We have used the chicken retina as a model for investigating cell cycle regulation and cell fate commitment during central nervous system development. This thesis focuses on the characterization of and commitment to the horizontal cell fate in the retina. Horizontal cells are interneurons that provide intraretinal signal processing prior to information relay to the brain. We have identified molecular markers that selectively distinguish the three subtypes of horizontal cells, previously described in the chicken retina based on morphology. Subtype specific birth-dating revealed that horizontal cell subtypes are generated consecutively by biased progenitors that are sensitive to the inhibitory effects of follistatin. Follistatin stimulates proliferation in progenitors by repressing the differentiation signal of activin. Initially, injection of follistatin led to a decrease in committed horizontal cells but as the inhibitory effect dissipated it resulted in an increased number of horizontal cells. During development committed horizontal cell progenitors migrate to the vitreal side of the retina where they become arrested in G2-phase for approximately two days. When the arrest is overcome the horizontal cell progenitors undergo ectopic mitosis followed by migration to their designated layer. The G2-phase arrest is not triggered or maintained by any of the classic G2-arrest pathways such as DNA damage or stress. Nevertheless, we show that the cyclin B1-Cdk1 complex has a central role in maintaining this G2-phase arrest. Two transcription factors, FoxN4 and Ptf1a, are required for the generation of horizontal cells. We show that these factors are also sufficient to promote horizontal cell fate. Overexpression of FoxN4 and Ptf1a resulted in an overproduction of horizontal- and amacrine cells at the expense of ganglion- and photoreceptor cells. We identified Atoh7, a transcription factor required for the generation of ganglion cells, as a Ptf1a transcriptional target for downregulation. Our data support a common horizontal/amacrine lineage separated from the ganglion/photoreceptor lineage by the action of Ptf1a. In conclusion, these data describe several novel characteristics of horizontal cells enhancing our understanding of neural development and cell fate commitment.

Sutherlandia frutescens is a South African herbal remedy traditionally used for various ailments and lately to improve the overall health in cancer and HIV/AIDS patients. Relatively little is known about the mechanisms of action of the constituents present in S. frutescens. The aim of this project was to examine the in vitro influence of crude ethanolic S. frutescens extracts in human breast adenocarcinoma (MCF-7) and non-tumorigenic breast epithelial (MCF-12A) cells after 48 h of exposure. Dose-dependent studies were conducted on cell numbers and metabolic activity by means of spectrophotometry. Morphological changes were determined with light-, fluorescent- and transmission electron microscopy (TEM). Cell cycle progression and apoptosis were analyzed using flow cytometry. The differential effects of S. frutescens extracts on gene expression levels in both the MCF-7 and MCF-12A cells were conducted utilizing micro array analysis. mTOR kinase activity was measured with an ELISA assay. S. frutescens reduced cell proliferation in both the non-tumorigenic MCF-12A and the tumorigenic MCF-7 cell line in a dose-dependent manner. The tumorigenic MCF-7 cells were more susceptible to S. frutescens treatment compared to the non-tumorigenic MCF-12A cells. Morphological characteristics of apoptosis and autophagy, including cytoplasmic shrinking, membrane blebbing and an increase in autophagic vacuoles were observed in both cell lines with the MCF-7 cells being more susceptible to autophagy and the MCF-12A cells less susceptible to autophagy and apoptotic cell death. TEM confirmed ultrastructural characteristics of autophagy in both cell lines. Flow cytometry revealed a G2/M arrest with no increase in apoptosis in MCF-7 cells and a G2/M arrest with an increase in apoptosis in MCF-12A cells treated with 1.5mg/ml S. frutescens extract. Microarray analyses revealed 325 statistically significantly differentially expressed genes in MCF-7 cells and 1467 genes in MCF-12A cells. The majority of S. frutescens-treated genes were down-regulated when compared to the vehicle-treated control in both cell lines. Several genes involved in DNA replication and repair were differentially expressed in response to S. frutescens exposure. These include Poly (ADP-ribose) polymerase family, member 2 (PARP-2) (down-regulated in both cell lines), PCNA (down-regulated in MCF-7 cells) and growth arrest and DNA-damage-inducible beta (GADD45B) (up¬regulated in MCF-12A cells). This suggests that abrogated expression of genes involved in DNA replication and repair play a role in inducing a G2/M cell cycle arrest in S. frutescens-treated cells. ELISA analysis of the mTOR kinase revealed a decrease in mTOR kinase activity in both cell lines after S. frutescens exposure. Therefore, attenuated mTOR kinase activity as a result of S. frutescens treatment in both cell lines is regarded as a central mediator in inducing autophagy suppressing gene expression and inhibiting ribosome biogenesis. Understanding of in vitro molecular mechanisms of S. frutescens enables researchers to focus on affected cellular mechanisms and identify active compounds with subsequent evaluation as possible candidates for use in anticancer therapy. The current study contributes to the unraveling of the in vitro molecular mechanisms and signal transduction associated with 70% ethanolic S. frutescens extracts, providing a basis for further research on this multi-purpose medicinal plant in Southern Africa. / Dissertation (MSc)--University of Pretoria, 2007. / Physiology / unrestricted

京都大学 / 0048 / 新制・課程博士 / 博士(生命科学) / 甲第22136号 / 生博第423号 / 新制||生||55(附属図書館) / 京都大学大学院生命科学研究科高次生命科学専攻 / (主査)教授 垣塚 彰, 教授 原田 浩, 教授 豊島 文子 / 学位規則第4条第1項該当 / Doctor of Philosophy in Life Sciences / Kyoto University / DFAM

DNA damage is a form of cell stress and injury. Increased systemic DNA damage is related to the pathogenic development of neurodegenerative diseases. Depression occurs in a relatively high percentage of patients suffering from degenerative diseases, for whom antidepressants are often used to relieve depressive symptoms. However, few studies have attempted to elucidate why different groups of antidepressants have similar effects on relieving symptoms of depression. Previously, we demonstrated that neurotoxins N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4)- and camptothecin (CPT) induced the DNA damage response in SH-SY5Y cells, and DSP4 caused cell cycle arrest which was predominately in the S-phase. The present study shows that CPT treatment also resulted in similar cell cycle arrest. Some classic antidepressants could reduce the DNA damage response induced by DSP4 or CPT in SH-SY5Y cells. Cell viability examination demonstrated that both DSP4 and CPT caused cell death, which was prevented by spontaneous administration of some tested antidepressants. Flow cytometric analysis demonstrated that a majority of the tested antidepressants protect cells from being arrested in S-phase. These results suggest that blocking the DNA damage response may be an important pharmacologic characteristic of antidepressants. Exploring the underlying mechanisms may allow for advances in the effort to improve therapeutic strategies for depression appearing in degenerative and psychiatric diseases.

京都大学 / 新制・課程博士 / 博士(医学) / 甲第24511号 / 医博第4953号 / 新制||医||1064(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 伊藤 貴浩, 教授 岩田 想, 教授 河本 宏 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Lung cancer is the leading cause of cancer-related death worldwide. Exclusively found in citrus peels, the inhibitory effects of polymethoxyflavones (PMFs) on 3 human non-small cell lung cancer cells have been investigated. Results showed that monodemethylated PMFs at 5-position potently inhibited lung cancer cells than those of their permethoxylated counterparts. The inhibition of cancer cells caused by monodemethylated PMFs was associated with both extensive cell cycle arrest and apoptosis as a result of modulation of key oncogenic signaling proteins. Treatment with different bioactive compounds in combination may enhance inhibitory effects on lung cancer due to their synergistic interaction among these agents. Results showed that both nobiletin/atorvastatin (NBT/ATST) and tangeretin/atorvastatin (TAN/ATST) co-treatments at low doses exerted strong synergy as confirmed by isobologram analysis, and also produced much stronger inhibitory effects on lung cancer cells in comparison to those produced by NBT, TAN, or ATST alone at higher doses. Flow cytometry analysis showed both NBT/ATST and TAN/ATST co-treatments significantly induced cell cycle arrest and apoptosis, and these molecular events were involved with prenylation of RhoA which subsequently resulted in alteration of key signaling proteins. Supplementation of mevalonate or geranylgeranyl pyrophosphate significantly counteracted the effects caused by NBT/ATST. Inhibitory effects of metabolites of PMFs against lung cancer cells were significantly stronger than those produced by their parental compounds. Treatments of PMFs significantly inhibited lung tumorsphere formation and aldehyde dehydrogenase bright cells implicating the potential utilization of these compounds to target lung cancer stem cells.

20 svenska barn diagnostiseras årligen med barntumören neuroblastom (NB). Läkemedelsresistens och intratumoral heterogenitet försvårar behandlingen och 50-60% av hög-risk NB-patienter drabbas av återfall. Subpopulationer av resistenta celler har identifierats i hög-risk NB-cellinjer, vilket belyser behovet av nya behandlingsalternativ. Dessa celler har visats vara känsliga mot antimetaboliter, som är S-fas specifika läkemedel. Syftet med detta projekt är att utvärdera antimetaboliter som singelbehan-dling eller i kombination med kemoterapi som en ny behandlingsmetod i resistenta NB-celler. Cellvia-bilitiet, cellåterväxt efter långtidsbehandling och cellcykelarrest samt cellcykelns förlopp analyserades på en panel bestående av de fem TP53-muterade ultra-högrisk NB-cellinjerna Kelly, SK-N-DZ, SK-N-AS, BE(2)-C och SK-N-FI. Läkemedlena som utvärderades var kemoterapierna doxorubicin (doxo) och cisplatin samt antimetaboliterna cytarabine (Ara-C), gemcitabine, 5-fluorouracil (5-FU) och hy-droxyurea (HU). Resultaten indikerar att Kelly och SK-N-FI var de cellinjer som var mest känsliga mot kombinationer av doxo tillsammans med antimetaboliter. Detta styrktes ytterligare av analysen av cellcykelarrest som visade att dessa cellinjer föredrar att arrestera i S-fas. Cellinjerna SK-N-DZ, SK-N-AS och BE(2)-C var mindre känsliga mot kombinationsbehandlingarna och visade preferens för att arrestera i andra faser av cellcykeln. Eftersom cellinjerna visade variationer i cellcykelarrest så föreslår vi en utvärdering av trippelkombinationer med läkemedel som är G2/M-fas specifika för att ytterligare eliminera resistenta subpopulationer. / Every year, 20 Swedish children are diagnosed with the pediatric tumor neuroblastoma (NB). Therapy resistance and intratumor heterogeneities complicate treatment of NB and ultimately, 50-60% of high- risk NB patients relapse. Subpopulations of resistant cells have been identified in high-risk NB cell lines, which elucidates the need for novel treatment options. These cells have been suggested to be sensitive to the S-phase specific drugs antimetabolites. The objective of this project is to evaluate antimetabolites as monotherapy and in combination with chemotherapy as a novel treatment option in high-risk NB. Analyses of cell viability, cell regrowth following long-term treatment, and cell cycle progression and mitotic arrest were performed in a panel of five TP53 mutated ultra-high risk NB cell lines, Kelly, SK- N-DZ, SK-N-AS, BE(2)-C, and SK-N-FI. The evaluated drugs were the chemotherapies doxorubicin (doxo) and cisplatin, and the antimetabolites cytarabine (Ara-C), gemcitabine, 5-fluorouracil (5-FU), and hydroxyurea (HU). Obtained results indicated that out of the tested cell lines, Kelly and SK-N-FI are the most sensitive to combinations of doxo with antimetabolites. This was further corroborated via analysis of cell cycle progression and mitotic arrest which demonstrated that Kelly and SK-N-FI have a preference for S-phase arrest. Cell lines SK-N-DZ, SK-N-AS, and BE(2)-C were less sensitive to combination treatments and showed preference for arrest in other phases of the cell cycle. Since resistant cell lines show variations in mitotic arrest, we suggest evaluating triple combinations with targeted treatments for G2/M-phase, in order to further eliminate resistant subpopulations.

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