TSHZ1-dependent gene regulation is essential for olfactory bulb development and olfaction

Parenting behaviors in mice: Olfactory mechanisms and features in models of autism spectrum disorders

Rodents, along with numerous other mammals, heavily depend on olfactory cues to navigate their social interactions. Processing of olfactory sensory inputs is mediated by conserved brain circuits that ultimately trigger social behaviors, such as social interactions and parental care. Although innate, parenting is influenced by internal states, social experience, genetics, and the environment, and any significant disruption of these factors can impact the social circuits. Here, we review the molecular mechanisms and social circuits from the olfactory epithelium to central processing that initiate parental behaviors and their dysregulations that may contribute to the social impairments in mouse models of autism spectrum disorders (ASD). We discuss recent advances of the crucial role of olfaction in parental care, its consequences for social interactions, and the reciprocal influence on social interaction impairments in mouse models of ASD.

Olfactory bulb anomalies in KBG syndrome mouse model and patients

ANKRD11 (ankyrin repeat domain 11) is a chromatin regulator and the only gene associated with KBG syndrome, a rare neurodevelopmental disorder. We have previously shown that Ankrd11 regulates murine embryonic cortical neurogenesis. Here, we show a novel olfactory bulb phenotype in a KBG syndrome mouse model and two diagnosed patients. Conditional knockout of Ankrd11 in murine embryonic neural stem cells leads to aberrant postnatal olfactory bulb development and reduced size due to reduction of the olfactory bulb granule cell layer. We further show that the rostral migratory stream has incomplete migration of neuroblasts, reduced cell proliferation as well as aberrant differentiation of neurons. This leads to reduced neuroblasts and neurons in the olfactory bulb granule cell layer. In vitro, Ankrd11-deficient neural stem cells from the postnatal subventricular zone display reduced migration, proliferation, and neurogenesis. Finally, we describe two clinically and molecularly confirmed KBG syndrome patients with anosmia and olfactory bulb and groove hypo-dysgenesis/agenesis. Our report provides evidence that Ankrd11 is a novel regulator of olfactory bulb development and neuroblast migration. Moreover, our study highlights a novel clinical sign of KBG syndrome linked to ANKRD11 perturbations in mice and humans.

Baf-mediated transcriptional regulation of teashirt is essential for the development of neural progenitor cell lineages

Accumulating evidence hints heterochromatin anchoring to the inner nuclear membrane as an upstream regulatory process of gene expression. Given that the formation of neural progenitor cell lineages and the subsequent maintenance of postmitotic neuronal cell identity critically rely on transcriptional regulation, it seems possible that the development of neuronal cells is influenced by cell type-specific and/or context-dependent programmed regulation of heterochromatin anchoring. Here, we explored this possibility by genetically disrupting the evolutionarily conserved barrier-to-autointegration factor (Baf) in the Drosophila nervous system. Through single-cell RNA sequencing, we demonstrated that Baf knockdown induces prominent transcriptomic changes, particularly in type I neuroblasts. Among the differentially expressed genes, our genetic analyses identified teashirt (tsh), a transcription factor that interacts with beta-catenin, to be closely associated with Baf knockdown-induced phenotypes that were suppressed by the overexpression of tsh or beta-catenin. We also found that Baf and tsh colocalized in a region adjacent to heterochromatin in type I NBs. Notably, the subnuclear localization pattern remained unchanged when one of these two proteins was knocked down, indicating that both proteins contribute to the anchoring of heterochromatin to the inner nuclear membrane. Overall, this study reveals that the Baf-mediated transcriptional regulation of teashirt is a novel molecular mechanism that regulates the development of neural progenitor cell lineages.

A protein-coding gene expression atlas from the brain of pregnant and non-pregnant goats

Background: The brain is an extraordinarily complex organ with multiple anatomical structures involved in highly specialized functions related with behavior and physiological homeostasis. Our goal was to build an atlas of protein-coding gene expression in the goat brain by sequencing the transcriptomes of 12 brain regions in seven female Murciano-Granadina goats, from which three of them were 1-month pregnant. Results: Between 14,889 (cerebellar hemisphere) and 15,592 (pineal gland) protein-coding genes were expressed in goat brain regions, and most of them displayed ubiquitous or broad patterns of expression across tissues. Principal component analysis and hierarchical clustering based on the patterns of mRNA expression revealed that samples from certain brain regions tend to group according to their position in the anterior-posterior axis of the neural tube, i.e., hindbrain (pons and medulla oblongata), midbrain (rostral colliculus) and forebrain (frontal neocortex, olfactory bulb, hypothalamus, and hippocampus). Exceptions to this observation were cerebellum and glandular tissues (pineal gland and hypophysis), which showed highly divergent mRNA expression profiles. Differential expression analysis between pregnant and non-pregnant goats revealed moderate changes of mRNA expression in the frontal neocortex, hippocampus, adenohypophysis and pons, and very dramatic changes in the olfactory bulb. Many genes showing differential expression in this organ are related to olfactory function and behavior in humans. Conclusion: With the exception of cerebellum and glandular tissues, there is a relationship between the cellular origin of sampled regions along the anterior-posterior axis of the neural tube and their mRNA expression patterns in the goat adult brain. Gestation induces substantial changes in the mRNA expression of the olfactory bulb, a finding consistent with the key role of this anatomical structure on the development of maternal behavior.

Sex-specific transcriptional rewiring in the brain of Alzheimer’s disease patients

Sex-specific differences may contribute to Alzheimer’s disease (AD) development. AD is more prevalent in women worldwide, and female sex has been suggested as a disease risk factor. Nevertheless, the molecular mechanisms underlying sex-biased differences in AD remain poorly characterized. To this end, we analyzed the transcriptional changes in the entorhinal cortex of symptomatic and asymptomatic AD patients stratified by sex. Co-expression network analysis implemented by SWItchMiner software identified sex-specific signatures of switch genes responsible for drastic transcriptional changes in the brain of AD and asymptomatic AD individuals. Pathway analysis of the switch genes revealed that morphine addiction, retrograde endocannabinoid signaling, and autophagy are associated with both females with AD (F-AD) and males with (M-AD). In contrast, nicotine addiction, cell adhesion molecules, oxytocin signaling, adipocytokine signaling, prolactin signaling, and alcoholism are uniquely associated with M-AD. Similarly, some of the unique pathways associated with F-AD switch genes are viral myocarditis, Hippo signaling pathway, endometrial cancer, insulin signaling, and PI3K-AKT signaling. Together these results reveal that there are many sex-specific pathways that may lead to AD. Approximately 20–30% of the elderly have an accumulation of amyloid beta in the brain, but show no cognitive deficit. Asymptomatic females (F-asymAD) and males (M-asymAD) both shared dysregulation of endocytosis. In contrast, pathways uniquely associated with F-asymAD switch genes are insulin secretion, progesterone-mediated oocyte maturation, axon guidance, renal cell carcinoma, and ErbB signaling pathway. Similarly, pathways uniquely associated with M-asymAD switch genes are fluid shear stress and atherosclerosis, FcγR mediated phagocytosis, and proteoglycans in cancer. These results reveal for the first time unique pathways associated with either disease progression or cognitive resilience in asymptomatic individuals. Additionally, we identified numerous sex-specific transcription factors and potential neurotoxic chemicals that may be involved in the pathogenesis of AD. Together these results reveal likely molecular drivers of sex differences in the brain of AD patients. Future molecular studies dissecting the functional role of these switch genes in driving sex differences in AD are warranted.

Prokineticin-Receptor Network: Mechanisms of Regulation

Prokineticins are a new class of chemokine-like peptides that bind their G protein-coupled receptors, PKR1 and PKR2, and promote chemotaxis and the production of pro-inflammatory cytokines following tissue injury or infection. This review summarizes the major cellular and biochemical mechanisms of prokineticins pathway regulation that, like other chemokines, include: genetic polymorphisms; mRNA splice modulation; expression regulation at transcriptional and post-transcriptional levels; prokineticins interactions with cell-surface glycosaminoglycans; PKRs degradation, localization, post-translational modifications and oligomerization; alternative signaling responses; binding to pharmacological inhibitors. Understanding these mechanisms, which together exert substantial biochemical control and greatly enhance the complexity of the prokineticin-receptor network, leads to novel opportunities for therapeutic intervention. In this way, besides targeting prokineticins or their receptors directly, it could be possible to indirectly influence their activity by modulating their expression and localization or blocking the downstream signaling pathways.

Genetics of congenital olfactory dysfunction: a systematic review of the literature

Olfaction, as one of our 5 senses, plays an important role in our daily lives. It is connected to proper nutrition, social interaction, and protection mechanisms. Disorders affecting this sense consequently also affect the patients' general quality of life. Because the underlying genetics of congenital olfactory disorders (COD) have not been thoroughly investigated yet, this systematic review aimed at providing information on genes that have previously been reported to be mutated in patients suffering from COD. This was achieved by systematically reviewing existing literature on 3 databases, namely PubMed, Ovid Medline, and ISI Web of Science. Genes and the type of disorder, that is, isolated and/or syndromic COD were included in this study, as were the patients' associated abnormal features, which were categorized according to the affected organ(-system). Our research yielded 82 candidate genes/chromosome loci for isolated and/or syndromic COD. Our results revealed that the majority of these are implicated in syndromic COD, a few accounted for syndromic and isolated COD, and the least underly isolated COD. Most commonly, structures of the central nervous system displayed abnormalities. This study is meant to assist clinicians in determining the type of COD and detecting potentially abnormal features in patients with confirmed genetic variations. Future research will hopefully expand this list and thereby further improve our understanding of COD.

Novel Perspectives on the Development of the Amygdala in Rodents

The amygdala is a hyperspecialized brain region composed of strongly inter- and intraconnected nuclei involved in emotional learning and behavior. The cellular heterogeneity of the amygdalar nuclei has complicated straightforward conclusions on their developmental origin, and even resulted in contradictory data. Recently, the concentric ring theory of the pallium and the radial histogenetic model of the pallial amygdala have cleared up several uncertainties that plagued previous models of amygdalar development. Here, we provide an extensive overview on the developmental origin of the nuclei of the amygdaloid complex. Starting from older gene expression data, transplantation and lineage tracing studies, we systematically summarize and reinterpret previous findings in light of the novel perspectives on amygdalar development. In addition, migratory routes that these cells take on their way to the amygdala are explored, and known transcription factors and guidance cues that seemingly drive these cells toward the amygdala are emphasized. We propose some future directions for research on amygdalar development and highlight that a better understanding of its development could prove critical for the treatment of several neurodevelopmental and neuropsychiatric disorders.

Developmental Origins of Human Cortical Oligodendrocytes and Astrocytes

Human cortical radial glial cells are primary neural stem cells that give rise to cortical glutaminergic projection pyramidal neurons, glial cells (oligodendrocytes and astrocytes) and olfactory bulb GABAergic interneurons. One of prominent features of the human cortex is enriched with glial cells, but there are major gaps in understanding how these glial cells are generated. Herein, by integrating analysis of published human cortical single-cell RNA-Seq datasets with our immunohistochemistical analyses, we show that around gestational week 18, EGFR-expressing human cortical truncated radial glial cells (tRGs) give rise to basal multipotent intermediate progenitors (bMIPCs) that express EGFR, ASCL1, OLIG2 and OLIG1. These bMIPCs undergo several rounds of mitosis and generate cortical oligodendrocytes, astrocytes and olfactory bulb interneurons. We also characterized molecular features of the cortical tRG. Integration of our findings suggests a general picture of the lineage progression of cortical radial glial cells, a fundamental process of the developing human cerebral cortex.

A systematic-review of olfactory deficits in neurodevelopmental disorders: From mouse to human

Olfactory impairment is a common clinical motif across neurodevelopmental disorders, suggesting olfactory circuits are particularly vulnerable to disease processes and can provide insight into underlying disease mechanisms. The mouse olfactory bulb is an ideal model system to study mechanisms of neurodevelopmental disease due to its anatomical accessibility, behavioral relevance, ease of measuring circuit input and output, and the feature of adult neurogenesis. Despite the clinical relevance and experimental benefits, olfactory testing across animal models of neurodevelopmental disease has been inconsistent and non-standardized. Here we performed a systematic literature review of olfactory function testing in mouse models of neurodevelopmental disorders, and identified intriguing inconsistencies that include evidence for both increased and decreased acuity in odor detection in various mouse models of Autism Spectrum Disorder (ASD). Based on our identified gaps in the literature, we recommend direct comparison of different mouse models of ASD using standardized tests for odor detection and discrimination. This review provides a framework to guide future olfactory function testing in mouse models of neurodevelopmental diseases.

Congenital Agenesis of the Olfactory Bulbs: What to Suspect?

Complete agenesis of the olfactory bulbs (OB) constitutes a rare cause of congenital anosmia, which is more often associated with cerebral malformations or genetic disorders. The authors present a very rare case of a 28-year-old caucasian male with complaints of complete lack of the sense of smell since childhood. Radiologic study confirmed complete bilateral agenesis of the OB, with no other radiologic or clinical findings, such as delayed sexual development. Laboratorial investigation confirmed no signs of adrenocortical insufficiency. Despite being immature in the term neonate, the OB are already functional at birth. Congenital agenesis of the OB can occur as an isolated deformity. On the other hand, it is a constant feature of several genetic syndromes, such as Kallmann's syndrome or alobar holoprosencephaly. Most cases of isolated congenital anosmia occur sporadically, with no family history of the condition. Given the fact that no curative treatment is available, counselling for daily living precautions should be given to all patients. This is one of the first case reports about complete and isolated agenesia of the OB diagnosed in adulthood. The authors highlight the need to exclude several genetic syndromes that may be associated, albeit in a dissimulated way.

Temporally Distinct Roles for the Zinc Finger Transcription Factor Sp8 in the Generation and Migration of Dorsal Lateral Ganglionic Eminence (dLGE)-Derived Neuronal Subtypes in the Mouse

Progenitors in the dorsal lateral ganglionic eminence (dLGE) are known to give rise to olfactory bulb (OB) interneurons and intercalated cells (ITCs) of the amygdala. The dLGE enriched transcription factor Sp8 is required for the normal generation of ITCs as well as OB interneurons, particularly the calretinin (CR)-expressing subtype. In this study, we used a genetic gain-of-function approach in mice to examine the roles Sp8 plays in controlling the development of dLGE-derived neuronal subtypes. Misexpression of Sp8 throughout the ventral telencephalic subventricular zone (SVZ) from early embryonic stages, led to an increased generation of ITCs which was dependent on Tshz1 gene dosage. Additionally, Sp8 misexpression impaired rostral migration of OB interneurons with clusters of CR interneurons seen in the SVZ along with decreased differentiation of calbindin OB interneurons. Sp8 misexpression throughout the ventral telencephalon also reduced ventral LGE neuronal subtypes including striatal projection neurons. Delaying Sp8 misexpression until E14-15 rescued the striatal and amygdala phenotypes but only partially rescued OB interneuron reductions, consistent with an early window of striatal and amygdala neurogenesis and ongoing OB interneuron generation at this late stage. Our results demonstrate critical roles for the timing and neuronal cell-type specificity of Sp8 expression in mouse LGE neurogenesis.

Survey on Olfactory Testing by Pediatric Neurologists: Is the Olfactory a "True" Cranial Nerve?

BACKGROUND

The olfactory nerve was conceptualized in the 4th century BC by Alcmaeon and described anatomically by Winslow in 1733. Cranial nerves (CNs) were named and numbered by Soemmerring in 1791. Notions still prevail that the olfactory (CN1) is not a "true" cranial nerve.

METHODS

To confirm our impression that the olfactory nerve is infrequently tested by North American pediatric neurologists, a survey was distributed to members of national pediatric neurology societies in Mexico, Canada, and the United States. A total of 233 responses were received to 6 multiple-choice questions regarding practice patterns examining CN1 in neonates and children and in metabolic, endocrine, and genetic disorders and cerebral malformations. Two of the questions addressed familiarity with neonatal olfactory reflexes and asked whether the olfactory is a "true" cranial nerve.

RESULTS

Only 16% to 24% of North American pediatric neurologists examine CN1 in neonates, even in conditions in which olfaction may be impaired. About 40% of respondents were aware of olfactory reflexes. A minority 15% did not consider CN1 as a "true" cranial nerve.

CONCLUSIONS

Olfactory evaluation in neonates is simple, rapid, and inexpensive. It tests parts of the brain not otherwise examined. It may assist diagnosis in cerebral malformations; metabolic, endocrine, and hypoxic encephalopathies; and some genetic diseases, including chromosomopathies. CN1 is neuroanatomically unique and fulfills criteria of a true sensory cranial nerve. We recommend that olfaction be routinely or selectively included during neurologic examination of neonates and children.

Enhancer-gene maps in the human and zebrafish genomes using evolutionary linkage conservation

The spatiotemporal expression of genes is controlled by enhancer sequences that bind transcription factors. Identifying the target genes of enhancers remains difficult because enhancers regulate gene expression over long genomic distances. To address this, we used an evolutionary approach to build two genome-wide maps of predicted enhancer-gene associations in the human and zebrafish genomes. Evolutionary conserved sequences were linked to their predicted target genes using PEGASUS, a bioinformatics method that relies on evolutionary conservation of synteny. The analysis of these maps revealed that the number of predicted enhancers linked to a gene correlate with its expression breadth. Comparison of both maps identified hundreds of putative vertebrate ancestral regulatory relationships from which we could determine that predicted enhancer-gene distances scale with genome size despite strong positional conservation. The two maps represent a resource for further studies, including the prioritization of sequence variants in whole genome sequence of patients affected by genetic diseases.

Dlx1/2 are Central and Essential Components in the Transcriptional Code for Generating Olfactory Bulb Interneurons

Generation of olfactory bulb (OB) interneurons requires neural stem/progenitor cell specification, proliferation, differentiation, and young interneuron migration and maturation. Here, we show that the homeobox transcription factors Dlx1/2 are central and essential components in the transcriptional code for generating OB interneurons. In Dlx1/2 constitutive null mutants, the differentiation of GSX2+ and ASCL1+ neural stem/progenitor cells in the dorsal lateral ganglionic eminence is blocked, resulting in a failure of OB interneuron generation. In Dlx1/2 conditional mutants (hGFAP-Cre; Dlx1/2F/- mice), GSX2+ and ASCL1+ neural stem/progenitor cells in the postnatal subventricular zone also fail to differentiate into OB interneurons. In contrast, overexpression of Dlx1&2 in embryonic mouse cortex led to ectopic production of OB-like interneurons that expressed Gad1, Sp8, Sp9, Arx, Pbx3, Etv1, Tshz1, and Prokr2. Pax6 mutants generate cortical ectopia with OB-like interneurons, but do not do so in compound Pax6; Dlx1/2 mutants. We propose that DLX1/2 promote OB interneuron development mainly through activating the expression of Sp8/9, which further promote Tshz1 and Prokr2 expression. Based on this study, in combination with earlier ones, we propose a transcriptional network for the process of OB interneuron development.

Transcription Factors Sp8 and Sp9 Coordinately Regulate Olfactory Bulb Interneuron Development

Neural stem cells in the postnatal telencephalic ventricular-subventricular zone (V-SVZ) generate new interneurons, which migrate tangentially through the rostral migratory stream (RMS) into the olfactory bulb (OB). The Sp8 and Sp9 transcription factors are expressed in neuroblasts, as well as in the immature and mature interneurons in the V-SVZ-RMS-OB system. Here we show that Sp8 and Sp9 coordinately regulate OB interneuron development: although Sp9 null mutants show no major OB interneuron defect, conditional deletion of both Sp8 and Sp9 resulted in a much more severe reduction of OB interneuron number than that observed in the Sp8 conditional mutant mice, due to defects in neuronal differentiation, tangential and radial migration, and increased cell death in the V-SVZ-RMS-OB system. RNA-Seq and RNA in situ hybridization reveal that, in Sp8/Sp9 double mutant mice, but not in Sp8 or Sp9 single mutant mice, newly born neuroblasts in the V-SVZ-RMS-OB system fail to express Prokr2 and Tshz1 expression, genes with known roles in promoting OB interneuron differentiation and migration, and that are involved in human Kallmann syndrome.

Teashirt 1 (Tshz1) is essential for the development, survival and function of hypoglossal and phrenic motor neurons in mouse

Feeding and breathing are essential motor functions and rely on the activity of hypoglossal and phrenic motor neurons that innervate the tongue and diaphragm, respectively. Little is known about the genetic programs that control the development of these neuronal subtypes. The transcription factor Tshz1 is strongly and persistently expressed in developing hypoglossal and phrenic motor neurons. We used conditional mutation of Tshz1 in the progenitor zone of motor neurons (Tshz1^{MN Δ}) to show that Tshz1 is essential for survival and function of hypoglossal and phrenic motor neurons. Hypoglossal and phrenic motor neurons are born in correct numbers, but many die between embryonic day 13.5 and 14.5 in Tshz1^{MN Δ} mutant mice. In addition, innervation and electrophysiological properties of phrenic and hypoglossal motor neurons are altered. Severe feeding and breathing problems accompany this developmental deficit. Although motor neuron survival can be rescued by elimination of the pro-apoptotic factor Bax, innervation, feeding and breathing defects persist in Bax^-/-; Tshz1^{MN Δ} mutants. We conclude that Tshz1 is an essential transcription factor for the development and physiological function of phrenic and hypoglossal motor neurons.

Loss of function BMP4 mutation supports the implication of the BMP/TGF-β pathway in the etiology of combined pituitary hormone deficiency

Despite BMP4 signaling being critical to Rathke's pouch induction and maintenance during early stages of pituitary development, its implication in the etiology of combined pituitary hormone deficiency (CPHD) and other clinical presentations of congenital hypopituitarism has not yet been definitely demonstrated. We report here the first CPHD patient with a de novo pathogenic loss-of-function variant in BMP4. A 6-year-old boy, with macrocephaly, myopia/astigmatism, mild psychomotor retardation, anterior pituitary hypoplasia and ectopic posterior pituitary, clinically diagnosed with growth hormone deficiency, and central hypothyroidism, was referred for genetic analysis of CPHD. Targeted NGS analysis with a custom panel (n = 310 genes) identified a novel heterozygous de novo nonsense variant, NM_001202.5:c.794G > A, p.(Trp265*) in BMP4, which introduces a premature stop codon in the BMP4 pro-domain, impairing the transcription of the TGF-β mature peptide domain. Additional relevant variants in other genes implicated in pituitary development signaling pathways such as SMAD4 and E2F4 (BMP/TGF-pathway), ALMS1 (NOTCH-pathway), and TSHZ1 (Prokineticin-pathway), were also identified. Our results support the implication of the BMP/TGF-β signaling pathway in the etiology of CPHD and suggest that oligogenic contribution of additional inherited variants may modify the phenotypic expressivity of BMP4 pathogenic variants.

Development of the human olfactory system

This chapter focuses on the development of the human olfactory system. In this system, function does not require full neuroanatomical maturity. Thus, discrimination of odorous molecules, including a number within the mother's diet, occurs in amniotic fluid after 28-30 weeks of gestation, at which time the olfactory bulbs are identifiable by MRI. Hypoplasia/aplasia of the bulbs is documented in the third trimester and postnatally. Interestingly, olfactory axons project from the nasal epithelium to the telencephalon before formation of the olfactory bulbs and lack a peripheral ganglion, but the synaptic glomeruli of the future olfactory bulb serves this function. Histologic lamination of the olfactory bulb is present by 14 weeks, but maturation remains incomplete at term for neuronal differentiation, synaptogenesis, myelination, and persistence of the normal transitory fetal ventricular recess. Myelination occurs postnatally. Although olfaction is the only sensory system without direct thalamic projections, the olfactory bulb and anterior olfactory nucleus are, in effect, thalamic surrogates. For example, many dendro-dendritic synapses occur within the bulb between GABAergic granular neurons and periglomerular neurons. Moreover, bulbar synaptic glomeruli are analogous to peripheral ganglia of other sensory cranial nerves. The olfactory tract contains much gray as well as white matter. The olfactory epithelium and bulb both incorporate progenitor cells at all ages. Diverse malformations of the olfactory bulb can be detected by clinical examination, imaging, and neuropathology; indeed, olfactory reflexes of the neonate can be reliably tested. We recommend that such testing be routine in the neonatal neurologic examination, especially in children with brain malformations, endocrinopathies, chromosomopathies, genetic/metabolic disorders, and perinatal hypoxic/ischemic encephalopathy.

E2F1 Mediates the Retinoic Acid-Induced Transcription of Tshz1 during Neuronal Differentiation in a Cell Division-Dependent Manner

The involvement of cell division in cellular differentiation has long been accepted. Cell division may be required not only for the expansion of a differentiated cell population but also for the execution of differentiation processes. Nonetheless, knowledge regarding how specific differentiation processes are controlled in a cell division-dependent manner is far from complete. Here, we determined the involvement of cell division in neuronal differentiation. We initially confirmed that cell division is an essential event for the neuronal differentiation of P19 embryonic carcinoma cells. We investigated the induction mechanisms of Tshz1, whose expression is induced by retinoic acid (RA) in a cell division-dependent manner. Promoter analysis of Tshz1 revealed a specific region required for RA-dependent transcription. A series of experiments was used to identify E2F1 as the induction factor for the RA-dependent transcription of Tshz1 We propose that E2F1 mediates neuronal differentiation in a cell division-dependent manner.

SP8 and SP9 coordinately promote D2-type medium spiny neuron production by activating Six3 expression

Dopamine receptor DRD1-expressing medium spiny neurons (D1 MSNs) and dopamine receptor DRD2-expressing medium spiny neurons (D2 MSNs) are the principal projection neurons in the striatum, which is divided into dorsal striatum (caudate nucleus and putamen) and ventral striatum (nucleus accumbens and olfactory tubercle). Progenitors of these neurons arise in the lateral ganglionic eminence (LGE). Using conditional deletion, we show that mice lacking the transcription factor genes Sp8 and Sp9 lose virtually all D2 MSNs as a result of reduced neurogenesis in the LGE, whereas D1 MSNs are largely unaffected. SP8 and SP9 together drive expression of the transcription factor Six3 in a spatially restricted domain of the LGE subventricular zone. Conditional deletion of Six3 also prevents the formation of most D2 MSNs, phenocopying the Sp8/9 mutants. Finally, ChIP-Seq reveals that SP9 directly binds to the promoter and a putative enhancer of Six3 Thus, this study defines components of a transcription pathway in a regionally restricted LGE progenitor domain that selectively drives the generation of D2 MSNs.

Wnt Signalling Drives Context-Dependent Differentiation or Proliferation in Neuroblastoma

Neuroblastoma is one of the commonest and deadliest solid tumours of childhood, and is thought to result from disrupted differentiation of the developing sympathoadrenergic lineage of the neural crest. Neuroblastoma exhibits intra- and intertumoural heterogeneity, with high risk tumours characterised by poor differentiation, which can be attributable to MYCN-mediated repression of genes involved in neuronal differentiation. MYCN is known to co-operate with oncogenic signalling pathways such as Alk, Akt and MEK/ERK signalling, and, together with c-MYC has been shown to be activated by Wnt signalling in various tissues. However, our previous work demonstrated that Wnt3a/Rspo2 treatment of some neuroblastoma cell lines can, paradoxically, decrease c-MYC and MYCN proteins. This prompted us to define the neuroblastoma-specific Wnt3a/Rspo2-driven transcriptome using RNA sequencing, and characterise the accompanying changes in cell biology. Here we report the identification of ninety Wnt target genes, and show that Wnt signalling is upstream of numerous transcription factors and signalling pathways in neuroblastoma. Using live-cell imaging, we show that Wnt signalling can drive differentiation of SK-N-BE(2)-C and SH-SY5Y cell-lines, but, conversely, proliferation of SK-N-AS cells. We show that cell-lines that differentiate show induction of pro-differentiation BMP4 and EPAS1 proteins, which is not apparent in the SK-N-AS cells. In contrast, SK-N-AS cells show increased CCND1, phosphorylated RB and E2F1 in response to Wnt3a/Rspo2, consistent with their proliferative response, and these proteins are not increased in differentiating lines. By meta-analysis of the expression of our 90 genes in primary tumour gene expression databases, we demonstrate discrete expression patterns of our Wnt genes in patient cohorts with different prognosis. Furthermore our analysis reveals interconnectivity within subsets of our Wnt genes, with one subset comprised of novel putative drivers of neuronal differentiation repressed by MYCN. Assessment of β-catenin immunohistochemistry shows high levels of β-catenin in tumours with better differentiation, further supporting a role for canonical Wnt signalling in neuroblastoma differentiation.

Loss of Intercalated Cells (ITCs) in the Mouse Amygdala of Tshz1 Mutants Correlates with Fear, Depression, and Social Interaction Phenotypes

The intercalated cells (ITCs) of the amygdala have been shown to be critical regulatory components of amygdalar circuits, which control appropriate fear responses. Despite this, the molecular processes guiding ITC development remain poorly understood. Here we establish the zinc finger transcription factor Tshz1 as a marker of ITCs during their migration from the dorsal lateral ganglionic eminence through maturity. Using germline and conditional knock-out (cKO) mouse models, we show that Tshz1 is required for the proper migration and differentiation of ITCs. In the absence of Tshz1, migrating ITC precursors fail to settle in their stereotypical locations encapsulating the lateral amygdala and BLA. Furthermore, they display reductions in the ITC marker Foxp2 and ectopic persistence of the dorsal lateral ganglionic eminence marker Sp8. Tshz1 mutant ITCs show increased cell death at postnatal time points, leading to a dramatic reduction by 3 weeks of age. In line with this, Foxp2-null mutants also show a loss of ITCs at postnatal time points, suggesting that Foxp2 may function downstream of Tshz1 in the maintenance of ITCs. Behavioral analysis of male Tshz1 cKOs revealed defects in fear extinction as well as an increase in floating during the forced swim test, indicative of a depression-like phenotype. Moreover, Tshz1 cKOs display significantly impaired social interaction (i.e., increased passivity) regardless of partner genetics. Together, these results suggest that Tshz1 plays a critical role in the development of ITCs and that fear, depression-like and social behavioral deficits arise in their absence.SIGNIFICANCE STATEMENT We show here that the zinc finger transcription factor Tshz1 is expressed during development of the intercalated cells (ITCs) within the mouse amygdala. These neurons have previously been shown to play a crucial role in fear extinction. Tshz1 mouse mutants exhibit severely reduced numbers of ITCs as a result of abnormal migration, differentiation, and survival of these neurons. Furthermore, the loss of ITCs in mouse Tshz1 mutants correlates well with defects in fear extinction as well as the appearance of depression-like and abnormal social interaction behaviors reminiscent of depressive disorders observed in human patients with distal 18q deletions, including the Tshz1 locus.

Modulation of Neurogenesis through the Promotion of Energy Production Activity Is behind the Antidepressant-Like Effect of Colonial Green Alga, Botryococcus braunii

Algae have been recognized as important resources providing functional components due to their capacity to exert beneficial effects on health. Therefore, there is increasing interest in investigating the biological activity of algae. In this study, we evaluated the antidepressant-like effect of the administration of 100 mg/kg/day of the ethanol extract of colonial green alga Botryococcus braunii (EEB) for 14 consecutive days in the forced swimming test (FST)-induced depression in imprinting control region (ICR) mice. Imipramine, a commercial antidepressant drug, was used as a positive control. In addition, we investigated the molecular mechanisms underlying the effect of EEB by measuring ATP production and by assessing any change in gene expression at the end of the treatment using real-time polymerase chain reaction (PCR) and microarray assays. We showed that the immobility time in the water-administered control (FST stress) group gradually increased from day 1 to day 14. However, treatment with EEB caused a significant decrease of immobility time in the FST compared with that in the FST stress group. Microarray and real-time PCR results revealed that EEB treatment induced variation in the expression of several genes associated with neurogenesis, energy metabolism, and dopamine synthesis. Interestingly, we revealed that only EEB treatment enhanced the promotion of energy production, while treatment with imipramine was ineffective. Our study provides the first evidence that B. braunii enhances energy production, which may contribute to the modulation of neurogenesis and to the enhancement of dopaminergic function, in turn potentially underlying the antistress- and antidepressant-like effects that we observed.

Characterization of Glcci1 expression in a subpopulation of lateral ganglionic eminence progenitors in the mouse telencephalon

BACKGROUND

The lateral ganglionic eminence (LGE) in the ventral telencephalon is a diverse progenitor domain subdivided by distinct gene expression into a dorsal region (dLGE) that gives rise to olfactory bulb and amygdalar interneurons and a ventral region (vLGE) that gives rise to striatal projection neurons. The homeobox gene, Gsx2, is an enriched marker of the LGE and is expressed in a high dorsal to low ventral gradient in the ventricular zone (VZ) as development proceeds. Aside from Gsx2, markers restricted to the VZ in the dLGE and/or vLGE remain largely unknown.

RESULTS

Here, we show that the gene and protein expression of Glucocorticoid-induced transcript 1 (Glcci1) has a similar dorsal to ventral gradient of expression in the VZ as Gsx2. We found that Glcci1 gene and protein expression are reduced in Gsx2 mutants, and are increased in the cortex after early and late Gsx2 misexpression. Moreover, Glcci1 expressing cells are restricted to a subpopulation of Gsx2 positive cells on the basal side of the VZ and co-express Ascl1, but not the subventricular zone dLGE marker, Sp8.

CONCLUSIONS

These findings suggest that Glcci1 is a new marker of a subpopulation of LGE VZ progenitor cells in the Gsx2 lineage. Developmental Dynamics 247:222-228, 2018. © 2017 Wiley Periodicals, Inc.

Septal contributions to olfactory bulb interneuron diversity in the embryonic mouse telencephalon: role of the homeobox gene Gsx2

Background

Olfactory bulb (OB) interneurons are known to represent diverse neuronal subtypes, which are thought to originate from a number of telencephalic regions including the embryonic dorsal lateral ganglionic eminence (dLGE) and septum. These cells migrate rostrally toward the OB, where they then radially migrate to populate different OB layers including the granule cell layer (GCL) and the outer glomerular layer (GL). Although previous studies have attempted to investigate regional contributions to OB interneuron diversity, few genetic tools have been used to address this question at embryonic time points when the earliest populations are specified.

Methods

In this study, we utilized Zic3-lacZ and Gsx2e-CIE transgenic mice as genetic fate-mapping tools to study OB interneuron contributions derived from septum and LGE, respectively. Moreover, to address the regional (i.e. septal) requirements of the homeobox gene Gsx2 for OB interneuron diversity, we conditionally inactivated Gsx2 in the septum, leaving it largely intact in the dLGE, by recombining the Gsx2 floxed allele using Olig2^Cre/+ mice.

Results

Our fate mapping studies demonstrated that the dLGE and septum gave rise to OB interneuron subtypes differently. Notably, the embryonic septum was found to give rise largely to the calretinin⁺ (CR⁺) GL subtype, while the dLGE was more diverse, generating all major GL subpopulations as well as many GCL interneurons. Moreover, Gsx2 conditional mutants (cKOs), with septum but not dLGE recombination, showed impaired generation of CR⁺ interneurons within the OB GL. These Gsx2 cKOs exhibited reduced proliferation within the septal subventricular zone (SVZ), which correlated well with the reduced number of CR⁺ interneurons observed.

Conclusions

Our findings indicate that the septum and LGE contribute differently to OB interneuron diversity. While the dLGE provides a wide range of OB interneuron subtypes, the septum is more restricted in its contribution to the CR⁺ subtype. Gsx2 is required in septal progenitors for the correct expansion of SVZ progenitors specified toward the CR⁺ subtype. Finally, the septum has been suggested to be the exclusive source of CR⁺ interneurons in postnatal studies. Our results here demonstrate that dLGE progenitors in the embryo also contribute to this OB neuronal subtype.

Electronic supplementary material

The online version of this article (doi:10.1186/s13064-017-0090-5) contains supplementary material, which is available to authorized users.

Olfactory Development, Part 2: Neuroanatomic Maturation and Dysgeneses

Olfactory axons project from nasal epithelium to the primitive telencephalon before olfactory bulbs form. Olfactory bulb neurons do not differentiate in situ but arrive via the rostral migratory stream. Synaptic glomeruli and concentric laminar architecture are unlike other cortices. Fetal olfactory maturation of neuronal differentiation, synaptogenesis, and myelination remains incomplete at term and have a protracted course of postnatal development. The olfactory ventricular recess involutes postnatally but dilates in congenital hydrocephalus. Olfactory bulb, tract and epithelium are repositories of progenitor stem cells in fetal and adult life. Diverse malformations of the olfactory bulb can be diagnosed by clinical examination, imaging, and neuropathologically. Cellular markers of neuronal differentiation and synaptogenesis demonstrate immaturity of the olfactory system at birth, previously believed by histology alone to occur early in fetal life. Immaturity does not preclude function.

Olfactory Development, Part 1: Function, From Fetal Perception to Adult Wine-Tasting

Discrimination of odorous molecules in amniotic fluid occur after 30 weeks' gestation; fetuses exhibit differential responses to maternal diet. Olfactory reflexes enable reliable neonatal testing. Olfactory bulbs can be demonstrated reliably by MRI after 30 weeks' gestation, and their hypoplasia or aplasia also documented by late prenatal and postnatal MRI. Olfactory axons project from nasal epithelium to telencephalon before olfactory bulbs form. Fetal olfactory maturation remains incomplete at term for neuronal differentiation, synaptogenesis, myelination, and persistence of the transitory fetal ventricular recess. Immaturity does not signify nonfunction. Olfaction is the only sensory system without thalamic projection because of its own intrinsic thalamic equivalent. Diverse malformations of the olfactory bulb can be diagnosed by clinical examination, imaging, and neuropathology. Some epileptic auras might be primarily generated in the olfactory bulb. Cranial nerve 1 should be tested in all neonates and especially in patients with brain malformations, endocrinopathies, chromosomopathies, and genetic/metabolic diseases.

Interstitial de novo 18q22.3q23 deletion: clinical, neuroradiological and molecular characterization of a new case and review of the literature

Background

Deletions of the long arm of chromosome 18 cause a common autosomal syndrome clinically characterized by a protean clinical phenotype.

Case presentation

We report on a 16-month-old male infant affected by fever attacks apparently unrelated with any infectious or inflammatory symptoms, growth retardation, bilateral vertical talus, congenital aural atresia, dysmorphisms, mild psychomotor delay, and peculiar neuroradiological features. Array-CGH analysis revealed one of the smallest 18q22.3q23 interstitial deletions involving five genes: TSHZ1, ZNF516, ZNF236, MBP, and GALR1.

Conclusions

Herein we focus on previously unreported heralding symptoms and neuroradiological abnormalities which enlarge the spectrum of 18q deletion syndrome demonstrating that a small deletion can determine a complex phenotype.

Partial Conservation between Mice and Humans in Olfactory Bulb Interneuron Transcription Factor Codes

The mammalian main olfactory bulb (OB) has a large population of GABAergic inhibitory interneurons that contains several subtypes defined by the co-expression other neurotransmitters and calcium binding proteins. The three most commonly studied OB interneuron subtypes co-express either Calretinin, Calbindin, or Tyrosine hydroxylase (Th). Combinations of transcription factors used to specify the phenotype of progenitors are referred to as transcription factor codes, and the current understanding of transcription factor codes that specify OB inhibitory neuron phenotypes are largely based on studies in mice. The conservation of these transcription factor codes in the human OB, however, has not been investigated. The aim of this study was to establish whether transcription factor codes in OB interneurons are conserved between mice and humans. This study compared the co-expression of Foxp2, Meis2, Pax6, and Sp8 transcription factors with Calretinin, Calbindin, or Th in human and mouse OB interneurons. This analysis found strong conservation of Calretinin co-expression with Sp8 and Meis2 as well as Th co-expression with Pax6 and Meis2. This analysis also showed that selective Foxp2 co-expression with Calbindin was conserved between mice and humans, which suggests Foxp2 is a novel determinant of the OB Calbindin interneuron phenotype. Together, the findings in this study provide insight into the conservation of transcription codes for OB interneuron phenotypes between humans and mice, as well as reveal some important differences between the species. This advance in our understanding of transcription factor codes in OB interneurons provides an important complement to the codes that have been established for other regions within the mammalian central nervous system, such as the cortex and spinal cord.

Consequences of chromsome18q deletions

Providing clinically relevant prognoses and treatment information for people with a chromsome18q deletion is particularly challenging because every unrelated person has a unique region of hemizygosity. The hemizygous region can involve almost any region of 18q including between 1 and 101 genes (30 Mb of DNA). Most individuals have terminal deletions, but in our cohort of over 350 individuals 23% have interstitial deletions. Because of this heterogeneity, we take a gene by gene approach to understanding the clinical consequences. There are 196 genes on 18q. We classified 133 of them as dosage insensitive, 15 (8%) as dosage sensitive leading to haploinsufficiency while another 10 (5%) have effects that are conditionally haploinsufficient and are dependent on another factor, genetic or environmental in order to cause an abnormal phenotype. Thirty-seven genes (19%) have insufficient information to classify their dosage effect. Phenotypes attributed to single genes include: congenital heart disease, minor bone morphology changes, central nervous system dysmyelination, expressive speech delay, vesicouretreral reflux, polyposis, Pitt-Hopkins syndrome, intellectual disability, executive function impairment, male infertility, aural atresia, and high frequency sensorineural hearing loss. Additionally, identified critical regions for other phenotypes include: adolescent idiopathic scoliosis and pectus excavatum, Virchow-Robin perivascular spaces, small corpus callosum, strabismus, atopic disorders, mood disorder, IgA deficiency, nystagmus, congenital heart disease, kidney malformation, vertical talus, CNS dysmyelination growth hormone deficiency and cleft palate. Together these findings make it increasingly feasible to compile an individualized syndrome description based on each person's individuated genotype. Future work will focus on understanding molecular mechanisms leading to treatment.

Tshz1 Regulates Pancreatic β-Cell Maturation

The homeodomain transcription factor Pdx1 controls pancreas organogenesis, specification of endocrine pancreas progenitors, and the postnatal growth and function of pancreatic β-cells. Pdx1 expression in human-derived stem cells is used as a marker for induced pancreatic precursor cells. Unfortunately, the differentiation efficiency of human pancreatic progenitors into functional β-cells is poor. In order to gain insight into the genes that Pdx1 regulates during differentiation, we performed Pdx1 chromatin immunoprecipitation followed by high-throughput sequencing of embryonic day (e) 13.5 and 15.5 mouse pancreata. From this, we identified the transcription factor Teashirt zinc finger 1 (Tshz1) as a direct Pdx1 target. Tshz1 is expressed in developing and adult insulin- and glucagon-positive cells. Endocrine cells are properly specified in Tshz1-null embryos, but critical regulators of β-cell (Pdx1 and Nkx6.1) and α-cell (MafB and Arx) formation and function are downregulated. Adult Tshz1(+/-) mice display glucose intolerance due to defects in glucose-stimulated insulin secretion associated with reduced Pdx1 and Clec16a expression in Tshz1(+/-) islets. Lastly, we demonstrate that TSHZ1 levels are reduced in human islets of donors with type 2 diabetes. Thus, we position Tshz1 in the transcriptional network of maturing β-cells and suggest that its dysregulation could contribute to the islet phenotype of human type 2 diabetes.

GnRH, anosmia and hypogonadotropic hypogonadism--where are we?

Gonadotropin releasing hormone (GnRH) neurons originate the nasal placode and migrate into the brain during prenatal development. Once within the brain, these cells become integral components of the hypothalamic-pituitary-gonadal axis, essential for reproductive function. Disruption of this system causes hypogonadotropic hypogonadism (HH). HH associated with anosmia is clinically defined as Kallman syndrome (KS). Recent work examining the developing nasal region has shed new light on cellular composition, cell interactions and molecular cues responsible for the development of this system in different species. This review discusses some developmental aspects, animal models and current advancements in our understanding of pathologies affecting GnRH. In addition we discuss how development of neural crest derivatives such as the glia of the olfactory system and craniofacial structures control GnRH development and reproductive function.

Central hypogonadotropic hypogonadism: genetic complexity of a complex disease

Central hypogonadotropic hypogonadism (CHH) is an emerging pathological condition frequently associated with overweight, metabolic syndrome, diabetes, and midline defects. The genetic mechanisms involve mutations in at least twenty-four genes regulating GnRH neuronal migration, secretion, and activity. So far, the mechanisms underlying CHH, both in prepubertal and in adulthood onset forms, remain unknown in most of the cases. Indeed, all detected gene variants may explain a small proportion of the affected patients (43%), indicating that other genes or epigenetic mechanisms are involved in the onset of CHH. The aim of this review is to summarize the current knowledge on genetic background of CHH, organizing the large amount of data present in the literature in a clear and concise manner, to produce a useful guide available for researchers and clinicians.