Cloning and characterization of seizure-related gene, SEZ-6

ABBV-011, A Novel, Calicheamicin-Based Antibody-Drug Conjugate, Targets SEZ6 to Eradicate Small Cell Lung Cancer Tumors

In the past year, four antibody-drug conjugates (ADC) were approved, nearly doubling the marketed ADCs in oncology. Among other attributes, successful ADCs optimize targeting antibody, conjugation chemistry, and payload mechanism of action. Here, we describe the development of ABBV-011, a novel SEZ6-targeted, calicheamicin-based ADC for the treatment of small cell lung cancer (SCLC). We engineered a calicheamicin conjugate that lacks the acid-labile hydrazine linker that leads to systemic release of a toxic catabolite. We then screened a patient-derived xenograft library to identify SCLC as a tumor type with enhanced sensitivity to calicheamicin ADCs. Using RNA sequencing (RNA-seq) data from primary and xenograft SCLC samples, we identified seizure-related homolog 6 (SEZ6) as a surface-expressed SCLC target with broad expression in SCLC and minimal normal tissue expression by both RNA-seq and IHC. We developed an antibody targeting SEZ6 that is rapidly internalized upon receptor binding and, when conjugated to the calicheamicin linker drug, drives potent tumor regression in vitro and in vivo. These preclinical data suggest that ABBV-011 may provide a novel treatment for patients with SCLC and a rationale for ongoing phase I studies (NCT03639194).

Synapse Formation and Function Across Species: Ancient Roles for CCP, CUB, and TSP-1 Structural Domains

The appearance of synapses was a crucial step in the creation of the variety of nervous systems that are found in the animal kingdom. With increased complexity of the organisms came a greater number of synaptic proteins. In this review we describe synaptic proteins that contain the structural domains CUB, CCP, or TSP-1. These domains are found in invertebrates and vertebrates, and CUB and CCP domains were initially described in proteins belonging to the complement system of innate immunity. Interestingly, they are found in synapses of the nematode C. elegans, which does not have a complement system, suggesting an ancient function. Comparison of the roles of CUB-, CCP-, and TSP-1 containing synaptic proteins in various species shows that in more complex nervous systems, these structural domains are combined with other domains and that there is partial conservation of their function. These three domains are thus basic building blocks of the synaptic architecture. Further studies of structural domains characteristic of synaptic proteins in invertebrates such as C. elegans and comparison of their role in mammals will help identify other conserved synaptic molecular building blocks. Furthermore, this type of functional comparison across species will also identify structural domains added during evolution in correlation with increased complexity, shedding light on mechanisms underlying cognition and brain diseases.

Characterization of the mitogenome of Gongronella sp. w5 reveals substantial variation in Mucoromycota

Gongronella is a genus of fungi in Mucorales (Mucoromycota). Some of its members have important biotechnological applications, but until now, not a single mitogenome has been characterized in Gongronella. Here, we present the complete mitogenome assembly of Gongronella sp. w5, a soil isolate known to interact with plants and several fungi. Its 36,593-bp circular mitogenome encodes the large and small subunit rRNAs, 14 standard mitochondrial proteins, 24 tRNAs, three free-standing ORF proteins, and the RNA subunit of RNase P (rnpB). These genes arrange in an order novel to known fungal mitogenomes. Three group I introns are present in the cob, cox1, and nad5 genes, respectively, and they are probably acquired by horizontal gene transfer. Phylogenetic analysis based on mitochondrion-encoded proteins supports the grouping of Gongronella sp. w5 with Absidia glauca, forming the Cunninghamellaceae clade within Mucoromycota. Gongronella and most other Mucoromycota species are predicted to use the standard genetic code in mitochondrial translation, rather than code 4 assigned by GenBank. A comparison among seven publicly available mitogenomes in Mucoromycota reveals the presence of the same 14 typical protein-coding genes plus rnpB, yet substantial variation in mitogenome size, intron number, gene order, and orientation. In this comparison, the uniqueness of Gongronella is evident from similarly large differences to its closest phylogenetic neighbor, A. glauca. This study promotes our understanding of fungal evolution in Mucoromycota. KEY POINTS: • This study reports the first mitogenome in Gongronella, which presents a novel gene order. • Different Mucoromycota mitogenomes show substantial variation of gene organizations. • Most Mucoromycota species use the standard genetic code to translate mitochondrial genes.

Structural characterization of the third scavenger receptor cysteine-rich domain of murine neurotrypsin

Neurotrypsin (NT) is a multi-domain serine protease of the nervous system with only one known substrate: the large proteoglycan Agrin. NT has seen to be involved in the maintenance/turnover of neuromuscular junctions and in processes of synaptic plasticity in the central nervous system. Roles which have been tied to its enzymatic activity, localized in the C-terminal serine-protease (SP) domain. However the purpose of NT's remaining 3-4 scavenger receptor cysteine-rich (SRCR) domains is still unclear. We have determined the crystal structure of the third SRCR domain of murine NT (mmNT-SRCR3), immediately preceding the SP domain and performed a comparative structural analysis using homologous SRCR structures. Our data and the elevated degree of structural conservation with homologous domains highlight possible functional roles for NT SRCRs. Computational and experimental analyses suggest the identification of a putative binding region for Ca²⁺ ions, known to regulate NT enzymatic activity. Furthermore, sequence and structure comparisons allow to single out regions of interest that, in future studies, might be implicated in Agrin recognition/binding or in interactions with as of yet undiscovered NT partners.

Exome sequencing in an Italian family with Alzheimer's disease points to a role for seizure-related gene 6 (SEZ6) rare variant R615H

BACKGROUND

The typical familial form of Alzheimer's disease (FAD) accounts for about 5% of total Alzheimer's disease (AD) cases. Presenilins (PSEN1 and PSEN2) and amyloid-β (A4) precursor protein (APP) genes carry all reported FAD-linked mutations. However, other genetic loci may be involved in AD. For instance, seizure-related gene 6 (SEZ6) has been reported in brain development and psychiatric disorders and is differentially expressed in the cerebrospinal fluid of AD cases.

METHODS

We describe a targeted exome sequencing analysis of a large Italian kindred with AD, negative for PSEN and APP variants, that indicated the SEZ6 heterozygous mutation R615H is associated with the pathology.

RESULTS

We overexpressed R615H mutation in H4-SW cells, finding a reduction of amyloid peptide Aβ(1-42). Sez6 expression decreased with age in a mouse model of AD (3xTG-AD), but independently from transgene expression.

CONCLUSIONS

These results support a role of exome sequencing for disease-associated variant discovery and reinforce available data on SEZ6 in AD models.

Beta-Site Amyloid Precursor Protein Cleaving Enzyme 1 Inhibition Impairs Synaptic Plasticity via Seizure Protein 6

BACKGROUND

Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) is a promising drug target for the treatment of Alzheimer's disease. Prolonged BACE1 inhibition interferes with structural and functional synaptic plasticity in mice, most likely by altering the metabolism of BACE1 substrates. Seizure protein 6 (SEZ6) is predominantly cleaved by BACE1, and Sez6 knockout mice share some phenotypes with BACE1 inhibitor-treated mice. We investigated whether SEZ6 is involved in BACE1 inhibition-induced structural and functional synaptic alterations.

METHODS

The function of NB-360, a novel blood-brain barrier penetrant and orally available BACE1 inhibitor, was verified by immunoblotting. In vivo microscopy was applied to monitor the impact of long-term pharmacological BACE1 inhibition on dendritic spines in the cerebral cortex of constitutive and conditional Sez6 knockout mice. Finally, synaptic functions were characterized using electrophysiological field recordings in hippocampal slices.

RESULTS

BACE1 enzymatic activity was strongly suppressed by NB-360. Prolonged NB-360 treatment caused a reversible spine density reduction in wild-type mice, but it did not affect Sez6^-/- mice. Knocking out Sez6 in a small subset of mature neurons also prevented the structural postsynaptic changes induced by BACE1 inhibition. Hippocampal long-term potentiation was decreased in both chronic BACE1 inhibitor-treated wild-type mice and vehicle-treated Sez6^-/- mice. However, chronic NB-360 treatment did not alter long-term potentiation in CA1 neurons of Sez6^-/- mice.

CONCLUSIONS

Our results suggest that SEZ6 plays an important role in maintaining normal dendritic spine dynamics. Furthermore, SEZ6 is involved in BACE1 inhibition-induced structural and functional synaptic alterations.

Functions of the Alzheimer's Disease Protease BACE1 at the Synapse in the Central Nervous System

Inhibition of the protease β-site amyloid precursor protein-cleaving enzyme 1 (BACE1) is a promising treatment strategy for Alzheimer's disease, and a number of BACE inhibitors are currently progressing through clinical trials. The strategy aims to decrease production of amyloid-β (Aβ) peptide from the amyloid precursor protein (APP), thus reducing or preventing Aβ toxicity. Over the last decade, it has become clear that BACE1 proteolytically cleaves a number of substrates in addition to APP. These substrates are not known to be involved in the pathogenesis of Alzheimer's disease but have other roles in the developing and/or mature central nervous system. Consequently, BACE inhibition and knockout in mice results in synaptic and other neuronal dysfunctions and the key substrates responsible for these deficits are still being elucidated. Of the BACE1 substrates that have been validated to date, a number may contribute to the synaptic deficits seen with BACE blockade, including neuregulin 1, close homologue of L1 and seizure-related gene 6. It is important to understand the impact that BACE blockade may have on these substrates and other proteins detected in substrate screens and, if necessary, develop substrate-selective BACE inhibitors.

A novel de novo microdeletion at 17q11.2 adjacent to NF1 gene associated with developmental delay, short stature, microcephaly and dysmorphic features

Background

Microdeletions at 17q11.2 often encompass NF1 gene, is the cause for NF1 microdeletion syndrome. Microdeletion at 17q11.2 without the involvement of NF1 gene is rarely reported.

Case presentation

Here we reported a patient carrying a novel de novo deletion at 17q11.2 adjacent to NF1 gene, who presented with developmental delay, short stature, postnatal microcephaly, underweight and dysmorphic features including flat facial profile, dolicocephaly, hypertelorism, short philtrum, flat nasal bridge and posteriorly rotated and low set ears. Chromosomal microarray analysis revealed a 1.69 Mb de novo deletion at 17q11.2 adjacent to NF1 gene, which involves 43 RefSeq genes. We compared this with four overlapping deletions at this interval.

Conclusions

A rare de novo microdeletion at 17q11.2 not involving NF1 gene is associated with developmental delay and dysmorphic features. Seven genes, TAOK1, PHF12, NUFIP2, SLC26A4, SEZ6, GIT1 and TRAF4 are possible candidates for the clinical features of our patient. The delineation of this rare deletion and description of associated clinical phenotypes will help to understand the genotype-phenotype correlation of genomic imbalances at this locus.

N-Glycosylation modulates filopodia-like protrusions induced by sez-6 through regulating the distribution of this protein on the cell surface

Seizure-related gene 6 (sez-6) is a trans-membrane protein expressed by neuronal cells that modulates dendritic branching. It has three clusters of eleven possible N-glycosylation sites in the extracellular domain region: sugar chain (SC)1-3, SC4-7, and SC8-11. Recent reports suggest that N-glycosylation modulates the membrane trafficking and function of trans-membrane proteins. Here, we studied the role of N-glycosylation in sez-6 function. We transfected mutants lacking one, two, or all N-glycosylation clusters into neuro2a cells. A mutant lacking all N-glycosylation was transported to the cell membrane. Mutants lacking one cluster (sez-6 ΔSC1-3, ΔSC4-7, ΔSC8-11) were evenly distributed on the cell membrane and secreted into the conditioned medium, as in wild-type sez-6; in contrast, the unglycosylated mutant, sez-6 ΔSC1-11, and mutants having only one cluster (sez-6 SC1-3, SC8-11) were localized in some portions on the cell membrane. Despite sez-6 SC4-7 having only one cluster, it was transported like the wild type. Among mutants behaving like the wild type, sez-6 ΔSC1-3 and ΔSC4-7 reduced neurite formation. Interestingly, mutants lacking SC4-7 (sez-6 ΔSC4-7) did not affect the formation of filopodia-like protrusions. In contrast, other mutants as well as the wild type induced it, suggesting that SC4-7 is crucial for filopodia-like protrusions. Our results indicate that N-glycosylation regulates cell morphology through modulating the cell surface distribution of sez-6 protein.

Correlation between human seizure-related gene 6 variants and idiopathic generalized epilepsy in a Southern Chinese Han population

This study sought to analyze the genotype and gene mutations of human seizure-related gene 6 in 98 patients with idiopathic generalized epilepsy (non-febrile seizures), who were selected from three generations of the Chinese Han population living in Shanghai, Zhejiang Province, Wuxi of Jiangsu Province, and Jiangxi Province of Southern China. Twenty-six patients’ parents were available as a first-degree relatives group and 100 biologically unrelated healthy controls were collected as the control group. Based on the age of onset and seizure type, the patients were divided into six subgroups. Polymerase chain reaction and DNA direct sequencing analysis showed that the most frequent mutations c.1249dupC (p.Gly418Argfx31) and c.1636A > G (p.Thr546Ala) were detected in some idiopathic generalized epilepsy patients and their asymptomatic first-degree relatives (30.6% vs. 19.2% and 11.2% vs. 26.9%). A novel mutation c.1807G > A (p.Val603Met) was found in a patient with late-onset idiopathic generalized epilepsy. There was no significant difference in the incidence of these three mutations among the different subgroups of idiopathic generalized epilepsy and controls. Thus, further analysis of a larger population is needed to confirm the assumption that human seizure-related gene 6 is a susceptibility gene for idiopathic generalized epilepsy with various sub-syndromes.

Full-length sequence of mouse acupuncture-induced 1-L (aig1l) gene including its transcriptional start site

We have been investigating the molecular efficacy of electroacupuncture (EA), which is one type of acupuncture therapy. In our previous molecular biological study of acupuncture, we found an EA-induced gene, named acupuncture-induced 1-L (Aig1l), in mouse skeletal muscle. The aims of this study consisted of identification of the full-length cDNA sequence of Aig1l including the transcriptional start site, determination of the tissue distribution of Aig1l and analysis of the effect of EA on Aig1l gene expression. We determined the complete cDNA sequence including the transcriptional start site via cDNA cloning with the cap site hunting method. We then analyzed the tissue distribution of Aig1l by means of northern blot analysis and real-time quantitative polymerase chain reaction. We used the semiquantitative reverse transcriptase-polymerase chain reaction to examine the effect of EA on Aig1l gene expression. Our results showed that the complete cDNA sequence of Aig1l was 6073 bp long, and the putative protein consisted of 962 amino acids. All seven tissues that we analyzed expressed the Aig1l gene. In skeletal muscle, EA induced expression of the Aig1l gene, with high expression observed after 3 hours of EA. Our findings thus suggest that the Aig1l gene may play a key role in the molecular mechanisms of EA efficacy.

The distribution of the seizure-related gene 6 (Sez-6) protein during postnatal development of the mouse forebrain suggests multiple functions for this protein: an analysis using a new antibody

The seizure-related gene 6 (Sez-6) encodes a transmembrane protein that is expressed in neuronal cells. A Sez-6-deficient mouse exhibits impaired spatial memory, motor deficits, and decreased anxiety levels. To understand the function of Sez-6 during the postnatal development of the forebrain, the spatiotemporal pattern of distribution of the Sez-6 protein was immunohistochemically analyzed using a new anti-Sez-6 antibody. Western blot analysis confirmed the specificity of this new antibody, and showed that the content of the Sez-6 protein in the cerebral cortex was highest during the neonatal period and decreased gradually thereafter. Immunohistochemical analysis revealed that Sez-6 immunoreactivity (IR) was detected in various brain regions, such as the hippocampus, cerebral cortex, piriform cortex, striatum, lateral amygdala, and olfactory tubercle. The expression patterns of Sez-6 in these brain regions was divided into three groups: i) in the cerebral cortex, hippocampus, and lateral amygdala, moderate-to-strong Sez-6 IR was detected in the first postnatal week and decreased gradually thereafter; ii) Sez-6 IR was not observed during the neonatal period in the striatum and the intensity of the signal increased gradually toward adulthood; and iii) strong Sez-6 IR was observed in the olfactory tubercle, regardless of the developmental stage. Furthermore, Sez-6 IR was detected in dendrites of hippocampal and cortical pyramidal neurons neonatally, whereas it localized around the soma after postnatal day 10. These spatiotemporal alterations of the regional and intracellular distribution of the Sez-6 protein suggest multiple functions for this protein during the postnatal development of the forebrain.

Duplication 16p11.2 in a child with infantile seizure disorder

Submicroscopic recurrent 16p11.2 rearrangements are associated with several neurodevelopmental disorders, including autism, mental retardation, and schizophrenia. The common 16p11.2 region includes 24 known genes, of which 22 are expressed in the developing human fetal nervous system. As yet, the mechanisms leading to neurodevelopmental abnormalities and the broader phenotypes associated with deletion or duplication of 16p11.2 have not been clarified. Here we report a child with spastic quadriparesis, refractory infantile seizures, severe global developmental delay, hypotonia, and microcephaly, and a de novo 598 kb 16p11.2 microduplication. Family history is negative for any of these features in parents and immediate family members. Sequencing analyses showed no mutations in DOC2A, QPRT, and SEZ6L2, genes within the duplicated 16p11.2 region that have been implicated in neuronal function and/or seizure related phenotypes. The child's clinical course is consistent with a rare seizure disorder called malignant migrating partial seizure disorder of infancy, raising the possibility that duplication or disruption of genes in the 16p11.2 interval may contribute to this severe disorder.

Seizure-related gene 6 (Sez-6) in amacrine cells of the rodent retina and the consequence of gene deletion

Background

Seizure-related gene 6 (Sez-6) is expressed in neurons of the mouse brain, retina and spinal cord. In the cortex, Sez-6 plays a role in specifying dendritic branching patterns and excitatory synapse numbers during development.

Methodology/Principal Findings

The distribution pattern of Sez-6 in the retina was studied using a polyclonal antibody that detects the multiple isoforms of Sez-6. Prominent immunostaining was detected in GABAergic, but not in AII glycinergic, amacrine cell subpopulations of the rat and mouse retina. Amacrine cell somata displayed a distinct staining pattern with the Sez-6 antibody: a discrete, often roughly triangular-shaped bright spot positioned between the nucleus and the apical dendrite superimposed over weaker general cytoplasmic staining. Displaced amacrines in the ganglion cell layer were also positive for Sez-6 and weaker staining was occasionally observed in neurons with the morphology of alpha ganglion cells. Two distinct Sez-6 positive strata were present in the inner plexiform layer in addition to generalized punctate staining. Certain inner nuclear layer cells, including bipolar cells, stained more weakly and diffusely than amacrine cells, although some bipolar cells exhibited a perinuclear “bright spot” similar to amacrine cells. In order to assess the role of Sez-6 in the retina, we analyzed the morphology of the Sez-6 knockout mouse retina with immunohistochemical markers and compared ganglion cell dendritic arbor patterning in Sez-6 null retinae with controls. The functional importance of Sez-6 was assessed by dark-adapted paired-flash electroretinography (ERG).

Conclusions

In summary, we have reported the detailed expression pattern of a novel retinal marker with broad cell specificity, useful for retinal characterization in rodent experimental models. Retinal morphology, ganglion cell dendritic branching and ERG waveforms appeared normal in the Sez-6 knockout mouse suggesting that, in spite of widespread expression of Sez-6, retinal function in the absence of Sez-6 is not affected.

Association and mutation analyses of 16p11.2 autism candidate genes

Background

Autism is a complex childhood neurodevelopmental disorder with a strong genetic basis. Microdeletion or duplication of a ∼500–700-kb genomic rearrangement on 16p11.2 that contains 24 genes represents the second most frequent chromosomal disorder associated with autism. The role of common and rare 16p11.2 sequence variants in autism etiology is unknown.

Methodology/Principal Findings

To identify common 16p11.2 variants with a potential role in autism, we performed association studies using existing data generated from three microarray platforms: Affymetrix 5.0 (777 families), Illumina 550 K (943 families), and Affymetrix 500 K (60 families). No common variants were identified that were significantly associated with autism. To look for rare variants, we performed resequencing of coding and promoter regions for eight candidate genes selected based on their known expression patterns and functions. In total, we identified 26 novel variants in autism: 13 exonic (nine non-synonymous, three synonymous, and one untranslated region) and 13 promoter variants. We found a significant association between autism and a coding variant in the seizure-related gene SEZ6L2 (12/1106 autism vs. 3/1161 controls; p = 0.018). Sez6l2 expression in mouse embryos was restricted to the spinal cord and brain. SEZ6L2 expression in human fetal brain was highest in post-mitotic cortical layers, hippocampus, amygdala, and thalamus. Association analysis of SEZ6L2 in an independent sample set failed to replicate our initial findings.

Conclusions/Significance

We have identified sequence variation in at least one candidate gene in 16p11.2 that may represent a novel genetic risk factor for autism. However, further studies are required to substantiate these preliminary findings.

A novel microdeletion at 16p11.2 harbors candidate genes for aortic valve development, seizure disorder, and mild mental retardation

Many multiple congenital anomalies (MCA) are caused by recombination between homologous segmental duplications. In this report, we describe a novel "de novo" microdeletion in male monozygotic twins presenting with aortic valve abnormality, seizure disorder, and mild mental retardation. Using array based comparative genomic hybridization, we mapped the microdeletion to the short arm of chromosome 16 at 16p11.2 and refined it using hemizygosity mapping to about 593 kb, a region that overlaps with 24 genes. The most probable mechanism for this microdeletion is through a specific intrachromosomal recombination between two, nearly identical, segmental duplications each spanning 147 kb that are flanking the microdeletion. Based on the phenotypes presented in the twins and what is known about the genes within the 16p11.2 microdeletion, we identified several genes that are strong candidates for the normal development of the aortic valve, as well as the development of seizure disorder and mental retardation.

Febrile seizures are associated with mutation of seizure-related (SEZ) 6, a brain-specific gene

Genetic factors contribute significantly to the etiology of febrile seizures (FS), the most common type of seizures in childhood. However, in most patients with FS, the causative gene is unknown. The purpose of this study was to explore the relationship between human brain-specific gene SEZ-6 and FS. Through amplification of genomic DNA by PCR and sequencing of the resulting products, we screened 75 subjects for mutations in the coding region (17 exons) of the SEZ-6 gene. Fifteen subjects were healthy individuals and 60 subjects had FS. Patients with FS could be divided into sub-groups based on seizure type (42 simple and 18 complex) and family history (41 had a positive family history). All patients have been followed to date to evaluate seizure recurrence and the development of epilepsy. No mutations were found in healthy controls, but 21 of the patients with FS had mutations in SEZ-6, and the most common type of mutation was a heterozygous, cytosine insertion (frame shift mutation) at position 1435 of the cDNA. The mutation incidence was significantly higher in patients with complex FS (vs. simple FS) and in patients with a positive family history. Sixteen of 42 patients with simple FS experienced seizure recurrence during the 1-5-year follow-up period. Fifteen of 18 patients with complex FS also experienced a recurrence during this period. Among these patients with recurrences, five patients with simple FS and six patients with complex FS have developed epilepsy. The mutation incidence among these epileptic patients is 72.7%. The human SEZ-6 gene is related to the occurrence and development of FS and may be a novel candidate gene for epilepsy. Screening for mutations in SEZ-6 may be valuable in predicting FS recurrence or the development of epilepsy.

Disturbance of cerebellar synaptic maturation in mutant mice lacking BSRPs, a novel brain-specific receptor-like protein family

By DNA cloning, we have identified the BSRP (brain-specific receptor-like proteins) family of three members in mammalian genomes. BSRPs were predominantly expressed in the soma and dendrites of neurons and localized in the endoplasmic reticulum (ER). Expression levels of BSRPs seemed to fluctuate greatly during postnatal cerebellar maturation. Triple-knockout mice lacking BSRP members exhibited motor discoordination, and Purkinje cells (PCs) were often innervated by multiple climbing fibers with different neuronal origins in the mutant cerebellum. Moreover, the phosphorylation levels of protein kinase Calpha (PKCalpha) were significantly downregulated in the mutant cerebellum. Because cerebellar maturation and plasticity require metabotropic glutamate receptor signaling and resulting PKC activation, BSRPs are likely involved in ER functions supporting PKCalpha activation in PCs.

Structural Analysis of the Complement Control Protein (CCP) Modules of GABAB Receptor 1a

The gamma-aminobutyric acid type B (GABA(B)) receptor is a heterodimeric G-protein-coupled receptor. In humans, three splice variants of the GABA(B) receptor 1 (R1) subunit differ in having one, both, or neither of two putative complement control protein (CCP) modules at the extracellular N terminus, prior to the GABA-binding domain. The in vivo function of these predicted modules remains to be discovered, but a likely association with extracellular matrix proteins is intriguing. The portion of the GABA(B) R1a variant encompassing both of its CCP module-like sequences has been expressed, as have the sequences corresponding to each individual module. Each putative CCP module exhibits the expected pattern of disulfide formation. However, the second module (CCP2) is more compactly folded than the first, and the three-dimensional structure of this more C-terminal module (expressed alone) was solved on the basis of NMR-derived nuclear Overhauser effects. This revealed a strong similarity to previously determined CCP module structures in the regulators of complement activation. The N-terminal module (CCP1) displayed conformational heterogeneity under a wide range of conditions whether expressed alone or together with CCP2. Several lines of evidence indicated the presence of native disorder in CCP1, despite the fact that recombinant CCP1 contributes to binding to the extracellular matrix protein fibulin-2. Thus, we have shown that the two CCP modules of GABA(B) R1a have strikingly different structural properties, reflecting their different functions.

Localized expression of the seizure-related gene SEZ-6 in developing and adult forebrains

Despite its initial identification in neurons exposed to the seizure-inducing drug pentylentetrazole (PTZ), the function of the seizure-related gene SEZ-6 remains obscure. Expression analysis indicates specific expression in the adult brain and testis, and the structure of the predicted protein suggests putative roles in cell-cell recognition and signalling. We report here that type I SEZ-6 mRNA is strongly expressed in highly specific regions in the developing forebrain. Specifically, the pattern of SEZ-6 expression is closely tied with the emergence of the neocortical layers and hippocampus, and implies a forebrain-specific role for this gene during development. In the adult hippocampus, SEZ-6 appears to be a CA1-specific regional marker.

Transcript map of the 8p23 putative tumor suppressor region

Cancers of the head and neck, prostate, liver, and bladder exhibit minimal regions of deletion within chromosomal band 8p23 that either overlap or map very close to one another. We previously refined a minimal region of deletion in squamous cell carcinomas to a 112-kb interval within 8p23. There seems to be only a single gene within this region that is expressed in normal upper aerodigestive tract epithelium. This candidate for the squamous cancer suppressor, CUB and sushi multiple domains-1 (CSMD1), extends into the minimal regions of deletions defined for the other types of cancer with 8p23 deletions. RT-PCR and EST data indicate that CSMD1 is also expressed in those organs,making this gene a candidate for a suppressor of multiple types of cancer. Both the sequence of the gene and the organization of the protein are highly conserved in the mouse.

NMR studies of a viral protein that mimics the regulators of complement activation

Vaccinia virus complement control protein (VCP) is a 243-residue protein that is similar in sequence to the regulators of complement activation; its role is to defend the virus against attack by the host complement system. A fragment of this protein spanning the two complement protein (CP)-modules (residues 126 to 243) which make up the C-terminal half of VCP has been expressed in Pichia pastoris. A 15N-labelled sample was purified for the purposes of structure determination and measurements of dynamics in solution using NMR. Structures were calculated on the basis of 1767 NMR-derived distance and angle restraints, with a longer than normal high-temperature simulated annealing (SA) protocol which improved convergence. The viral CP-modules are structurally very similar to the 15th and 16th CP-modules of human factor H (fH; average r.m.s.d., for invariant Trp and Cys, four pair-wise comparisons,=1.2 A) but less similar to the fifth CP-module of fH (average r.m.s.d.=2.2 A). In the VCP fragment, the orientation of one module with respect to the other is clearly defined by the experimental data, and T1 measurements are consistent with only limited flexibility at the module-module interface. The r.m.s.d. over all of the 118 residues (backbone atoms) is 0.73 A. The intermodular orientation is better defined than, and significantly different from, that observed in a CP-module pair from fH (re-calculated using the extended SA protocol). In VCP the long axis of the second module is tilted by 59(+/-4) degrees with respect to the first module (50(+/-13) degrees in the fH pair), and twisted with respect to the first module by 22(+/-6) degrees (223(+/-17) degrees in fH). The differences between the human and viral proteins may be rationalised in terms of the lack of hydrogen-bond stabilised secondary structure in the N-terminal portion of fH module 16, and the number and type of amino acid side-chains which make up the interface. A similar intermodular interface may be predicted between the third and fourth module of human C4 binding protein and, probably, between the third and fourth modules of the guinea pig acrosomal matrix protein 67; but the formulation of general rules for predicting the structure of interfaces between CP-modules awaits further experimental data.

Molecular mechanism of regulation of pentylenetetrazol-induced calcium entry by 3'-untranslated region of a seizure-related cDNA, PTZ-17, in Xenopus oocytes

To determine the molecular mechanism of regulation of pentylenetetrazol (PTZ)-induced calcium entry by the seizure-related gene, PTZ-17, the role of the 3'-untranslated region (3'UTR) and also interaction between 3'UTR and intracellular factors were investigated. PTZ-induced calcium inward current in Xenopus oocytes injected with PTZ-17 RNA varied in magnitude among strains of mice: RNA derived from the DBA/2 mouse, which has a high susceptibility to convulsions, showed the largest current and that from the BALB/c mouse with a low susceptibility to convulsions showed no PTZ response. The sequence of 3'UTR showed alterations among mouse strains: 3'UTR of BALB/c showed a sequence alteration from T to G and that of DBA/2 showed a GTG insertion compared with that of B6. The 3'UTR also regulated the translation of chloramphenicol acetyltransferase (CAT) RNA depending on its sequence. A particular region within the 3'UTR demonstrated interaction with 60- and 47-kDa proteins. Sequence alterations in this region corresponded to disappearance or increase in PTZ-induced calcium entry. These findings suggest that a particular region within 3'UTR of the seizure-related gene, PTZ-17, is involved in PTZ-induced calcium entry via interaction between mRNA and specific RNA-binding proteins.

SEZ-6: promoter selectivity, genomic structure and localized expression in the brain

AP-1-binding elements from promoter proximal DNA (the small HpaII-digested fraction of mouse genomic DNA) were affinity-selected with recombinant AP-1 complexes. One of the selected AP-1-binding elements originated from 1 kb 3' of the transcription start site of SEZ-6. We show that the mouse SEZ-6 gene extends over 49 kbp and contains 17 exons. SEZ-6 has been reported as a mouse brain-specific transcript encoding an integral membrane protein with a short cytoplasmic tail which we note may have a signalling function. We show that SEZ-6 mRNA expression in rat brain is specific to neurons but shows sharp regional differences, unconnected with the localization of major neurotransmitters. Full-length and a 3' truncated transcript are also abundant in testis. We define the origins of all reported sequence variants. The hypothetical domain structure of the protein is in excellent agreement with the exonic structure of the gene. The SEZ-6 promoter is a CpG island. In transient transfections, even the smallest promoter fragment tested (157 bp) was extremely selective towards a mouse neuronal cell line, Neuro 2a, compared with NIH-3T3, a non-expressing line.