as sodium channels and other ion pumps. We then used proteomic approaches to quantify plasma proteins, where we found several protein abundance differences between wild and laboratory frogs, including the amphibian neurotoxin binding protein saxiphilin. Finally, because many blood proteins are synthesized in the liver, we used thermal proteome profiling as an untargeted screen for soluble proteins that bind the alkaloid decahydroquinoline. Using this approach, we identified several candidate proteins that interact with this alkaloid, including saxiphilin. These transcript and protein abundance patterns suggest the presence of alkaloids influences frog physiology and that small molecule transport proteins may be involved in toxin bioaccumulation in dendrobatid poison frogs.\n\nResumenLas ranas venenosas obtienen moleculas lipofilicas a partir de su dieta de artropodos que luego usan como una defensa quimica contra depredadores. Mientras que la acumulacion de toxinas dieteticas ha sido bien documentada, el mecanismo fisiologico de obtencion de alcaloides no ha sido investigado. En este estudio usamos secuenciacion de RNA y proteomica para determinar como la presencia de alcaloides afecta la abundancia de mRNA y proteinas en ranas diablito (Oophaga sylvatica) silvestres con defensas quimicas en comparacion a ranas diablito criadas en laboratorio con una dieta sin alcaloides. Para entender como las ranas venenosas mueven los alcaloides de su dieta a las glandulas granulares en su piel, nos enfocamos en medir la expresion de genes en tres tejidos: intestinos, piel e higado. En estos tejidos, encontramos varios transcriptomas regulados diferencialmente que tienen actividades involucradas con el transporte y metabolismo de pequenas moleculas, ademas de canales de sodio y bombas de iones. Luego usamos metodos proteomicos para cuantificar proteinas en plasma, donde encontramos varias diferencias en abundancia de proteinas entre las ranas silvestres y de laboratorio, incluyendo la proteina anfibia de fijacion de toxinas, saxifilina. Finalmente, debido a que muchas proteinas encontradas en la sangre se sintetizan en el higado, usamos la tecnica de perfilacion proteomica termal para seleccionar imparcialmente las proteinas solubles que fijan el alcaloide decahydroquinolina. Usando este metodo, identificamos varias posibles proteinas que interactuan con este alcaloide, incluyendo saxifilina. Estos patrones de cambios en abundancia de transcriptomas y proteinas en ranas con y sin defensas quimicas sugieren que la presencia de alcaloides influye en la fisiologia de las ranas y que moleculas proteicas pequenas de transporte podrian estar involucradas en la bioacumulacion de toxinas en ranas venenosas dendrobatidos.\n\nSummary StatementChemically defended wild poison frogs have gene expression and protein abundance differences across several tissue systems compared to poison frogs reared on an alkaloid-free diet.

physiology↗