A tool for examining the role of the zinc finger myelin transcription factor 1 (Myt1) in neural development: Myt1 knock-in mice

Developmental Cues and Molecular Drivers in Myelinogenesis: Revisiting Early Life to Re-Evaluate the Integrity of CNS Myelin

The mammalian central nervous system (CNS) coordinates its communication through saltatory conduction, facilitated by myelin-forming oligodendrocytes (OLs). Despite the fact that neurogenesis from stem cell niches has caught the majority of attention in recent years, oligodendrogenesis and, more specifically, the molecular underpinnings behind OL-dependent myelinogenesis, remain largely unknown. In this comprehensive review, we determine the developmental cues and molecular drivers which regulate normal myelination both at the prenatal and postnatal periods. We have indexed the individual stages of myelinogenesis sequentially; from the initiation of oligodendrocyte precursor cells, including migration and proliferation, to first contact with the axon that enlists positive and negative regulators for myelination, until the ultimate maintenance of the axon ensheathment and myelin growth. Here, we highlight multiple developmental pathways that are key to successful myelin formation and define the molecular pathways that can potentially be targets for pharmacological interventions in a variety of neurological disorders that exhibit demyelination.

Single-cell transcriptomic landscapes of the otic neuronal lineage at multiple early embryonic ages

Inner ear vestibular and spiral ganglion neurons (VGNs and SGNs) are known to play pivotal roles in balance control and sound detection. However, the molecular mechanisms underlying otic neurogenesis at early embryonic ages have remained unclear. Here, we use single-cell RNA sequencing to reveal the transcriptomes of mouse otic tissues at three embryonic ages, embryonic day 9.5 (E9.5), E11.5, and E13.5, covering proliferating and undifferentiated otic neuroblasts and differentiating VGNs and SGNs. We validate the high quality of our studies by using multiple assays, including genetic fate mapping analysis, and we uncover several genes upregulated in neuroblasts or differentiating VGNs and SGNs, such as Shox2, Myt1, Casz1, and Sall3. Notably, our findings suggest a general cascaded differentiation trajectory during early otic neurogenesis. The comprehensive understanding of early otic neurogenesis provided by our study holds critical implications for both basic and translational research.

MYT1 role in the microtia-craniofacial microsomia spectrum

Background

Craniofacial microsomia (CFM), also known as the oculo‐auriculo‐vertebral spectrum, comprises a variable phenotype with the most common features including microtia and mandibular hypoplasia on one or both sides, in addition to lateral oral clefts, epibulbar dermoids, cardiac, vertebral, and renal abnormalities. The etiology of CFM is largely unknown. The MYT1 gene has been reported as a candidate based in mutations found in three unrelated individuals. Additional patients with mutations in this gene are required to establish its causality. We present two individuals with CFM that have rare variants in MYT1 contributing to better understand the genotype and phenotype associated with mutations in this gene.

Methods/Results

We conducted genetic analysis using whole‐exome and ‐genome sequencing in 128 trios with CFM. Two novel MYT1 mutations were identified in two participants. Sanger sequencing was used to confirm these mutations.

Conclusion

We identified two additional individuals with CFM who carry rare variants in MYT1, further supporting the presumptive role of this gene in the CFM spectrum.

MYT1 attenuates neuroblastoma cell differentiation by interacting with the LSD1/CoREST complex

Impaired neuronal differentiation is a feature of neuroblastoma tumorigenesis, and the differentiation grade of neuroblastoma tumors is associated with patient prognosis. Detailed understanding of the molecular mechanisms underlying neuroblastoma differentiation will facilitate the development of effective treatment strategies. Recent studies have shown that myelin transcription factor 1 (MYT1) promotes vertebrate neurogenesis by regulating gene expression. We performed quantitative analysis of neuroblastoma samples, which revealed that MYT1 was differentially expressed among neuroblastoma patients with different pathological diagnoses. Analysis of clinical data showed that MYT1 overexpression was associated with a significantly shorter 3-year overall survival rate and poor differentiation in neuroblastoma specimens. MYT1 knockdown inhibited proliferation and promoted the expression of multiple differentiation-associated proteins. Integrated omics data indicated that many genes involved in neuro-differentiation were regulated by MYT1. Interestingly, many of these genes are targets of the REST complex; therefore, we further identified the physical interaction of MYT1 with LSD1/CoREST. Depletion of LSD1 or inhibition of LSD1 by ORY-1001 decreased MYT1 expression, providing an alternative approach to target MYT1. Taken together, our results indicate that MYT1 significantly attenuates cell differentiation by interacting with the LSD1/CoREST complex. MYT1 is, therefore, a promising therapeutic target for enhancing the neurite-inducing effect of retinoic acid and for inhibiting the growth of neuroblastoma.

MyT1 Counteracts the Neural Progenitor Program to Promote Vertebrate Neurogenesis

The generation of neurons from neural stem cells requires large-scale changes in gene expression that are controlled to a large extent by proneural transcription factors, such as Ascl1. While recent studies have characterized the differentiation genes activated by proneural factors, less is known on the mechanisms that suppress progenitor cell identity. Here, we show that Ascl1 induces the transcription factor MyT1 while promoting neuronal differentiation. We combined functional studies of MyT1 during neurogenesis with the characterization of its transcriptional program. MyT1 binding is associated with repression of gene transcription in neural progenitor cells. It promotes neuronal differentiation by counteracting the inhibitory activity of Notch signaling at multiple levels, targeting the Notch1 receptor and many of its downstream targets. These include regulators of the neural progenitor program, such as Hes1, Sox2, Id3, and Olig1. Thus, Ascl1 suppresses Notch signaling cell-autonomously via MyT1, coupling neuronal differentiation with repression of the progenitor fate.

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MyT1 promotes neurogenesis downstream Ascl1

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MyT1 represses Notch1 receptor and many of its downstream target genes

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MyT1 represses Hes1 expression by direct DNA binding and competition with RBPJ

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Ascl1 suppresses Notch signaling cell-autonomously while promoting differentiation

Analysis of neural progenitors from embryogenesis to juvenile adult in Xenopus laevis reveals biphasic neurogenesis and continuous lengthening of the cell cycle

Xenopus laevis is a prominent model system for studying neural development, but our understanding of the long-term temporal dynamics of neurogenesis remains incomplete. Here, we present the first continuous description of neurogenesis in X. laevis, covering the entire period of development from the specification of neural ectoderm during gastrulation to juvenile frog. We have used molecular markers to identify progenitors and neurons, short-term bromodeoxyuridine (BrdU) incorporation to map the generation of newborn neurons and dual pulse S-phase labelling to characterise changes in their cell cycle length. Our study revealed the persistence of Sox3-positive progenitor cells from the earliest stages of neural development through to the juvenile adult. Two periods of intense neuronal generation were observed, confirming the existence of primary and secondary waves of neurogenesis, punctuated by a period of quiescence before metamorphosis and culminating in another period of quiescence in the young adult. Analysis of multiple parameters indicates that neural progenitors alternate between global phases of differentiation and amplification and that, regardless of their behaviour, their cell cycle lengthens monotonically during development, at least at the population level.

Pancreas-specific Cre driver lines and considerations for their prudent use

Cre/LoxP has broad utility for studying the function, development, and oncogenic transformation of pancreatic cells in mice. Here we provide an overview of the Cre driver lines that are available for such studies. We discuss how variegated expression, transgene silencing, and recombination in undesired cell types have conspired to limit the performance of these lines, sometimes leading to serious experimental concerns. We also discuss preferred strategies for achieving high-fidelity driver lines and remind investigators of the continuing need for caution when interpreting results obtained from any Cre/LoxP-based experiment performed in mice.

Molecular analysis of the human SLC13A4 sulfate transporter gene promoter

The human solute linked carrier (SLC) 13A4 gene is primarily expressed in the placenta where it is proposed to mediate the transport of nutrient sulfate from mother to fetus. The molecular mechanisms involved in the regulation of SLC13A4 expression remain unknown. To investigate the regulation of SLC13A4 gene expression, we analysed the transcriptional activity of the human SLC13A4 5'-flanking region in the JEG-3 placental cell line using luciferase reporter assays. Basal transcriptional activity was identified in the region -57 to -192 nucleotides upstream of the SLC13A4 transcription initiation site. Mutational analysis of the minimal promoter region identified Nuclear factor Y (NFY), Specificity protein 1 (SP1) and Krüppel like factor 7 (KLF7) motifs which conferred positive transcriptional activity, as well as Zinc finger protein of the cerebellum 2 (ZIC2) and helix-loop-helix protein 1 (HEN1) motifs that repressed transcription. The conserved NFY, SP1, KLF7, ZIC2 and HEN1 motifs in the SLC13A4 promoter of placental species but not in non-placental species, suggests a potential role for these putative transcriptional factor binding motifs in the physiological control of SLC13A4 mRNA expression.

Hippocampal CA3 transcriptome signature correlates with initial precipitating injury in refractory mesial temporal lobe epilepsy

BACKGROUND

Prolonged febrile seizures constitute an initial precipitating injury (IPI) commonly associated with refractory mesial temporal lobe epilepsy (RMTLE). In order to investigate IPI influence on the transcriptional phenotype underlying RMTLE we comparatively analyzed the transcriptomic signatures of CA3 explants surgically obtained from RMTLE patients with (FS) or without (NFS) febrile seizure history. Texture analyses on MRI images of dentate gyrus were conducted in a subset of surgically removed sclerotic hippocampi for identifying IPI-associated histo-radiological alterations.

METHODOLOGY/PRINCIPAL FINDINGS

DNA microarray analysis revealed that CA3 global gene expression differed significantly between FS and NFS subgroups. An integrative functional genomics methodology was used for characterizing the relations between GO biological processes themes and constructing transcriptional interaction networks defining the FS and NFS transcriptomic signatures and its major gene-gene links (hubs). Co-expression network analysis showed that: i) CA3 transcriptomic profiles differ according to the IPI; ii) FS distinctive hubs are mostly linked to glutamatergic signalization while NFS hubs predominantly involve GABAergic pathways and neurotransmission modulation. Both networks have relevant hubs related to nervous system development, what is consistent with cell genesis activity in the hippocampus of RMTLE patients. Moreover, two candidate genes for therapeutic targeting came out from this analysis: SSTR1, a relevant common hub in febrile and afebrile transcriptomes, and CHRM3, due to its putative role in epilepsy susceptibility development. MRI texture analysis allowed an overall accuracy of 90% for pixels correctly classified as belonging to FS or NFS groups. Histological examination revealed that granule cell loss was significantly higher in FS hippocampi.

CONCLUSIONS/SIGNIFICANCE

CA3 transcriptional signatures and dentate gyrus morphology fairly correlate with IPI in RMTLE, indicating that FS-RMTLE represents a distinct phenotype. These findings may shed light on the molecular mechanisms underlying refractory epilepsy phenotypes and contribute to the discovery of novel specific drug targets for therapeutic interventions.