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.

Overexpression of human wild-type FUS causes progressive motor neuron degeneration in an age- and dose-dependent fashion.

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are relentlessly progressive neurodegenerative disorders with overlapping clinical, genetic and pathological features. Cytoplasmic inclusions of fused in sarcoma (FUS) are the hallmark of several forms of FTLD and ALS patients with mutations in the FUS gene. FUS is a multifunctional, predominantly nuclear, DNA and RNA binding protein. Here, we report that transgenic mice overexpressing wild-type human FUS develop an aggressive phenotype with an early onset tremor followed by progressive hind limb paralysis and death by 12 weeks in homozygous animals. Large motor neurons were lost from the spinal cord accompanied by neurophysiological evidence of denervation and focal muscle atrophy. Surviving motor neurons in the spinal cord had greatly increased cytoplasmic expression of FUS, with globular and skein-like FUS-positive and ubiquitin-negative inclusions associated with astroglial and microglial reactivity. Cytoplasmic FUS inclusions were also detected in the brain of transgenic mice without apparent neuronal loss and little astroglial or microglial activation. Hemizygous FUS overexpressing mice showed no evidence of a motor phenotype or pathology. These findings recapitulate several pathological features seen in human ALS and FTLD patients, and suggest that overexpression of wild-type FUS in vulnerable neurons may be one of the root causes of disease. Furthermore, these mice will provide a new model to study disease mechanism, and test therapies.

Conserved cis-regulatory regions in a large genomic landscape control SHH and BMP-regulated Gremlin1 expression in mouse limb buds.

BACKGROUND: Mouse limb bud is a prime model to study the regulatory interactions that control vertebrate organogenesis. Major aspects of limb bud development are controlled by feedback loops that define a self-regulatory signalling system. The SHH/GREM1/AER-FGF feedback loop forms the core of this signalling system that operates between the posterior mesenchymal organiser and the ectodermal signalling centre. The BMP antagonist Gremlin1 (GREM1) is a critical node in this system, whose dynamic expression is controlled by BMP, SHH, and FGF signalling and key to normal progression of limb bud development. Previous analysis identified a distant cis-regulatory landscape within the neighbouring Formin1 (Fmn1) locus that is required for Grem1 expression, reminiscent of the genomic landscapes controlling HoxD and Shh expression in limb buds. RESULTS: Three highly conserved regions (HMCO1-3) were identified within the previously defined critical genomic region and tested for their ability to regulate Grem1 expression in mouse limb buds. Using a combination of BAC and conventional transgenic approaches, a 9 kb region located ~70 kb downstream of the Grem1 transcription unit was identified. This region, termed Grem1 Regulatory Sequence 1 (GRS1), is able to recapitulate major aspects of Grem1 expression, as it drives expression of a LacZ reporter into the posterior and, to a lesser extent, in the distal-anterior mesenchyme. Crossing the GRS1 transgene into embryos with alterations in the SHH and BMP pathways established that GRS1 depends on SHH and is modulated by BMP signalling, i.e. integrates inputs from these pathways. Chromatin immunoprecipitation revealed interaction of endogenous GLI3 proteins with the core cis-regulatory elements in the GRS1 region. As GLI3 is a mediator of SHH signal transduction, these results indicated that SHH directly controls Grem1 expression through the GRS1 region. Finally, all cis-regulatory regions within the Grem1 genomic landscape locate to the DNAse I hypersensitive sites identified in this genomic region by the ENCODE consortium. CONCLUSIONS: This study establishes that distant cis-regulatory regions scattered through a larger genomic landscape control the highly dynamic expression of Grem1, which is key to normal progression of mouse limb bud development.

Generation of chimeras by microinjection.

Since the technique of introducing a targeted mutation ('gene targeting') into the mouse genome was published almost 20 years ago (Cell 51:503-512, 1987), the number of mouse mutants (mouse models) is increasing, especially after the advent of the full mouse genomic sequence in 2002 and the human genomic sequences in 2003 that reveals more and more large stretches of similarity between the two species at the genomic level. This chapter describes the tools and the experimental route of targeted manipulation by microinjection in the mouse using targeted embryonic stem cells (ES cells).The techniques have become standardized over recent years (Nature 309:255-256, 1984; Practical Approach. IRL Press, Oxford, 254 pp, 1987; Science 240:1468-1475, 1988; Practical Approach. IRL Press, Oxford, New York, 1993; Transgenic Animal Technology: A Laboratory Handbook, 2nd edition. Academic Press, San Deigo, 2002; Manipulating the Mouse Embryo - A Laboratory Manual, 3rd edition. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 2003) and basically two methods have been used to generate chimeric mice that transmit the mutation of interest via the ES cell genome to the offspring:Microinjection of ES cells into blastocyst or morula stage embryos (this chapter) or aggregation of ES cells with morula stage embryos (see Chapter 14 ).Microinjection of ES cells into the blastocoel (cavity) of the blastocyst stage embryo and also morula injections using micropipettes driven by micromanipulators require sophisticated manual skills and an expensive phase contrast inverted microscope. Although most commonly used, it is quite expensive to establish this technique in a laboratory, in particular, if piezo- or laser- supported routes come into play. Although the establishment of germ-line potent ES cells was first published in 1981 (Proc Natl Acad Sci U S A 78:7634-7636, 1981; Nature 292:154-156, 1981), up to now it has not been possible to establish germ-line transmitting ES cells from any other mammalian species, not even from rat which is closely related, nor was it possible to introduce targeted mutations by different means to the germ-line of mammals. After 20 years, the mouse is still the only mammalian species where mutations can be introduced in a targeted manner and therefore it is very important to many fields in biology, like immunology, neurobiology, and developmental biology to study gene function and disease. Through means of introducing even point mutations to single relevant molecules of a signal transduction pathway in order to study regulation of cellular and physiological processes in complex organisms in a tissue specific or inducible manner (conditional gene targeting, (Cell 73:1155-1164, 1993; Science 265:103-106, 1994)), more recently the field has expanded exponentially.

Generation of chimeras by morula aggregation.

This chapter describes the tools and the experimental route of targeted manipulation by aggregation in the mouse using targeted embryonic stem cells (ES cells). Instead of injecting ES cells into the blastocoel of a diploid blastocyst-stage embryo (3.5 dpc) ES cells can be brought together with diploid morula-stage embryos (2.5 dpc). The zona pellucida of the embryo needs to be removed and one or two embryos (sandwich aggregation) are put together with ES cells into an indentation well of a cell culture grade dish overnight for aggregation. This can be performed manually using a stereomicroscope and does not require any special training or expensive instrumentation.The next day, the embryo would have developed into a blastocyst in vitro and can be transferred to a pseudopregnant female mouse (see Chapter 15 ).The use of tetraploid embryos generated by electrofusion will lead to entirely ES cell-derived fetuses.

Surgical techniques for the generation of mutant mice.

The previous two chapters have described the generation of chimeric embryos by blastocyst microinjection and morula aggregation. This chapter describes the reimplantation of these embryos into pseudopregnant female recipient mice (foster mice) in order for the embryos to develop to term. Four different surgical techniques will be described in detail.The transfer of blastocyst-stage embryos back into the uterus is most commonly used for chimeric embryos generated by microinjection or aggregation, or for rederivation purposes when strains are transferred to a clean environment. Fertilized oocytes manipulated by pronuclear microinjection or two-cell-stage embryos are reintroduced to the infundibulum of the oviduct of pseudopregnant female mice.To generate pseudopregnant females, they need to be mated to sterile male mice. These males can be either generated by vasectomy of stud males or naturally sterile males can be used. Two different techniques for the vasectomy are shown: the vas deferens is accessed through an incision in the scrotal sac or through an abdominal incision.

Murine inner cell mass-derived lineages depend on Sall4 function.

Sall4 is a mammalian Spalt transcription factor expressed by cells of the early embryo and germ cells, an expression pattern similar to that of both Oct4 and Sox2, which play essential roles during early murine development. We show that the activity of Sall4 is cell-autonomously required for the development of the epiblast and primitive endoderm from the inner cell mass. Furthermore, no embryonic or extraembryonic endoderm stem cell lines could be established from Sall4-deficient blastocysts. In contrast, neither the development of the trophoblast lineage nor the ability to generate trophoblast cell lines from murine blastocysts was impaired in the absence of Sall4. These data establish Sall4 as an essential transcription factor required for the early development of inner cell mass-derived cell lineages.

Mouse limb deformity mutations disrupt a global control region within the large regulatory landscape required for Gremlin expression.

The mouse limb deformity (ld) mutations cause limb malformations by disrupting epithelial-mesenchymal signaling between the polarizing region and the apical ectodermal ridge. Formin was proposed as the relevant gene because three of the five ld alleles disrupt its C-terminal domain. In contrast, our studies establish that the two other ld alleles directly disrupt the neighboring Gremlin gene, corroborating the requirement of this BMP antagonist for limb morphogenesis. Further doubts concerning an involvement of Formin in the ld limb phenotype are cast, as a targeted mutation removing the C-terminal Formin domain by frame shift does not affect embryogenesis. In contrast, the deletion of the corresponding genomic region reproduces the ld limb phenotype and is allelic to mutations in Gremlin. We resolve these conflicting results by identifying a cis-regulatory region within the deletion that is required for Gremlin activation in the limb bud mesenchyme. This distant cis-regulatory region within Formin is also altered by three of the ld mutations. Therefore, the ld limb bud patterning defects are not caused by disruption of Formin, but by alteration of a global control region (GCR) required for Gremlin transcription. Our studies reveal the large genomic landscape harboring this GCR, which is required for tissue-specific coexpression of two structurally and functionally unrelated genes.