Deletion of neural tube defect-associated gene Mthfd1l causes reduced cranial mesenchyme density

Brain development and bioenergetic changes

Bioenergetics describe the biochemical processes responsible for energy supply in organisms. When these changes become dysregulated in brain development, multiple neurodevelopmental diseases can occur, implicating bioenergetics as key regulators of neural development. Historically, the discovery of disease processes affecting individual stages of brain development has revealed critical roles that bioenergetics play in generating the nervous system. Bioenergetic-dependent neurodevelopmental disorders include neural tube closure defects, microcephaly, intellectual disability, autism spectrum disorders, epilepsy, mTORopathies, and oncogenic processes. Developmental timing and cell-type specificity of these changes determine the long-term effects of bioenergetic disease mechanisms on brain form and function. Here, we discuss key metabolic regulators of neural progenitor specification, neuronal differentiation (neurogenesis), and gliogenesis. In general, transitions between glycolysis and oxidative phosphorylation are regulated in early brain development and in oncogenesis, and reactive oxygen species (ROS) and mitochondrial maturity play key roles later in differentiation. We also discuss how bioenergetics interface with the developmental regulation of other key neural elements, including the cerebrospinal fluid brain environment. While questions remain about the interplay between bioenergetics and brain development, this review integrates the current state of known key intersections between these processes in health and disease.

Optical coherence tomography-guided Brillouin microscopy highlights regional tissue stiffness differences during anterior neural tube closure in the Mthfd1l murine mutant

Neurulation is a highly synchronized biomechanical process leading to the formation of the brain and spinal cord, and its failure leads to neural tube defects (NTDs). Although we are rapidly learning the genetic mechanisms underlying NTDs, the biomechanical aspects are largely unknown. To understand the correlation between NTDs and tissue stiffness during neural tube closure (NTC), we imaged an NTD murine model using optical coherence tomography (OCT), Brillouin microscopy and confocal fluorescence microscopy. Here, we associate structural information from OCT with local stiffness from the Brillouin signal of embryos undergoing neurulation. The stiffness of neuroepithelial tissues in Mthfd1l null embryos was significantly lower than that of wild-type embryos. Additionally, exogenous formate supplementation improved tissue stiffness and gross embryonic morphology in nullizygous and heterozygous embryos. Our results demonstrate the significance of proper tissue stiffness in normal NTC and pave the way for future studies on the mechanobiology of normal and abnormal embryonic development.

Genome-wide association study reveals new QTL and functional candidate genes for the number of ribs and carcass length in pigs

The number of ribs (NR) and carcass length (CL) are important economic traits in pig breeding programs. Pigs with a higher NR and longer CL produce greater pork yields. In the present study, Suhuai pigs with NR and CL phenotypes were genotyped using the Neogen^® GGP Porcine 80 K SNP array to identify the QTL affecting NR and CL and dissect the candidate genes for the two traits. The SNP-chip data was imputed to the whole-genome sequence (iWGS) to increase the probability of identifying causal variants. Through genome-wide association studies (GWAS) based on both chip and iWGS data, significant SNPs were detected on Sus scrofa chromosome (SSC) 1, SSC4 and SSC7 for NR and on SSC5, SSC16 and SSC17 for CL. Moreover, two SNPs (H3GA0022644 and WU_10.2_7_103460706) on SSC7 detected in chip-based GWAS were significantly associated with both NR and CL. Through Bayes fine mapping, one reported QTL for NR on SSC7 and two reported QTL for CL on SSC17 were verified, and two new QTL (SSC1: 14.05-15.84 Mb and SSC4: 64.83-66.59 Mb) affecting NR and two new QTL (SSC5: 58.31-59.84 Mb and SSC16: 22.98-23.43 Mb) affecting CL were detected. According to the biological functions of genes, MTHFD1L on SSC1 and SULF1 on SSC4 are novel functional candidate genes for NR, and EMP1 on SSC5 and EGFLAM on SSC16 are novel functional candidate genes for CL. Overall, our findings provide a basis for identifying new causal genes and mutations affecting NR and CL.

Pathogenesis of neural tube defects: The regulation and disruption of cellular processes underlying neural tube closure

Neural tube closure (NTC) is crucial for proper development of the brain and spinal cord and requires precise morphogenesis from a sheet of cells to an intact three-dimensional structure. NTC is dependent on successful regulation of hundreds of genes, a myriad of signaling pathways, concentration gradients, and is influenced by epigenetic and environmental cues. Failure of NTC is termed a neural tube defect (NTD) and is a leading class of congenital defects in the United States and worldwide. Though NTDs are all defined as incomplete closure of the neural tube, the pathogenesis of an NTD determines the type, severity, positioning, and accompanying phenotypes. In this review, we survey pathogenesis of NTDs relating to disruption of cellular processes arising from genetic mutations, altered epigenetic regulation, and environmental influences by micronutrients and maternal condition. This article is categorized under: Congenital Diseases > Genetics/Genomics/Epigenetics Neurological Diseases > Genetics/Genomics/Epigenetics Neurological Diseases > Stem Cells and Development.

Metal transporter Slc30a1 controls pharyngeal neural crest differentiation via the zinc-Snai2-Jag1 cascade

The pharyngeal arch (PA) is a neural crest (NC)-derived organ that is transiently developed during embryogenesis and is required for the subsequent development of various tissues. However, the role of zinc during PA differentiation from NC progenitor cells is unknown. Here, we found that the metal transporters Slc30a1a and Slc30a1b mediate zinc homeostasis during PA differentiation. Slc30a1-deficient zebrafish develop zinc accumulation in NC cells, with increased expression of stemness markers and PA dorsal genes, and SMART-seq analyses revealed that the genes snai2 and jag1b may serve as downstream targets. Furthermore, functional studies showed that knocking down either snai2 or jag1b rescues PA development in Slc30a1-deficient zebrafish. Notably, we identified the double zinc-finger domain in the transcription factor Snai2 as a zinc-responsive element that regulates jag1b expression. Our findings indicate that the Slc30a1/zinc-snai2-jag1b axis is an essential regulatory network controlling PA differentiation, shedding new light on the function of zinc homeostasis in maintaining NC cell stemness and multipotency in vertebrates.

Metabotype analysis of Mthfd1l-null mouse embryos using desorption electrospray ionization mass spectrometry imaging

Mammalian folate-dependent one-carbon (1C) metabolism provides the building blocks essential during development via amino acid interconversion, methyl-donor production, regeneration of redox factors, and de novo purine and thymidylate synthesis. Folate supplementation prevents many neural tube defects (NTDs) that occur during the embryonic process of neurulation. The mechanism by which folate functions during neurulation is not well understood, and not all NTDs are preventable by folate supplementation. Mthfd1l is a mitochondrial 1C metabolism enzyme that produces formate, a 1C donor that fuels biosynthesis and the methyl cycle in the cytoplasm. Homozygous deletion of the Mthfd1l gene in mice (Mthfd1l^z/z) causes embryonic lethality, developmental delay, and folate-resistant NTDs. These mice also have defects in cranial mesenchyme formation. In this work, mass spectrometry imaging was used to obtain ion maps of the cranial mesenchyme that identified the spatial distribution and relative abundance of metabolites in wild-type and Mthfd1l^z/z embryos. The relative abundances of purine and thymidylate derivatives, as well as amino acids, were diminished in the cranial mesenchyme of Mthfd1l^z/z embryos. Loss of Mthfd1l activity in this region also led to abnormal levels of methionine and dysregulated energy metabolism. These alterations in metabolism suggest possible approaches to preventing NTDs in humans.