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K-ras/PI3K-Akt signaling is essential for zebrafish hematopoiesis and angiogenesis.

Liu L, Zhu S, Gong Z, Low BC - PLoS ONE (2008)

Bottom Line: Using wild-type and fli1:GFP transgenic zebrafish, we showed that K-ras-knockdown resulted in specific hematopoietic and angiogenic defects, including the impaired expression of erythroid-specific gene gata1 and sse3-hemoglobin, reduced blood circulation and disorganized blood vessels.Consistently, the functional rescue by k-ras mRNA was significantly suppressed by wortmannin, a PI3K-specific inhibitor.Our results provide direct evidence that PI3K-Akt plays a crucial role in mediating K-ras signaling during hematopoiesis and angiogenesis in vivo, thus offering new targets and alternative vertebrate model for studying these processes and their related diseases.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Cell Signaling and Developmental Biology Laboratory, The National University of Singapore, Singapore, The Republic of Singapore.

ABSTRACT
The RAS small GTPases orchestrate multiple cellular processes. Studies on knock-out mice showed the essential and sufficient role of K-RAS, but not N-RAS and H-RAS in embryonic development. However, many physiological functions of K-RAS in vivo remain unclear. Using wild-type and fli1:GFP transgenic zebrafish, we showed that K-ras-knockdown resulted in specific hematopoietic and angiogenic defects, including the impaired expression of erythroid-specific gene gata1 and sse3-hemoglobin, reduced blood circulation and disorganized blood vessels. Expression of either K-rasC40 that links to phosphoinositide 3-kinase (PI3K) activation, or Akt2 that acts downstream of PI3K, could rescue both hematopoietic and angiogenic defects in the K-ras knockdown. Consistently, the functional rescue by k-ras mRNA was significantly suppressed by wortmannin, a PI3K-specific inhibitor. Our results provide direct evidence that PI3K-Akt plays a crucial role in mediating K-ras signaling during hematopoiesis and angiogenesis in vivo, thus offering new targets and alternative vertebrate model for studying these processes and their related diseases.

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Related in: MedlinePlus

Zebrafish N-ras can rescue hematopoietic defects induced by K-ras knockdown, but not angiogenic defects.(A) Hematopoietic defects caused by K-ras knockdown could be rescued by zebrafish N-ras effectively. Embryo numbers n1 = 475, n2 = 344 and n3 = 131, from >3 independent sets of experiments. (B) Angiogenic defects caused by K-ras knockdown could not be rescued by zebrafish N-ras. Embryo numbers n1 = 133, n2 = 92 and n3 = 151, from 3 independent sets of experiments. All data are means±SD. Values indicated by the same letter are not significantly different at p<0.05.
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pone-0002850-g006: Zebrafish N-ras can rescue hematopoietic defects induced by K-ras knockdown, but not angiogenic defects.(A) Hematopoietic defects caused by K-ras knockdown could be rescued by zebrafish N-ras effectively. Embryo numbers n1 = 475, n2 = 344 and n3 = 131, from >3 independent sets of experiments. (B) Angiogenic defects caused by K-ras knockdown could not be rescued by zebrafish N-ras. Embryo numbers n1 = 133, n2 = 92 and n3 = 151, from 3 independent sets of experiments. All data are means±SD. Values indicated by the same letter are not significantly different at p<0.05.

Mentions: To further elucidate the specificity versus redundancy in mediating Ras signaling in hematopoiesis and angiogenesis, zebrafish N-ras was introduced to rescue K-ras knockdown. The N-ras was shown to confer comparable functional rescue only for hematopoiesis but not for angiogenesis (Figure 6), thus, suggesting a unique function of K-ras which is not shared by N-ras. This is in agreement with the notion that distinct signal outputs from different RAS isoforms are necessary for diverse biological responses [19]. In essence, applying targeted gene knockdown for individual Ras isoforms in zebrafish will help clarify their distinct mechanisms, establish their relative contributions to normal physiological functions, and further analyze their potential downstream pathways. Such information will serve as the basis for developing the targeted therapeutics without disruption for other normal RAS signaling. Thus, zebrafish presents a significant model for faithfully reflecting the in vivo status of Ras signaling, bypassing the limitation by their over-expression that might re-route them to ectopic compartments.


K-ras/PI3K-Akt signaling is essential for zebrafish hematopoiesis and angiogenesis.

Liu L, Zhu S, Gong Z, Low BC - PLoS ONE (2008)

Zebrafish N-ras can rescue hematopoietic defects induced by K-ras knockdown, but not angiogenic defects.(A) Hematopoietic defects caused by K-ras knockdown could be rescued by zebrafish N-ras effectively. Embryo numbers n1 = 475, n2 = 344 and n3 = 131, from >3 independent sets of experiments. (B) Angiogenic defects caused by K-ras knockdown could not be rescued by zebrafish N-ras. Embryo numbers n1 = 133, n2 = 92 and n3 = 151, from 3 independent sets of experiments. All data are means±SD. Values indicated by the same letter are not significantly different at p<0.05.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2483249&req=5

pone-0002850-g006: Zebrafish N-ras can rescue hematopoietic defects induced by K-ras knockdown, but not angiogenic defects.(A) Hematopoietic defects caused by K-ras knockdown could be rescued by zebrafish N-ras effectively. Embryo numbers n1 = 475, n2 = 344 and n3 = 131, from >3 independent sets of experiments. (B) Angiogenic defects caused by K-ras knockdown could not be rescued by zebrafish N-ras. Embryo numbers n1 = 133, n2 = 92 and n3 = 151, from 3 independent sets of experiments. All data are means±SD. Values indicated by the same letter are not significantly different at p<0.05.
Mentions: To further elucidate the specificity versus redundancy in mediating Ras signaling in hematopoiesis and angiogenesis, zebrafish N-ras was introduced to rescue K-ras knockdown. The N-ras was shown to confer comparable functional rescue only for hematopoiesis but not for angiogenesis (Figure 6), thus, suggesting a unique function of K-ras which is not shared by N-ras. This is in agreement with the notion that distinct signal outputs from different RAS isoforms are necessary for diverse biological responses [19]. In essence, applying targeted gene knockdown for individual Ras isoforms in zebrafish will help clarify their distinct mechanisms, establish their relative contributions to normal physiological functions, and further analyze their potential downstream pathways. Such information will serve as the basis for developing the targeted therapeutics without disruption for other normal RAS signaling. Thus, zebrafish presents a significant model for faithfully reflecting the in vivo status of Ras signaling, bypassing the limitation by their over-expression that might re-route them to ectopic compartments.

Bottom Line: Using wild-type and fli1:GFP transgenic zebrafish, we showed that K-ras-knockdown resulted in specific hematopoietic and angiogenic defects, including the impaired expression of erythroid-specific gene gata1 and sse3-hemoglobin, reduced blood circulation and disorganized blood vessels.Consistently, the functional rescue by k-ras mRNA was significantly suppressed by wortmannin, a PI3K-specific inhibitor.Our results provide direct evidence that PI3K-Akt plays a crucial role in mediating K-ras signaling during hematopoiesis and angiogenesis in vivo, thus offering new targets and alternative vertebrate model for studying these processes and their related diseases.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Cell Signaling and Developmental Biology Laboratory, The National University of Singapore, Singapore, The Republic of Singapore.

ABSTRACT
The RAS small GTPases orchestrate multiple cellular processes. Studies on knock-out mice showed the essential and sufficient role of K-RAS, but not N-RAS and H-RAS in embryonic development. However, many physiological functions of K-RAS in vivo remain unclear. Using wild-type and fli1:GFP transgenic zebrafish, we showed that K-ras-knockdown resulted in specific hematopoietic and angiogenic defects, including the impaired expression of erythroid-specific gene gata1 and sse3-hemoglobin, reduced blood circulation and disorganized blood vessels. Expression of either K-rasC40 that links to phosphoinositide 3-kinase (PI3K) activation, or Akt2 that acts downstream of PI3K, could rescue both hematopoietic and angiogenic defects in the K-ras knockdown. Consistently, the functional rescue by k-ras mRNA was significantly suppressed by wortmannin, a PI3K-specific inhibitor. Our results provide direct evidence that PI3K-Akt plays a crucial role in mediating K-ras signaling during hematopoiesis and angiogenesis in vivo, thus offering new targets and alternative vertebrate model for studying these processes and their related diseases.

Show MeSH
Related in: MedlinePlus