ACRYFROM THE KRILL

Abstract

Antarctic krill (Euphausia superba) inhabit a region with strong seasonality in several parameters, such as photoperiod, light intensity, extent of sea ice, and food availability. In particular, seasonal changes in environmental light regimes have been shown to strongly influence krill metabolism, representing control signals for seasonal regulation of physiology of this key Southern Ocean species. Here, we report the identification of a cryptochrome gene, a cardinal component of the clockwork machinery in several organisms. EsCRY appears to be an ortholog of mammalian-like CRYs and clusters with the insect CRY2 subfamily. EsCRY has the canonical bipartite CRY structure, with a conserved N-terminal domain and a highly divergent C-terminus, that bears several binding motifs, some of them shared with insect CRY2 and others peculiar for EsCRY. We have evaluated the temporal expression of Escry both at mRNA and protein levels in individuals harvested from the Ross Sea at different times throughout the 24 h cycle during the Antarctic summer. We observed a daily fluctuation in abundance for Escry mRNA in the head, with high levels around 06:00 h, which is not mirrored by a cycle in the corresponding protein. Our findings represent a first step toward establishing the presence of an endogenous circadian time-keeping mechanism that might allow this organism to synchronize its physiology and behavior to the Antarctic light regimes.

The overwintering of Antarctic krill, Euphausia superba, from an ecophysiological perspective

“…Recent studies provide evidence that the synchronisation of krill to its environment depends upon an endogenous circadian clock (Teschke et al 2011). Such a clock would be entrained by external environmental signals and controls circardian phenotypes and also may modulate photoperiodic responses (Gaten et al 2008;Mazzotta et al 2010).…”

Physiological response of adult Antarctic krill, Euphausia superba, to long-term starvation

“…The presence of food alone is not sufficient to trigger feeding activity (Atkinson et al 2002;Teschke et al 2007). Recent research indicated that endogenous (inherent) mechanisms exist to synchronise the seasonal and circadian rhythmicity of metabolic and physiological output (Teschke et al 2007(Teschke et al , 2008(Teschke et al , 2011Mazzotta et al 2010), triggered by light (Seear et al 2009;Teschke et al 2011;Brown et al 2013). On the other hand, it was clearly shown in short-term starvation experiments that food availability does play a role: even after only 18 days without food, krill switched to a mode that reduced energy consumption and initiated consumption of body lipids (Atkinson et al 2002;Auerswald et al 2009).…”

The opsin repertoire of the Antarctic krill Euphausia superba

“…qPCR was performed on specimens collected in the Ross Sea at different times of the day (01:00, 06:00, 10:00, 15:00, and 18:00) during the Antarctic summer (Mazzotta et al, 2010), when they were exposed to an almost continuous 24 h photoperiod characterized by daily variations in solar irradiance (Fig. 5).…”

“…The relative levels of each RNA were calculated by the 2 − ΔΔCT method (where CT is the cycle number at which the signal reaches the threshold of detection) (Livak and Schmittgen, 2001). As previously reported (Mazzotta et al, 2010;De Pittà et al, 2013), 18S was used as housekeeping gene (QuantumRNA™ 18S Internal Standards, Ambion, Austin, TX, USA). Each CT value used for these calculations is the mean of three replicates of the same reaction.…”

“…For the temporal expression analysis Antarctic krill were collected in the Ross Sea (longitude: 167°28′81′′ E -179°54′68′′ W, latitude 68°40′ 54′′ S -77°01′′81′′ S) in January 2004 during the XIX Italian Antarctic Expedition with procedures described in Mazzotta et al (2010). Adult specimens were caught at different times throughout the 24-hour cycle (local times: 01:00, 06:00, 10:00, 15:00, and 18:00) and stored at −80°C in RNA-later (Life Technologies, CA, USA).…”