The structure of the shell and outer membranes in encysted Artemia salina embryos during cryptobiosis and development

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

“…Significant amounts of SGEG1 mRNA reside in the ovisacs of females producing diapause-destined embryos, but only minor amounts appear in ovisacs containing nauplius-destined embryos (Liu et al 2009). SGEG1 is expressed exclusively in the shell gland and loss of SGEG1 affects the chorion layer, agreeing with the earlier conclusion that the chorion arises from shell gland secretions (Morris and Afzelius 1967). SGEG2, also expressed only in shell gland secreting cells, is cleaved into two proteins, SGEG2a and SGEG2b, found predominately in the cortical and alveolar layers of cyst shells, but not in the embryonic cuticle or embryo cells (Dai et al 2011a).…”

“…The layers of the shell are, from the exterior of the cyst to the interior, the cortical and alveolar layers of maternal origin which shape the non-cellular chorion, and the outer cuticular membrane, the chitinous fibrous layer, and the inner cuticular membrane of embryonic origin, establishing the embryonic cuticle ( Fig. 2) (Morris and Afzelius 1967;Hofmann and Hand 1990).…”

“…Removal of the outer shell layer by decapsulation correlates with increased sensitivity to ultraviolet (UV) light, faster water loss, and reduced tolerance to drying and rehydration (Morris and Afzelius 1967;Anderson et al 1970;Tanguay et al 2004;Clegg 2005;Liu et al 2009;Dai et al 2011a;. The outer cuticular membrane is impermeable to most nonvolatile compounds including amino acids, glycerol, glucose, inorganic phosphate, and uracil, although H 2 O and CO 2 penetrate this layer (Clegg 1966(Clegg , 1967Golub and Clegg 1968;Clegg and Golub 1969;De Chaffoy et al 1978).…”

“…The chorion, comprised of the maternally derived cortical and alveolar layers, surrounds the embryonic cuticular layer, protecting cysts against environmental stress (Morris and Afzelius 1967;Anderson et al 1970;Tanguay et al 2004;Liu et al 2009;Dai et al 2011a;. cDNAs representing shell gland specifically expressed genes (SGEGs), termed SGEG1 and SGEG2, were isolated from A. parthenogenetica by subtractive hybridization (Liu et al 2009;Dai et al 2011a).…”

Selective resistance to desiccation of nuclear ribonucleic acid synthesis in isolated nuclei of Artemia salina embryos during pre-emergence development

“…We show here that developing gastrula embryos are resistant to a complete redesiccation, and isolated nuclei from these dehydrated embryos retain transcriptional activity comparable with that of non-desiccated controls. However, the resistance to redesiccation is limited only to a pre-emergence period, namely a period of development before emergence of prenauplii from the protective alveolar chorionic shell (Morris & Afzelius, 1967). It is suggested that glycerol accumulated in the encysted embryos during pre-emergence development (Clegg, 1964) might play an important role in protection of nuclear activity against dehydration.…”