Revealing genes associated with vitellogenesis in the liver of the zebrafish (Danio rerio) by transcriptome profiling.

BACKGROUND: In oviparous vertebrates, including fish, vitellogenesis consists of highly regulated pathways involving 17beta-estradiol (E2). Previous studies focused on a relatively small number of hepatic expressed genes during vitellogenesis. This study aims to identify hepatic genes involved in vitellogenesis and regulated by E2, by using zebrafish microarray gene expression profiling, and to provide information on functional distinctive genes expressed in the liver of a vitellogenic female, using zebrafish as a model fish. RESULTS: Genes associated with vitellogenesis were revealed by the following paired t-tests (SAM) comparisons: a) two-month old vitellogenic (Vit2) females were compared with non-vitellogenic (NV) females, showing 825 differentially expressed transcripts during early stages of vitellogenesis, b) four-month old vitellogenic (Vit4) females were compared with NV females, showing 1,046 differentially expressed transcripts during vitellogenesis and c) E2-treated males were compared with control males, showing 1,828 differentially expressed transcripts regulated by E2. A Venn diagram revealed 822 common transcripts in the three groups, indicating that these transcripts were involved in vitellogenesis and putatively regulated by E2. In addition, 431 transcripts were differentially expressed in Vit2 and Vit4 females but not in E2-treated males, indicating that they were putatively not up-regulated by E2. Correspondence analysis showed high similarity in expression profiles of Vit2 with Vit4 and of NV females with control males. The E2-treated males differed from the other groups. The repertoire of genes putatively regulated by E2 in vitellogenic females included genes associated with protein synthesis and reproduction. Genes associated with the immune system processes and biological adhesion, were among the genes that were putatively not regulated by E2. E2-treated males expressed a large array of transcripts that were not associated with vitellogenesis.The study revealed several genes that were not reported before as being regulated by E2. Also, the hepatic expression of several genes was reported here for the first time. CONCLUSION: Gene expression profiling of liver samples revealed 1,046 differentially expressed transcripts during vitellogenesis of which at least ~64% were regulated by E2. The results raise the question on the regulation pattern and temporal pleiotropic expression of hepatic genes in vitellogenic females.

miR-17/20 sensitization of breast cancer cells to chemotherapy-induced apoptosis requires Akt1.

The serine threonine kinase Akt1 has been implicated in the control of cellular metabolism, survival and growth. Herein, disruption of the ubiquitously expressed member of the Akt family of genes, Akt1, in the mouse, demonstrates a requirement for Akt1 in miRNA-mediated cellular apoptosis. The miR-17/20 cluster is known to inhibit breast cancer cellular proliferation through G1/S cell cycle arrest via binding to the cyclin D1 3'UTR. Here we show that miR-17/20 overexpression sensitizes cells to apoptosis induced by either Doxorubicin or UV irradiation in MCF-7 cells via Akt1. miR-17/20 mediates apoptosis via increased p53 expression which promotes Akt degradation. Akt1⁻/⁻ mammary epithelial cells which express Akt2 and Akt3 demonstrated increased apoptosis to DNA damaging agents. Akt1 deficiency abolished the miR-17/20-mediated apoptosis. These results demonstrated a novel pathway through which miR17/20 regulate p53 and Akt controlling breast cancer cell apoptosis.

Hearts lacking caveolin-1 develop hypertrophy with normal cardiac substrate metabolism.

Long-chain fatty acids (FA) are the primary energy source utilized by the adult heart. However, during pathological cardiac hypertrophy the fetal gene program is reactivated and glucose becomes the major fuel source metabolized by the heart. Herein we describe the metabolic phenotype associated with caveolin-1(Cav1) gene ablation (Cav1ko) in cardiac fibroblasts. Cav1, the primary protein component of caveolae in non-muscle cells co-localizes with a number of proteins involved in substrate metabolism, including, FA translocase (CD36) and the insulin receptor. We demonstrate that Cav1ko hearts develop cardiac hypertrophy and contractile dysfunction at 5-6mos of age. Surprisingly, we observed an increase in the uptake of Intralipid triglyceride and albumin bound FA by 25% and 47%, respectively, in Cav1ko hearts. Isolated perfused heart studies revealed no significant difference in glucose oxidation and glycolysis, however, we observed a trend toward increased FA oxidation in Cav1ko hearts. Real-time PCR analysis revealed no significant changes in the expression of genes involved in FA and glucose metabolism. We also report myocardial triglyceride, fatty acid and cholesterol levels are significantly reduced in Cav1ko hearts. Microarray gene expression analysis revealed changes in genes that regulate calcium ion and lipid transport as well as a number of genes not previously linked to cardiac hypertrophy. We observed a 4-fold increase in tetraspanin-2 gene expression, a transmembrane protein implicated in regulating intracellular trafficking. Oxysterol binding protein related protein-3, which has been implicated in intracellular lipid synthesis and transport, was increased 3.6-fold. In addition, sarcoplasmic reticulum Ca(2+)-ATPase 3, and calcyclin gene transcripts were significantly increased in Cav1ko hearts. In summary, targeted loss of Cav1 produces a unique model of cardiac hypertrophy with normal substrate utilization and expression of genes involved in energy metabolism.