FGF9, activin and TGFß promote testicular characteristics in an XX gonad organ culture model.

Testis development is dependent on the key sex-determining factors SRY and SOX9, which activate the essential ligand FGF9. Although FGF9 plays a central role in testis development, it is unable to induce testis formation on its own. However, other growth factors, including activins and TGFßs, also present testis during testis formation. In this study, we investigated the potential of FGF9 combined with activin and TGFß to induce testis development in cultured XX gonads. Our data demonstrated differing individual and combined abilities of FGF9, activin and TGFß to promote supporting cell proliferation, Sertoli cell development and male germ line differentiation in cultured XX gonads. FGF9 promoted proliferation of supporting cells in XX foetal gonads at rates similar to those observed in vivo during testis cord formation in XY gonads but was insufficient to initiate testis development. However, when FGF9, activin and TGFß were combined, aspects of testicular development were induced, including the expression of Sox9, morphological reorganisation of the gonad and deposition of laminin around germ cells. Enhancing ß-catenin activity diminished the testis-promoting activities of the combined growth factors. The male promoting activity of FGF9 and the combined growth factors directly or indirectly extended to the germ line, in which a mixed phenotype was observed. FGF9 and the combined growth factors promoted male germ line development, including mitotic arrest, but expression of pluripotency genes was maintained, rather than being repressed. Together, our data provide evidence that combined signalling by FGF9, activin and TGFß can induce testicular characteristics in XX gonads.

WNT/ß-catenin and p27/FOXL2 differentially regulate supporting cell proliferation in the developing ovary.

Sexual development is initiated through differentiation of testicular Sertoli cells or ovarian granulosa cells. Although these supporting cells are considered to develop from common bipotential precursors, recent evidence suggests that distinct supporting cell populations are present in the ovary, with one providing granulosa cells of the medullary follicles and the other providing granulosa cells of the cortical follicles, the latter of which support lifelong fertility. Here, we demonstrate that XX fetal gonads contain GATA4 expressing supporting cells that either enter mitotic arrest, or remain proliferative. Blocking WNT signalling reduces XX supporting cell proliferation, while stabilising ß-catenin signalling promotes proliferation, indicating that the renewal of pre-granulosa cells is dependent on WNT/ß-catenin signalling in the proliferative supporting cell population. In contrast, XX supporting cells express p27 and FOXL2 and are maintained in mitotic arrest. Although FOXL2 is required for maintaining high levels of p27 expression, it is dispensable for entry and maintenance of mitotic arrest in XX supporting cells. Combined our data suggest that both medullary and cortical precursors arise from a common GATA4 expressing cell type. In addition, this work indicates that a balance between supporting cell self-renewal and differentiation is maintained in the developing ovary by relative WNT/ß-catenin and p27/FOXL2 activities. This study provides significant new insights into the origin and formation of ovarian follicles and evidence supporting a common fetal origin of medullary and cortical granulosa cells.

Testis development, fertility, and survival in Ethanolamine kinase 2-deficient mice.

Ethanolamine kinase 2 (Eki2) was previously isolated from a differential expression screen designed to identify candidate genes involved in testis development and differentiation. In mouse, Eki2 is specifically up-regulated in Sertoli cells of the developing testis at the time of sex determination. Based on this expression profile, Eki2 was considered a good candidate testis-determining gene. To investigate a possible role of Eki2 in testis development, we have generated a mouse with targeted disruption of the Eki2 gene by using an EGFP replacement strategy. No abnormalities were detected in the Eki2-deficient mice with regard to embryonic and adult testis morphology, differentiation, function, or fertility. Furthermore, no significant differences were observed in litter sizes, pup mortality rates, or distribution of the sexes among the offspring. Ethanolamine kinases are involved in the biosynthesis of phosphatidylethanolamine, a major membrane phospholipid. Expression analysis indicates that the absence of an apparent phenotype in the Eki2-deficient mice may be due to compensation by Eki2-family members or the activation of an alternative pathway to generate phosphatidylethanolamine. Expression of EGFP in this mouse model enabled the isolation of gonad cell populations, providing a useful resource from which to obtain relatively pure early steroidogenic cells for further studies.

Cbl-b is a negative regulator of inflammatory cytokines produced by IgE-activated mast cells.

c-Cbl and Cbl-b E3 ubiquitin ligases are abundantly expressed in hemopoietic cells where they negatively regulate the activity and levels of many cell surface receptors and associated signaling molecules. By comparing bone marrow-derived mast cells from c-Cbl and Cbl-b-deficient mice it has recently been shown that Cbl-b is the dominant family member for negatively regulating signaling responses from high-affinity IgE receptors. In this study, we suggest that a possible reason for the greater enhancement of IgE receptor signaling in Cbl-b-deficient mice is the relatively higher levels of Cbl-b protein over c-Cbl in mast cells compared with other hemopoietic cells. We also directly compare mast cells from c-Cbl and Cbl-b-deficient mice and find that loss of Cbl-b, but not c-Cbl, increases cell growth, retards receptor internalization, and causes the sustained tyrosine phosphorylation of Syk and its substrates. However, loss of Cbl-b does not enhance the activation of ERK or Akt, nor does it promote a greater calcium response. Furthermore, loss of Cbl-b or c-Cbl does not increase levels of the Syk or Lyn protein tyrosine kinases. Most notable, however, is the extremely large increase in the production of proinflammatory cytokines TNF-alpha, IL-6, and MCP-1 by Cbl-b(-/-) mast cells compared with levels produced by c-Cbl(-/-) or wild-type cells. This marked induction, which appears to be restricted to these three cytokines, is dependent on IgE receptor activation and correlates with enhanced IkappaB kinase phosphorylation. Thus, Cbl-b functions as a potent negative regulator of cytokines that promote allergic and inflammatory reactions.

In vivo fate-tracing studies using the Scl stem cell enhancer: embryonic hematopoietic stem cells significantly contribute to adult hematopoiesis.

Evidence for the lineage relationship between embryonic and adult hematopoietic stem cells (HSCs) in the mouse is primarily indirect. In order to study this relationship in a direct manner, we expressed the tamoxifen-inducible Cre-ER(T) recombinase under the control of the stem cell leukemia (Scl) stem-cell enhancer in transgenic mice (HSC-SCL-Cre-ER(T)). To determine functionality, HSC-SCL-Cre-ER(T) transgenics were bred with Cre reporter mice. Flow cytometric and transplantation studies revealed tamoxifen-dependent recombination occurring in more than 90% of adult long-term HSCs, whereas the targeted proportion within mature progenitor populations was significantly lower. Moreover, the transgene was able to irreversibly tag embryonic HSCs on days 10 and 11 of gestation. These cells contributed to bone marrow hematopoiesis 5 months later. In order to investigate whether the de novo HSC generation is completed during embryogenesis, HSC-SCL-Cre-ER(T)-marked fetal liver cells were transplanted into adult recipients. Strikingly, the proportion of marked cells within the transplanted and the in vivo-remaining HSC compartment was not different, implying that no further HSC generation occurred during late fetal and neonatal stages of development. These data demonstrate for the first time the direct lineage relationship between midgestation embryonic and adult HSCs in the mouse. Additionally, the HSC-SCL-Cre-ER(T) mice will provide a valuable tool to achieve temporally controlled genetic manipulation of HSCs.

Genetically tagging endothelial cells in vivo: bone marrow-derived cells do not contribute to tumor endothelium.

Tumor growth is dependent in part on "neoangiogenesis." Functional involvement of bone marrow (BM)-derived cells in this process has been demonstrated. However, it remains controversial as to whether tumor endothelium itself is BM derived. Here we sought to address this issue with an endothelial-specific, inducible transgenic model. We generated Cretransgenic mice (endothelial-SCL-Cre-ER(T)) using the tamoxifen-inducible Cre-ER(T) recombinase driven by the 5' endothelial enhancer of the stem cell leukemia (SCL) locus. These mice were intercrossed with Cre reporter strains in which beta-galactosidase (LacZ) or enhanced yellow fluorescent protein (EYFP) are expressed upon Cre-mediated recombination. After tamoxifen administration, endothelial LacZ staining was observed in embryonic and adult tissues. Cre-mediated recombination was also observed in newly generated tumor endothelium. In adult BM cells we could only detect trace amounts of recombination by flow cytometry. Subsequently, BM from endothelial-SCL-Cre-ER(T);R26R mice was transplanted into irradiated recipients. When tumors were grown in recipient mice, which received tamoxifen, no tumor LacZ staining was detected. However, when tumors were grown in endothelial-SCL-Cre-ER(T);R26R mice 3 weeks after the cessation of tamoxifen treatment, there was widespread endothelial LacZ staining present. Thus, this genetic model strongly suggests that BM cells do not contribute to tumor endothelium and demonstrates the lineage relation between pre-existing endothelium and newly generated tumor endothelial cells.

Interleukin-3 binding to the murine betaIL-3 and human betac receptors involves functional epitopes formed by domains 1 and 4 of different protein chains.

Interleukin-3 (IL-3) is a cytokine produced by activated T-cells and mast cells that is active on a broad range of hematopoietic cells and in the nervous system and appears to be important in several chronic inflammatory diseases. In this study, alanine substitutions were used to investigate the role of residues of the human beta-common (hbetac) receptor and the murine IL-3-specific (beta(IL-3)) receptor in IL-3 binding. We show that the domain 1 residues, Tyr(15) and Phe(79), of the hbetac receptor are important for high affinity IL-3 binding and receptor activation as shown previously for the related cytokines, interleukin-5 and granulocyte-macrophage colony-stimulating factor, which also signal through this receptor subunit. From the x-ray structure of hbetac, it is clear that the domain 1 residues cooperate with domain 4 residues to form a novel ligand-binding interface involving the two protein chains of the intertwined homodimer receptor. We demonstrate by ultracentrifugation that the beta(IL-3) receptor is also a homodimer. Its high sequence homology with hbetac suggests that their structures are homologous, and we identified an analogous binding interface in beta(IL-3) for direct IL-3 binding to the high affinity binding site in hbetac. Tyr(21) (A-B loop), Phe(85), and Asn(87) (E-F loop) of domain 1; Ile(320) of the interdomain loop; and Tyr(348) (B'-C' loop) and Tyr(401) (F'-G' loop) of domain 4 were shown to have critical individual roles and Arg(84) and Tyr(317) major secondary roles in direct murine IL-3 binding to the beta(IL-3)receptor. Most surprising, none of the key residues for direct IL-3 binding were critical for high affinity binding in the presence of the murine IL-3 alpha receptor, indicating a fundamentally different mechanism of high affinity binding to that used by hbetac.