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Haploinsufficiency of FOXL2, a new forkhead transcription factor, causes blepharophimosis/ptosis/epicanthus inversus syndrome (BPES), a rare developmental disorder affecting the eyelid and sometimes the ovary. A new study implicates FOXL2 as the first human gene required for the maintenance of ovarian follicles. The discovery of FOXL2 may provide insight into the causes of idiopathic premature ovarian failure, a disease that burdens many infertile couples.
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PMID:A fork in the road to fertility. 1117 83

In type I blepharophimosis/ptosis/epicanthus inversus syndrome (BPES), eyelid abnormalities are associated with ovarian failure. Type II BPES shows only the eyelid defects, but both types map to chromosome 3q23. We have positionally cloned a novel, putative winged helix/forkhead transcription factor gene, FOXL2, that is mutated to produce truncated proteins in type I families and larger proteins in type II. Consistent with an involvement in those tissues, FOXL2 is selectively expressed in the mesenchyme of developing mouse eyelids and in adult ovarian follicles; in adult humans, it appears predominantly in the ovary. FOXL2 represents a candidate gene for the polled/intersex syndrome XX sex-reversal goat.
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PMID:The putative forkhead transcription factor FOXL2 is mutated in blepharophimosis/ptosis/epicanthus inversus syndrome. 1117 72

Mammalian sex determination is governed by the presence of the sex determining region Y gene (SRY) on the Y chromosome. Familial cases of SRY-negative XX sex reversal are rare in humans, often hampering the discovery of new sex-determining genes. The mouse model is also insufficient to correctly apprehend the sex-determination cascade, as the human pathway is much more sensitive to gene dosage. Other species might therefore be considered in this respect. In goats, the polled intersex syndrome (PIS) mutation associates polledness and intersexuality. The sex reversal affects exclusively the XX individuals in a recessive manner, whereas the absence of horns is dominant in both sexes. The syndrome is caused by an autosomal gene located at chromosome band 1q43 (ref. 9), shown to be homologous to human chromosome band 3q23 (ref. 10). Through a positional cloning approach, we demonstrate that the mutation underlying PIS is the deletion of a critical 11.7-kb DNA element containing mainly repetitive sequences. This deletion affects the transcription of at least two genes: PISRT1, encoding a 1.5-kb mRNA devoid of open reading frame (ORF), and FOXL2, recently shown to be responsible for blepharophimosis ptosis epicanthus inversus syndrome (BPES) in humans. These two genes are located 20 and 200 kb telomeric from the deletion, respectively.
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PMID:A 11.7-kb deletion triggers intersexuality and polledness in goats. 1172 32

Blepharophimosis/ptosis/epicanthus inversus syndrome (BPES) is an autosomal dominant disorder that is characterized by distinctive eyelid abnormalities. Two clinical subtypes have been described in which type I, but not type II, is associated with premature ovarian failure. Both types of BPES are linked to 3q22-23, and the gene has recently been identified as the putative forkhead transcription factor FOXL2. We report mutation screening of FOXL2 in two families with this condition. The two mutations detected were frameshift mutations resulting from a small insertion or duplication within the gene. Both mutations would result in the production of novel carboxyl terminii, one terminating the predicted protein earlier than the wild type, and the other giving rise to a larger protein product, assuming these proteins or their mRNA were not degraded. Based on the present data, this would suggest that the first family should be type I and the second, type II. Although there is evidence of infertility in the first family, all 3 females in the youngest generation have normal pelvic ultrasound and hormone levels, suggesting that the divide between types I and II may not be as distinct as has been suggested.
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PMID:Two families with blepharophimosis/ptosis/epicanthus inversus syndrome have mutations in the putative forkhead transcription factor FOXL2. 1196 May 81

The analysis of the FOXL2 gene (3q23) in a series of two families and two sporadic cases affected with Blepharophimosis-Ptosis-Epicanthus Inversus Syndrome (BPES) is presented. This study detected two novel FOXL2 mutations (missence and nonsens mutations) and confirmed the recurrence of a previously described duplication. Magnetic Resonance Imaging (MRI) of the orbit, in one family, showed absence or hypotrophy of the eyelid superior levator muscle suggesting a possible role of FOXL2 in the development of this extra-ocular muscle.
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PMID:Sporadic and familial blepharophimosis -ptosis-epicanthus inversus syndrome: FOXL2 mutation screen and MRI study of the superior levator eyelid muscle. 1263 Sep 57

Blepharophimosis ptosis epicanthus inversus syndrome (BPES) is a human disorder caused by mutations in the forkhead transcription factor gene FOXL2 and is characterized by facial dysmorphology combined in some cases with ovarian failure. To better understand the role of FOXL2 in the etiology of ovarian failure in BPES, we examined its expression in embryonic ovaries of mice, chickens, and red-eared slider turtles, representatives of three phylogenetically distant vertebrate groups that have different mechanisms of sex determination. Expression of Foxl2 was detected in early ovaries of all three species around the time of sex determination and was associated with both somatic and germ cell populations in mice. Expression was sexually dimorphic in all cases. Sequence analysis of turtle and chicken FoxL2 orthologues indicated an unusually high degree of structural conservation during evolution. FoxL2 was found to be autosomal in chickens, and therefore unlikely to represent the dominant ovarian-determining gene that has been postulated to exist as a possible explanation for female heterogamety in birds. Our observations suggest that BPES may result from early abnormalities in regulating the development of the fetal ovary, rather than premature degeneration of the postnatal or adult ovary. Further, our results suggest that FOXL2 is a highly conserved early regulator of vertebrate ovarian development.
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PMID:Etiology of ovarian failure in blepharophimosis ptosis epicanthus inversus syndrome: FOXL2 is a conserved, early-acting gene in vertebrate ovarian development. 1281 May 80

Bleparophimosis ptosis epicanthus inversus syndrome (BPES) is a rare disorder characterized by eyelid malformation and in some cases associated with premature ovarian failure. Although the familial form is autosomal dominant, many cases are also sporadic. The mutations causing this disorder were found in a winged/forkhead transcription factor gene named FOXL2. We have sequenced the mouse homolog for the FOXL2 gene and identified the Fugu rubripes (pufferfish) ortholog from the database. By alignment of the three sequences, we found an almost complete conservation of the forkhead domain in the three species. There is 95% and 61% conservation at the protein level between human-mouse and human-pufferfish, respectively. The polyalanine and polyproline tracts within the gene are absent in Fugu rubripes. An overview identifies four breaks in the conservation of the gene within these species. Using a direct sequencing approach, we performed mutation analysis from DNA of nine affected individuals from familial and sporadic cases. The mutations are distributed throughout the coding region of the FOXL2 gene. We identified five novel mutations: g.292delG (E19fsX149); g.530G>A (W98X); g.548A>G (H104R); g.652G>T (E139X); and g.1178_1185del8 (A314fsX530). In addition we also identified two known mutations g.823C>T (Q196X) and g.1092_1108dup17, the latter in individuals from three unrelated pedigrees.
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PMID:Comparative analysis of the FOXL2 gene and characterization of mutations in BPES patients. 1293 87

Human Blepharophimosis/ptosis/epicanthus inversus syndrome (BPES) type I is an autosomal dominant disorder associated with premature ovarian failure (POF) caused by mutations in FOXL2, a winged-helix/forkhead domain transcription factor. Although it has been shown that FOXL2 is expressed in adult ovaries, its function during folliculogenesis is not known. Here, we show that the murine Foxl2 gene is essential for granulosa cell differentiation and ovary maintenance. In Foxl2(lacZ) homozygous mutant ovaries granulosa cells do not complete the squamous to cuboidal transition leading to the absence of secondary follicles and oocyte atresia. We further demonstrate that activin-betaA and anti-Mullerian inhibiting hormone expression is absent or strongly diminished in Foxl2(lacZ) homozygous mutant ovaries. Unexpectedly, two weeks after birth most if not all oocytes expressed Gdf9 in Foxl2(lacZ) homozygous mutant ovaries, indicating that nearly all primordial follicles have already initiated folliculogenesis at this stage. This activation, in the absence of functional granulosa cells, leads to oocyte atresia and progressive follicular depletion. In addition to providing a molecular mechanism for premature ovarian failure in BPES, these results suggest that granulosa cell function is not only crucial for oocyte growth but also to maintain follicular quiescence in vivo.
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PMID:The murine winged-helix transcription factor Foxl2 is required for granulosa cell differentiation and ovary maintenance. 1473 45

Premature ovarian failure in a subgroup of women with blepharophimosis-ptosis-epicanthus inversus type 1 syndrome has been associated with nonsense mutations in the gene encoding a Forkhead transcription factor, Forkhead L2 (FOXL2). However, the exact function of FOXL2 in the ovary is unclear. We investigated the expression of FOXL2 in the mouse ovary during follicular development and maturation by RT-PCR and in situ hybridization. The FOXL2 mRNA is expressed in ovaries throughout development and adulthood and is localized to the undifferentiated granulosa cells in small and medium follicles as well as cumulus cells of preovulatory follicles. FOXL2 belongs to a group of transcription factors capable of interacting with specific DNA sequences in diverse gene promoters. With the presence of multiple putative forkhead DNA consensus sites, the promoter of the human steroidogenic acute regulatory (StAR) gene was used to test for regulation by FOXL2. Cotransfection studies revealed that wild-type FOXL2 represses the activity of the StAR promoter, and the first 95 bp upstream of the transcriptional start site of the StAR gene is sufficient for FOXL2 repression. EMSAs confirmed that FOXL2 interacts directly with this region. Analyses using FOXL2 mutants also demonstrated the importance of the entire alanine/proline-rich carboxyl terminus of FOXL2 for transcriptional repression. Furthermore, these mutations produce a protein with a dominant-negative effect that disables the transcriptional repressor activity of wild-type FOXL2. Dominant-negative mutations of FOXL2 could increase expression of StAR and other follicle differentiation genes in small and medium follicles to accelerate follicle development, resulting in increased initial recruitment of dormant follicles and thus the premature ovarian failure phenotype.
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PMID:Forkhead l2 is expressed in the ovary and represses the promoter activity of the steroidogenic acute regulatory gene. 1505 56

A translocation breakpoint 171 kb 5' of the transcription start of FOXL2 causes blepharophimosis/ptosis/epicanthus inversus syndrome (BPES) and associated premature ovarian failure. The breakpoint falls within another gene, MRPS22, that has been sequenced in 500 kb of continuous DNA. MRPS22 encodes 20 exons and a number of alternative transcripts. Three CpG islands (>91% identical) are followed by noncoding exons 4-12 and coding exons 13-20. The 3'UTR extends into the 3'UTR of COPB2. Based on the sequence, three reported translocations that cause BPES all fall within intron 6 of MRPS22. Comparisons reveal conserved segments in introns 6, 11, and 12 of human and mouse. Notably intron 11 sequence is also deleted in goat PIS syndrome (which combines craniofacial defects, female infertility, and XX sex reversal). The conserved sequences are candidates for models in which they are distant enhancers or otherwise affect higher order chromatin structure to impose long-range cis regulation of FOXL2 expression.
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PMID:FOXL2 inactivation by a translocation 171 kb away: analysis of 500 kb of chromosome 3 for candidate long-range regulatory sequences. 1508 Nov 6


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