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Midkine (MDK) and Pleiotrophin (PTN) are small heparin-binding cytokines with closely related structures. The Drosophila genome harbours two genes encoding members of the MDK/PTN family of proteins, known as miple1 and miple2. We have investigated the role of Miple proteins in vivo, in particular with regard to their proposed role as ligands for the Alk receptor tyrosine kinase (RTK). Here we show that Miple proteins are neither required to drive Alk signaling during Drosophila embryogenesis, nor are they essential for development in the fruit fly. Additionally we show that neither MDK nor PTN can activate hALK in vivo when ectopically co-expressed in the fly. In conclusion, our data suggest that Alk is not activated by MDK/PTN related growth factors Miple1 and Miple 2 in vivo.

Midkine (MDK) and Pleiotrophin (PTN) are small heparin-binding cytokines with closely related structures. The Drosophila genome harbours two genes encoding members of the MDK/PTN family of proteins, known as miple1 and miple2. We have investigated the role of Miple proteins in vivo, in particular with regard to their proposed role as ligands for the Alk receptor tyrosine kinase (RTK). Here we show that Miple proteins are neither required to drive Alk signaling during Drosophila embryogenesis, nor are they essential for development in the fruit fly. Additionally we show that neither MDK nor PTN can activate hALK in vivo when ectopically co-expressed in the fly. In conclusion, our data suggest that Alk is not activated by MDK/PTN related growth factors Miple1 and Miple 2 in vivo.

Midkine (MDK) and Pleiotrophin (PTN) are small heparin-binding cytokines with closely related structures. The Drosophila genome harbours two genes encoding members of the MDK/PTN family of proteins, known as miple1 and miple2. We have investigated the role of Miple proteins in vivo, in particular with regard to their proposed role as ligands for the Alk receptor tyrosine kinase (RTK). Here we show that Miple proteins are neither required to drive Alk signaling during Drosophila embryogenesis, nor are they essential for development in the fruit fly. Additionally we show that neither MDK nor PTN can activate hALK in vivo when ectopically co-expressed in the fly. In conclusion, our data suggest that Alk is not activated by MDK/PTN related growth factors Miple1 and Miple 2 in vivo.

Midkine (MDK) and Pleiotrophin (PTN) are small heparin-binding cytokines with closely related structures. The Drosophila genome harbours two genes encoding members of the MDK/PTN family of proteins, known as miple1 and miple2. We have investigated the role of Miple proteins in vivo, in particular with regard to their proposed role as ligands for the Alk receptor tyrosine kinase (RTK). Here we show that Miple proteins are neither required to drive Alk signaling during Drosophila embryogenesis, nor are they essential for development in the fruit fly. Additionally we show that neither MDK nor PTN can activate hALK in vivo when ectopically co-expressed in the fly. In conclusion, our data suggest that Alk is not activated by MDK/PTN related growth factors Miple1 and Miple 2 in vivo.

Midkine (MDK) and Pleiotrophin (PTN) are small heparin-binding cytokines with closely related structures. The Drosophila genome harbours two genes encoding members of the MDK/PTN family of proteins, known as miple1 and miple2. We have investigated the role of Miple proteins in vivo, in particular with regard to their proposed role as ligands for the Alk receptor tyrosine kinase (RTK). Here we show that Miple proteins are neither required to drive Alk signaling during Drosophila embryogenesis, nor are they essential for development in the fruit fly. Additionally we show that neither MDK nor PTN can activate hALK in vivo when ectopically co-expressed in the fly. In conclusion, our data suggest that Alk is not activated by MDK/PTN related growth factors Miple1 and Miple 2 in vivo.

Polycomb group (PcG) proteins are required to maintain a stable repression of the homeotic genes during Drosophila development. Mutants in the PcG gene Supressor of zeste 12 (Su(z)12) exhibit strong homeotic transformations caused by widespread misexpression of several homeotic genes in embryos and larvae. Su(z)12 has also been suggested to be involved in position effect variegation and in regulation of the white gene expression in combination with zeste. To elucidate whether SU(Z)12 has any such direct functions we investigated the binding pattern to polytene chromosomes and compared the localization to other proteins. We found that SU(Z)12 binds to about 90 specific eukaryotic sites, however, not the white locus. We also find staining at the chromocenter and the nucleolus. The binding along chromosome arms is mostly in interbands and these sites correlate precisely with those of Enhancer-of-zeste and other components of the PRC2 silencing complex. This implies that SU(Z)12 mainly exists in complex with PRC2. Comparisons with other PcG protein-binding patterns reveal extensive overlap. However, SU(Z)12 binding sites and histone 3 trimethylated lysine 27 residues (3meK27 H3) do not correlate that well. Still, we show that Su(z)12 is essential for tri-methylation of the lysine 27 residue of histone H3 in vivo, and that overexpression of SU(Z)12 in somatic clones results in higher levels of histone methylation, indicating that SU(Z)12 is rate limiting for the enzymatic activity of PRC2. In addition, we analyzed the binding pattern of Heterochromatin Protein 1 (HP1) and found that SU(Z)12 and HP1 do not co-localize.

Polycomb group (PcG) proteins are required to maintain stable repression of the homeotic genes and others throughout development. The PcG proteins ESC and E(Z) are present in a prominent 600-kDa complex as well as in a number of higher-molecular-mass complexes. Here we identify and characterize a 1-MDa ESC/E(Z) complex that is distinguished from the 600-kDa complex by the presence of the PcG protein Polycomblike (PCL) and the histone deacetylase RPD3. In addition, the 1-MDa complex shares with the 600-kDa complex the histone binding protein p55 and the PcG protein SU(Z)12. Coimmunoprecipitation assays performed on embryo extracts and gel filtration column fractions indicate that, during embryogenesis E(Z), SU(Z)12, and p55 are present in all ESC complexes, while PCL and RPD3 are associated with ESC, E(Z), SU(Z)12, and p55 only in the 1-MDa complex. Glutathione transferase pulldown assays demonstrate that RPD3 binds directly to PCL via the conserved PHD fingers of PCL and the N terminus of RPD3. PCL and E(Z) colocalize virtually completely on polytene chromosomes and are associated with a subset of RPD3 sites. As previously shown for E(Z) and RPD3, PCL and SU(Z)12 are also recruited to the insertion site of a minimal Ubx Polycomb response element transgene in vivo. Consistent with these biochemical and cytological results, Rpd3 mutations enhance the phenotypes of Pcl mutants, further indicating that RPD3 is required for PcG silencing and possibly for PCL function. These results suggest that there may be multiple ESC/E(Z) complexes with distinct functions in vivo.

Polycomb Group (PcG) genes are known to encode a large chromatin-associated family of proteins which are involved in genomic regulation of many cellular processes. Su(z)12 is a key component in PcG silencing. It is needed for three levels of methylation of histone 3 lysine 27 in vivo in Drosophila. Here, we report that Su(z)12 may exist in different isoforms and that these isoforms are spatially and temporally regulated. The biological function of the Su(z)12-A and -B isoforms seems to be very different. For instance the transgenic Su(z)12-B and the human homolog SUZ12, but not Su(z)12-A, rescue Su(z)12 mutants. Furthermore, transgenic flies over-expressing Su(z)12-B show typical homeotic transformation phenotypes, while over-expression of Su(z)12-A does not. However, the two isoforms appears to be able to substitute for each other in some aspects. During larval and pupal stages, Su(z)12-A seems to play the main role.

Polycomb Group (PcG) genes are known to encode a large chromatin-associated family of proteins which are involved in genomic regulation of many cellular processes. Su(z)12 is a key component in PcG silencing. It is needed for three levels of methylation of histone 3 lysine 27 in vivo in Drosophila. Here, we report that Su(z)12 may exist in different isoforms and that these isoforms are spatially and temporally regulated. The biological function of the Su(z)12-A and -B isoforms seems to be very different. For instance the transgenic Su(z)12-B and the human homolog SUZ12, but not Su(z)12-A, rescue Su(z)12 mutants. Furthermore, transgenic flies over-expressing Su(z)12-B show typical homeotic transformation phenotypes, while over-expression of Su(z)12-A does not. However, the two isoforms appears to be able to substitute for each other in some aspects. During larval and pupal stages, Su(z)12-A seems to play the main role.