Our work began with our findings that the forkhead tanscription factor 2 (Foxl2) is important in preventing POF; most strikingly, we showed that Foxl2 hereditary deficiency provokes POF in women with the Blephariphomisis-Ptosis-Epicanthus Inversus Syndrome (BPES). We have then shown over the last 6 years that Foxl2 is critical throughout female reproductive life, vitally involved in the ovary in somatic sex determination and maintenance as well as in the development and stabilization of ovarian follicles. The studies have led to a significant change in the paradigm for somatic sex determination and maintenance, from a formulation in which the ovary was a default pathway when the male-determining gene Sry was absent or inactive to a model in which Sry remains male-determinative but several other genes, and especially Foxl2, are actively required to determine ovary formation and stability, continually repressing the male pathway. We have continued to analyze the action of Foxl2 by generating mouse models in which Foxl2 is ablated or overexpressed, either alone or in combination with other important ovarian factors. We have now progressed further in the elucidation of the role of Foxl2 in the formation and maintenance of follicles and in germ cell survival, and are extending the studies to the comparative action of other master genes affecting follicle dynamics. In extensions of studies, we demonstrated that Cyp26b1, as well as transcription factor genes steroidogenic factor-1 (Sf1) and Sox9 are co-expressed in Sertoli cells in mouse fetal testes (and Cyp26b1 and Sf1 are co-expressed in Leydig cells). Furthermore, qRT-PCR showed that Cyp26b1 up-regulation by Sox9/Sf1 was attenuated by Foxl2, whereas in Foxl2-null mice, Cyp26b1 expression in XX gonads was increased 20-fold relative to WT controls. These data support the hypothesis that Sox9 and Sf1 ensure the male fate of germ cells in part by up-regulating Cyp26b1, and that Foxl2 antagonizes Cyp26b1 expression (and Sox9) in ovaries. We have now examined the effect of over-expression of Foxl2. We created transgenic mice over-expressing Foxl2 under the control of an Amhr2 promoter, active starting early in embryonic development. The transgene up-regulates genes downstream of Foxl2 in the ovary and down-regulates male-determining genes in the testis. A larger follicle pool was also seen in transgenic ovaries. . This finding is especially relevant to the role of Foxl2 in determining the ovarian reserve and thus, the age of menopause. In the reproductive system, Foxl2 is the only gene expressed uniquely in the ovary. However, Foxl2 is also expressed in the pituitary and in the eye of both sexes, and we have investigated its action in these extra-ovarian tissues as well. In the pituitary, we found that Foxl2 is not required for the specification of gonadotropes, which secrete LH and FSH, the endocrine signals that regulate folliculogenesis in the ovary and spermatogenesis in the testis. By contrast, in Foxl2-ablated mice FSH secretion is dramatically reduced and activin is unable to activate Fshb expression. Foxl2 function aeems required in the pituitary for normal expression of FSH.In the eye, we investigated the role of Notch signaling in the formation of corneal and eyelid stroma in mice. We found that over-expression of Notch1 intracellular domain (N1-ICD) impaired eyelid levator smooth muscle formation by down-regulating Foxl2. This is similar to the effect of haploinsufficiency of FOXL2 in the human eye. These data strongly indicate that low levels of Notch1 are crucial for proper Foxl2 expression in normal eyelid development. In an independent line of research, we have investigated the role of another forkhead transcription factor, Foxo3, which is not involved in the formation of ovarian follicles but acts to maintain them. Foxo3 is known from work in other systems to act in several biologic processes including cell cycle control, maturation, survival and apoptosis. In the ovary Foxo3 has a specific role in controlling the activation of primordial follicles, governing the size of the ovarian reserve. In its absence, others have shown that the entire cohort of primordial follicles activates and grows uncontrollably, leaving the ovary empty and female mice completely sterile by 15 weeks of age. We have now found that in young females the expression of a mutated form of Foxo3 that cannot be inactivated by phosphorylation causes a delay of follicular growth, with longer survival of primordial follicles, a lower expression of factors involved in follicle maturation, and increased fertility. We also studied adult, premenopausal, and perimenopausal mice, and showed that when active Foxo3 is present, aging processes are slowed and the ovary retains a larger pool of primordial follicles. Furthermore, gene expression levels of markers for further development and aging are consistent with either a developmental delay or slower aging in transgenic ovaries. In addition, we measured the production of gonadotropins, whose levels increase as menopause approaches (an assay method used clinically in humans to diagnose the onset of menopause). We found a higher level of gonadotropins in wild-type compared to age-matched transgenic mice, supporting the interpretation of slower aging in the transgenics. Finally, we studied the fertility of aging mice up to 12 months of age. With aging and approach of menopause, transgenic females showed a greater fertility (31-49%) compared with wild-type animals. This is the first gain-of-function change in a gene that gives greater fertility throughout the reproductive lifespan, and suggests a possible point for pharmaceutical intervention. Foxo3 is also involved in a range of crucial cellular processes regulating stress resistance, metabolism, and apoptosis; but its effects on the aging cardiovascular system remain to be elucidated. In an Interlaboratory Project, we have studied mice ablated for Foxo3 compared to wild-type (WT). In cardiomyocytes from mice 6 months old, we found autophagy significantly decreased in Foxo3 -/- vs WT. Also, the oxidant stress threshold of the mitochondrial permeability transition pore, a measure of mitochondrial fitness, was significantly decreased in Foxo3 -/- cardiomyocytes. In heart and aorta preparations in mice at 6 and 12 months, Foxo3-/- showed greater extracellular matrix remodeling and assembly and disassembly of aortic elastin network, determinant factors for cardiovascular stiffening with advancing age. We also compared the effects of loss of another transcription factor, Lhx8, highly expressed in oocytes. Lhx8 loss causes germ cell loss that is complete by puberty (21 days of age), but the mechanism of death of oocytes and follicles was poorly understood. We found that in Lhx8 mutant ovaries apoptosis does not seem to be involved in the death of oocytes. Germ cells die by activation of autophagy, involving impairment of vascularization and the formation of a nutrient starvation/oxidative stress microenvironment. These results were summarized in two extensive review articles on the ovarian reserve and genetic and environmental factors that affect it. Finally, we are now conducting in vitro experiments on primary isolated ovarian epithelial cells to assess their contribution to total ovary gene expression and function. In another model study of aging in C. elegans aging, a morphological biomarker was developed that detects multiple discrete sub-populations (or age states); we determined the timing of the transitions between states across the lifespan, and identified gene expression profiles specific for each state.
| Barban, Nicola (see original citation for additional authors) (2016) Genome-wide analysis identifies 12 loci influencing human reproductive behavior. Nat Genet 48:1462-1472 |
| Marongiu, Mara; Deiana, Manila; Marcia, Loredana et al. (2016) Novel action of FOXL2 as mediator of Col1a2 gene autoregulation. Dev Biol 416:200-211 |
| Pelosi, Emanuele; Simonsick, Eleanor; Forabosco, Antonino et al. (2015) Dynamics of the ovarian reserve and impact of genetic and epidemiological factors on age of menopause. Biol Reprod 92:130 |
| Marongiu, Mara; Marcia, Loredana; Pelosi, Emanuele et al. (2015) FOXL2 modulates cartilage, skeletal development and IGF1-dependent growth in mice. BMC Dev Biol 15:27 |
| Lunetta, Kathryn L; Day, Felix R; Sulem, Patrick et al. (2015) Rare coding variants and X-linked loci associated with age at menarche. Nat Commun 6:7756 |
| Pelosi, Emanuele; Forabosco, Antonino; Schlessinger, David (2015) Genetics of the ovarian reserve. Front Genet 6:308 |
| Takasawa, Kei; Kashimada, Kenichi; Pelosi, Emanuele et al. (2014) FOXL2 transcriptionally represses Sf1 expression by antagonizing WT1 during ovarian development in mice. FASEB J 28:2020-8 |
| Yamamizu, Kohei; Schlessinger, David; Ko, Minoru S H (2014) SOX9 accelerates ESC differentiation to three germ layer lineages by repressing SOX2 expression through P21 (WAF1/CIP1). Development 141:4254-66 |
| Pelosi, Emanuele; Omari, Shakib; Michel, Marc et al. (2013) Constitutively active Foxo3 in oocytes preserves ovarian reserve in mice. Nat Commun 4:1843 |
| Kashimada, Kenichi; Svingen, Terje; Feng, Chun-Wei et al. (2011) Antagonistic regulation of Cyp26b1 by transcription factors SOX9/SF1 and FOXL2 during gonadal development in mice. FASEB J 25:3561-9 |
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