Nolz1 promotes striatal neurogenesis through the regulation of retinoic acid signaling

Background: Nolz1 is a zinc finger transcription factor whose expression is enriched in the lateral ganglionic eminence (LGE), although its function is still unknown. Results: Here we analyze the role of Nolz1 during LGE development. We show that Nolz1 expression is high in proliferating neural progenitor cells (NPCs) of the LGE subventricular zone. In addition, low levels of Nolz1 are detected in the mantle zone, as well as in the adult striatum. Similarly, Nolz1 is highly expressed in proliferating LGE-derived NPC cultures, but its levels rapidly decrease upon cell differentiation, pointing to a role of Nolz1 in the control of NPC proliferation and/or differentiation. In agreement with this hypothesis, we find that Nolz1 over-expression promotes cell cycle exit of NPCs in neurosphere cultures and negatively regulates proliferation in telencephalic organotypic cultures. Within LGE primary cultures, Nolz1 over-expression promotes the acquisition of a neuronal phenotype, since it increases the number of β-III tubulin (Tuj1)- and microtubule-associated protein (MAP)2-positive neurons, and inhibits astrocyte generation and/or differentiation. Retinoic acid (RA) is one of the most important morphogens involved in striatal neurogenesis, and regulates Nolz1 expression in different systems. Here we show that Nolz1 also responds to this morphogen in E12.5 LGE-derived cell cultures. However, Nolz1 expression is not regulated by RA in E14.5 LGE-derived cell cultures, nor is it affected during LGE development in mouse models that present decreased RA levels. Interestingly, we find that Gsx2, which is necessary for normal RA signaling during LGE development, is also required for Nolz1 expression, which is lost in Gsx2 knockout mice. These findings suggest that Nolz1 might act downstream of Gsx2 to regulate RA-induced neurogenesis. Keeping with this hypothesis, we show that Nolz1 induces the selective expression of the RA receptor (RAR)β without altering RARα or RARγ. In addition, Nozl1 over-expression increases RA signaling since it stimulates the RA response element. This RA signaling is essential for Nolz1-induced neurogenesis, which is impaired in a RA-free environment or in the presence of a RAR inverse agonist. It has been proposed that Drosophila Gsx2 and Nolz1 homologues could cooperate with the transcriptional co-repressors Groucho-TLE to regulate cell proliferation. In agreement with this view, we show that Nolz1 could act in collaboration with TLE-4, as they are expressed at the same time in NPC cultures and during mouse development. Conclusions: Nolz1 promotes RA signaling in the LGE, contributing to the striatal neurogenesis during development

Developmental origin of the neuronal subtypes that comprise the amygdalar fear circuit in the mouse.

International audienceWe have taken a genetic-based fate-mapping approach to determine the specific contributions of telencephalic progenitors to the structures that comprise the amygdalar fear circuit including the central (CA), lateral (LA), and basolateral (BLA) amygdala. Our data indicate that progenitors in the ventral pallium (VP) contribute projection neurons to the LA and BLA but not the CA. Rather, the CA appears to derive, at least in part, from progenitors located in the ventral lateral ganglionic eminence (vLGE). Diverse groups of interneurons populate these amygdalar nuclei, and as predicted our data support the notion that they originate from subpallial progenitors. A rather specific population of amygdalar interneurons, the intercalated cells (ITCs), is known to play a fundamental role in fear-related behaviors. However, no information on their specific origin has, as yet, been provided. Our findings suggest that the ITCs arise from the dorsal lateral ganglionic eminence (dLGE) and migrate in the lateral migratory stream to populate the paracapsular regions as well as the main intercalated mass of the amygdala (IA). Germ-line Gsx2 mutants are known to exhibit an expansion of the VP into the LGE and a concomitant reduction in the dLGE and vLGE. Accordingly, Gsx2 conditional mutants display a significantly enlarged LA and a significant reduction in ITCs both within the paracapsular regions and the IA. Additional support for a dLGE origin of the ITCs was obtained in conditional mutants of the dLGE gene Sp8. Thus, our findings indicate diverse origins for the neuronal components that comprise the amygdalar fear circuit

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

Abstract 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

Distinct Temporal Requirements for the Homeobox Gene Gsx2 in Specifying Striatal and Olfactory Bulb Neuronal Fates

SummaryThe homeobox gene Gsx2 (formerly Gsh2) is known to be required for striatal and olfactory bulb neurogenesis; however, its specific role in the specification of these two neuronal subtypes remains unclear. To address this, we have employed a temporally regulated gain-of-function approach in transgenic mice and found that misexpression of Gsx2 at early stages of telencephalic neurogenesis favors the specification of striatal projection neuron identity over that of olfactory bulb interneurons. In contrast, delayed activation of the Gsx2 transgene until later stages exclusively promotes olfactory bulb interneuron identity. In a complementary approach, we have conditionally inactivated Gsx2 in a temporally progressive manner. Unlike germline Gsx2 mutants, which exhibit severe alterations in both striatal and olfactory bulb neurogenesis at birth, the conditional mutants exhibited defects restricted to olfactory bulb interneurons. These results demonstrate that Gsx2 specifies striatal projection neuron and olfactory bulb interneuron identity at distinct time points during telencephalic neurogenesis

Distinct requirements for Tcf3 and Tcf12 during oligodendrocyte development in the mouse telencephalon

Abstract Background E-proteins encoded by Tcf3, Tcf4, and Tcf12 are class I basic helix-loop-helix (bHLH) transcription factors (TFs) that are thought to be widely expressed during development. However, their function in the developing brain, specifically in the telencephalon remains an active area of research. Our study examines for the first time if combined loss of two E-proteins (Tcf3 and Tcf12) influence distinct cell fates and oligodendrocyte development in the mouse telencephalon. Methods We generated Tcf3/12 double conditional knockouts (dcKOs) using Olig2 Cre/+ or Olig1 Cre/+ to overcome compensatory mechanisms between E-proteins and to understand the specific requirement for Tcf3 and Tcf12 in the ventral telencephalon and during oligodendrogenesis. We utilized a combination of in situ hybridization, immunohistochemistry, and immunofluorescence to address development of the telencephalon and oligodendrogenesis at embryonic and postnatal stages in Tcf3/12 dcKOs. Results We show that the E-proteins Tcf3 and Tcf12 are expressed in progenitors of the embryonic telencephalon and throughout the oligodendrocyte lineage in the postnatal brain. Tcf3/12 dcKOs showed transient defects in progenitor cells with an enlarged medial ganglionic eminence (MGE) region which correlated with reduced generation of embryonic oligodendrocyte progenitor cells (OPCs) and increased expression of MGE interneuron genes. Postnatal Tcf3/12 dcKOs showed a recovery of OPCs but displayed a sustained reduction in mature oligodendrocytes (OLs). Interestingly, Tcf4 remained expressed in the dcKOs suggesting that it cannot compensate for the loss of Tcf3 and Tcf12. Generation of Tcf3/12 dcKOs with Olig1 Cre/+ avoided the MGE morphology defect caused by Olig2 Cre/+ but dcKOs still exhibited reduced embryonic OPCs and subsequent reduction in postnatal OLs. Conclusion Our data reveal that Tcf3 and Tcf12 play a role in controlling OPC versus cortical interneuron cell fate decisions in MGE progenitors in addition to playing roles in the generation of embryonic OPCs and differentiation of postnatal OLs in the oligodendrocyte lineage

Dek overexpression in murine epithelia increases overt esophageal squamous cell carcinoma incidence

<div><p>Esophageal cancer occurs as either squamous cell carcinoma (ESCC) or adenocarcinoma. ESCCs comprise almost 90% of cases worldwide, and recur with a less than 15% five-year survival rate despite available treatments. The identification of new ESCC drivers and therapeutic targets is critical for improving outcomes. Here we report that expression of the human DEK oncogene is strongly upregulated in esophageal SCC based on data in the cancer genome atlas (TCGA). DEK is a chromatin-associated protein with important roles in several nuclear processes including gene transcription, epigenetics, and DNA repair. Our previous data have utilized a murine knockout model to demonstrate that Dek expression is required for oral and esophageal SCC growth. Also, DEK overexpression in human keratinocytes, the cell of origin for SCC, was sufficient to cause hyperplasia in 3D organotypic raft cultures that mimic human skin, thus linking high DEK expression in keratinocytes to oncogenic phenotypes. However, the role of DEK over-expression in ESCC development remains unknown in human cells or genetic mouse models. To define the consequences of Dek overexpression <i>in vivo</i>, we generated and validated a tetracycline responsive <i>Dek</i> transgenic mouse model referred to as <i>Bi-L-Dek</i>. Dek overexpression was induced in the basal keratinocytes of stratified squamous epithelium by crossing <i>Bi-L-Dek</i> mice to keratin 5 tetracycline transactivator (<i>K5-tTA</i>) mice. Conditional transgene expression was validated in the resulting <i>Bi-L-Dek_K5-tTA</i> mice and was suppressed with doxycycline treatment in the tetracycline-off system. The mice were subjected to an established HNSCC and esophageal carcinogenesis protocol using the chemical carcinogen 4-nitroquinoline 1-oxide (4NQO). Dek overexpression stimulated gross esophageal tumor development, when compared to doxycycline treated control mice. Furthermore, high Dek expression caused a trend toward esophageal hyperplasia in 4NQO treated mice. Taken together, these data demonstrate that Dek overexpression in the cell of origin for SCC is sufficient to promote esophageal SCC development <i>in vivo</i>.</p></div