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Heinz Arnheiter

Publications and source records attributed to Heinz Arnheiter.

13 recordsLinked to original sources
PubMed2006

Interspecies difference in the regulation of melanocyte development by SOX10 and MITF.

There is increasing indication that interspecific phenotypic differences result from variations in gene-regulatory interactions. Here we provide evidence that mice differ from zebrafish in the way they use homologous key components to regulate pigment cell differentiation. In both zebrafish and mice, one transcription factor, SOX10, controls the expression of another, MITF (microphthalmia-associated transcription factor), which in turn regulates a set of genes critical for pigment cell development and pigmentation. Mutations in either Sox10 or Mitf impair pigment cell development. In Sox10-mutant zebrafish, experimentally induced expression of Mitf fully rescues pigmentation. Using lineage-directed gene transfer, we show that, in the mouse, Mitf can rescue Sox10-mutant precursor cells only partially. In fact, retrovirally mediated, Sox10-independent Mitf expression in mouse melanoblasts leads to cell survival and expression of a number of pigment biosynthetic genes but does not lead to expression of tyrosinase, the rate-limiting pigment gene which critically depends on both Sox10 and Mitf. Hence, compared with fish, mice have evolved a regulation of tyrosinase expression that includes feed-forward loops between Sox10 and tyrosinase regulatory regions. The results may help to explain how some embryos, such as zebrafish, can achieve rapid pigmentation after fertilization, whereas others, such as mice, become pigmented only several days after birth.

Animals↗
PubMed2006

The other pigment cell: specification and development of the pigmented epithelium of the vertebrate eye.

Vertebrate retinal pigment epithelium (RPE) cells are derived from the multipotent optic neuroepithelium, develop in close proximity to the retina, and are indispensible for eye organogenesis and vision. Recent advances in our understanding of RPE development provide evidence for how critical signaling factors operating in dorso-ventral and distal-proximal gradients interact with key transcription factors to specify three distinct domains in the budding optic neuroepithelium: the distal future retina, the proximal future optic stalk/optic nerve, and the dorsal future RPE. Concomitantly with domain specification, the eye primordium progresses from a vesicle to a cup, RPE pigmentation extends towards the ventral side, and the future ciliary body and iris form from the margin zone between RPE and retina. While much has been learned about the molecular networks controlling RPE cell specification, key questions concerning the cell proliferative parameters in RPE and the subsequent morphogenetic events still need to be addressed in greater detail.

Animals↗
PubMed2005

Sumoylation modulates transcriptional activity of MITF in a promoter-specific manner.

The microphthalmia transcription factor MITF plays important roles in several cell lineages including retinal and neural crest-derived pigment cells. Previous reports have shown that besides its regulation at the transcriptional level, MITF is also regulated post-translationally by phosphorylation and ubiquitination which affect the protein's activity and stability. Here we demonstrate that in addition, MITF is modified in melanoma cells by small ubiquitin-like modifier (SUMO). In vitro assays further show that sumoylation occurs at two lysine residues, K182 and K316, and depends on SUMO E1 activating enzyme (SAE I/SAE II) and E2 conjugating enzyme (Ubc9). Interestingly, MITF with double lysine 182/316 to arginine mutations, although displaying normal DNA binding, stability and nuclear localization, shows a substantial increase in the transcriptional stimulation of promoters containing multiple but not single MITF binding sites. MITF containing the double lysine-to-arginine substitution also shows enhanced cooperation with Sox10 on the Dct promoter. We conclude that SUMO modification of MITF regulates the protein's transcriptional activity especially with respect to synergistic activation. The results suggest that sumoylation plays a significant role among the multiple mechanisms that regulate MITF during development and in adulthood.

Amino Acid Sequence↗
PubMed2005

MITF and cell proliferation: the role of alternative splice forms.

Recent studies show that the melanocyte transcription factor MITF not only activates differentiation genes but also genes involved in the regulation of the cell cycle, suggesting that it provides a link between cell proliferation and differentiation. MITF, however, comes in a variety of splice isoforms with potentially distinct biological activities. In particular, there are two isoforms, (-) and (+) MITF, that differ in six residues located upstream of the DNA binding basic domain and show slight differences in the efficiency with which they bind to target DNA. Using in vitro BrdU incorporation assays and FACS analysis in transiently transfected cells, we show that (+) MITF has a strong inhibitory effect on DNA synthesis while (-) MITF has none or only a mild one. The strong inhibitory activity of (+) MITF is not influenced by a number of mutations that modulate MITF's transcriptional activities and is independent of the protein's carboxyl terminus but dependent on its aminoterminus. A further dissection of the molecule points to the importance of an aminoterminal serine, serine-73, which in both isoforms is phosphorylated to comparable degrees. The results suggest that one or several aminoterminal domains cooperate with the alternatively spliced hexapeptide to render MITF anti-proliferative in a way that does not depend on direct E box binding.

Active Transport, Cell Nucleus↗
PubMed2004

Chx10 repression of Mitf is required for the maintenance of mammalian neuroretinal identity.

During vertebrate eye development, the cells of the optic vesicle (OV) become either neuroretinal progenitors expressing the transcription factor Chx10, or retinal pigment epithelium (RPE) progenitors expressing the transcription factor Mitf. Chx10 mutations lead to microphthalmia and impaired neuroretinal proliferation. Mitf mutants have a dorsal RPE-to-neuroretinal phenotypic transformation, indicating that Mitf is a determinant of RPE identity. We report here that Mitf is expressed ectopically in the Chx10(or-J/or-J) neuroretina (NR), demonstrating that Chx10 normally represses the neuroretinal expression of Mitf. The ectopic expression of Mitf in the Chx10(or-J/or-J) NR deflects it towards an RPE-like identity; this phenotype results not from a failure of neuroretinal specification, but from a partial loss of neuroretinal maintenance. Using Chx10 and Mitf transgenic and mutant mice, we have identified an antagonistic interaction between Chx10 and Mitf in regulating retinal cell identity. FGF (fibroblast growth factor) exposure in a developing OV has also been shown to repress Mitf expression. We demonstrate that the repression of Mitf by FGF is Chx10 dependent, indicating that FGF, Chx10 and Mitf are components of a pathway that determines and maintains the identity of the NR.

Animals↗
PubMed2004

Cell-autonomous and cell non-autonomous signaling through endothelin receptor B during melanocyte development.

The endothelin receptor B gene (Ednrb) encodes a G-protein-coupled receptor that is expressed in a variety of cell types and is specifically required for the development of neural crest-derived melanocytes and enteric ganglia. In humans, mutations in this gene are associated with Waardenburg-Shah syndrome, a disorder characterized by pigmentation defects, deafness and megacolon. To address the question of whether melanocyte development depends entirely on a cell-autonomous action of Ednrb, we performed a series of tissue recombination experiments in vitro, using neural crest cell cultures from mouse embryos carrying a novel Ednrb-null allele characterized by the insertion of a lacZ marker gene. The results show that Ednrb is not required for the generation of early neural crest-derived melanoblasts but is required for the expression of the differentiation marker tyrosinase. Tyrosinase expression can be rescued, however, by the addition of Ednrb wild-type neural tubes. These Ednrb wild-type neural tubes need not be capable of generating melanocytes themselves, but must be capable of providing KIT ligand, the cognate ligand for the tyrosine kinase receptor KIT. In fact, soluble KIT ligand is sufficient to induce tyrosinase expression in Ednrb-deficient cultures. Nevertheless, these tyrosinase-expressing, Ednrb-deficient cells do not develop to terminally differentiated, pigmented melanocytes. Pigmentation can be induced, however, by treatment with tetradecanoyl phorbol acetate, which mimics EDNRB signaling, but not by treatment with endothelin 1, which stimulates the paralogous receptor EDNRA. The results suggest that Ednrb plays a significant role during melanocyte differentiation and effects melanocyte development by both cell non-autonomous and cell-autonomous signaling mechanisms.

Alleles↗
PubMed2004

'Educated' dendritic cells act as messengers from memory to naive T helper cells.

Ingested antigens lead to the generation of effector T cells that secrete interleukin 4 (IL-4) rather than interferon-gamma (IFN-gamma) and are capable of influencing naive T cells in their immediate environment to do the same. Using chimeric mice generated by aggregation of two genotypically different embryos, we found that the conversion of a naive T cell occurs only if it can interact with the same antigen-presenting cell, although not necessarily the same antigen, as the effector T cell. Using a two-step culture system in vitro, we found that antigen-presenting dendritic cells can act as 'temporal bridges' to relay information from orally immunized memory CD4 T cells to naive CD4 T cells. The orally immunized T cells use IL-4 and IL-10 (but not CD40 ligand) to 'educate' dendritic cells, which in turn induce naive T cells to produce the same cytokines as those produced by the orally immunized memory T cells.

Animals↗
PubMed2004

The G12 family of heterotrimeric G proteins and Rho GTPase mediate Sonic hedgehog signalling.

Sonic hedgehog (Shh) is a secreted morphogen crucial for cell fate decision, cellular proliferation, and patterning during vertebrate development. The intracellular Shh signalling is transduced by Smoothened (Smo), a seven-transmembrane spanning protein that belongs to the G-protein coupled receptor family. Among four families of Galpha subunits, Galphai has been thought to be responsible for transducing Shh signalling, while several lines of evidence indicated that other signalling pathways may be involved. We found that the G12 family of heterotrimeric G proteins and the small GTPase RhoA are involved in Shh/Smo-mediated cellular responses, including stimulation of target gene promoter and inhibition of neurite outgrowth of neuroblastoma cells. We also found that the G12/RhoA pathway is responsible for Smo-induced nuclear import of GLI3 which is thought to transduce Shh signals to nucleus. Furthermore, misexpression of a G12-specific GTPase-activating protein in rat neural tubes leads to pertubation of motor neurone and interneurone development, mimicking the effects of decreased Shh signalling. These results show that Shh signalling is mediated in part by activating G12 family coupled signalling pathways. The participation of RhoA, a pivotal molecular switch in many signal transduction pathways, may help explain how Shh can trigger a variety of cellular responses.

Animals↗
PubMed2004

The basic helix-loop-helix leucine zipper transcription factor Mitf is conserved in Drosophila and functions in eye development.

The MITF protein is a member of the MYC family of basic helix-loop-helix leucine zipper (bHLH-Zip) transcription factors and is most closely related to the TFE3, TFEC, and TFEB proteins. In the mouse, MITF is required for the development of several different cell types, including the retinal pigment epithelial (RPE) cells of the eye. In Mitf mutant mice, the presumptive RPE cells hyperproliferate, abnormally express the retinal transcriptional regulator Pax6, and form an ectopic neural retina. Here we report the structure of the Mitf gene in Drosophila and demonstrate expression during embryonic development and in the eye-antennal imaginal disc. In vitro, transcriptional regulation by Drosophila Mitf, like its mouse counterpart, is modified by the Eyeless (Drosophila Pax6) transcription factor. In vivo, targeted expression of wild-type or dominant-negative Drosophila Mitf results in developmental abnormalities reminiscent of Mitf function in mouse eye development. Our results suggest that the Mitf gene is the original member of the Mitf-Tfe subfamily of bHLH-Zip proteins and that its developmental function is at least partially conserved between vertebrates and invertebrates. These findings further support the common origin of the vertebrate and invertebrate eyes.

Alleles↗
PubMed2003

Interallelic complementation at the mouse Mitf locus.

Mutations at the mouse microphthalmia locus (Mitf) affect the development of different cell types, including melanocytes, retinal pigment epithelial cells of the eye, and osteoclasts. The MITF protein is a member of the MYC supergene family of basic-helix-loop-helix-leucine-zipper (bHLHZip) transcription factors and is known to regulate the expression of cell-specific target genes by binding DNA as homodimer or as heterodimer with related proteins. The many mutations isolated at the locus have different effects on the phenotype and can be arranged in an allelic series in which the phenotypes range from near normal to white microphthalmic animals with osteopetrosis. Previous investigations have shown that certain combinations of Mitf alleles complement each other, resulting in a phenotype more normal than that of each homozygote alone. Here we analyze this interallelic complementation in detail and show that it is limited to one particular allele, Mitf(Mi-white) (Mitf(Mi-wh)), a mutation affecting the DNA-binding domain. Both loss- and gain-of-function mutations are complemented, as are other Mitf mutations affecting the DNA-binding domain. Furthermore, this behavior is not restricted to particular cell types: Both eye development and coat color phenotypes are complemented. Our analysis suggests that Mitf(Mi-wh)-associated interallelic complementation is due to the unique biochemical nature of this mutation.

Animals↗
PubMed2003

The concerted action of Meox homeobox genes is required upstream of genetic pathways essential for the formation, patterning and differentiation of somites.

The paraxial mesoderm of the somites of the vertebrate embryo contains the precursors of the axial skeleton, skeletal muscles and dermis. The Meox1 and Meox2 homeobox genes are expressed in the somites and their derivatives during embryogenesis. Mice homozygous for a null mutation in Meox1 display relatively mild defects in sclerotome derived vertebral and rib bones, whereas absence of Meox2 function leads to defective differentiation and morphogenesis of the limb muscles. By contrast, mice carrying null mutations for both Meox genes display a dramatic and wide-ranging synthetic phenotype associated with extremely disrupted somite morphogenesis, patterning and differentiation. Mutant animals lack an axial skeleton and skeletal muscles are severely deficient. Our results demonstrate that Meox1 and Meox2 genes function together and upstream of several genetic hierarchies that are required for the development of somites. In particular, our studies place Meox gene function upstream of Pax genes in the regulation of chondrogenic and myogenic differentiation of paraxial mesoderm.

Animals↗
PubMed2002

Mitf and Tfe3, two members of the Mitf-Tfe family of bHLH-Zip transcription factors, have important but functionally redundant roles in osteoclast development.

The Mitf-Tfe family of basic helix-loop-helix-leucine zipper (bHLH-Zip) transcription factors encodes four family members: Mitf, Tfe3, Tfeb, and Tfec. In vitro, each protein in the family can bind DNA as a homo- or heterodimer with other family members. Mutational studies in mice have shown that Mitf is essential for melanocyte and eye development, whereas Tfeb is required for placental vascularization. Here, we uncover a role for Tfe3 in osteoclast development, a role that is functionally redundant with Mitf. Although osteoclasts seem normal in Mitf or Tfe3 null mice, the combined loss of the two genes results in severe osteopetrosis. We also show that Tfec mutant mice are phenotypically normal, and that the Tfec mutation does not alter the phenotype of Mitf, Tfeb, or Tfe3 mutant mice. Surprisingly, our studies failed to identify any phenotypic overlap between the different Mitf-Tfe mutations. These results suggest that heterodimeric interactions are not essential for Mitf-Tfe function in contrast to other bHLH-Zip families like Myc/Max/Mad, where heterodimeric interactions seem to be essential.

Alleles↗