A novel family of Cys-Cys, His-Cys zinc finger transcription factors expressed in developing nervous system and pituitary gland

MYT1L variant inherited by a mosaic father in a case of severe developmental and epileptic encephalopathy

The MYT1L gene plays a critical role in brain development, promoting the differentiation and proliferation of cells, important for the formation of brain connections. MYT1L is also involved in regulating the development of the hypothalamus, which is a crucial actor in weight regulation. Genetic variants in the MYT1L are associated with a range of developmental disorders, including intellectual disability, autism spectrum disorder, facial dysmorphisms, and epilepsy. The specific role of MYT1L in epilepsy remains elusive and no patients with developmental and epileptic encephalopathy (DEE) have been described so far. In this study, we report a patient with DEE presenting with severe refractory epilepsy, obesity, and behavioral abnormalities. Exome sequencing led to the identification of the heterozygous variant NM_001303052.2: c.1717G>A, p.(Gly573Arg) (chr2-1910340-C-T; GRCh38.p14) in the MYT1L gene. This variant was found to be inherited by the father, who was a mosaic and did not suffer from any neuropsychiatric disorders. Our observations expand the molecular and phenotype spectrum of MYT1L-related disorders, suggesting that affected individuals may present with severe epileptic phenotype leading to neurocognitive deterioration. Furthermore, we show that mosaic parents may not display the disease phenotype, with relevant implications for genetic counseling.

Complex Autism Spectrum Disorder in a Patient with a Novel De Novo Heterozygous MYT1L Variant

Autism spectrum disorder (ASD) comprises a group of complex neurodevelopmental features seen in many different forms due to variable causes. Highly impactful ASD-susceptibility genes are involved in pathways associated with brain development, chromatin remodeling, and transcription regulation. In this study, we investigate a proband with complex ASD. Whole genome sequencing revealed a novel de novo missense mutation of a highly conserved amino acid residue (NP_001289981.1:p.His516Gln; chr2:1917275; hg38) in the MYT1L neural transcription factor gene. In combination with in silico analysis on gene effect and pathogenicity, we described the proband's phenotype and made comparisons with previously reported cases to explore the spectrum of clinical features in MYT1L single nucleotide variant (SNV) cases. The phenotype-genotype correlation showed a high degree of clinical similarity with previously reported cases of missense variants in MYT1L, indicating MYT1L as the causal gene for the observed phenotype in our proband. The variant was also predicted to be damaging according to multiple in silico pathogenicity predicting tools. This study expands the clinical description of SNVs on the MYT1L gene and provides insight into its contribution to ASD.

MYT1L is required for suppressing earlier neuronal development programs in the adult mouse brain

In vitro studies indicate the neurodevelopmental disorder gene myelin transcription factor 1-like (MYT1L) suppresses non-neuronal lineage genes during fibroblast-to-neuron direct differentiation. However, MYT1L's molecular and cellular functions in the adult mammalian brain have not been fully characterized. Here, we found that MYT1L loss leads to up-regulated deep layer (DL) gene expression, corresponding to an increased ratio of DL/UL neurons in the adult mouse cortex. To define potential mechanisms, we conducted Cleavage Under Targets & Release Using Nuclease (CUT&RUN) to map MYT1L binding targets and epigenetic changes following MYT1L loss in mouse developing cortex and adult prefrontal cortex (PFC). We found MYT1L mainly binds to open chromatin, but with different transcription factor co-occupancies between promoters and enhancers. Likewise, multiomic data set integration revealed that, at promoters, MYT1L loss does not change chromatin accessibility but increases H3K4me3 and H3K27ac, activating both a subset of earlier neuronal development genes as well as Bcl11b, a key regulator for DL neuron development. Meanwhile, we discovered that MYT1L normally represses the activity of neurogenic enhancers associated with neuronal migration and neuronal projection development by closing chromatin structures and promoting removal of active histone marks. Further, we showed that MYT1L interacts with HDAC2 and transcriptional repressor SIN3B in vivo, providing potential mechanisms underlying repressive effects on histone acetylation and gene expression. Overall, our findings provide a comprehensive map of MYT1L binding in vivo and mechanistic insights into how MYT1L loss leads to aberrant activation of earlier neuronal development programs in the adult mouse brain.

MYT1L in the making: emerging insights on functions of a neurodevelopmental disorder gene

Large scale human genetic studies have shown that loss of function (LoF) mutations in MYT1L are implicated in neurodevelopmental disorders (NDDs). Here, we provide an overview of the growing number of published MYT1L patient cases, and summarize prior studies in cells, zebrafish, and mice, both to understand MYT1L's molecular and cellular role during brain development and consider how its dysfunction can lead to NDDs. We integrate the conclusions from these studies and highlight conflicting findings to reassess the current model of the role of MYT1L as a transcriptional activator and/or repressor based on the biological context. Finally, we highlight additional functional studies that are needed to understand the molecular mechanisms underlying pathophysiology and propose key questions to guide future preclinical studies.

Myt1l haploinsufficiency leads to obesity and multifaceted behavioral alterations in mice

BACKGROUND

The zinc finger domain containing transcription factor Myt1l is tightly associated with neuronal identity and is the only transcription factor known that is both neuron-specific and expressed in all neuronal subtypes. We identified Myt1l as a powerful reprogramming factor that, in combination with the proneural bHLH factor Ascl1, could induce neuronal fate in fibroblasts. Molecularly, we found it to repress many non-neuronal gene programs, explaining its supportive role to induce and safeguard neuronal identity in combination with proneural bHLH transcriptional activators. Moreover, human genetics studies found MYT1L mutations to cause intellectual disability and autism spectrum disorder often coupled with obesity.

METHODS

Here, we generated and characterized Myt1l-deficient mice. A comprehensive, longitudinal behavioral phenotyping approach was applied.

RESULTS

Myt1l was necessary for survival beyond 24 h but not for overall histological brain organization. Myt1l heterozygous mice became increasingly overweight and exhibited multifaceted behavioral alterations. In mouse pups, Myt1l haploinsufficiency caused mild alterations in early socio-affective communication through ultrasonic vocalizations. In adulthood, Myt1l heterozygous mice displayed hyperactivity due to impaired habituation learning. Motor performance was reduced in Myt1l heterozygous mice despite intact motor learning, possibly due to muscular hypotonia. While anxiety-related behavior was reduced, acoustic startle reactivity was enhanced, in line with higher sensitivity to loud sound. Finally, Myt1l haploinsufficiency had a negative impact on contextual fear memory retrieval, while cued fear memory retrieval appeared to be intact.

LIMITATIONS

In future studies, additional phenotypes might be identified and a detailed characterization of direct reciprocal social interaction behavior might help to reveal effects of Myt1l haploinsufficiency on social behavior in juvenile and adult mice.

CONCLUSIONS

Behavioral alterations in Myt1l haploinsufficient mice recapitulate several clinical phenotypes observed in humans carrying heterozygous MYT1L mutations and thus serve as an informative model of the human MYT1L syndrome.

MYT1L-associated neurodevelopmental disorder: description of 40 new cases and literature review of clinical and molecular aspects

Pathogenic variants of the myelin transcription factor-1 like (MYT1L) gene include heterozygous missense, truncating variants and 2p25.3 microdeletions and cause a syndromic neurodevelopmental disorder (OMIM#616,521). Despite enrichment in de novo mutations in several developmental disorders and autism studies, the data on clinical characteristics and genotype-phenotype correlations are scarce, with only 22 patients with single nucleotide pathogenic variants reported. We aimed to further characterize this disorder at both the clinical and molecular levels by gathering a large series of patients with MYT1L-associated neurodevelopmental disorder. We collected genetic information on 40 unreported patients with likely pathogenic/pathogenic MYT1L variants and performed a comprehensive review of published data (total = 62 patients). We confirm that the main phenotypic features of the MYT1L-related disorder are developmental delay with language delay (95%), intellectual disability (ID, 70%), overweight or obesity (58%), behavioral disorders (98%) and epilepsy (23%). We highlight novel clinical characteristics, such as learning disabilities without ID (30%) and feeding difficulties during infancy (18%). We further describe the varied dysmorphic features (67%) and present the changes in weight over time of 27 patients. We show that patients harboring highly clustered missense variants in the 2-3-ZNF domains are not clinically distinguishable from patients with truncating variants. We provide an updated overview of clinical and genetic data of the MYT1L-associated neurodevelopmental disorder, hence improving diagnosis and clinical management of these patients.

A MYT1L syndrome mouse model recapitulates patient phenotypes and reveals altered brain development due to disrupted neuronal maturation

Human genetics have defined a new neurodevelopmental syndrome caused by loss-of-function mutations in MYT1L, a transcription factor known for enabling fibroblast-to-neuron conversions. However, how MYT1L mutation causes intellectual disability, autism, ADHD, obesity, and brain anomalies is unknown. Here, we developed a Myt1l haploinsufficient mouse model that develops obesity, white-matter thinning, and microcephaly, mimicking common clinical phenotypes. During brain development we discovered disrupted gene expression, mediated in part by loss of Myt1l gene-target activation, and identified precocious neuronal differentiation as the mechanism for microcephaly. In contrast, in adults we discovered that mutation results in failure of transcriptional and chromatin maturation, echoed in disruptions in baseline physiological properties of neurons. Myt1l haploinsufficiency also results in behavioral anomalies, including hyperactivity, muscle weakness, and social alterations, with more severe phenotypes in males. Overall, our findings provide insight into the mechanistic underpinnings of this disorder and enable future preclinical studies.

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 and Myt1l transcription factors limit proliferation in GBM cells by repressing YAP1 expression

Myelin transcription factor 1 (Myt1) and Myt1l (Myt1-like) are zinc finger transcription factors that regulate neuronal differentiation. Reduced Myt1l expression has been implicated in glioblastoma (GBM), and the related St18 was originally identified as a potential tumor suppressor for breast cancer. We previously analyzed changes in gene expression in a human GBM cell line with re-expression of either Myt1 or Myt1l. This revealed largely overlapping gene expression changes, suggesting similar function in these cells. Here we show that re-expression of Myt1 or Myt1l reduces proliferation in two different GBM cell lines, activates gene expression programs associated with neuronal differentiation, and limits expression of proliferative and epithelial to mesenchymal transition gene-sets. Consistent with this, expression of both MYT1 and MYT1L is lower in more aggressive glioma sub-types. Examination of the gene expression changes in cells expressing Myt1 or Myt1l suggests that both repress expression of the YAP1 transcriptional coactivator, which functions primarily in the Hippo signaling pathway. Expression of YAP1 and its target genes is reduced in Myt-expressing cells, and there is an inverse correlation between YAP1 and MYT1/MYT1L expression in human brain cancer datasets. Proliferation of GBM cell lines is reduced by lowering YAP1 expression and increased with YAP1 over-expression, which overcomes the anti-proliferative effect of Myt1/Myt1l expression. Finally we show that reducing YAP1 expression in a GBM cell line slows the growth of orthotopic tumor xenografts. Together, our data suggest that Myt1 and Myt1l directly repress expression of YAP1, a protein which promotes proliferation and GBM growth.

Analysis of transcriptional activity by the Myt1 and Myt1l transcription factors

Myt1 and Myt1l (Myelin transcription factor 1, and Myt1-like) are members of a small family of closely related zinc finger transcription factors, characterized by two clusters of C2HC zinc fingers. Both are widely expressed during early embryogenesis, but are largely restricted to expression within the brain in the adult. Myt1l, as part of a three transcription factor mix, can reprogram fibroblasts to neurons and plays a role in maintaining neuronal identity. Previous analyses have indicated roles in both transcriptional activation and repression and suggested that Myt1 and Myt1l may have opposing functions in gene expression. We show that when targeted to DNA via multiple copies of the consensus Myt1/Myt1l binding site Myt1 represses transcription, whereas Myt1l activates. By targeting via a heterologous DNA binding domain we mapped an activation function in Myt1l to an amino-terminal region that is poorly conserved in Myt1. However, genome wide analyses of the effects of Myt1 and Myt1l expression in a glioblastoma cell line suggest that the two proteins have largely similar effects on endogenous gene expression. Transcriptional repression is likely mediated by binding to DNA via the known consensus site, whereas this site is not associated with the transcriptional start sites of genes with higher expression in the presence of Myt1 or Myt1l. This work suggests that these two proteins function similarly, despite differences observed in analyses based on synthetic reporter constructs.

Myt1L Promotes Differentiation of Oligodendrocyte Precursor Cells and is Necessary for Remyelination After Lysolecithin-Induced Demyelination

The differentiation and maturation of oligodendrocyte precursor cells (OPCs) is essential for myelination and remyelination in the CNS. The failure of OPCs to achieve terminal differentiation in demyelinating lesions often results in unsuccessful remyelination in a variety of human demyelinating diseases. However, the molecular mechanisms controlling OPC differentiation under pathological conditions remain largely unknown. Myt1L (myelin transcription factor 1-like), mainly expressed in neurons, has been associated with intellectual disability, schizophrenia, and depression. In the present study, we found that Myt1L was expressed in oligodendrocyte lineage cells during myelination and remyelination. The expression level of Myt1L in neuron/glia antigen 2-positive (NG2⁺) OPCs was significantly higher than that in mature CC1⁺ oligodendrocytes. In primary cultured OPCs, overexpression of Myt1L promoted, while knockdown inhibited OPC differentiation. Moreover, Myt1L was potently involved in promoting remyelination after lysolecithin-induced demyelination in vivo. ChIP assays showed that Myt1L bound to the promoter of Olig1 and transcriptionally regulated Olig1 expression. Taken together, our findings demonstrate that Myt1L is an essential regulator of OPC differentiation, thereby supporting Myt1L as a potential therapeutic target for demyelinating diseases.

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

Toxicity of triphenyltin on the development of retinal axons in zebrafish at low dose

The impacts of triphenyltin (TPT) on ecological health are of particular concern due to the unexpectedly high levels found in wild fish around the world. Here, zebrafish embryos were exposed to TPT via in ovo nano-injection to study its toxicity on the development of retinal axons in fish. Lipophilic dye labeling revealed obvious defects in retinal axon development in larvae with normally shaped eyes, with incidences of 0, 1.08%, 2.66%, 4.26%, and 6.85% observed in the control, 0.8, 4.0, 20.0, and 100ng TPT-Cl/g wet weight (ww) exposure groups, respectively, showing a dose-dependent increase. Since the lowest observable effective concentration of TPT to induce retinal axon development defects was 0.8ng TPT-Cl/g ww, which is lower than the concentrations in wild fish eggs, this defect would occur in wild fish larvae. Alterations in the expressions of pax6 and ephrinBs, which regulate the establishment of retinal polarity, were correlated with defect incidence. Expression levels of the CYP26A1 gene and protein were significantly up-regulated in all exposure groups compared with the control, which may lead to significant decreases in concentrations of all-trans retinoic acid (atRA). Such a disruption of RA metabolism would, at least partly, contribute to the incidence of developmental defects in retinal axons. This study is the first to report that TPT can interfere with development of retinal axons in fish at low dose.

Viral-mediated overexpression of the Myelin Transcription Factor 1 (MyT1) in the dentate gyrus attenuates anxiety- and ethanol-related behaviors in rats

RATIONALE

Myelin Transcription Factor 1 (MyT1), a member of the Zinc Finger gene family, plays a fundamental role in the nervous system. Recent research has suggested that this transcription factor is associated with the pathophysiology of psychiatric disorders including addiction, schizophrenia, and depression. However, the role of MyT1 in anxiety- and ethanol-related behaviors is still unknown.

OBJECTIVES

We evaluated the effects of lentiviral-mediated overexpression of MyT1 in the dentate gyrus (DG) on anxiety- and ethanol-related behaviors in rats.

METHODS

We used the elevated plus maze (EPM) and the open field (OF) tests to assess anxiety-like behavior and a two-bottle choice procedure to measure the effects of MyT1 on ethanol intake and preference.

RESULTS

MyT1 overexpression produced anxiolytic-like effects in the EPM test and decreased the number of fecal boli in the OF test, without affecting locomotor activity in both behavioral tests. Next, we demonstrated that ethanol intake and preference were decreased in the MyT1-overexpressing rats with no effect on saccharin and quinine, used to assess taste discrimination, and no effect on ethanol clearance suggesting specific alterations in the rewarding effects of ethanol. Most importantly, ectopic MyT1 overexpression increased both MyT1 and BDNF mRNA levels in the DG. Using Pearson's correlation, results showed a strong negative relationship between MyT1 mRNA and anxiety parameters and ethanol consumption and a positive correlation between MyT1 and BDNF mRNAs.

CONCLUSION

Taken together, MyT1 along with being a key component in anxiety may be a suitable candidate in the search of the molecular underpinnings of alcoholism.

Tracing of Zinc Nanocrystals in the Anterior Pituitary of Zinc-Deficient Wistar Rats

The aim of this study was to trace zinc nanocrystals in the anterior pituitary of zinc-deficient Wistar rats by using autometallographic technique. Male Wistar rats (30-40 days of age, pre-pubertal period) of 40-50 g body weight were divided into the following: the ZC (zinc control) group-fed with 100 ppm zinc in diet, the ZD (zinc-deficient) group-fed with zinc-deficient (1.00 ppm) diet and the PF (pair-fed) group-received 100 ppm zinc in diet. The experiments were set for 2 and 4 weeks. Pituitary was removed and processed for the autometallographic technique. The control and pair-fed groups retained their normal morphological features. However, male Wistar rats fed on zinc-deficient diet for 2 and 4 weeks displayed a wide range of symptoms such as significant (P < 0.05) decrease in diet consumption, body weight and pituitary weight and decrease in gradation of intensity of zinc nanocrystals in the nuclei. The present findings suggest that the dietary zinc deficiency causes decreased intensity of zinc nanocrystals localization and their distribution in the pituitary thereby contributing to the dysfunction of the pituitary of the male Wistar rats. The severity of zinc deficiency symptoms progressed after the second week of the experiment. Decreased intensity of zinc nanocrystals attenuates the pituitary function which would exert its affect on other endocrine organs impairing their functions indicating that the metabolic regulation of pituitary is mediated to a certain extent by zinc and/or hypothalamus-hypophysial system which also reflects its essentiality during the period of growth.

Myt1l safeguards neuronal identity by actively repressing many non-neuronal fates

Normal differentiation and induced reprogramming require the activation of target cell programs and silencing of donor cell programs. In reprogramming, the same factors are often used to reprogram many different donor cell types. As most developmental repressors, such as RE1-silencing transcription factor (REST) and Groucho (also known as TLE), are considered lineage-specific repressors, it remains unclear how identical combinations of transcription factors can silence so many different donor programs. Distinct lineage repressors would have to be induced in different donor cell types. Here, by studying the reprogramming of mouse fibroblasts to neurons, we found that the pan neuron-specific transcription factor Myt1-like (Myt1l) exerts its pro-neuronal function by direct repression of many different somatic lineage programs except the neuronal program. The repressive function of Myt1l is mediated via recruitment of a complex containing Sin3b by binding to a previously uncharacterized N-terminal domain. In agreement with its repressive function, the genomic binding sites of Myt1l are similar in neurons and fibroblasts and are preferentially in an open chromatin configuration. The Notch signalling pathway is repressed by Myt1l through silencing of several members, including Hes1. Acute knockdown of Myt1l in the developing mouse brain mimicked a Notch gain-of-function phenotype, suggesting that Myt1l allows newborn neurons to escape Notch activation during normal development. Depletion of Myt1l in primary postmitotic neurons de-repressed non-neuronal programs and impaired neuronal gene expression and function, indicating that many somatic lineage programs are actively and persistently repressed by Myt1l to maintain neuronal identity. It is now tempting to speculate that similar 'many-but-one' lineage repressors exist for other cell fates; such repressors, in combination with lineage-specific activators, would be prime candidates for use in reprogramming additional cell types.

Identification of a Functional Risk Variant for Pemphigus Vulgaris in the ST18 Gene

Pemphigus vulgaris (PV) is a life-threatening autoimmune mucocutaneous blistering disease caused by disruption of intercellular adhesion due to auto-antibodies directed against epithelial components. Treatment is limited to immunosuppressive agents, which are associated with serious adverse effects. The propensity to develop the disease is in part genetically determined. We therefore reasoned that the delineation of PV genetic basis may point to novel therapeutic strategies. Using a genome-wide association approach, we recently found that genetic variants in the vicinity of the ST18 gene confer a significant risk for the disease. Here, using targeted deep sequencing, we identified a PV-associated variant residing within the ST18 promoter region (p<0.0002; odds ratio = 2.03). This variant was found to drive increased gene transcription in a p53/p63-dependent manner, which may explain the fact that ST18 is up-regulated in the skin of PV patients. We then discovered that when overexpressed, ST18 stimulates PV serum-induced secretion of key inflammatory molecules and contributes to PV serum-induced disruption of keratinocyte cell-cell adhesion, two processes previously implicated in the pathogenesis of PV. Thus, the present findings indicate that ST18 may play a direct role in PV and consequently represents a potential target for the treatment of this disease.

Refinement of the critical 2p25.3 deletion region: the role of MYT1L in intellectual disability and obesity

PURPOSE

Submicroscopic deletions of chromosome band 2p25.3 are associated with intellectual disability and/or central obesity. Although MYT1L is believed to be a critical gene responsible for intellectual disability, so far no unequivocal data have confirmed this hypothesis.

METHODS

In this study we evaluated a cohort of 22 patients (15 sporadic patients and two families) with a 2p25.3 aberration to further refine the clinical phenotype and to delineate the role of MYT1L in intellectual disability and obesity. In addition, myt1l spatiotemporal expression in zebrafish embryos was analyzed by quantitative polymerase chain reaction and whole-mount in situ hybridization.

RESULTS

Complete MYT1L deletion, intragenic deletion, or duplication was observed in all sporadic patients, in addition to two patients with a de novo point mutation in MYT1L. The familial cases comprise a 6-Mb deletion in a father and his three children and a 5' MYT1L overlapping duplication in a father and his two children. Expression analysis in zebrafish embryos shows specific myt1l expression in the developing brain.

CONCLUSION

Our data strongly strengthen the hypothesis that MYT1L is the causal gene for the observed syndromal intellectual disability. Moreover, because 17 patients present with obesity/overweight, haploinsufficiency of MYT1L might predispose to weight problems with childhood onset.Genet Med 17 6, 460-466.

Identification of myelin transcription factor 1 (MyT1) as a subunit of the neural cell type-specific lysine-specific demethylase 1 (LSD1) complex

Regulation of spatiotemporal gene expression in higher eukaryotic cells is critical for the precise and orderly development of undifferentiated progenitors into committed cell types of the adult. It is well known that dynamic epigenomic regulation (including chromatin remodeling and histone modifications by transcriptional coregulator complexes) is involved in transcriptional regulation. Precisely how these coregulator complexes exert their cell type and developing stage-specific activity is largely unknown. In this study we aimed to isolate the histone demethylase lysine-specific demethylase 1 (LSD1) complex from neural cells by biochemical purification. In so doing, we identified myelin transcription factor 1 (MyT1) as a novel LSD1 complex component. MyT1 is a neural cell-specific zinc finger factor, and it forms a stable multiprotein complex with LSD1 through direct interaction. Target gene analysis using microarray and ChIP assays revealed that the Pten gene was directly regulated by the LSD1-MyT1 complex. Knockdown of either LSD1 or MyT1 derepressed the expression of endogenous target genes and inhibited cell proliferation of a neuroblastoma cell line, Neuro2a. We propose that formation of tissue-specific combinations of coregulator complexes is a critical mechanism for tissue-specific transcriptional regulation.

A role for hydrogen bonding in DNA recognition by the non-classical CCHHC type zinc finger, NZF-1

The non-classical zinc finger protein, Neural Zinc Finger Factor-1, contains six Cys2His2Cys domains. All three cysteines and the second histidine directly bind Zn(II). Using a combination of mutagenesis, metal coordination and DNA binding studies, we report that the first histidine is involved in a functionally important hydrogen bonding interaction.

Spatiotemporal expression pattern of Myt/NZF family zinc finger transcription factors during mouse nervous system development

BACKGROUND

Three members of the Myt/NZF family of transcription factors are involved in many processes of vertebrate development. Several studies have reported that Myt1/NZF-2 has a regulatory function in the development of cultured oligodendrocyte progenitors or in neuronal differentiation during Xenopus primary neurogenesis. However, little is known about the proper function of Myt/NZF family proteins during mammalian nervous system development. To assess the possible function of Myt/NZF transcription factors in mammalian neuronal differentiation, we determined the comparative spatial and temporal expression patterns of all three types of Myt/NZF family genes in the embryonic mouse nervous system using quantitative reverse transcriptase polymerase chain reaction and in situ hybridization.

RESULTS

All three Myt/NZF family genes were extensively expressed in developing mouse nervous tissues, and their expression was transient. NZF-1 was expressed later in post-mitotic neurons. NZF-2 was initially expressed in neuronal cells a little earlier than NZF-3. NZF-3 was initially expressed in neuronal cells, just after proliferation was complete.

CONCLUSION

These expression patterns suggest that the expression of NZF family genes is spatially and temporally regulated, and each Myt/NZF family gene may have a regulatory function in a specific phase during neuronal differentiation.

A structural analysis of DNA binding by myelin transcription factor 1 double zinc fingers

Myelin transcription factor 1 (MyT1/NZF2), a member of the neural zinc-finger (NZF) protein family, is a transcription factor that plays a central role in the developing central nervous system. It has also recently been shown that, in combination with two other transcription factors, the highly similar paralog MyT1L is able to direct the differentiation of murine and human stem cells into functional neurons. MyT1 contains seven zinc fingers (ZFs) that are highly conserved throughout the protein and throughout the NZF family. We recently presented a model for the interaction of the fifth ZF of MyT1 with a DNA sequence derived from the promoter of the retinoic acid receptor (RARE) gene. Here, we have used NMR spectroscopy, in combination with surface plasmon resonance and data-driven molecular docking, to delineate the mechanism of DNA binding for double ZF polypeptides derived from MyT1. Our data indicate that a two-ZF unit interacts with the major groove of the entire RARE motif and that both fingers bind in an identical manner and with overall two-fold rotational symmetry, consistent with the palindromic nature of the target DNA. Several key residues located in one of the irregular loops of the ZFs are utilized to achieve specific binding. Analysis of the human and mouse genomes based on our structural data reveals three putative MyT1 target genes involved in neuronal development.

Switching metal ion coordination and DNA Recognition in a Tandem CCHHC-type zinc finger peptide

Neural Zinc Finger Factor-1 (NZF-1) and Myelin Transcription Factor 1 (MyT1) are two homologous nonclassical zinc finger (ZF) proteins that are involved in the development of the central nervous system (CNS). Both NZF-1 and MyT1 contain multiple ZF domains, each of which contains an absolutely conserved Cys2His2Cys motif. All three cysteines and the second histidine have been shown to coordinate Zn(II); however, the role of the first histidine remains unresolved. Using a functional form of NZF-1 that contains two ZF domains (NZF-1-F2F3), mutant proteins in which each histidine was sequentially mutated to a phenylalanine were prepared to determine the role(s) of the histidine residues in DNA recognition. When the first histidine is mutated, the protein binds Zn(II) in an analogous manner to the native protein. Surprisingly, this mutant does not bind to target DNA (β-RAR), suggesting that the noncoordinating histidine is critical for sequence selective DNA recognition. The first histidine will coordinate Zn(II) when the second histidine is mutated; however, the overall fold of the protein is perturbed leading to abrogation of DNA binding. NZF-1-F2F3 selectively binds to a specific DNA target sequence (from β-RAR) with high affinity (nM); while its homologue MyT1 (MyT1-F2F3), which is 92% identical to NZF-1-F2F3, binds to this same DNA sequence nonspecifically. A single, nonconserved amino acid residue in NZF-1-F2F3 is shown to be responsible for this high affinity DNA binding to β-RAR. When this residue (arginine) is engineered into the MyT1-F2F3 sequence, the affinity for β-RAR DNA increases.

Endogenous retrotransposition activates oncogenic pathways in hepatocellular carcinoma

LINE-1 (L1) retrotransposons are mobile genetic elements comprising ~17% of the human genome. New L1 insertions can profoundly alter gene function and cause disease, though their significance in cancer remains unclear. Here, we applied enhanced retrotransposon capture sequencing (RC-seq) to 19 hepatocellular carcinoma (HCC) genomes and elucidated two archetypal L1-mediated mechanisms enabling tumorigenesis. In the first example, 4/19 (21.1%) donors presented germline retrotransposition events in the tumor suppressor mutated in colorectal cancers (MCC). MCC expression was ablated in each case, enabling oncogenic β-catenin/Wnt signaling. In the second example, suppression of tumorigenicity 18 (ST18) was activated by a tumor-specific L1 insertion. Experimental assays confirmed that the L1 interrupted a negative feedback loop by blocking ST18 repression of its enhancer. ST18 was also frequently amplified in HCC nodules from Mdr2(-/-) mice, supporting its assignment as a candidate liver oncogene. These proof-of-principle results substantiate L1-mediated retrotransposition as an important etiological factor in HCC.

The transcription factor Myt3 acts as a pro-survival factor in β-cells

Aims/Hypothesis

We previously identified the transcription factor Myt3 as specifically expressed in pancreatic islets. Here, we sought to determine the expression and regulation of Myt3 in islets and to determine its significance in regulating islet function and survival.

Methods

Myt3 expression was determined in embryonic pancreas and adult islets by qPCR and immunohistochemistry. ChIP-seq, ChIP-qPCR and luciferase assays were used to evaluate regulation of Myt3 expression. Suppression of Myt3 was used to evaluate gene expression, insulin secretion and apoptosis in islets.

Results

We show that Myt3 is the most abundant MYT family member in adult islets and that it is expressed in all the major endocrine cell types in the pancreas after E18.5. We demonstrate that Myt3 expression is directly regulated by Foxa2, Pdx1, and Neurod1, which are critical to normal β-cell development and function, and that Ngn3 induces Myt3 expression through alterations in the Myt3 promoter chromatin state. Further, we show that Myt3 expression is sensitive to both glucose and cytokine exposure. Of specific interest, suppressing Myt3 expression reduces insulin content and increases β-cell apoptosis, at least in part, due to reduced Pdx1, Mafa, Il-6, Bcl-xl, c-Iap2 and Igfr1 levels, while over-expression of Myt3 protects islets from cytokine induced apoptosis.

Conclusion/Interpretation

We have identified Myt3 as a novel transcriptional regulator with a critical role in β-cell survival. These data are an important step in clarifying the regulatory networks responsible for β-cell survival, and point to Myt3 as a potential therapeutic target for improving functional β-cell mass.

Thermodynamics of Zn2+ binding to Cys2His2 and Cys2HisCys zinc fingers and a Cys4 transcription factor site

The thermodynamics of Zn(2+) binding to three peptides corresponding to naturally occurring Zn-binding sequences in transcription factors have been quantified with isothermal titration calorimetry (ITC). These peptides, the third zinc finger of Sp1 (Sp1-3), the second zinc finger of myelin transcription factor 1 (MyT1-2), and the second Zn-binding sequence of the DNA-binding domain of glucocorticoid receptor (GR-2), bind Zn(2+) with Cys(2)His(2), Cys(2)HisCys, and Cys(4) coordination, respectively. Circular dichroism confirms that Sp1-3 and MyT1-2 have considerable and negligible Zn-stabilized secondary structure, respectively, and indicate only a small amount for GR-2. The pK(a)'s of the Sp1-3 cysteines and histidines were determined by NMR and used to estimate the number of protons displaced by Zn(2+) at pH 7.4. ITC was also used to determine this number, and the two methods agree. Subtraction of buffer contributions to the calorimetric data reveals that all three peptides have a similar affinity for Zn(2+), which has equal enthalpy and entropy components for Sp1-3 but is more enthalpically disfavored and entropically favored with increasing Cys ligands. The resulting enthalpy-entropy compensation originates from the Zn-Cys coordination, as subtraction of the cysteine deprotonation enthalpy results in a similar Zn(2+)-binding enthalpy for all three peptides, and the binding entropy tracks with the number of displaced protons. Metal and protein components of the binding enthalpy and entropy have been estimated. While dominated by Zn(2+) coordination to the cysteines and histidines, other residues in the sequence affect the protein contributions that modulate the stability of these motifs.

MYT1L is a candidate gene for intellectual disability in patients with 2p25.3 (2pter) deletions

A partial deletion of chromosome band 2p25.3 (2pter) is a rarely described cytogenetic aberration in patients with intellectual disability (ID). Using microarrays we identified deletions of 2p25.3, sized 0.37-3.13 Mb, in three adult siblings and three unrelated patients. All patients had ID, obesity or overweight and/or a square-shaped stature without overt facial dysmorphic features. Combining our data with phenotypic and genotypic data of three patients from the literature we defined the minimal region of overlap which contained one gene, i.e., MYT1L. MYT1L is highly transcribed in the mouse embryonic brain where its expression is restricted to postmitotic differentiating neurons. In mouse-induced pluripotent stem cell (iPS) models, MYT1L is essential for inducing functional mature neurons. These resemble excitatory cortical neurons of the forebrain, suggesting a role for MYT1L in development of cognitive functions. Furthermore, MYT1L can directly convert human fibroblasts into functional neurons in conjunction with other transcription factors. MYT1L duplication was previously reported in schizophrenia, indicating that the gene is dosage-sensitive and that shared neurodevelopmental pathways may be affected in ID and schizophrenia. Finally, deletion of MYT1, another member of the Myelin Transcription Factor family involved in neurogenesis and highly similar to MYT1L, was recently described in ID as well. The identification of MYT1L as candidate gene for ID justifies further molecular studies aimed at detecting mutations and for mechanistic studies on its role in neuron development and on neuropathogenic effects of haploinsufficiency.

Cysteine and histidine shuffling: mixing and matching cysteine and histidine residues in zinc finger proteins to afford different folds and function

Zinc finger proteins utilize zinc for structural purposes: zinc binds to a combination of cysteine and histidine ligands in a tetrahedral coordination geometry facilitating protein folding and function. While much is known about the classical zinc finger proteins, which utilize a Cys(2)His(2) ligand set to coordinate zinc and fold into an anti-parallel beta sheet/alpha helical fold, there are thirteen other families of 'non-classical' zinc finger proteins for which relationships between metal coordination and protein structure/function are less defined. This 'Perspective' article focuses on two classes of these non-classical zinc finger proteins: Cys(3)His type zinc finger proteins and Cys(2)His(2)Cys type zinc finger proteins. These proteins bind zinc in a tetrahedral geometry, like the classical zinc finger proteins, yet they adopt completely different folds and target different oligonucleotides. Our current understanding of the relationships between ligand set, metal ion, fold and function for these non-classical zinc fingers is discussed.

Myt/NZF family transcription factors regulate neuronal differentiation of P19 cells

During mammalian central nervous system development, neural stem cells differentiate and then mature into various types of neurons. Myelin transcription factor (Myt)/neural zinc finger (NZF) family proteins were first identified as myelin proteolipid protein promoter binding factors and were shown to be involved in oligodendrocyte development. In this study, we found that Myt/NZF family molecules were expressed during neuronal differentiation in vivo and in vitro. Transient over-expression of Myt/NZF family genes could convert undifferentiated P19 cells into neurons without induction by retinoic acid (RA), and the ability of these genes to induce neuronal differentiation was comparable to that of Neurog1 and Neurod1. Additionally, we found that St18 (or NZF-3) was induced by several bHLH transcription factors. When NZF-3 and Neurog1 were co-expressed in P19 cells, the rate of neuronal differentiation was significantly increased. These data suggest not only that NZF-3 works downstream of Neurog1 but also that it plays a crucial role together with Neurog1 in neuronal differentiation.

Analysis of differential gene expression by fiber-optic BeadArray and pathway in prolactinomas

Prolactinomas are the most common secretory pituitary tumors; however, their pathogenesis is unclear. In order to explore the pathogenesis of prolactinomas, we used fiber-optic BeadArray to examine gene expression profiles in five prolactinomas compared with three normal pituitaries. Three down-regulated genes and one up-regulated gene were chosen for validation by quantitative real-time reverse-transcription polymerase chain reaction. We then performed pathway analysis on the identified differentially expressed genes using the Kyoto Encyclopedia of Genes and Genomes. Array analysis showed significant increases in the expression of 27 genes and 3 expressed sequence tags (ESTs), and decreases in 182 genes and 9 ESTs, including HIG1 domain family, member 1B, S100 calcium binding protein A9, angiopoietin 2, interleukin 8, hydroxyprostaglandin dehydrogenase 15-(NAD), suppression of tumorigenicity18, and WNT inhibitory factor 1. Pathway analysis showed that the P53 and GnRH signaling pathways may play an important role in tumorigenesis of prolactinomas. Our data suggest fiber-optic BeadArray combined with pathway analysis of differential gene expression profile appears to be a valid approach for investigating the pathogenesis of tumors.

A FOXA1-binding enhancer regulates Hoxb13 expression in the prostate gland

Hoxb13 is robustly transcribed in derivatives of posterior endoderm including the colon, rectum, and the prostate gland. Transcriptional activity in the prostate persists unabated under conditions of androgen deprivation and throughout the course of disease progression in a mouse prostate cancer model. To elucidate the molecular basis of prostate-restricted transcriptional activation of Hoxb13, a bacterial artificial chromosome (BAC)-based reporter gene deletion analysis was performed in transgenic mice. Two regions downstream of the Hoxb13 coding region were found to be required to support transcriptional activity in the prostate but were completely dispensable for expression in the colon and rectum. Bioinformatic analyses of one region identified a 37-bp element conserved in mammals. This element, which bears two potential binding sites for Forkhead class transcription factors, is occupied by FOXA1 in a human prostate cancer cell line. Precise replacement of this enhancer with an extended LoxP site in the context of a 218,555-bp BAC reporter nearly extinguished Hoxb13-mediated transcriptional activity in the mouse prostate. These data demonstrate that FOXA1 directly regulates HOXB13 in human prostate epithelial cells, and show that this prostate-specific regulatory mechanism is conserved in mice.

The transcription factor ST18 regulates proapoptotic and proinflammatory gene expression in fibroblasts

Suppression of tumorigenicity 18 (ST18) and the homologues neural zinc-finger protein-3 (NZF3) and myelin transcription factor 3 (Myt3) are transcription factors with unknown function. Previous studies have established that they repress transcription of a synthetic reporter construct consisting of the consensus sequence AAAGTTT linked to the thymidine kinase promoter. In addition, ST18 exhibits significantly reduced expression in breast cancer and breast cancer cell lines. We report here for the first time evidence that ST18 mediates tumor necrosis factor (TNF) -alpha induced mRNA levels of proapoptotic and proinflammatory genes in fibroblasts by mRNA profiling and silencing with ST18 small interfering RNA (siRNA). Gene set enrichment analysis and mRNA profiling support this conclusion by identifying several apoptotic and inflammatory pathways that are down-regulated by ST18 siRNA. In addition, ST18 siRNA reduces TNF-induced fibroblast apoptosis and caspase-3/7 activity. Fibroblasts that overexpress ST18 by transient transfection exhibit significantly increased apoptosis and increased expression of TNF-alpha, interleukin (IL) -1alpha, and IL-6. In addition, cotransfection of ST18 and a TNF-alpha or IL-1alpha reporter construct demonstrates that ST18 overexpression in fibroblasts significantly enhanced promoter activity of these genes. Taken together, these studies demonstrate that the transcription factor ST18/NZF3 regulates the mRNA levels of proapoptotic and proinflammatory genes in revealing a previously unrecognized function.

Structural and biophysical analysis of the DNA binding properties of myelin transcription factor 1

Zinc binding domains, or zinc fingers (ZnFs), form one of the most numerous and most diverse superclasses of protein structural motifs in eukaryotes. Although our understanding of the functions of several classes of these domains is relatively well developed, we know much less about the molecular mechanisms of action of many others. Myelin transcription factor 1 (MyT1) type ZnFs are found in organisms as diverse as nematodes and mammals and are found in a range of sequence contexts. MyT1, one of the early transcription factors expressed in the developing central nervous system, contains seven MyT1 ZnFs that are very highly conserved both within the protein and between species. We have used a range of biophysical techniques, including NMR spectroscopy and data-driven macromolecular docking, to investigate the structural basis for the interaction between MyT1 ZnFs and DNA. Our data indicate that MyT1 ZnFs recognize the major groove of DNA in a way that appears to differ from other known zinc binding domains.

Cloning and characterization of cDNAs expressed during chick development and encoding different isoforms of a putative zinc finger transcriptional regulator

Development proceeds through successive activation of different sets of genes by specific transcription factors as a consequence of cell interactions and signaling. It is thus of primary interest to identify new putative transcriptional regulators. We report here the isolation of chicken clones bearing sequences coding for a chicken zinc finger protein (chZFp) which contains four pairs of zinc fingers of mixed type C2-H-C/C2-H2. At least five chZFp isoforms are produced through differential splicing of four small exons. The amino acid domains encoded by these four exons are highly conserved across species. Northern blot analysis and RNase-protection assays showed that chZFp transcripts are present in brain, heart, skin and liver during chick development. Reverse transcription mediated polymerase chain reaction (RT-PCR) experiments suggested that the relative amount of some chZFp isoforms increases at critical stages of development and skin morphogenesis. Finally, the main chZFp isoforms are able to directly interact in vitro with the scaffold attachment factor-A (SAF-A, also known as heterogenous nuclear ribonucleoprotein U) through both their aminoterminal and carboxyterminal domains.

Myt1 family recruits histone deacetylase to regulate neural transcription

The myelin transcription factor 1 (Myt1) gene family is comprised of three zinc finger genes [Myt1, Myt1L (Myt1-Like) and NZF3] of the structurally unique CCHHC class that are expressed predominantly in the developing CNS. To understand the mechanism by which this family regulates neural differentiation, we searched for interaction partners. In both yeast and a mammalian two-hybrid system, Myt1 and Myt1L interacted with Sin3B, a protein that mediates transcriptional repression by binding to histone deacetylases (HDACs). Myt1-Sin3B complexes were co-immunoprecipitated from transfected mammalian cells and included HDAC1 and HDAC2. Myt1 and Myt1L could partner with all three Sin3B isoforms, the long form (Sin3B(LF)) that includes the HDAC-binding domain, and the two short forms (Sin3B(SF293) and Sin3B(SF302)) that lack this domain and may consequently antagonize Sin3B(LF)/HDAC-mediated co-repression. Myt1 or Myt1L interactions with the HDAC-binding form of Sin3B conferred repression on a heterologous promoter. Oligodendrocytes were shown to express transcripts encoding each of the Sin3B isoforms. We present a model in which the Myt1 family of zinc finger proteins, when bound to a neural promoter, can recruit Sin3B. Depending on the relative availability of Sin3B isoforms, the Myt1 gene family may favor the silencing of genes during neural development.

Immunohistochemical study of Ca2+/calmodulin-dependent protein kinase II in the Drosophila brain using a specific monoclonal antibody

To analyze the distribution of Drosophila calcium/calmodulin-dependent protein kinase II (dCaMKII) in the adult brain, we generated monoclonal antibodies against the bacterially expressed 490-amino acid (a.a.) form of dCaMKII. One of those, named #18 antibody, was used for this study. Western blot analysis of the adult head extracts showed that the antibody specifically detects multiple bands between 55 and 60 kDa corresponding to the molecular weights of the splicing isoforms of dCaMKII. Epitope mapping revealed that it was in the region between 199 and 283 a.a. of dCaMKII. Preferential dCaMKII immunoreactivity in the embryonic nervous system, adult thoracic ganglion and gut, and larval neuro-muscular junction (NMJ) was consistent with previous observations by in situ hybridization and immunostaining with a polyclonal antibody at the NMJ, indicating that the antibody is applicable to immunohistochemistry. Although dCaMKII immunoreactive signal was low in the retina, it was found at regular intervals in the outer margin of the compound eye. These signals were most likely to be interommatidial bristle mechanosensory neurons. dCaMKII immunoreactivity in the brain was observed in almost all regions and relatively higher staining was found in the neuropilar region than in the cortex. Higher dCaMKII immunoreactivity in the mushroom body (MB) was found in the entire gamma lobe including the heel, and dorsal tips of the alpha and alpha' lobes, while cores of alpha and beta lobes were stained light. Finding abundant dCaMKII accumulation in the gamma lobe suggested that this lobe might especially require high levels of dCaMKII expression to function properly among MB lobes.

NZF-2b is a novel predominant form of mouse NZF-2/MyT1, expressed in differentiated neurons especially at higher levels in newly generated ones

NZF-2 (MyT1) is a member of C2HC-type zinc finger transcription factors. A novel form of mouse NZF-2 has been isolated. This novel form, NZF-2b, has an additional C2HC-type zinc finger motif. The expression levels of NZF-2b are by far the more predominant than those of the already known form of NZF-2. In embryonic mouse nervous system, the expression of NZF-2b starts as early as at 9.5 days post-coitum (dpc) in newly differentiated neurons in the central nervous system (CNS) and the peripheral nervous system (PNS).

RAP80, a novel nuclear protein that interacts with the retinoid-related testis-associated receptor

In this study, we describe the characterization of a novel nuclear protein, referred to as RAP80. The RAP80 cDNA was cloned from a human testis cDNA library and encodes a 719-amino acid protein containing two potential CX(2)CX(11)HX(3)C-type zinc finger motifs at its carboxyl-terminal region. Analysis of its genomic structure revealed that the RAP80 gene covers more than 90 kb and consists of 15 exons and 14 introns. Fluorescence in situ hybridization mapped the RAP80 gene to human chromosome 5q35. RAP80 mRNA is expressed in many human tissues, but its expression is particularly high in testis. In situ hybridization showed that RAP80 is highly expressed in germ cells of mouse testis but is not differentially regulated during spermatogenesis. Confocal microscopy showed that RAP80 is localized to the nucleus, where it is distributed in a speckled pattern. Deletion analysis showed that a bipartite nuclear localization signal at the amino terminus is important in mediating nuclear transport of RAP80. Monohybrid analysis showed that RAP80 might function as an active repressor of transcription. Mammalian two-hybrid analysis demonstrated that RAP80 was able to interact with the retinoid-related testis-associated receptor (RTR), an orphan receptor that has been implicated in the control of embryonic development and spermatogenesis. Pull-down analysis showed that RAP80 and RTR physically interact in vitro. Deletion and point mutation analyses revealed that part of the hinge domain of RTR is required for this interaction. RAP80 is able to inhibit the interaction of RTR with the co-repressor N-CoR likely by competing with N-CoR for RTR binding. Our results suggest that RAP80 may be functioning as a modulator of RTR signaling.

Novel intronic promoter in the rat ER alpha gene responsible for the transient transcription of a variant receptor

To analyze the molecular origin of an ER variant, the truncated ER product-1, transiently expressed at the proestrus in lactotrope cells, we generated a 2.5-kb sequence of a genomic region upstream and downstream the specific sequence truncated ER product-1. Genomic Southern blot analysis showed that truncated ER product-1 is spliced from a noncoding leader exon localized within the intron 4 of the ER alpha gene. Analysis of the promoter sequence revealed the presence of a major transcriptional start site, a canonical TATA box and putative cis regulatory elements for pituitary specific expression as well as an E-responsive element. In transient transfection, the truncated ER product-1 promoter was transcriptionally the most active in the lactotrope cell lines (MMQ). Analysis of truncated ER product-1 functionality showed that: 1) the protein inhibited ER alpha binding to the E-responsive element in electromobility shift assays, 2) inhibited the E2 binding to ER alpha in binding assays, 3) the truncated ER product-1/ER alpha complex antagonized the transcriptional activity elicited by E2, 4) nuclear localization of green fluorescent protein-ER alpha was altered in Chinese hamster ovary cell lines stably expressing truncated ER product-1. Collectively, these data demonstrated that the protein exerts full dominant negative activity against ER alpha. Moreover, truncated ER product-1/ER alpha complex also repressed the activity of all promoters tested to date, suggesting a general inhibitory effect toward transcription. In conclusion, the data suggest that truncated ER product-1 could regulate estrogen signaling via a specific promoter in lactotrope cells.

The Pit-1 homeodomain and beta-domain interact with Ets-1 and modulate synergistic activation of the rat prolactin promoter

Pit-1/GHF-1 is a pituitary-specific, POU homeodomain transcription factor required for development of somatotroph, lactotroph, and thyrotroph cell lineages and regulation of the temporal and spatial expression of the growth hormone, prolactin (PRL), and thyrotropin-beta genes. Synergistic interaction of Pit-1 with a member of the Ets family of transcription factors, Ets-1, has been shown to be an important mechanism regulating basal and Ras-induced lactotroph-specific rat (r) PRL promoter activity. Pit-1beta/GHF-2, an alternatively spliced isoform containing a 26-amino acid insert (beta-domain) within its transcription-activation domain, physically interacts with Ets-1 but fails to synergize. By using a series of Pit-1 internal-deletion constructs in a transient transfection protocol to reconstitute rPRL promoter activity in HeLa cells, we have determined that the functional and physical interaction of Pit-1 and Ets-1 is mediated via the POU homeodomain, which is common to both Pit-1 and Pit-1beta. Although the Pit-1 homeodomain is both necessary and sufficient for direct binding to Ets-1 in a DNA-independent manner, an additional interaction surface was mapped to the beta-domain, specific to the Pit-1beta isoform. Thus, the unique transcriptional properties of Pit-1 and Pit-1beta on the rPRL promoter may be due to the formation of functionally distinct complexes of these two Pit-1 isoforms with Ets-1.

AATF, a novel transcription factor that interacts with Dlk/ZIP kinase and interferes with apoptosis

Dlk, also known as ZIP kinase, is a serine/threonine kinase that is tightly associated with nuclear structures. Under certain conditions, which require cytoplasmic localization, Dlk can induce apoptosis. In search for interaction partners that might serve as regulators or targets of this kinase we identified apoptosis antagonizing transcription factor (AATF), a nuclear phosphoprotein of 523 amino acids. The 1.8 kb mRNA seems to be ubiquitously expressed. AATF contains an extremely acidic domain and a putative leucine zipper characteristic of transcription factors. Indeed, a Gal4-BD-AATF fusion protein exhibited strong transactivation activity. Interestingly, AATF interfered with Dlk-induced apoptosis.

Isolation and characterization of a novel member of the neural zinc finger factor/myelin transcription factor family with transcriptional repression activity

Myelin transcription factor 1 (MyT1) and neural zinc finger factor 1 (NZF-1) represent the first two members of an emerging family of neural specific, zinc finger-containing DNA-binding proteins. MyT1 has been shown recently to play a critical role in neuronal cell differentiation during development. We have cloned the third member of the NZF/MyT family, referred to as neural zinc finger factor 3 (NZF-3). The cDNA sequence predicts a protein of 1,032 amino acids which contains two clusters of zinc fingers similar to MyT1 and NZF-1. Unlike MyT1 and NZF-1, NZF-3 does not contain an acidic domain at the amino terminus or a serine/threonine-rich region between the two finger clusters. NZF-3 binds to a DNA element containing a single copy of the previously described AAAGTTT consensus motif for these factors but exhibits a marked enhancement in relative affinity to a bipartite element containing two copies of the consensus motif. In contrast to MyT1 and NZF-1, which are known to activate transcription, cotransfection experiments revealed that NZF-3 confers repression on the basal activity of promoters containing the consensus binding elements. The identification of an additional member of the NZF/MyT family provides an opportunity to investigate the relative contribution of members of this family of transcription factors to the complex regulatory processes in neural development and homeostasis.

Myelin transcription factor 1 (Myt1) of the oligodendrocyte lineage, along with a closely related CCHC zinc finger, is expressed in developing neurons in the mammalian central nervous system

The establishment and operation of the nervous system requires genetic regulation by a network of DNA-binding proteins, among which is the zinc finger superfamily of transcription factors. We have cloned and characterized a member of the unusual Cys-Cys-His-Cys (also referred to as Cys2HisCys, CCHC, or C2HC) class of zinc finger proteins in the developing nervous system. The novel gene, Myt1-like (Myt1l), is highly homologous to the original representative of this class, Myelin transcription factor 1 (Myt1) (Kim and Hudson, 1992). The MYT1 gene maps to human chromosome 20, while MYT1L maps to a region of human chromosome 2. Both zinc finger proteins are found in neurons at early stages of differentiation, with germinal zone cells displaying intense staining for MyT1. Unlike Myt1, Myt1l has not been detected in the glial lineage. Neurons that express Myt1l also express TuJ1, which marks neurons around the period of terminal mitosis. The Myt1l protein resides in distinct domains within the neuronal nucleus, analogous to the discrete pattern previously noted for Myt1 (Armstrong et al.: 14:303-321, 1995). The developmental expression and localization of these two multifingered CCHC proteins suggests that each may play a role in the development of neurons and oligodendroglia in the mammalian central nervous system.

Pit-1 and GATA-2 interact and functionally cooperate to activate the thyrotropin beta-subunit promoter

The molecular determinants governing cell-specific expression of the thyrotropin (TSH) beta-subunit gene in pituitary thyrotropes are not well understood. The P1 region of the mouse TSHbeta promoter (-133 to -88) region interacts with Pit-1 and an additional 50-kDa factor at an adjacent site that resembles a consensus GATA binding site. Northern and Western blot assays demonstrated the presence of GATA-2 transcripts and protein in TtT-97 thyrotropic tumors. In electrophoretic mobility shift assays, a comigrating complex was observed with both TtT-97 nuclear extracts and GATA-2 expressed in COS cells. The complex demonstrated binding specificity to the P1 region DNA probe and could be disrupted by a GATA-2 antibody. When both Pit-1 and GATA-2 were combined, a slower migrating complex, indicative of a ternary protein-DNA interaction was observed. Cotransfection of both Pit-1 and GATA-2 into CV-1 cells synergistically stimulated mouse TSHbeta promoter activity 8.5-fold, while each factor alone had a minimal effect. Mutations that abrogated this functional stimulatory effect mapped to the P1 region. Finally, we show that GATA-2 directly interacts with Pit-1 in solution. In summary, these data demonstrate functional synergy and physical interaction between homeobox and zinc finger factors and provide insights into the transcriptional mechanisms of thyrotrope-specific gene expression.

Structure of the m1 muscarinic acetylcholine receptor gene and its promoter

The m1 receptor is one of five muscarinic receptors that mediate the metabotropic actions of acetylcholine in the nervous system where it is expressed predominantly in the telencephalon and autonomic ganglia. RNase protection, primer extension, and 5'-rapid amplification of cDNA ends analysis of a rat cosmid clone containing the entire m1 gene demonstrated that the rat m1 gene consists of a single 657-base pairs (bp) non-coding exon separated by a 13. 5-kilobase (kb) intron from a 2.54-kb coding exon that contains the entire open reading frame. The splice acceptor for the coding exon starting at -71 bp relative to the adenine of the initiating methionine. This genomic structure is similar to that of the m4 gene (Wood, I. C., Roopra, A., Harrington, C. A., and Buckley, N. J. (1995) J. Biol. Chem. 270, 30933-30940 and Wood, I. C., Roopra, A., and Buckley, N. J. (1996) J. Biol. Chem. 271, 14221-14225). Like the m4 gene, the m1 promoter lacks TATA and CAAT consensus motifs, and the first exon and 5'-flanking region are not gc-rich. The 5'-flanking region also contains the consensus regulatory elements Sp-1, NZF-1, AP-1, AP-2, E-box, NFkappaB, and Oct-1. Unike the m4 promoter, there is no evidence of a RE1/NRSE silencer element in the m1 promoter. Deletional analysis and transient transfection assays demonstrates that reporter constructs containing 0.9 kb of 5'-flanking sequence and the first exon are sufficient to drive cell-specific expression of reporter gene in IMR32 neuroblastoma cells while remaining silent in 3T3 fibrobasts.