Whole transcriptome organisation in the dehydrated supraoptic nucleus

Spatial transcriptomics reveal basal sex differences in supraoptic nucleus gene expression of adult rats related to cell signaling and ribosomal pathways

BACKGROUND

The supraoptic nucleus (SON) of the hypothalamus contains magnocellular neurosecretory cells that secrete the hormones vasopressin and oxytocin. Sex differences in SON gene expression have been relatively unexplored. Our study used spatially resolved transcriptomics to visualize gene expression profiles in the SON of adult male (n = 4) and female (n = 4) Sprague-Dawley rats using Visium Spatial Gene Expression (10x Genomics).

METHODS

Briefly, 10-μm coronal sections (~ 4 × 4 mm) containing the SON were collected from each rat and processed using Visium slides and recommended protocols. Data were analyzed using 10x Genomics' Space Ranger and Loupe Browser applications and other bioinformatic tools. Two unique differential expression (DE) analysis methods, Loupe Browser and DESeq2, were used.

RESULTS

Loupe Browser DE analysis of the SON identified 116 significant differentially expressed genes (DEGs) common to both sexes (e.g., Avp and Oxt), 31 significant DEGs unique to the males, and 73 significant DEGs unique to the females. DESeq2 analysis revealed 183 significant DEGs between the two groups. Gene Ontology (GO) enrichment and pathway analyses using significant genes identified via Loupe Browser revealed GO terms and pathways related to (1) neurohypophyseal hormone activity, regulation of peptide hormone secretion, and regulation of ion transport for the significant genes common to both males and females, (2) Gi signaling/G-protein mediated events for the significant genes unique to males, and (3) potassium ion transport/voltage-gated potassium channels for the significant genes unique to females, as some examples. GO/pathway analyses using significant genes identified via DESeq2 comparing female vs. male groups revealed GO terms/pathways related to ribosomal structure/function. Ingenuity Pathway Analysis (IPA) identified additional sex differences in canonical pathways (e.g., 'Mitochondrial Dysfunction', 'Oxidative Phosphorylation') and upstream regulators (e.g., CSF3, NFKB complex, TNF, GRIN3A).

CONCLUSION

There was little overlap in the IPA results for the two different DE methods. These results suggest sex differences in SON gene expression that are associated with cell signaling and ribosomal pathways.

Mapping Molecular Datasets Back to the Brain Regions They are Extracted from: Remembering the Native Countries of Hypothalamic Expatriates and Refugees

This article focuses on approaches to link transcriptomic, proteomic, and peptidomic datasets mined from brain tissue to the original locations within the brain that they are derived from using digital atlas mapping techniques. We use, as an example, the transcriptomic, proteomic and peptidomic analyses conducted in the mammalian hypothalamus. Following a brief historical overview, we highlight studies that have mined biochemical and molecular information from the hypothalamus and then lay out a strategy for how these data can be linked spatially to the mapped locations in a canonical brain atlas where the data come from, thereby allowing researchers to integrate these data with other datasets across multiple scales. A key methodology that enables atlas-based mapping of extracted datasets-laser-capture microdissection-is discussed in detail, with a view of how this technology is a bridge between systems biology and systems neuroscience.

Unsupervised Network Analysis of the Plastic Supraoptic Nucleus Transcriptome Predicts Caprin2 Regulatory Interactions

The supraoptic nucleus (SON) is a group of neurons in the hypothalamus responsible for the synthesis and secretion of the peptide hormones vasopressin and oxytocin. Following physiological cues, such as dehydration, salt-loading and lactation, the SON undergoes a function related plasticity that we have previously described in the rat at the transcriptome level. Using the unsupervised graphical lasso (Glasso) algorithm, we reconstructed a putative network from 500 plastic SON genes in which genes are the nodes and the edges are the inferred interactions. The most active nodal gene identified within the network was Caprin2. Caprin2 encodes an RNA-binding protein that we have previously shown to be vital for the functioning of osmoregulatory neuroendocrine neurons in the SON of the rat hypothalamus. To test the validity of the Glasso network, we either overexpressed or knocked down Caprin2 transcripts in differentiated rat pheochromocytoma PC12 cells and showed that these manipulations had significant opposite effects on the levels of putative target mRNAs. These studies suggest that the predicative power of the Glasso algorithm within an in vivo system is accurate, and identifies biological targets that may be important to the functional plasticity of the SON.

A comparison of physiological and transcriptome responses to water deprivation and salt loading in the rat supraoptic nucleus

Salt loading (SL) and water deprivation (WD) are experimental challenges that are often used to study the osmotic circuitry of the brain. Central to this circuit is the supraoptic nucleus (SON) of the hypothalamus, which is responsible for the biosynthesis of the hormones, arginine vasopressin (AVP) and oxytocin (OXT), and their transport to terminals that reside in the posterior lobe of the pituitary. On osmotic challenge evoked by a change in blood volume or osmolality, the SON undergoes a function-related plasticity that creates an environment that allows for an appropriate hormone response. Here, we have described the impact of SL and WD compared with euhydrated (EU) controls in terms of drinking and eating behavior, body weight, and recorded physiological data including circulating hormone data and plasma and urine osmolality. We have also used microarrays to profile the transcriptome of the SON following SL and remined data from the SON that describes the transcriptome response to WD. From a list of 2,783 commonly regulated transcripts, we selected 20 genes for validation by qPCR. All of the 9 genes that have already been described as expressed or regulated in the SON by osmotic stimuli were confirmed in our models. Of the 11 novel genes, 5 were successfully validated while 6 were false discoveries.