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A tunable reflector enabling crustaceans to see but not be seen.
Many oceanic prey animals use transparent bodies to avoid detection. However, conspicuous eye pigments, required for vision, compromise the organisms' ability to remain unseen. We report the discovery of a reflector overlying the eye pigments in larval decapod crustaceans and show how it is tuned to render the organisms inconspicuous against the background. The ultracompact reflector is constructed from a photonic glass of crystalline isoxanthopterin nanospheres. The nanospheres' size and ordering are modulated to tune the reflectance from deep blue to yellow, enabling concealment in different habitats. The reflector may also function to enhance the acuity or sensitivity of the minute eyes by acting as an optical screen between photoreceptors. This multifunctional reflector offers inspiration for constructing tunable artificial photonic materials from biocompatible organic molecules
Short versus long double-stranded RNA activation of a post-transcriptional gene knockdown pathway
<p>RNA interference (RNAi) utilizes a conserved cellular autoimmune defense mechanism involving the internalization of dsRNA into cells and the activation of a set of RNAi related genes. Using RNAi, complete sex reversal is achievable in males of the prawn <i>Macrobrachium rosenbergii</i> by knocking down the transcript level of an insulin-like androgenic gland hormone (<i>Mr-IAG</i>) through injections of dsRNA of the entire <i>Mr-IAG</i> ORF sequence (ds<i>Mr-IAG</i> – 518bp). Interestingly, <i>in-vivo</i> knockdown success and ds<i>Mr-IAG</i> lengths seemed to correlate, with long dsRNA being the most effective and short dsRNA fragments showing no effect. However, little is known about the RNAi machinery in <i>M. rosenbergii</i>. We discovered the <i>Mr-Dicer</i> and <i>Mr-Argonaute</i> gene families, associated with the major knockdown pathways, in our <i>M. rosenbergii</i> transcriptomic library. In response to ds<i>Mr-IAG</i> administration, only post-transcriptional pathway-related gene transcript levels were upregulated. In addition, a passive dsRNA channel (a <i>SID1</i> gene ortholog) that allows external dsRNA to enter cells was found. Its function was validated by observing <i>Mr-SID1</i> specific upregulation dependent on dsRNA lengths, while attempted loss-of-function experiments were lethal. Our results, which suggest differential systemic responses to dsRNA lengths, provide evidence that the above RNAi-based manipulation occurs via the post-transcriptional pathway. The temporal nature of the latter pathway supports the safety of using such RNAi-based biotechnologies in aquaculture and environmental applications. Unlike reports of RNAi driven by the administration of small dsRNA fragments <i>in-vitro</i>, the case presented here demonstrates length dependency <i>in-vivo</i>, suggesting further complexity in the context of the entire organism.</p