Effect of the d‐glucose analog,d‐allose,on the growth of Arabidopsis roots

Although d ‐glucose increased the root growth of Arabidopsis seedlings, d ‐allose (a d ‐glucose epimer at the third carbon atom) inhibited the root growth at concentrations >0.1 mmol L^?1 and the inhibition increased with increasing d ‐allose concentrations. Allitol (a reduction product of d ‐allose) did not show any significant effect on the growth. The addition of d ‐glucose into the growth medium of Arabidopsis reversed the d ‐allose‐induced growth inhibition, which suggests that the inhibition is not caused by the toxicity of the accumulation of d ‐allose and/or its metabolites in the seedlings. d ‐Allose is phosphorylated by hexokinase, using ATP and phosphate, to allose‐6‐phosphate, with no known capacity for further metabolism. The addition of phosphate into the growth medium did not affect the d ‐allose‐induced growth inhibition and d ‐allose did not reduce the ATP level in the roots. These results suggest that the inhibition is not due to phosphate starvation and ATP depletion. d ‐Mannoheptulose, a specific competitive inhibitor of hexokinase, defeated the d ‐allose‐induced growth inhibition. Hexokinase is known to have a sugar‐sensing function and possibly triggers a signal cascade, resulting in the change of several gene expressions. Therefore, the phosphorylation of d ‐allose by hexokinase might trigger a signal cascade, resulting in the inhibition of Arabidopsis root growth. This is probably a useful model system for studies of the hexokinase‐mediated sugar‐sensing function and for developing new types of weed‐control agents.     

Oocyte-specific gene knockdown by intronic artificial microRNAs driven by Zp3 transcription in mice

Conditional knockout technology is a powerful tool for investigating the spatiotemporal functions of target genes. However, generation of conditional knockout mice involves complicated breeding programs and considerable time. A recent study has shown that artificially designed microRNAs (amiRNAs), inserted into an intron of the constitutively expressed gene, induce knockdown of the targeted gene in mice, thus creating a simpler method to analyze the functions of target genes in oocytes. Here, to establish an oocyte-specific knockdown system, amiRNA sequences against enhanced green fluorescent protein (EGFP) were knocked into the intronic sites of the Zp3 gene. Knock-in mice were then bred with EGFP transgenic mice. Our results showed that Zp3-derived amiRNA successfully reduced EGFP fluorescence in the oocytes in a size-dependent manner. Importantly, knockdown of EGFP did not occur in somatic cells. Thus, we present our knockdown system as a tool for screening gene functions in mouse oocytes.