Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterized by the occurrence of tumors of the parathyroids, pancreas, and anterior pituitary. The MEN1 gene, which was identified in 1997, consists of 10 exons that encode a 610–amino acid protein referred to as menin. Menin is predominantly a nuclear protein that has roles in transcriptional regulation, genome stability, cell division, and proliferation. Germline mutations usually result in MEN1 or occasionally in an allelic variant referred to as familial isolated hyperparathyroidism (FIHP). MEN1 tumors frequently have loss of heterozygosity (LOH) of the MEN1 locus, which is consistent with a tumor suppressor role of MEN1. Furthermore, somatic abnormalities of MEN1 have been reported in MEN1 and non-MEN1 endocrine tumors. The clinical aspects and molecular genetics of MEN1 are reviewed together with the reported 1,336 mutations. The majority (>70%) of these mutations are predicted to lead to truncated forms of menin. The mutations are scattered throughout the>9-kb genomic sequence of the MEN1 gene. Four, which consist of c.249_252delGTCT (deletion at codons 83–84), c.1546_1547insC (insertion at codon 516), c.1378C>T (Arg460Ter), and c.628_631delACAG (deletion at codons 210–211) have been reported to occur frequently in 4.5%, 2.7%, 2.6%, and 2.5% of families, respectively. However, a comparison of the clinical features in patients and their families with the same mutations reveals an absence of phenotype–genotype correlations. The majority of MEN1 mutations are likely to disrupt the interactions of menin with other proteins and thereby alter critical events in cell cycle regulation and proliferation. Hum Mutat 29(1), 22–32, 2008. © 2007 Wiley-Liss, Inc.

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Multiple endocrine neoplasia type 1 (MEN1): analysis of 1336 mutations reported in the first decade following identification of the gene

Synapse formation is a crucial step in the development of neuronal circuits and requires precise coordination of presynaptic and postsynaptic activities However, molecular mechanisms that control the formation of functionally mature synaptic contacts, in particular between central neurons, remain poorly understood To identify genes that are involved in the formation of central synapses, we made use of molluscan neurons that in culture form synaptic contacts between their somata (soma‐ soma synapses) in the absence of neurite outgrowth Using single-cell mRNA differential display, we have identified a molluscan homolog of the multiple endocrine neoplasia type 1 (MEN1) tumor suppressor gene encoding the transcription factor menin as a gene that is upregulated during synapse formation In vitro antisense knock-down of MEN1 mRNA blocks the formation of mature synapses between different types of identified central neurons Moreover, immunocytochemistry and cell-specific knock-down of MEN1 mRNA show that postsynaptic but not presynaptic expression is required for synapses to form Together, our data demonstrate that menin is a synaptogenic factor that is critically involved in a general postsynaptic mechanism of synapse formation between central neurons

https://www.jneurosci.org/content/jneuro/21/16/RC161.full.pdf

Synapse formation between central neurons requires postsynaptic expression of the MEN1 tumor suppressor gene.

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant cancer syndrome, characterized primarily by multiple tumors in the parathyroid glands, endocrine pancreas, and anterior pituitary. Other tumors, including gastrinoma, carcinoid, adrenal cortical tumors, angiofibroma, collagenoma, and lipoma, also occur in some patients. Individuals with MEN1 almost always have loss-of-function mutations in the MEN1 gene on chromosome 11, and endocrine tumors arising in these patients usually show somatic loss of the remaining wild-type allele. To examine the role of MEN1 in tumor formation, a mouse model was generated through homologous recombination of the mouse homolog Men1. Homozygous mice die in utero at embryonic days 11.5-12.5, whereas heterozygous mice develop features remarkably similar to those of the human disorder. As early as 9 months, pancreatic islets show a range of lesions from hyperplasia to insulin-producing islet cell tumors, and parathyroid adenomas are also frequently observed. Larger, more numerous tumors involving pancreatic islets, parathyroids, thyroid, adrenal cortex, and pituitary are seen by 16 months. All of the tumors tested to date show loss of the wild-type Men1 allele, further supporting its role as a tumor suppressor gene.

https://www.pnas.org/content/pnas/98/3/1118.full.pdf

A mouse model of multiple endocrine neoplasia, type 1, develops multiple endocrine tumors

Multiple endocrine neoplasia type 1 (MEN1) is a hereditary syndrome characterized by the occurrence of multiple endocrine tumors of the parathyroid, pancreas, and anterior pituitary in patients. To study tumorigenesis related to the MEN1 syndrome, we have generated Men1 knockout mice using the gene targeting approach. Heterozygous Men1 mutant mice developed the same range of major endocrine tumors as is seen in MEN1 patients, affecting the parathyroid, pancreatic islets, pituitary and adrenal glands, as well as the thyroid, and exhibiting multistage tumor progression with metastatic potential. In particular, extrapancreatic gastrinoma, pancreatic glucagonoma, and mixed hormone-producing tumors in islets were observed. In addition, there was a high incidence of gonadal tumors of endocrine origin, i.e. Leydig cell tumors, and ovary sex-cord stromal cell tumors in heterozygous Men1 mutant mice. Hormonal disturbance, such as abnormal PTH and insulin levels, was also observed in these mice. These tumors were associated with loss of heterozygosity of the wild-type Men1 allele, suggesting that menin is involved in suppressing the development of these endocrine tumors. All of these features are reminiscent of MEN1 symptoms in humans and establish heterozygous Men1 mutant mice as a suitable model for this disease.

/pdf/heterozygous-men1-mutant-mice-develop-a-range-of-endocrine-3qppwvd5sj.pdf

Heterozygous Men1 Mutant Mice Develop a Range of Endocrine Tumors Mimicking Multiple Endocrine Neoplasia Type 1

Patients with multiple endocrine neoplasia type 1 (MEN1) develop multiple endocrine tumors, primarily affecting the parathyroid, pituitary, and endocrine pancreas, due to the inactivation of the MEN1 gene. A conditional mouse model was developed to evaluate the loss of the mouse homolog, Men1, in the pancreatic beta cell. Men1 in these mice contains exons 3 to 8 flanked by loxP sites, such that, when the mice are crossed to transgenic mice expressing cre from the rat insulin promoter (RIP-cre), exons 3 to 8 are deleted in beta cells. By 60 weeks of age, >80% of mice homozygous for the floxed Men1 gene and expressing RIP-cre develop multiple pancreatic islet adenomas. The formation of adenomas results in elevated serum insulin levels and decreased blood glucose levels. The delay in tumor appearance, even with early loss of both copies of Men1, implies that additional somatic events are required for adenoma formation in beta cells. Comparative genomic hybridization of beta cell tumor DNA from these mice reveals duplication of chromosome 11, potentially revealing regions of interest with respect to tumorigenesis.

Of Mice and MEN1: Insulinomas in a Conditional Mouse Knockout

The gene responsible for multiple endocrine neoplasia type 1 (MEN1), a heritable predisposition to endocrine tumours in man, has recently been identified. Here we have characterized the murine homologue with regard to cDNA sequence, genomic structure, expression pattern and chromosomal localisation. The murine Men1 gene spans approximately 6.7 kb of genomic DNA and is comprised of 10 exons with similar genomic structure to the human locus. It was mapped to the pericentromeric region of mouse chromosome 19, which is conserved with the human 11q13 band where MEN1 is located. The predicted protein is 611 amino acids in length and overall is 97% homologous to the human orthologue. The 45 reported MEN1 mutations which alter or delete a single amino acid in human all occur at conserved residues, thereby supporting their functional significance. Two transcripts of approximately 3.2 and 2.8 kb were detected in both embryonal and adult murine tissues, resulting from alternative splicing of intron 1. By RNA in situ hybridization and Northern analysis the spatiotemporal expression pattern of Men1 was determined during mouse development. Men1 gene activity was detected already at gestational day 7. At embryonic day 14 expression was generally high throughout the embryo, while at day 17 the thymus, skeletal muscle, and CNS showed the strongest signal. In selected tissues from postnatal mouse Men1 was detected in all tissues analysed and was expressed at high levels in cerebral cortex, hippocampus, testis, and thymus. In brain the menin protein was detected mainly in nerve cell nuclei, whereas in testis it appeared perinuclear in spermatogonia. These results show that Men1 expression is not confined to organs affected in MEN1, suggesting that Men1 has a significant function in many different cell types including the CNS and testis.

Vim Van de Vem

Papers

Characterization of the mouse Men1 gene and its expression during development.