Evolution and origin of merlin, the product of the Neurofibromatosis type 2 (NF2) tumor-suppressor gene

BACKGROUND: Merlin, the product of the Neurofibromatosis type 2 (NF2) tumor suppressor gene, belongs to the ezrin-radixin-moesin (ERM) subgroup of the protein 4.1 superfamily, which links cell surface glycoproteins to the actin cytoskeleton. While merlin's functional activity has been examined in mammalian and Drosophila models, little is understood about its evolution, diversity, and overall distribution among different taxa. RESULTS: By combining bioinformatic and phylogenetic approaches, we demonstrate that merlin homologs are present across a wide range of metazoan lineages. While the phylogenetic tree shows a monophyletic origin of the ERM family, the origin of the merlin proteins is robustly separated from that of the ERM proteins. The derivation of merlin is thought to be in early metazoa. We have also observed the expansion of the ERM-like proteins within the vertebrate clade, which occurred after its separation from Urochordata (Ciona intestinalis). Amino acid sequence alignment reveals the absence of an actin-binding site in the C-terminal region of all merlin proteins from various species but the presence of a conserved internal binding site in the N-terminal domain of the merlin and ERM proteins. In addition, a more conserved pattern of amino acid residues is found in the region containing the so-called "Blue Box," although some amino acid substitutions in this region exist in the merlin sequences of worms, fish, and Ciona. Examination of sequence variability at functionally significant sites, including the serine-518 residue, the phosphorylation of which modulates merlin's intra-molecular association and function as a tumor suppressor, identifies several potentially important sites that are conserved among all merlin proteins but divergent in the ERM proteins. Secondary structure prediction reveals the presence of a conserved α-helical domain in the central to C-terminal region of the merlin proteins of various species. The conserved residues and structures identified correspond to the important sites highlighted by the available crystal structures of the merlin and ERM proteins. Furthermore, analysis of the merlin gene structures from various organisms reveals the increase of gene length during evolution due to the expansion of introns; however, a reduction of intron number and length appears to occur in the merlin gene of the insect group. CONCLUSION: Our results demonstrate a monophyletic origin of the merlin proteins with their root in the early metazoa. The overall similarity among the primary and secondary structures of all merlin proteins and the conservation of several functionally important residues suggest a universal role for merlin in a wide range of metazoa

The role of Drosophila Merlin in spermatogenesis

<p>Abstract</p> <p>Background</p> <p><it>Drosophila </it>Merlin, the homolog of the human <it>Neurofibromatosis 2 </it>(<it>NF2</it>) gene, is important for the regulation of cell proliferation and receptor endocytosis. Male flies carrying a <it>Mer</it>³allele, a missense mutation (Met¹⁷⁷→Ile) in the <it>Merlin </it>gene, are viable but sterile; however, the cause of sterility is unknown.</p> <p>Results</p> <p>Testis examination reveals that hemizygous <it>Mer</it>³mutant males have small seminal vesicles that contain only a few immotile sperm. By cytological and electron microscopy analyses of the <it>Mer</it>³, <it>Mer</it>⁴(Gln¹⁷⁰→stop), and control testes at various stages of spermatogenesis, we show that <it>Merlin </it>mutations affect meiotic cytokinesis of spermatocytes, cyst polarization and nuclear shaping during spermatid elongation, and spermatid individualization. We also demonstrate that the lethality and sterility phenotype of the <it>Mer</it>⁴mutant is rescued by the introduction of a wild-type <it>Merlin </it>gene. Immunostaining demonstrates that the Merlin protein is redistributed to the area associated with the microtubules of the central spindle in telophase and its staining is less in the region of the contractile ring during meiotic cytokinesis. At the onion stage, Merlin is concentrated in the Nebenkern of spermatids, and this mitochondrial localization is maintained throughout sperm formation. Also, Merlin exhibits punctate staining in the acrosomal region of mature sperm.</p> <p>Conclusion</p> <p><it>Merlin </it>mutations affect spermatogenesis at multiple stages. The Merlin protein is dynamically redistributed during meiosis of spermatocytes and is concentrated in the Nebenkern of spermatids. Our results demonstrated for the first time the mitochondrial localization of Merlin and suggest that Merlin may play a role in mitochondria formation and function during spermatogenesis.</p

Intracellular distribution of the Merlin protein at various stages of spermatogenesis

<p><b>Copyright information:</b></p><p>Taken from "The role of Merlin in spermatogenesis"</p><p>http://www.biomedcentral.com/1471-2121/9/1</p><p>BMC Cell Biology 2008;9():1-1.</p><p>Published online 10 Jan 2008</p><p>PMCID:PMC2253521.</p><p></p> In the control cyst, Merlin was detected in the cellular cortex of spermatocytes (A). In prometaphase (B) and metaphase (C) of meiosis, the cortical localization of Merlin became more evident. In telophase (D), Merlin redistributed and accumulated in the area associated with the microtubules of the central spindle. During cytokinesis (E), Merlin staining remained associated with the microtubules but was less intense in the region of the contractile ring. In the onion-stage spermatids (F), Merlin was highly concentrated in the Nebenkern. This localization pattern was maintained through the comet stage of spermatid elongation (G). The insert in panel G shows intense Merlin staining in the two subunits of Nebenkern in spermatids. In the control cyst, containing mature sperm, bright Merlin staining was also seen as a punctate dot in the acrosomal region (H). Merlin staining was still detected in the cyst at the comet stage; however, sperm nuclei were scattered throughout the cyst, and the arrangement of spermatids was irregular (I)

Difference in nuclear grouping during cyst polarization between the control and Merlin mutant spermatids

<p><b>Copyright information:</b></p><p>Taken from "The role of Merlin in spermatogenesis"</p><p>http://www.biomedcentral.com/1471-2121/9/1</p><p>BMC Cell Biology 2008;9():1-1.</p><p>Published online 10 Jan 2008</p><p>PMCID:PMC2253521.</p><p></p> Dissected testes from the control (A), (B-E), and (F-H) males were stained with DAPI and examined as described before. Note that while the spermatid nuclei were grouped in one area (arrow) of the control cyst (A), the spermatid nuclei in the (B-E) and (F-G) cysts were seen as two diffuse groups (arrows). In some cases, the spermatid nuclei were scattered in the mutant cyst (H). Panel C shows a phase-contrast image of a cyst, panel D displays the same cyst stained with DAPI, and panel E represents a merged image. The cyst shown in panels F and G was obtained from a male carrying the mutation and a GFP marker as described in Materials and Methods

Ultrastructural analysis of the control and Merlin mutant cysts during the elongation and individualization stages

<p><b>Copyright information:</b></p><p>Taken from "The role of Merlin in spermatogenesis"</p><p>http://www.biomedcentral.com/1471-2121/9/1</p><p>BMC Cell Biology 2008;9():1-1.</p><p>Published online 10 Jan 2008</p><p>PMCID:PMC2253521.</p><p></p> (A-C) Sections of the cysts from the control (A), (B), or (C) testis at the elongation stage. (A) A dark paracrystalline body was seen within the major mitochondrial derivative in the control spermatid. Bar = 2 μm. (B) Some of the spermatids in the cyst contained two paracrystalline bodies (filled arrowhead points to one example). Also, some spermatids had two axonemes (open arrowhead). Bar = 0.5 μm. (C) Two paracrystalline bodies within the major mitochondrial derivative were frequently seen in the elongating spermatids of the cyst. Bar = 0.5 μm. (D-F) Cysts from the control (D), (E), or (F) testis at the individualization stage. (D) The association of axoneme with the mitochondrial derivatives was seen in the spermatids of the control cyst. Bar = 2 μm. (E) Spermatids in the cyst might contain two abnormally-shaped (filled arrowhead) or three (arrow) paracrystalline bodies together with one axoneme, or have two paracrystalline-filled Nebenkerns but without the axoneme (open arrowhead). Bar = 0.5 μm. (F) Spermatids with multiple Nebenkerns with (open arrowhead) or without (filled arrowhead) axonemes together with cytoplasmic fragmentation were seen in the cyst. Bar = 0.5 μm. (G-I) Cysts from the control (G), (H), or (I) testis at the late stage of individualization. (G) Individualized spermatids in the control cyst displayed a highly-ordered axoneme-Nebenkern pair. Bar = 0.5 μm. (H) The spermatids in the cyst were poorly arranged and some of them appeared to be fused together. Bar = 0.5 μm. (I) The cyst showed a complete destruction of spermatid individualization, resulting in empty spermatids with or without axoneme or Nebenkern. Insert illustrates the structure of axoneme appeared to be intact. Bar = 1 μm. Bar in the insert = 0.2 μm

Growth of Benign and Malignant Schwannoma Xenografts in Severe Combined Immunodeficiency Mice

OBJECTIVES: Models for the development of new treatment options in vestibular schwannoma (VS) treatment are lacking. The purpose of this study is to establish a quantifiable human VS xenograft model in mice. STUDY DESIGN AND METHODS: Both rat malignant schwannoma cells (KE-F11 and RT4) and human malignant schwannoma (HMS-97) cells were implanted near the sciatic nerve in the thigh of severe combined immunodeficiency (SCID) mice. Additionally, human benign VS specimens were implanted in another set of SCID mice. Three-dimensional tumor volumes were calculated from magnetic resonance images over the next 6 months. RESULTS: Mice implanted with malignant schwannoma cells developed visible tumors within 2 weeks. Imaging using a 4.7-tesla magnetic resonance imaging and immunohistopathologic examination identified solid tumors in all KE-F11 and HMS-97 xenografts, whereas RT4 xenografts consistently developed cystic schwannomas. VS xenografts demonstrated variability in their growth rates similar to human VS. The majority of VS xenografts did not grow but persisted throughout the study, whereas two of 15 xenografts grew significantly. Histopathologic examination and immunohistochemistry confirmed that VS xenografts retained their original microscopic and immunohistochemical characteristics after prolonged implantation. CONCLUSIONS: This study describes the first animal model for cystic schwannomas. Also, we demonstrate the use of high-field magnetic resonance imaging to quantify VS xenograft growth over time. The VS xenografts represent a model complimentary to Nf2 transgenic and knockout mice for translational VS research

AR42, a novel histone deacetylase inhibitor, as a potential therapy for vestibular schwannomas and meningiomas

Neurofibromatosis type 2 (NF2) is an autosomal-dominant disease that results in the formation of bilateral vestibular schwannomas (VSs) and multiple meningiomas. Treatment options for NF2-associated tumors are limited, and to date, no medical therapies are FDA approved. The ideal chemotherapeutic agent would inhibit both VS and meningiomas simultaneously. The objectives of this study are (1) to test the efficacy of AR42, a novel histone deacetylase inhibitor, to inhibit VS and meningioma growth and (2) to investigate this drug\u27s mechanisms of action. Primary cultures of human VS and meningioma cells were established. Nf2-deficient mouse schwannoma and benign human meningioma Ben-Men-1 cells were also cultured. Cells were treated with AR42, and the drug\u27s effects on proliferation and the cell cycle were analyzed using a methanethiosulfonate assay and flow cytometry, respectively. Human phospho-kinase arrays and Western blots were used to evaluate the effects of AR42 on intracellular signaling. The in vivo efficacy of AR42 was investigated using schwannoma xenografts. Tumor volumes were quantified using high-field, volumetric MRI, and molecular target analysis was performed using immunohistochemistry. AR42 inhibited the growth of primary human VS and Nf2-deficient mouse schwannoma cells with a half maximal inhibitory concentration (IC50) of 500 nM and 250-350 nM, respectively. AR42 also inhibited primary meningioma cells and the benign meningioma cell line, Ben-Men-1, with IC50 values of 1.5 mM and 1.0 mM, respectively. AR42 treatment induced cell-cycle arrest at G2 and apoptosis in both VS and meningioma cells. Also, AR42 exposure decreased phosphorylated Akt in schwannoma and meningioma cells. In vivo treatment with AR42 inhibited the growth of schwannoma xenografts, induced apoptosis, and decreased Akt activation. The potent growth inhibitory activity of AR42 in schwannoma and meningioma cells suggests that AR42 should be further evaluated as a potential treatment for NF2-associated tumors. © 2011 The Author(s)