Yoshihiro Takihara

Lack of the Polycomb-group gene rae28 causes maturation arrest at the early B-cell developmental stage

The rae28 gene (rae28) is a murine homologue of the Drosophila polyhomeotic gene, which is a member of the Polycomb-group genes. In this study, we examined the role of rae28 in lymphocyte development. Because homozygous rae28-deficient (rae28-/-) mice died in the perinatal period, we examined lymphocyte development by generating chimeric mice reconstituted with green fluorescence protein-labeled mutant fetal liver cells as well as in in vitro culture systems. We further examined RAE28 expression by reverse transcriptase polymerase chain reaction assay in human leukemic cells with B-lineage acute lymphoblastic leukemia (ALL). Severe B-cell maturation arrest was observed in rae28-/- between pro- and pre-B lymphocyte stages. B-cell development was also delayed in heterozygous neonates. Furthermore, interleukin-7-dependent colony-forming ability was impaired not only in homozygous lymphocytes but also in heterozygotes. Its human homologue, RAE28, is located on chromosome 12p13, which frequently is associated with chromosomal abnormalities and loss of heterozygosity in patients with hematologic malignancies. To determine whether a link exists between RAE28 and leukemia, we examined RAE28 expression in leukemic cells from pediatric patients with B-lineage ALL. RAE28 expression was not detected in four B-cell precursor ALL cases of a total of 43 examined, although RAE28 is normally expressed constitutively during the process of B-cell maturation as assessed in isolated cell populations. rae28 plays an important role in the early B-cell developmental stage in a gene dosage-dependent manner. Furthermore, the human RAE28 locus may provide a candidate gene causing the molecular pathogenesis of childhood B-cell precursor ALL.

The human homolog of Sex comb on midleg (SCMH1) maps to chromosome 1p34.

Polycomb group genes were originally identified in Drosophila as repressors required to maintain the silenced state of homeotic loci. About ten Polycomb group genes have been cloned in Drosophila, and mammalian homologs have been identified for most of these. Here, we isolate cDNAs encoding two isoforms of a human homolog of Drosophila Sex comb on midleg (Scm), named Sex comb on midleg homolog-1 (SCMH1). Overall, SCMH1 has 94% identity to its mouse counterpart Scmh1, and 41% identity to Scm, and contains two 1(3)mbt domains, and the SPM domain that are characteristic of Scm. SCMH1 is widely expressed in adult tissues, and maps to chromosome 1p34.

Expression of vinexin α in the dorsal half of the eye and in the cardiac outflow tract and atrioventricular canal

Vinexin, a recently identified cytoskeletal protein, contains three SH3 domains and plays important roles in regulation of cytoskeletal organization and signal transduction. Using whole-mount in situ hybridization, we showed here that expression of vinexin alpha, the longer vinexin transcript, is strictly regulated, although the shorter transcript, vinexin beta, is expressed almost ubiquitously during embryonic development in mice. Expression of vinexin alpha was limited to within part of the eye and heart in 10.5 dpc embryos. Analysis of cryosections of 10.5 dpc embryos showed that vinexin alpha was expressed in a dorsal half of the retinal pigment epithelium and in the outflow tract and atrioventricular canal of the heart. Furthermore, we also found that vinexin alpha was expressed in the gonad and in a ventral part of the pons of 12.5 dpc embryos. These results indicated that the expression of vinexin alpha is strictly regulated in a temporally and spatially restricted manner.

Regulation of Hoxb3 expression in the hindbrain and pharyngeal arches by rae28, a member of the mammalian Polycomb group of genes

During animal development, Hox genes are expressed in characteristic, spatially restricted patterns and specify regional identities along the anterior-posterior (A-P) axis. Polycomb group (PcG) proteins in Drosophila repress Hox expression and maintain the expression patterns during development. Mice deficient for homologues of the Drosophila PcG genes, such as M33, bmi1, mel18, rae28 and eed, show altered Hox expression patterns. In this study, we examined the time course of Hoxb3 expression during late gastrulation and early segmentation of rae28-deficient mice. Hoxb3 was expressed ectopically in pharyngeal arch and hindbrain from embryonic day (E) 9.5 and 10.5, respectively. The anterior boundary of ectopic expression in the hindbrain extended gradually in the rostral direction as development proceeded from E10.5 to E12.5. Expression of kreisler and Krox20, which function as positive regulators of Hoxb3 expression, was not affected in rae28-deficient embryos. Analysis of a neural crest marker, p75, in rae28-deficient mice revealed that the neural crest cells begin to ectopically express Hoxb3 after leaving the hindbrain. Our results suggest that rae28 is not required for the establishment but maintenance of Hoxb3 expression.

One of the retinoic acid‐inducible cDNA clones in mouse embryonal carcinoma F9 cells encodes a novel isoenzyme of fructose 1,6‐bisphosphatase

Rae‐30, one of the retinoic acid (RA)‐inducible cDNA clones in mouse embryonal carcinoma F9 cells, was sequenced and the deduced RAE‐30 protein showed about a 70% homology to mammalian fructose 1,6‐bisphosphatase (EC 3.1.3.11) (FBPase), in comparison to over 85% homology observed among the previously documented rat liver, pig kidney and human leukemic HL‐60 cell FBPases. The Rae‐30 mRNAs were not detected in various tissues of adult mice, including the liver and kidney, but were detected in a placenta and predominantly in the intestine of adult mice. These findings indicate that the Rae‐30 cDNA encodes a novel isoenzyme of FBPase, which is likely to be involved in early differentiation in mammalian cells.

Isolation of a cDNA clone encoding mouse 3-hydroxyacyl CoA dehydrogenase ☆

Rae-38, a cDNA clone isolated from mouse embryonal carcinoma F9 cells, was sequenced, and the deduced RAE-38 protein showed about 86% homology to pig 3-hydroxyacyl CoA dehydrogenase (HCDH; EC 1.1.1.35). This clone can be used to elucidate the regulatory mechanism of HCDH gene expression in mammals.

Sequence‐specific DNA binding activity in the RAE28 protein, a mouse homologue of the Drosophila polyhomeotic protein

The rae28 gene, a mouse homologue of the Drosophila polyhomeotic gene, is involved in the maintenance of the transcriptional repression states of Hox genes. In this study we synthesized the glutathione S transferase‐RAE28 (GST‐RAE28) fusion protein and examined sequence‐specific DNA binding activity in the RAE28 protein by using the selected and amplified binding site method. After five rounds of enrichment, the eluted DNAs were amplified, cloned and sequenced. The sequences of individual oligonucleotides included the following consensus sequences; 5′‐ACCA‐3′, 5′‐ACCCA‐3′, 5′‐CTATCA‐3′ and 5′‐TGCC‐3′. The oligonucleotides including these consensus sequences were show to have significant affinity with the GST‐RAE28 fusion protein. The RAE28 protein was recently shown to form multimeric protein complexes with other members of mouse Pc‐G proteins in the nucleus. These findings strongly suggest that the RAE28 protein constitutes a sequence‐specific DNA binding domain in multimeric Pc‐G protein complexes.