The Homothorax homeoprotein activates the nuclear localization of another homeoprotein, extradenticle, and suppresses eye development in Drosophila

The Extradenticle (Exd) protein in Drosophila acts as a cofactor to homeotic proteins. Its nuclear localization is regulated. We report the cloning of the Drosophila homothorax (hth) gene, a homolog of the mouse Meis1 proto-oncogene that has a homeobox related to that of exd. Comparison with Meis1 finds two regions of high homology: a novel MH domain and the homeodomain. In imaginal discs, hth expression coincides with nuclear Exd. hth and exd also have virtually identical, mutant clonal phenotypes in adults. These results suggest that hth and exd function in the same pathway. We show that hth acts upstream of exd and is required and sufficient for Exd protein nuclear localization. We also show that hth and exd are both negative regulators of eye development; their mutant clones caused ectopic eye formation. Targeted expression of hth, but not of exd, in the eye disc abolished eye development completely. We suggest that hth acts with exd to delimit the eye field and prevent inappropriate eye development.     

Control of antennal versus leg development in Drosophila

During the evolution of insects from a millipede-like ancestor, the Hox genes are thought to have promoted the diversification of originally identical body structures. In Drosophila melanogaster, antennae and legs are homologous structures that differ from each other as a result of the Hox gene Antennapedia (Antp), which promotes leg identities by repressing unknown antennal-determining genes. Here we present four lines of evidence that identify extradenticle (exd) and homothorax (hth) as antennal-determining genes. First, removing the function of exd or hth, which is required for the nuclear localization of Exd protein, transforms the antenna into leg; such transformations occur without activation of Antp. Second, hth is expressed and Exd is nuclear in most antennal cells, whereas both are restricted to proximal cells of the leg. Third, Antp is a repressor of hth. Fourth, ectopic expression of Meis1, a murine hth homologue, can trigger antennal development elsewhere in the fly. Taken together, these data indicate that hth is an antennal selector gene, and that Antp promotes leg development by repressing hth and consequently nuclear Exd.     

Bright light: a countermeasure for jet lag?

We report the cDNA cloning, partial genomic organization, and expression pattern of Stra10, a novel retinoic acid-inducible gene in P19 embryonal carcinoma cells. Four murine cDNA isoforms have been isolated, which are likely to result from alternative splicing. The predicted protein sequences exhibit approximately 85% identity with the Pbx-related Meis1 homeobox gene products, which are involved in myeloid leukemia in BXH-2 mice, and one of the Stra10 isoforms corresponds to the recently published Meis2 sequence (Nakamura et al. [1996] Oncogene 13:2235-2242). The Meis2 homeodomain is identical to that of Meis1, and is most closely related to those of the Pbx/TGIF homeobox gene products. By in situ hybridization analysis, we show that the Meis2 gene displays spatially restricted expression patterns in the developing nervous system, limbs, face, and in various viscera. In adult mice, Meis2 is mainly expressed in the brain and female genital tract, with a different distribution of the alternative splice forms in these organs.     

AbdB-like Hox proteins stabilize DNA binding by the Meis1 homeodomain proteins

Recent studies show that Hox homeodomain proteins from paralog groups 1 to 10 gain DNA binding specificity and affinity through cooperative binding with the divergent homeodomain protein Pbx1. However, the AbdB-like Hox proteins from paralogs 11, 12, and 13 do not interact with Pbx1a, raising the possibility of different protein partners. The Meis1 homeobox gene has 44% identity to Pbx within the homeodomain and was identified as a common site of viral integration in myeloid leukemias arising in BXH-2 mice. These integrations result in constitutive activation of Meis1. Furthermore, the Hoxa-9 gene is frequently activated by viral integration in the same BXH-2 leukemias, suggesting a biological synergy between these two distinct classes of homeodomain proteins in causing malignant transformation. We now show that the Hoxa-9 protein physically interacts with Meis1 proteins by forming heterodimeric binding complexes on a DNA target containing a Meis1 site (TGACAG) and an AbdB-like Hox site (TTTTACGAC). Hox proteins from the other AbdB-like paralogs, Hoxa-10, Hoxa-11, Hoxd-12, and Hoxb-13, also form DNA binding complexes with Meis1b, while Hox proteins from other paralogs do not appear to interact with Meis1 proteins. DNA binding complexes formed by Meis1 with Hox proteins dissociate much more slowly than DNA complexes with Meis1 alone, suggesting that Hox proteins stabilize the interactions of Meis1 proteins with their DNA targets.     

Medea is a Drosophila Smad4 homolog that is differentially required to potentiate DPP responses

Mothers against dpp (Mad) mediates Decapentaplegic (DPP) signaling throughout Drosophila development. Here we demonstrate that Medea encodes a MAD-related protein that functions in DPP signaling. MEDEA is most similar to mammalian Smad4 and forms heteromeric complexes with MAD. Like dpp, Medea is essential for embryonic dorsal/ventral patterning. However, Mad is essential in the germline for oogenesis whereas Medea is dispensable. In the wing primordium, loss of Medea most severely affects regions receiving low DPP signal. MEDEA is localized in the cytoplasm, is not regulated by phosphorylation, and requires physical association with MAD for nuclear translocation. Furthermore, inactivating MEDEA mutations prevent nuclear translocation either by preventing interaction with MAD or by trapping MAD/MEDEA complexes in the cytosol. Thus MAD-mediated nuclear translocation is essential for MEDEA function. Together these data show that, while MAD is essential for mediating all DPP signals, heteromeric MAD/MEDEA complexes function to modify or enhance DPP responses. We propose that this provides a general model for Smad4/MEDEA function in signaling by the TGF-beta family.     

Aberrant dipeptidyl peptidase IV (DPP IV/CD26) expression in human hepatocellular carcinoma

The HOX11/TCL3 homeobox gene was identified at the breakpoint region in pediatric T-cell acute lymphoblastic leukemia harboring 10q24 chromosomal translocations. We previously reported that primary murine bone marrow cells transduced ex vivo with a recombinant HOX11-containing retrovirus, MSCV-HOX11, gave rise to cell lines at high frequency having characteristics of early myeloid cells. Cell lines were also established from the bone marrow and spleen of transplant recipients sacrificed 5 months after engraftment with MSCV-HOX11-transduced bone marrow cells. These latter lines, which exhibited a more differentiated myelomonocytic phenotype, harbored proviruses encoding a smaller HOX11 protein. None of the mice that received HOX11-expressing bone marrow cells or myeloid cell lines developed leukemia during 6-month observation periods. Here, we report that two bone marrow transplant recipients eventually developed T-cell acute lymphoblastic leukemia-like malignancies at 7 and 12 months posttransplant, indicating that progression to a fully malignant state required additional mutations. One tumor synthesized full-length HOX11 whereas the other expressed the smaller version of the protein. The smaller HOX11 protein suffered a carboxyl-terminal truncation. We subsequently constructed MSCV-based retroviral vectors expressing deleted forms of HOX11 and identified an amino-terminal region that was dispensible for generation of myeloid cell lines having a similar phenotype as those induced by full-length HOX11. We thus conclude that regions near the amino and carboxyl termini of HOX11 are not essential for transforming function, nor do they appear to determine the lineage or stage of differentiation of the target cell for transformation.     

Modulation of homeobox B6 and B9 genes expression in human leukemia cell lines during myelomonocytic differentiation

Homeobox genes (HOX) may have a regulatory function in the differentiation process of hematopoiesis. We examined the change of HOX B6 and HOX B9 mRNA expressions during the in vitro differentiation of four myeloid leukemia cell lines because HOX B6 may be involved closely in myeloid differentiation. HL-60, NB4, NKM-1 and NOMO-1 were established from acute leukemia of M2, M3, M2 and M5 subtype of the French-American-British classification, respectively. All-trans retinoic acid (ATRA), TPA, and G-CSF were used as differentiation inducers. Each cell line was cultured with each inducer and total RNA was isolated on day 1, 2, 3, or 5. HOX B mRNA was detected by Northern blotting and RT-PCR methods. HOX B6 and HOX B9 mRNAs were constitutively expressed in NB4, NKM-1 and NOMO-1, but were expressed at very low levels in HL-60. HOX B6 and HOX B9 mRNAs were also expressed in fresh acute myelocytic leukemia blasts. HOX B6 mRNA expression in HL-60, NB4, and NKM-1 cultured with ATRA increased on day 3 and decreased on day 5. HOX B6 mRNA expression in NB4 and NKM-1 cultured with TPA decreased on day 3. HOX B9 mRNA expression displayed changes similar to those of HOX B6 mRNA in NB4 and NKM-1. These results indicate that myeloid leukemia cell lines express HOX B6 and HOX B9, and that their respective mRNA expressions in NB4 and HL-60 increase at a mid stage of myeloid differentiation by ATRA induction and then decrease during a late stage. HOX B6 mRNA expression decreased in monocytoid differentiation by TPA induction in NB4, HL-60 and NKM-1. HOX B6 antisense-oligonucleotide inhibited the proliferation of NB4 and NKM-1. These results suggest that HOX B gene expression is related to simultaneous activation of cellular proliferation and differentiation in leukemic cells.     

Interplay of signal mediators of decapentaplegic (Dpp): molecular characterization of mothers against dpp, Medea, and daughters against dpp

Decapentaplegic (Dpp) plays an essential role in Drosophila development, and analyses of the Dpp signaling pathway have contributed greatly to understanding of the actions of the TGF-beta superfamily. Intracellular signaling of the TGF-beta superfamily is mediated by Smad proteins, which are now grouped into three classes. Two Smads have been identified in Drosophila. Mothers against dpp (Mad) is a pathway-specific Smad, whereas Daughters against dpp (Dad) is an inhibitory Smad genetically shown to antagonize Dpp signaling. Here we report the identification of a common mediator Smad in Drosophila, which is closely related to human Smad4. Mad forms a heteromeric complex with Drosophila Smad4 (Medea) upon phosphorylation by Thick veins (Tkv), a type I receptor for Dpp. Dad stably associates with Tkv and thereby inhibits Tkv-induced Mad phosphorylation. Dad also blocks hetero-oligomerization and nuclear translocation of Mad. We also show that Mad exists as a monomer in the absence of Tkv stimulation. Tkv induces homo-oligomerization of Mad, and Dad inhibits this step. Finally, we propose a model for Dpp signaling by Drosophila Smad proteins.     

Effects of tenoxicam on neutrophil chemotaxis in rheumatoid arthritis and healthy controls

Craniosynostosis (CRS) is frequently seen in the del(7p) syndrome, and the gene for this cranial anomaly (CRS1) has been assigned to 7p21. We present a 3-year-old boy with CRS involving the sagittal and coronal sutures, who had a de novo and apparently balanced translocation, t(6;7)(q16.2;p15.3). Southern blot analysis of several loci on 7p14-->pter showed that the patient was heterozygous for HOX1I and IL6, possibly homozygous for D7S149, but hemizygous for D7S135 with a loss of the paternal allele. These findings suggest the localization of a candidate gene for CRS1 to be on 7p15.3 in the close proximity to the D7S135 locus.     

Acute toxicity of several organophosphorous insecticides and protection by cholinergic antagonists and 2-PAM on Artemia salina larvae

Western blot analysis and indirect immunofluorescence microscopy were used to evaluate the fate of the aryl-hydrocarbon receptor (AhR) and aryl-hydrocarbon receptor nuclear translocator (Arnt) protein in culture cell models exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In wild-type (WT) murine Hepa-1c1c7 cells, AhR protein was depleted by 85% after 4 hr of TCDD treatment as measured in total cell lysates. In contrast, the concentration of Arnt protein was unaffected by TCDD treatment in WT cells. Analysis of the AhR with immunofluorescence microscopy revealed that nuclear translocation of the liganded AhR preceded its depletion from cells. AhR protein was depleted from Hepa-1 type I variants (that contain a concentration of AhR that is 10% of WT) with a similar time course and to the same maximal level observed in WT cells (85%). The EC50 for AhR depletion in Hepa-1 cells was 39 pm TCDD and correspond to the EC50 for induction of P4501A1 protein. Murine embryonic fibroblasts (NIH-3T3), rat aortic smooth muscle cells (A7), and murine skeletal muscle cells (C2C12) all exhibited >90% depletion of the AhR after 2-4 hr of TCDD treatment. Arnt concentration was not affected by TCDD in these cell lines. These results indicate that the liganded AhR is rapidly depleted within the nuclear compartment of hepatic and nonhepatic cells in a manner independent of the Arnt protein.     

Murine Otx1 and Drosophila otd genes share conserved genetic functions required in invertebrate and vertebrate brain development

Despite the obvious differences in anatomy between invertebrate and vertebrate brains, several genes involved in the development of both brain types belong to the same family and share similarities in expression patterns. Drosophila orthodenticle (otd) and murine Otx genes exemplify this, both in terms of expression patterns and mutant phenotypes. In contrast, sequence comparison of OTD and OTX gene products indicates that homology is restricted to the homeodomain suggesting that protein divergence outside the homeodomain might account for functional differences acquired during brain evolution. In order to gain insight into this possibility, we replaced the murine Otx1 gene with a Drosophila otd cDNA. Strikingly, epilepsy and corticogenesis defects due to the absence of Otx1 were fully rescued in homozygous otd mice. A partial rescue was also observed for the impairments of mesencephalon, eye and lachrymal gland. In contrast, defects of the inner ear were not improved suggesting a vertebrate Otx1-specific function involved in morphogenesis of this structure. Furthermore, otd, like Otx1, was able to cooperate genetically with Otx2 in brain patterning, although with reduced efficiency. These data favour an extended functional conservation between Drosophila otd and murine Otx1 genes and support the idea that conserved genetic functions required in mammalian brain development evolved in a primitive ancestor of both flies and mice.     

M32, a murine homologue of Drosophila heterochromatin protein 1 (HP1), localises to euchromatin within interphase nuclei and is largely excluded from constitutive heterochromatin

Mice possess two structural homologues of Drosophila HP1, termed M31 and M32 (Singh et al., 1991). We have previously shown that an M31-specific monoclonal antibody (MoAb), MAC 353, localises to constitutive heterochromatin (Wreggett et al., 1994). Here we report that a MoAb raised against the M32 protein (MAC 385) recognises a 22-kDa protein in murine nuclear extracts and that M32 is distributed in a fine-grain "speckled" pattern within interphase nuclei. M32 is also largely excluded from the large masses of constitutive heterochromatin that are labelled by MAC 353.