Apoptotic cells can induce compensatory cell proliferation through the JNK and the Wingless signaling pathways

In many metazoans, damaged and potentially dangerous cells are rapidly eliminated by apoptosis. In Drosophila, this is often compensated for by extraproliferation of neighboring cells, which allows the organism to tolerate considerable cell death without compromising development and body size. Despite its importance, the mechanistic basis of such compensatory proliferation remains poorly understood. Here, we show that apoptotic cells express the secretory factors wingless (wg) and decapentaplegic (dpp). When cells undergoing apoptosis were kept alive with the caspase inhibitor p35, excessive nonautonomous cell proliferation was observed. Significantly, wg signaling is necessary and, at least in some cells, also sufficient for mitogenesis under these conditions. Finally, we provide evidence that the DIAP1 antagonists reaper and hid can activate the JNK pathway and that this pathway is required for inducing wg and cell proliferation. These findings support a model where apoptotic cells activate signaling cascades for compensatory proliferation.     

Fine mapping of the circling (cir) gene on the distal portion of mouse chromosome 9

Circling mice manifest profound deafness, head-tossing, and bi-directional circling behavior, which they inherit in autosomal recessive manner. Histologic examination of the inner ear reveals abnormalities of the region around the organ of Corti, spiral ganglion neurons, and outer hair cells. A genetic linkage map was constructed for an intraspecific backcross between cir and C57BL/6J mice. The cir gene was mapped to a region between D9Mit116/D9Mit15 and D9Mit38 on mouse chromosome (Chr) 9. Estimated distances between cir and D9Mit116, and between cir and D9Mit38 were 0.70 +/- 0.40 and 0.23 +/- 0.23 cM, respectively. Order of the markers was defined as follows: centromere - D9Mit182 - D9Mit51/D9Mit79/D9Mit310 - D9Mit212/D184 - D9Mit116/D9Mit15 - cir - D9Mit38 - D9Mit20 - D9Mit243 - D9Mit16 - D9Mit55/D9Mit125 - D9Mit281. On the basis of genetic mapping, we constructed a yeast artificial chromosome (YAC) contig across the cir region. The cir gene is located between the lactotransferrin (ltf) and microtubule-associated protein (map4) genes. The distal portion of mouse Chr 9 encompassing the cir region is homologous with human chromosome 3p21, which contains the Deafness, form B: Autosomal Recessive Deafness (DFNB6) locus. Therefore, the circling mouse is a potential animal model for DFNB6 deafness in humans.     

Tetrachloroethylene, trichloroethylene, and chlorinated phenols induce toluene-o-xylene monooxygenase activity in Pseudomonas stutzeri OX1

Pseudomonas stutzeri OX1 naphthalene-oxidation activity is induced 3.0-fold by tetrachloroethylene (PCE) and 3.1-fold by trichloroethylene (TCE) at 100 microM. With the mutant P. stutzeri M1, which does not express toluene-o-xylene monooxygenase (ToMO, product of the tou operon), no naphthalene-oxidation activity induction by PCE and TCE was found; hence, PCE and TCE induce ToMO of P. stutzeri OX1. The chlorinated phenols 2-, 3-, and 4-chlorophenol induced ToMO expression 0.58-, 0.23- and 0.37-fold, respectively, compared to the direct inducer of the pathway, o-cresol. Using P. putida PaW340 (pPP4062, pFP3028), which has the tou promoter fused to the reporter catechol-2,3-dioxygenase, and the regulator gene touR, it was determined that the tou promoter was induced directly 5.7-, 7.1-, and 5.1-fold for 2-, 3-, and 4-chlorophenol, respectively (compared to an 8.8-fold induction with o-cresol). In addition, it was found that TCE and PCE do not directly induce the tou pathway and that components other than the tou structural and regulatory genes are necessary for induction. Gas chromatography results also showed that 100 microM TCE induced its own degradation (8-9%) in 16 h in P. stutzeri OX1, and all of the stoichiometric chloride from the degraded TCE was detected in solution.     

Epidermal growth factor receptor regulates osteoclast differentiation and survival through cross-talking with RANK signaling

The epidermal growth factor receptor (EGFR) functions in various cellular physiological processes such as proliferation, differentiation, and motility. Although recent studies have reported that EGFR signaling is involved in osteoclast recruitment and formation, the molecular mechanism of EGFR signaling for the regulation of osteoclastogenesis remains unclear. We investigated the role of the EGFR in osteoclast differentiation and survival and show that the expression of the EGFR was highly up-regulated by receptor activator of nuclear factor-kappaB ligand (RANKL) during osteoclast differentiation. EGFR-specific tyrosine kinase inhibitors and EGFR knockdown blocked RANKL-dependent osteoclast formation, suggesting that EGFR signaling plays an important role in osteoclastogenesis. EGFR inhibition impaired the RANKL-mediated activation of osteoclastogenic signaling pathways, including c-Jun N-terminal kinase (JNK), NF-kappaB, and Akt/protein kinase B (PKB). In addition, EGFR inhibition in differentiated osteoclasts caused apoptosis through caspase activation. Inhibition of the phosphoinositide-3 kinase (PI3K)-Akt/PKB pathway and subsequent activation of BAD and caspases-9 and -3 may be responsible for the EGFR inhibition-induced apoptosis. The EGFR physically associated with receptor activator of nuclear factor-kappaB (RANK) and Grb2-associated binder 2 (Gab2). Moreover, RANKL transactivated EGFR. These data indicate that EGFR regulates RANKL-activated signaling pathways by cross-talking with RANK, suggesting that the EGFR may play a crucial role as a RANK downstream signal and/or a novel type of RANK co-receptor in osteoclast differentiation and survival.     

A TGF‐β‐induced gene, βig‐h3, is crucial for the apoptotic disappearance of the medial edge epithelium in palate fusion

TGF‐β3, TβR‐I, and TGF‐β‐activated Smad2 has been suggested to be a series of signaling molecules for secondary palate fusion. In this article, we show that a gene induced by TGF‐β, βig‐h3, is coincidentally expressed with TGF‐β3 in medial edge epithelial (MEE) cells undergoing apoptosis during normal palatal fusion. βig‐h3 was also highly expressed in the areas of post‐weaning mammary gland cells and developing phalangeal joints in which TGF‐β3 or BMP‐4‐induced apoptosis occurs, respectively. Blocking of βig‐h3 expression in E12.5 embryos with antisense oligodeoxynucleotides (ODN) resulted in cleft of the secondary palate in 84% of the treated mice that were born. Moreover, the antisense ODN treatment resulted in a failure of apoptosis in the MEE between palatal shelves in physical contact in organ culture. We conclude that βig‐h3 expression in the MEE is stimulated by TGF‐β3, causes cell death, and consequently results in complete fusion of the apposed palatal shelves. J. Cell. Biochem. 107: 818–825, 2009. © 2009 Wiley‐Liss, Inc.     

Retroviral Infection of Murine Embryonic Stem Cell Derived Embryoid Body Cells for Analysis of Hematopoietic Differentiation

Embryonic stem cells (ESCs) are an outstanding model for elucidating the molecular mechanisms of cellular differentiation. They are especially useful for investigating the development of early hematopoietic progenitor cells (HPCs). Gene expression in ESCs can be manipulated by several techniques that allow the role for individual molecules in development to be determined. One difficulty is that expression of specific genes often has different phenotypic effects dependent on their temporal expression. This problem can be circumvented by the generation of ESCs that inducibly express a gene of interest using technology such as the doxycycline-inducible transgene system. However, generation of these inducible cell lines is costly and time consuming. Described here is a method for disaggregating ESC-derived embryoid bodies (EBs) into single cell suspensions, retrovirally infecting the cell suspensions, and then reforming the EBs by hanging drop. Downstream differentiation is then evaluated by flow cytometry. Using this protocol, it was demonstrated that exogenous expression of a microRNA gene at the beginning of ESC differentiation blocks HPC generation. However, when expressed in EB derived cells after nascent mesoderm is produced, the microRNA gene enhances hematopoietic differentiation. This method is useful for investigating the role of genes after specific germ layer tissue is derived.