Biology subjects

Hof, P. R.

Publications and source records attributed to Hof, P. R..

25 records · Page 2Linked to original sources

bioRxiv2020

Evolution of regulatory signatures in primate cortical neurons at cell type resolution

The human cerebral cortex contains many cell types that likely underwent independent functional changes during evolution. However, cell type-specific regulatory landscapes in the cortex remain largely unexplored. Here we report epigenomic and transcriptomic analyses of the two main cortical neuronal subtypes, glutamatergic projection neurons and GABAergic interneurons, in human, chimpanzee and rhesus macaque. Using genome-wide profiling of the H3K27ac histone modification, we identify neuron-subtype-specific regulatory elements that previously went undetected in bulk brain tissue samples. Human-specific regulatory changes are uncovered in multiple genes, including those associated with language, autism spectrum disorder and drug addiction. We observe preferential evolutionary divergence in neuron-subtype-specific regulatory elements and show that a substantial fraction of pan-neuronal regulatory elements undergo subtype-specific evolutionary changes. This study sheds light on the interplay between regulatory evolution and cell-type-dependent gene expression programs, and provides a resource for further exploration of human brain evolution and function. SIGNIFICANCEThe cerebral cortex of the human brain is a highly complex, heterogeneous tissue that contains many cell types which are exquisitely regulated at the level of gene expression by non-coding regulatory elements, presumably, in a cell-type-dependent manner. However, assessing the regulatory elements in individual cell types is technically challenging, and therefore, most of the previous studies on gene regulation were performed with bulk brain tissue. Here we analyze two major types of neurons isolated from the cerebral cortex of humans, chimpanzees and rhesus macaques, and report complex patterns of cell-type-specific evolution of the regulatory elements in numerous genes. Many genes with evolving regulation are implicated in language abilities as well as psychiatric disorders.

evolutionary biology↗

bioRxiv2020

An adolescent sensitive period of heightened frontal top-down projection activity promotes local circuit integration and attentional behavior

Frontal top-down cortical neurons projecting to sensory cortical regions are well-positioned to integrate long-range inputs with local circuitry in frontal cortex to implement top-down attentional control of sensory regions. How adolescence contributes to the maturation of top-down neurons and associated local/long-range input balance, and the establishment of attentional control is poorly understood. Here we combine projection-specific electrophysiological and rabies-mediated input mapping in mice to uncover adolescence as a developmental stage when frontal top-down neurons projecting from the anterior cingulate to visual cortex are highly functionally integrated into local excitatory circuitry and have heightened activity compared to adulthood. Chemogenetic suppression of top-down neuron activity selectively during adolescence, but not later periods, produces long-lasting visual attentional behavior deficits, and results in excessive loss of local excitatory inputs in adulthood. Our study reveals an adolescent sensitive period when top-down neurons integrate local circuits with long-range connectivity to produce attentional behavior.

neuroscience↗

bioRxiv2019

Reduced axonal caliber and white matter changes in a rat model of Fragile X syndrome with a deletion of a K Homology domain of Fmr1.

Fragile X syndrome (FXS) is a neurodevelopmental disorder that is caused by mutations in the FMR1 gene that are known to cause neuroanatomical alterations. The morphological underpinnings of these alterations have not been elucidated. Furthermore, while alterations have been identified in both male and female individuals, neuroanatomy in female rodent models has not been assessed. We identified structural differences in regions that are also altered in FXS in male and female rat models, including the splenium of the corpus callosum. Interestingly, different sets of regions were disrupted in male and female rat models and, remarkably, male rats had higher brain-wide diffusion than female rats overall. We found reduced axonal caliber in the splenium, offering a mechanism for its structural changes. Our results provide insight into which brain regions are vulnerable to a loss of Fmr1 expression and suggest a potential mechanism for how its loss causes white matter dysfunction in FXS.

neuroscience↗

bioRxiv2019

Repeated hypoglycemia blunts the responsiveness of glucose-inhibited GHRH neurons by remodeling neural inputs and disrupting mitochondrial structure and function.

Hypoglycemia is a frequent complication of diabetes, limiting therapy and increasing morbidity and mortality. With recurrent hypoglycemia, the counter-regulatory response (CRR) to decreased blood glucose is blunted, resulting in hypoglycemia unawareness. The mechanisms leading to these blunted effects remain incompletely understood. Here, we identify, with in situ hybridization, immunohistochemistry and the tissue clearing capability of iDisco, that GHRH neurons represent a unique population of arcuate nucleus neurons activated by glucose deprivation in vivo. Repeated glucose deprivation reduces GHRH neuron activation and remodels excitatory and inhibitory inputs to GHRH neurons. We show low glucose sensing is coupled to GHRH neuron depolarization, decreased ATP production and mitochondrial fusion. Repeated hypoglycemia attenuates these responses during low glucose. By maintaining mitochondrial length with the small molecule, mdivi-1, we preserved hypoglycemia sensitivity in vitro and in vivo. Our findings present possible mechanisms for the blunting of the CRR, broaden significantly our understanding of the structure of GHRH neurons and for the fist time, propose that mitochondrial dynamics play an important role in hypoglycemia unawareness. We conclude that interventions targeting mitochondrial fission in GHRH neurons may offer a new pathway to prevent hypoglycemia unawareness in diabetic patients.

physiology↗

bioRxiv2018

Automatic navigation system for the mouse brain

Identification and delineation of brain regions in histologic mouse brain sections is especially pivotal for many neurogenomics, transcriptomics, proteomics and connectomics studies, yet this process is prone to observer error and bias. Here we present a novel brain navigation system, named NeuroInfo, whose general principle is similar to that of a global positioning system (GPS) in a car. NeuroInfo automatically navigates an investigator through the complex microscopic anatomy of histologic sections of mouse brains (thereafter: \"experimental mouse brain sections\"). This is achieved by automatically registering a digital image of an experimental mouse brain section with a three-dimensional (3D) digital mouse brain atlas that is essentially based on the third version of the Allen Mouse Brain Common Coordinate Framework (CCF v3), retrieving graphical region delineations and annotations from the 3D digital mouse brain atlas, and superimposing this information onto the digital image of the experimental mouse brain section on a computer screen. By doing so, NeuroInfo helps in solving the long-standing problem faced by researchers investigating experimental mouse brain sections under a light microscope--that of correctly identifying the distinct brain regions contained within the experimental mouse brain sections. Specifically, NeuroInfo provides an intuitive, readily-available computer microscopy tool to enhance researchers ability to correctly identify specific brain regions in experimental mouse brain sections. Extensive validation studies of NeuroInfo demonstrated that this novel technology performs remarkably well in accurately delineating regions that are large and/or located in the dorsal parts of mouse brains, independent on whether the sections were imaged with fluorescence or brightfield microscopy. This novel navigation system provides a highly efficient way for registering a digital image of an experimental mouse brain section with the 3D digital mouse brain atlas in a minute and accurate delineation of the image in real-time.

neuroscience↗

bioRxiv2018

Behavioral effect of chemogenetic inhibition is directly related to receptor transduction levels in rhesus monkeys

We used inhibitory DREADDs (Designer Receptors Exclusively Activated by Designer Drugs) to reversibly disrupt dorsolateral prefrontal cortex (dlPFC) function in male macaque monkeys. Monkeys were tested on a spatial delayed response task to assess working memory function after intramuscular injection of either clozapine-N-oxide (CNO) or vehicle. CNO injections given before DREADD transduction were without effect on behavior. rAAV5/hsyn-hM4Di-mCherry was injected bilaterally into the dlPFC of five male rhesus monkeys, to produce neuronal expression of the inhibitory (Gi-coupled) DREADD receptor. We quantified the percentage of DREADD- transduced cells using stereological analysis of mCherry-immunolabeled cells. We found a greater number of immunolabeled neurons in monkeys that displayed CNO-induced behavioral impairment after DREADD transduction compared to monkeys that showed no behavioral effect after CNO. Even in monkeys that showed reliable effects of CNO on behavior after DREADD transduction, the number of prefrontal neurons transduced with DREADD receptor was on the order of 3% of total prefrontal neurons counted. This level of histological analysis facilitates our understanding of behavioral effects, or lack thereof, after DREADD vector injection in monkeys. It also implies that a functional silencing of a relatively small fraction of dlPFC neurons, albeit in a widely distributed area, is sufficient to disrupt spatial working memory.\n\nSignificance StatementCognitive domains such as working memory and executive function are mediated by the dorsolateral prefrontal cortex (dlPFC). Impairments in these domains are common in neurodegenerative diseases as well as normal aging. The present study sought to measure deficits in a spatial delayed response task following activation of viral-vector transduced inhibitory DREADD (Designer Receptor Exclusively Activated by Designer Drug) receptors in rhesus macaques and compare this to the level of transduction in dlPFC using stereology. We found a significant relationship between the extent of DREADD transduction and the magnitude of behavioral deficit following administration of the DREADD actuator compound clozapine-N- oxide (CNO). These results demonstrate it will be critical to validate transduction to ensure DREADDs remain a powerful tool for neuronal disruption.

neuroscience↗

bioRxiv2018

Human neuroblastoma SH-SY5Y cells treated with okadaic acid express phosphorylated high molecular weight tau immunoreactive protein species

Recent data suggest that early stages of Alzheimers disease (AD) are characterized by an abnormally high phosphorylation of microtubule-associated protein tau and truncation of its C-terminus. Tau hyperphosphorylation may result from the downregulation of phosphatases, especially protein phosphatase 2A. In an attempt to model and analyze these molecular events we treated SH-SY5Y cells with okadaic acid (OA), an inhibitor of protein phosphatases. In addition to the low molecular weight tau, such treatment lead to the appearance of heat-stable protein species with apparent high molecular weight around 100 kDa, which were immunoreactive to tau antibodies against phosphorylated Ser202 and phosphorylated Ser396. Based on the observation that high molecular weight tau-immunoreactive proteins (HMW-TIP) correspond to the predicted size of two monomers of tau, one possibility is that HMW-TIP represent tau oligomers. The absence of HMW-TIP detection by anti-total tau antibodies used may be a consequence of epitope masking, or a combination of epitope masking and protein truncation. We noted the stability of HMW-TIP in the presence of strong denaturing agents, such as urea and guanidine, as well as upon partial dephosphorylation by the alkaline phosphatase. Moreover, as HMW-TIP did not dissociate the presence of {beta}-mercaptoethanol, it was also independent from disulfide bonds. Taken together, these data show that OA treatment of SH-SY5Y cells induces the appearance of HMW-TIP, which may represent tau oligomer or tau-crossreactive phospho-proteins. Our findings have implications for further studies of tau under the conditions of protein phosphatase downregulation.

neuroscience↗