Etiology of craniofacial malformations in mouse models of blepharophimosis, ptosis and epicanthus inversus syndrome.

Blepharophimosis, ptosis, epicanthus-inversus syndrome (BPES) is an autosomal dominant genetic disorder characterized by narrow palpebral fissures and eyelid levator muscle defects. BPES is often associated to premature ovarian insufficiency (BPES type I). FOXL2, a member of the forkhead transcription factor family, is the only gene known to be mutated in BPES. Foxl2 is essential for maintenance of ovarian identity, but the developmental origin of the facial malformations of BPES remains, so far, unexplained. In this study, we provide the first detailed account of the developmental processes leading to the craniofacial malformations associated to Foxl2. We show that, during development, Foxl2 is expressed both by Cranial Neural Crest Cells (CNCCs) and by Cranial Mesodermal Cells (CMCs), which give rise to skeletal (CNCCs and CMCs) and muscular (CMCs) components of the head. Using mice in which Foxl2 is selectively inactivated in either CNCCs or CMCs, we reveal that expression of Foxl2 in CNCCs is essential for the development of extraocular muscles. Indeed, inactivation of Foxl2 in CMCs has only minor effects on muscle development, whereas its inactivation in CNCCs provokes a severe hypoplasia of the levator palpabrae superioris and of the superior and inferior oblique muscles. We further show that Foxl2 deletion in either CNCCs or CMCs prevents eyelid closure and induces subtle skeletal developmental defects. Our results provide new insights in the complex developmental origin of human BPES and could help to understand the origin of other ocular anomalies associated to this syndrome.

Somatic sex reprogramming of adult ovaries to testes by FOXL2 ablation.

In mammals, the transcription factor SRY, encoded by the Y chromosome, is normally responsible for triggering the indifferent gonads to develop as testes rather than ovaries. However, testis differentiation can occur in its absence. Here we demonstrate in the mouse that a single factor, the forkhead transcriptional regulator FOXL2, is required to prevent transdifferentiation of an adult ovary to a testis. Inducible deletion of Foxl2 in adult ovarian follicles leads to immediate upregulation of testis-specific genes including the critical SRY target gene Sox9. Concordantly, reprogramming of granulosa and theca cell lineages into Sertoli-like and Leydig-like cell lineages occurs with testosterone levels comparable to those of normal XY male littermates. Our results show that maintenance of the ovarian phenotype is an active process throughout life. They might also have important medical implications for the understanding and treatment of some disorders of sexual development in children and premature menopause in women.

Loss of GLIS2 causes nephronophthisis in humans and mice by increased apoptosis and fibrosis.

Nephronophthisis (NPHP), an autosomal recessive kidney disease, is the most frequent genetic cause of end-stage renal failure in the first three decades of life. Positional cloning of the six known NPHP genes has linked its pathogenesis to primary cilia function. Here we identify mutation of GLIS2 as causing an NPHP-like phenotype in humans and mice, using positional cloning and mouse transgenics, respectively. Kidneys of Glis2 mutant mice show severe renal atrophy and fibrosis starting at 8 weeks of age. Differential gene expression studies on Glis2 mutant kidneys demonstrate that genes promoting epithelial-to-mesenchymal transition and fibrosis are upregulated in the absence of Glis2. Thus, we identify Glis2 as a transcription factor mutated in NPHP and demonstrate its essential role for the maintenance of renal tissue architecture through prevention of apoptosis and fibrosis.

The murine winged-helix transcription factor Foxl2 is required for granulosa cell differentiation and ovary maintenance.

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.