Research Objective

 

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The lab is interested in several aspects of basic biomedical research.

I.) Germ cells and germ cell tumors.

Germ cells propagate the genetic information from generation to generation. After fertilization, they give rise to the totipotent zygote.  In the developing mammalian embryo, primordial germ cells (PGCs) are specified after induction by Bmps. These PGCs start to migrate and enter the genital ridge where they initiate sexual differentiation and eventually become oogonia or spermatogonia. PGCs express the pluripotency factors Oct3/4 and Nanog, but do not differentiate. This is due to the fact, that PGCs also express of Tfap2c, Prdm14 and Blimp1, which supress somatic differentiation. Using germ cell specific deletion of Tfap2c we demonstrated, that Tfap2c is indispensable for this repression (Weber, et al., 2010). Germ cell tumors arise mostly from developmentally arrested PGCs. In the gonad, they can be detected as dormant precursor lesion, the carcinoma in situ (CIS). With puberty, CIS cells start to proliferate and develop into a seminoma, which remains undifferentiated, or an embryonal carcinoma, which displays features indicative of pluri- or totipotency. Of note, CIS and seminomas are highly similar to PGCs with regard to global gene expression and epigenetic pattern. We showed, that the PGC-specification genes Tfap2c and Blimp1 are expressed in CIS and seminoma but are downregulated in embryonal carcinoma (Pauls et al., 2005, Eckert et al., 2008). Our results suggest, that the cancer/testis antigen PRAME supports the pluripotency network and represses somatic and germ cell differentiation in seminomas (Nettersheim et al 2016a) (commented in Brit. Journal of Cancer)

Using an interspecies transplantation approach, we demonstrated, that molecular crosstalk between tumor and stroma cells influences the fate of the tumor (Nettersheim et al., 2015). Recent investigations revealed that epigenetic drugs (Romidespin and JQ1) have a profound effect on germ cell tumor cell lines suggesting that such drugs could add to the treatment regimen of patients suffering from e.g. cisplatin resistant germ cell tumors (Nettersheim et al. 2016b, Jostes et al. 2016) see press release.

 

From Nettersheim et al., PLOS Genetics, 2015. See also the press release (in german).

II.) Spermatogenesis

Further to topic I., we recently became interested further stages of germ cell development, especially the spermiogenesis. Here, one of the last steps is the replacement of the histones by basic proteins, the protamines resulting in chromatin-hypercondensation. Using CRISPR/Cas9 gene editing in murine oocytes, we established a Protamine-2 deficient mouse strain. While male mice deficient for Protamine-2 are sterile, Prm-2 heterozygous animals are fertile while showing a reduction in Protamine-2 protein levels. These results contradict previous findings leading to the assumption that an species-specific ratio of Protamine proteins is required for sperm to be fertile (Schneider et al. 2016), see also the press release.

III.) Trophoblast Stem Cells and development of the placenta

Short after fertilization, in the early blastocyst lineage segregation results in the separation of multipotent trophectoderm (TE), which represents the extraembryonic trophoblast lineage and the pluripotent inner cell mass (ICM). The extraembryonic lineage and the somatic lineage are separated by a distinct genetic and epigenetic barrier. The TE-fate is specified in direct competition to the pluripotent ICM by expression of Tead4, Cdx2, Gata3 and Tfap2c. We demonstrated, that the cells from the extraembryonic compartment can be converted into fully functional pluripotent embryonic stem cells using the reprogramming factors Oct3/4, Sox2, c-Myc and Klf4 (Kuckenberg, 2011). Further, embryonic stem cells can adopt a trophoblast-like fate after forced expression of Tfap2c (Kuckenberg 2010). Recently, we were able to define the cocktail of transcriptionfactors required to induce full trophoblast stem cell competence in fibroblasts(Kubaczka et al., 2015). This strategy will now be employed to derive the elusive human trophoblast stem cell population.

 

From Kubaczka et al., Cell Stem Cell 2015. See also the press release (in german).

IV.) Hematopoiesis in development and disease

The hematopoetic system is perfectly suited to study the signaling networks required for the orchestrated and fine tuned balance of proliferation versus differentiation. We have developed a transgenic mouse, allowing for the conditional expression of a mutated (autoactivated) cKIT-receptor tyrosine kinase.  We found that Kit transduced signals counteract erythroid maturation by MAPK-dependent modulation of erythropoietin signaling and apoptosis induction in mouse fetal liver (Haas et al 2015). Further, we will utilize this model system to analyze the effect of such cKIT expression in the adult hematopoetic system. See also the press release (in german).

V.) Transgenic technologies

Since our experiments require the establishment of genetically modified mice, our lab features a complete transgenic facility. Using homologous recombination in embryonic stem cells (ESCs), we have established several knock-out (Werling et al 2002, 2003) and knock-in (Jger et al., 2004, Moenning et al., 2009, Holl et al., 2011, Haas et al., 2015) mouse lines. Recently, we have established the production of genome edited mice technology using oocyte injection of the CRISPR-Cas9 system (Schneider et al 2016). We further have the setup to derive ESCs, TSCs and also EG-lines (from PGCs). All these techniques are available to the general scientific community on a collaborative basis. If interested please inquire.

 

References (see Publications page)

 

 

                                           Questions, comments and reprint requests to: schorle@uni-bonn.de 
                                           Last Modified: 01/06/17