BRN2 as a key gene drives the early primate telencephalon development

Human-chimpanzee tetraploid system defines mechanisms of species-specific neural gene regulation

A major challenge in human evolutionary biology is to pinpoint genetic differences that underlie human-specific traits, such as increased neuron number and differences in cognitive behaviors. We used human-chimpanzee tetraploid cells to distinguish gene expression changes due to cis -acting sequence variants that change local gene regulation, from trans expression changes due to species differences in the cellular environment. In neural progenitor cells, examination of both cis and trans changes - combined with CRISPR inhibition and transcription factor motif analyses - identified cis -acting, species-specific gene regulatory changes, including to TNIK, FOSL2 , and MAZ , with widespread trans effects on neurogenesis-related gene programs. In excitatory neurons, we identified POU3F2 as a key cis -regulated gene with trans effects on synaptic gene expression and neuronal firing. This study identifies cis -acting genomic changes that cause cascading trans gene regulatory effects to contribute to human neural specializations, and provides a general framework for discovering genetic differences underlying human traits.

Novel rhesus macaque immunoglobulin germline genes identified by three sequencing approaches

Introduction

Rhesus macaques have long been a focus of research for understanding immune responses to human pathogens due to their close phylogenetic relationship with humans. As rhesus macaque antibody germlines show high degrees of polymorphism, the spectrum of database-covered genes expressed in individual macaques remains to be determined.

Methods

Here, four rhesus macaques infected with SHIVSF162P3N became a study of interest because they developed broadly neutralizing antibodies against HIV-1. To identify the immunoglobulin heavy chain V-gene (IGHV) germlines in these macaques, we applied three sequencing approaches - genomic DNA (gDNA) TOPO sequencing, gDNA MiSeq, and messenger RNA (mRNA) MiSeq inference with IgDiscover, and illustrated the detection power of each method.

Results

Of the 197 new rhesus IGHV germline sequences identified, 116 (59%) were validated by at least two methods, and 143 (73%) were found in at least two macaques or two sample sources. About 20% of germlines in each macaque are missing from the current database, including a subset frequently expressed. Overall, gDNA MiSeq determined the greatest number of germline sequences, followed by gDNA TOPO sequencing and mRNA MiSeq inference by IgDiscover, with IgDiscover providing direct evidence of allele expression and usage.

Discussion

Our interdisciplinary study sheds light on germline sequencing, enhances the rhesus IGHV germline database, and highlights the importance of germline sequencing in rhesus immune repertoire studies.

Conserved transcriptional regulation by BRN1 and BRN2 in neocortical progenitors drives mammalian neural specification and neocortical expansion

The neocortex varies in size and complexity among mammals due to the tremendous variability in the number and diversity of neuronal subtypes across species. The increased cellular diversity is paralleled by the expansion of the pool of neocortical progenitors and the emergence of indirect neurogenesis during brain evolution. The molecular pathways that control these biological processes and are disrupted in neurological disorders remain largely unknown. Here we show that the transcription factors BRN1 and BRN2 have an evolutionary conserved function in neocortical progenitors to control their proliferative capacity and the switch from direct to indirect neurogenesis. Functional studies in mice and ferrets show that BRN1/2 act in concert with NOTCH and primary microcephaly genes to regulate progenitor behavior. Analysis of transcriptomics data from genetically modified macaques provides evidence that these molecular pathways are conserved in non-human primates. Our findings thus demonstrate that BRN1/2 are central regulators of gene expression programs in neocortical progenitors critical to determine brain size during evolution.

Tanycyte radial morphology and proliferation are influenced by fibroblast growth factor receptor 1 and high-fat diet

Fibroblast growth factor receptor 1 (FGFR1) is a widely expressed, membrane-bound receptor that transduces extracellular signals from FGF ligands and cadherins, resulting in intracellular signals influencing cellular growth, proliferation, calcium, and transcription. FGF21 and FGF2 stimulate the proliferation of tanycytes, specialized radial astrocytes along the ventricle of the hypothalamus, and influence metabolism. Tanycytes are in a privileged position between the cerebrospinal fluid, the blood supply in the median eminence, and neurons within nuclei in the hypothalamus. The effect of FGFR1 signaling upon tanycyte morphology and metabolism was examined in adult mice with conditional deletion of the Fgfr1 gene using the Fgfr1flox/flox; Nestin-Cre+ line. Loss of Fgfr1 resulted in shorter β tanycytes along the medial eminence. Control Fgfr1flox/flox littermates and Fgfr1flox/flox, Nestin-Cre+ (Fgfr1 cKO) knockout mice were placed on a 1-month long high-fat diet (HFD) or a normal-fat diet (NFD), to investigate differences in body homeostasis and tanycyte morphology under an obesity inducing diet. We found that FGFR1 is a vital contributor to tanycyte morphology and quantity and that it promotes stem cell maintenance in the hypothalamus and hippocampal dentate gyrus. The Fgfr1 cKO mice developed impaired tolerance to a glucose challenge test on a HFD without gaining more weight than control mice. The combination of HFD and loss of Fgfr1 gene resulted in altered β and α tanycyte morphology, and reduced stem cell numbers along the third ventricle of the hypothalamus and hippocampus.

Progress of reprogramming astrocytes into neuron

As the main players in the central nervous system (CNS), neurons dominate most life activities. However, after accidental trauma or neurodegenerative diseases, neurons are unable to regenerate themselves. The loss of this important role can seriously affect the quality of life of patients, ranging from movement disorders to disability and even death. There is no suitable treatment to prevent or reverse this process. Therefore, the regeneration of neurons after loss has been a major clinical problem and the key to treatment. Replacing the lost neurons by transdifferentiation of other cells is the only viable approach. Although much progress has been made in stem cell therapy, ethical issues, immune rejection, and limited cell sources still hinder its clinical application. In recent years, somatic cell reprogramming technology has brought a new dawn. Among them, astrocytes, as endogenously abundant cells homologous to neurons, have good potential and application value for reprogramming into neurons, having been reprogrammed into neurons in vitro and in vivo in a variety of ways.

Cortical somatostatin long-range projection neurons and interneurons exhibit divergent developmental trajectories

The mammalian cerebral cortex contains an extraordinary diversity of cell types that emerge by implementing different developmental programs. Delineating when and how cellular diversification occurs is particularly challenging for cortical inhibitory neurons because they represent a small proportion of all cortical cells and have a protracted development. Here, we combine single-cell RNA sequencing and spatial transcriptomics to characterize the emergence of neuronal diversity among somatostatin-expressing (SST+) cells in mice. We found that SST+ inhibitory neurons segregate during embryonic stages into long-range projection (LRP) neurons and two types of interneurons, Martinotti cells and non-Martinotti cells, following distinct developmental trajectories. Two main subtypes of LRP neurons and several subtypes of interneurons are readily distinguishable in the embryo, although interneuron diversity is likely refined during early postnatal life. Our results suggest that the timing for cellular diversification is unique for different subtypes of SST+ neurons and particularly divergent for LRP neurons and interneurons.

Neurogenesis in primates versus rodents and the value of non-human primate models

Neurogenesis, the process of generating neurons from neural stem cells, occurs during both embryonic and adult stages, with each stage possessing distinct characteristics. Dysfunction in either stage can disrupt normal neural development, impair cognitive functions, and lead to various neurological disorders. Recent technological advancements in single-cell multiomics and gene-editing have facilitated investigations into primate neurogenesis. Here, we provide a comprehensive overview of neurogenesis across rodents, non-human primates, and humans, covering embryonic development to adulthood and focusing on the conservation and diversity among species. While non-human primates, especially monkeys, serve as valuable models with closer neural resemblance to humans, we highlight the potential impacts and limitations of non-human primate models on both physiological and pathological neurogenesis research.