Artemin, a Diapause-Specific Chaperone, Contributes to the Stress Tolerance of Artemia Cysts and Influences Their Release from Females

Abstract

Females of the crustacean Artemia franciscana produce either motile nauplii or gastrula stage embryos enclosed in a shell impermeable to nonvolatile compounds and known as cysts. The encysted embryos enter diapause, a state of greatly reduced metabolism and profound stress tolerance. Artemin, a diapause-specific ferritin homolog in cysts has molecular chaperone activity in vitro. Artemin represents 7.2% of soluble protein in cysts, approximately equal to the amount of p26, a small heat shock protein. However, there is almost twice as much artemin mRNA in cysts as compared with p26 mRNA, suggesting that artemin mRNA is translated less efficiently. RNA interference employing the injection of artemin double-stranded RNA into the egg sacs of A. franciscana females substantially reduced artemin mRNA and protein in cysts. Decreasing artemin diminished desiccation and freezing tolerance of cysts, demonstrating a role for this protein in stress resistance. Knockdown of artemin increased the time required for complete discharge of a brood of cysts carried within a female from a few hours up to 4 days, an effect weakened in successive broods. Artemin, an abundant molecular chaperone, contributes to stress tolerance of A. franciscana cysts while influencing their development and/or exit from females.

Stress tolerance during diapause and quiescence of the brine shrimp, Artemia

“…Artemin appears in the cytosol of cyst-destined, but not nauplius-destined, embryos by 4 days post-fertilization (Grosfeld and Littauer 1976;De Herdt et al 1979Tanguay et al 2004), and it constitutes about 7 % of the soluble protein in mature cysts (King et al 2014). Most artemin mRNA is gone from early cyst-derived nauplii (Chen et al 2003) but when the protein disappears is unknown.…”

“…Artemin is extremely stable, enduring extended cyst storage, years of anoxia, and heating in vitro at 70°C which causes binding of non-polyadenylated RNA (Warner et al 2004;Shahangian et al 2011). Structural stability and the correspondence between abundance and elevated stress resistance imply that artemin protects Artemia cysts, a proposition proven by reduced tolerance to desiccation and freezing after knockdown of artemin (King et al 2014).…”

“…The need for a termination cue differentiates diapause from quiescence, a hypometabolic, stress-tolerant state requiring only return to favorable growth parameters for termination (Drinkwater and Clegg 1991). Stress tolerance during diapause and quiescence in Artemia has been examined from several perspectives including the synthesis, composition, and structure of the cyst shell (Liu et al 2009;Dai et al 2011a;, the role of trehalose (Clegg 1965;Clegg and Jackson 1992;Yang et al 2013), the composition and activity of late embryogenesis abundant (LEA) proteins (Sharon et al 2009;Wu et al 2011;Toxopeus et al 2014), and the function of molecular chaperones such as small heat shock proteins (sHsps) and artemin (King and MacRae 2012;King et al 2013King et al , 2014.…”

ArHsp40, a type 1 J-domain protein, is developmentally regulated and stress inducible in post-diapause Artemia franciscana

“…Diapause terminates upon exposure to external cues such as desiccation and cold, and the cysts either enter quiescence if conditions are unfavorable for growth or undergo post-diapause development into swimming larvae (nauplii) (MacRae 2003;Robbins et al 2010). The survival of A. franciscana cysts during diapause and quiescence depends on molecular chaperones including the small heat shock protein (sHsp) p26 (Sun et al 2004;Villeneuve et al 2006;King and MacRae 2012), the ferritin homolog artemin (Chen et al 2007;Hu et al 2011;King et al 2014) and Late Embryogenesis Abundant (LEA) proteins (Warner et al 2010;Toxopeus et al 2014). These proteins disappear subsequent to diapause termination and have, at most, a minor part in post-diapause development of A. franciscana.…”

Courtship behavior and potential indications for chemical communication in Artemia franciscana (Kellog 1906)

“…Firstly, the species has overlapping generations (Rode et al 2011) due to the ability of females to switch offspring quality between freeswimming nauplii and resting eggs (embryo at gastrula stage), commonly referred as cyst (King et al 2014), if environmental conditions are perceived as stable or stressful respectively (Van Stappen 2002;Gajardo et al 2002). Second, while nauplii allow rapid population expansion in a short period of time, eggs account for overlapping generations due to their ability to resist several environmental stresses, thanks to a protective shell (chorion) and physiological mechanisms that allow them to remain viable for years almost dehydrated (Clegg & Gajardo 2009;Gajardo & Beardmore 1989).…”