Ectopic expression of Irx3 and Irx5 in the paraventricular nucleus of the hypothalamus contributes to defects in Sim1 haploinsufficiency

The Iroquois (Iro/Irx) homeobox genes are conserved Hox targets involved in motor neuron development

The Iroquois (Iro/Irx) homeobox genes encode transcription factors with fundamental roles in animal development. Despite their link to various congenital conditions in humans, our understanding of Iro/Irx gene expression, function, and regulation remains incomplete. Here, we conducted a systematic expression analysis of all six mouse Irx genes in the embryonic spinal cord. We found that Irx1, Irx2, Irx3, Irx5, and Irx6 are expressed in specific groups of motor neurons (MNs). Further, we employed CRISPR-Cas9 gene editing to uncover essential but distinct roles for Irx2 and Irx6 in MN development. We also found that HOX proteins, which are conserved regulators of MN development across species, control Irx gene expression both in mouse and Caenorhabditis elegans MNs. Altogether, our study provides insights into Iro/Irx expression and function in the developing spinal cord and uncovers an ancient gene regulatory relationship between HOX and Iro/Irx genes.

The paraventricular nucleus of the hypothalamus: a key node in the control of behavioural states

The paraventricular nucleus (PVN) of the hypothalamus contains diverse populations of neuropeptide-producing neurons. These include neurons that synthesise oxytocin, vasopressin, corticotropin-releasing hormone, thyrotropin-releasing hormone and somatostatin. While it is well established that these neurons control the secretion of neuroendocrine hormones, there is growing evidence that they also control the expression of important homeostatic behaviours. Here we review recent data showing a critical role of PVN neurons in controlling arousal, social behaviour, defensive behaviour and pain. Collectively, this suggests that the PVN is a key node in a wider neural network controlling behavioural states.

Unlocking biological mechanisms with integrative functional genomics approaches

Reverse genetics offers precise functional insights into genes through the targeted manipulation of gene expression followed by phenotypic assessment. While these approaches have proven effective in model organisms such as Saccharomyces cerevisiae, large-scale genetic manipulations in human cells were historically unfeasible due to methodological limitations. However, recent advancements in functional genomics, particularly clustered regularly interspaced short palindromic repeats (CRISPR)-based screening technologies and next-generation sequencing platforms, have enabled pooled screening technologies that allow massively parallel, unbiased assessments of biological phenomena in human cells. This review provides a comprehensive overview of cutting-edge functional genomic screening technologies applicable to human cells, ranging from short hairpin RNA screens to modern CRISPR screens. Additionally, we explore the integration of CRISPR platforms with single-cell approaches to monitor gene expression, chromatin accessibility, epigenetic regulation, and chromatin architecture following genetic perturbations at the omics level. By offering an in-depth understanding of these genomic screening methods, this review aims to provide insights into more targeted and effective strategies for genomic research and personalized medicine.

The Iroquois (Iro/Irx) homeobox genes are conserved Hox targets involved in motor neuron development

The Iroquois (Iro/Irx) homeobox genes encode transcription factors with fundamental roles in animal development. Despite their link to various congenital conditions in humans, our understanding of Iro/Irx gene expression, function, and regulation remains incomplete. Here, we conducted a systematic expression analysis of all six mouse Irx genes in the embryonic spinal cord. We found five Irx genes (Irx1, Irx2, Irx3, Irx5, and Irx6) to be confined mostly to ventral spinal domains, offering new molecular markers for specific groups of post-mitotic motor neurons (MNs). Further, we engineered Irx2, Irx5, and Irx6 mouse mutants and uncovered essential but distinct roles for Irx2 and Irx6 in MN development. Last, we found that the highly conserved regulators of MN development across species, the HOX proteins, directly control Irx gene expression both in mouse and C. elegans MNs, critically expanding the repertoire of HOX target genes in the developing nervous system. Altogether, our study provides important insights into Iro/Irx expression and function in the developing spinal cord, and uncovers an ancient gene regulatory relationship between HOX and Iro/Irx genes.

Genetics, pharmacotherapy, and dietary interventions in childhood obesity

Childhood obesity has emerged as a major global health issue, contributing to the increased prevalence of chronic conditions and adversely affecting the quality of life and future prospects of affected individuals, thereby presenting a substantial societal challenge. This complex condition, influenced by the interplay of genetic predispositions and environmental factors, is characterized by excessive energy intake due to uncontrolled appetite regulation and a Westernized diet. Managing obesity in childhood requires specific considerations compared with adulthood, given the vulnerability of the critical juvenile-adolescent period to toxicity and developmental defects. Consequently, common treatment options for adult obesity may not directly apply to younger populations. Therefore, research on childhood obesity has focused on genetic defects in regulating energy intake, alongside pharmacotherapy and dietary interventions as management approaches, with an emphasis on safety concerns. This review aims to summarize canonical knowledge and recent findings on genetic factors contributing to childhood obesity. Additionally, it assesses the efficacy and safety of existing pharmacotherapies and dietary interventions and suggests future research directions. By providing a comprehensive understanding of the complex dynamics of childhood obesity, this review aims to offer insights into more targeted and effective strategies for addressing this condition, including personalized healthcare solutions.

An integrated single-cell RNA-seq atlas of the mouse hypothalamic paraventricular nucleus links transcriptomic and functional types

The hypothalamic paraventricular nucleus (PVN) is a highly complex brain region that is crucial for homeostatic regulation through neuroendocrine signaling, outflow of the autonomic nervous system, and projections to other brain areas. In the past years, single-cell datasets of the hypothalamus have contributed immensely to the current understanding of the diverse hypothalamic cellular composition. While the PVN has been adequately classified functionally, its molecular classification is currently still insufficient. To address this, we created a detailed atlas of PVN transcriptomic cell types by integrating various PVN single-cell datasets into a recently published hypothalamus single-cell transcriptome atlas. Furthermore, we functionally profiled transcriptomic cell types, based on relevant literature, existing retrograde tracing data, and existing single-cell data of a PVN-projection target region. Finally, we validated our findings with immunofluorescent stainings. In our PVN atlas dataset, we identify the well-known different neuropeptide types, each composed of multiple novel subtypes. We identify Avp-Tac1, Avp-Th, Oxt-Foxp1, Crh-Nr3c1, and Trh-Nfib as the most important neuroendocrine subtypes based on markers described in literature. To characterize the preautonomic functional population, we integrated a single-cell retrograde tracing study of spinally projecting preautonomic neurons into our PVN atlas. We identify these (presympathetic) neurons to cocluster with the Adarb2+ clusters in our dataset. Further, we identify the expression of receptors for Crh, Oxt, Penk, Sst, and Trh in the dorsal motor nucleus of the vagus, a key region that the pre-parasympathetic PVN neurons project to. Finally, we identify Trh-Ucn3 and Brs3-Adarb2 as some centrally projecting populations. In conclusion, our study presents a detailed overview of the transcriptomic cell types of the murine PVN and provides a first attempt to resolve functionality for the identified populations.

A Spacetime Odyssey of Neural Progenitors to Generate Neuronal Diversity

To understand how the nervous system develops from a small pool of progenitors during early embryonic development, it is fundamentally important to identify the diversity of neuronal subtypes, decode the origin of neuronal diversity, and uncover the principles governing neuronal specification across different regions. Recent single-cell analyses have systematically identified neuronal diversity at unprecedented scale and speed, leaving the deconstruction of spatiotemporal mechanisms for generating neuronal diversity an imperative and paramount challenge. In this review, we highlight three distinct strategies deployed by neural progenitors to produce diverse neuronal subtypes, including predetermined, stochastic, and cascade diversifying models, and elaborate how these strategies are implemented in distinct regions such as the neocortex, spinal cord, retina, and hypothalamus. Importantly, the identity of neural progenitors is defined by their spatial position and temporal patterning factors, and each type of progenitor cell gives rise to distinguishable cohorts of neuronal subtypes. Microenvironmental cues, spontaneous activity, and connectional pattern further reshape and diversify the fate of unspecialized neurons in particular regions. The illumination of how neuronal diversity is generated will pave the way for producing specific brain organoids to model human disease and desired neuronal subtypes for cell therapy, as well as understanding the organization of functional neural circuits and the evolution of the nervous system.

Genetic Regulation of Vertebrate Forebrain Development by Homeobox Genes

Forebrain development in vertebrates is regulated by transcription factors encoded by homeobox, bHLH and forkhead gene families throughout the progressive and overlapping stages of neural induction and patterning, regional specification and generation of neurons and glia from central nervous system (CNS) progenitor cells. Moreover, cell fate decisions, differentiation and migration of these committed CNS progenitors are controlled by the gene regulatory networks that are regulated by various homeodomain-containing transcription factors, including but not limited to those of the Pax (paired), Nkx, Otx (orthodenticle), Gsx/Gsh (genetic screened), and Dlx (distal-less) homeobox gene families. This comprehensive review outlines the integral role of key homeobox transcription factors and their target genes on forebrain development, focused primarily on the telencephalon. Furthermore, links of these transcription factors to human diseases, such as neurodevelopmental disorders and brain tumors are provided.