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Sandra Fehsenfeld

Publications and source records attributed to Sandra Fehsenfeld.

5 recordsLinked to original sources
PubMed2004

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.

Animals↗
PubMed2003

Alpha complementation in the Cre recombinase enzyme.

The Cre-loxP system is increasingly exploited for spatial and temporal gene inactivation. Here we present a novel approach to achieve this goal of selective gene inactivation. Following the model of alpha complementation in the beta-galactosidase enzyme, where the enzyme is split into independent polypeptides which are able to associate and maintain the enzymatic activity, we divided the Cre recombinase into two independent polypeptides (one containing the NH(2) terminus (alpha) and a second one containing the COOH-terminus (beta)). Individually, the two polypeptides have no detectable activity. However, when coexpressed the polypeptides are able to associate, giving rise to Cre enzymatic activity, which optimally is as high as 30% of that seen with wildtype Cre recombinase in vitro. We present this strategy as a modification of the traditional Cre-loxP system, which could be used to obtain a highly specific recombination pattern by expressing the two halves under the control of separate promoters.

Amino Acid Sequence↗
PubMed2002

ER-based double iCre fusion protein allows partial recombination in forebrain.

Here we describe the generation of a new tamoxifen-inducible double Cre fusion protein generated by fusing two ERT2 domains onto both ends of the iCre recombinase (a codon improved Cre recombinase). This Cre fusion protein (ERiCreER) had a twofold increased activity in cell culture assays than the previously described MerCreMer Cre double fusion protein. ERiCreER was targeted to the brain by placing it under the control of the promoter from the CamKIIalpha gene using a 170 kb BAC. The fusion protein was detected in hippocampus, cortex, striatum, thalamus, and hypothalamus but not in cerebellum. The ERiCreER was cytoplasmatic in the absence of tamoxifen and translocated into the nucleus upon tamoxifen administration. The activity of the ERiCreER was tested in vivo by mating the CamKIIalpha ERiCreER transgenic line with mice harbouring exon 10 of the CREB gene flanked by two LoxP sites. In the absence of tamoxifen, no background activity was detected in mice older than 6 months. After tamoxifen administration, most if not all of the ERiCreER fusion protein translocated from the cytoplasm to the nucleus; however, only 5-10% of the "floxed" CREB allele was recombined. Recombination was also visualised at the cellular level by following the upregulation of the CREM protein, which corresponds precisely with CREB loss/recombination. Unlike in other tissues (Sohal et al., 2001; Tannour-Louet et al., 2002), it appears that in brain, although ERiCreER can bind tamoxifen, the Cre-recombinase cannot be fully activated.

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