Identification and characterization of a Ste20-like kinase in Artemia and its role in the developmental regulation and resistance to environmental stress

Effect of Different Culture Conditions on Gene Expression Associated With Cyst Production in Populations of Artemia franciscana

Artemia franciscana inhabits hypersaline environments in the Americas and has a well-adapted reproductive system that allows it to survive in these extreme conditions, represented by the production of diapause cysts (oviparous reproduction). This reproduction mode is controlled by numerous genes that are expressed in response to different environmental stressors, enabling this species to avoid population extinction. However, to date, the expression of these genes has not been sufficiently studied to clarify their levels in response to a combination of different environmental factors under controlled conditions. We analyzed the expression of eight genes related to oviparous reproduction (SGEG, Arp-CBP, artemin, BRCA1, p8, ArHsp21, ArHsp22, and p26) to determine their association with cyst production in two populations of A. franciscana with contrasting phenotypes, one with high (Barro Negro, BNE, Chile) and one with low (San Francisco Bay, SFB, United States) cyst production. Populations were cultured under controlled conditions of salinity (SAL, 35 and 75 ppt), photoperiod (PHO, 12L:12D and 24L:00D), iron concentration (IC, 0[Fe] and 5[Fe]), and microalgae diet (DIE; Dunaliella tertiolecta (DUN) and Tetraselmis suecica (TETRA)). Sixteen treatments were performed by combining the two conditions of each of the four factors. Data on nine reproductive parameters per female were recorded, including the percent of offspring encysted (%) (POE). The gene expression levels were analyzed by semiquantitative RT-PCR. The mean POE was significantly greater in BNE than in SFB (32.40 versus 12.74%, Mann-Whitney's test, p < 0.05). Significantly upregulated expression of seven genes in BNE (more than twofold, p < 0.05) was observed in 38.28% of the treatments (e.g., DUN-75ppt-12L:12D-5[Fe] and TETRA-35ppt-12L:12D-5[Fe]). In SFB, seven genes showed significant differential expression, but most were downregulated in 29.69% of the treatments (e.g., DUN-75ppt-12L:12D-0[Fe] and DUN-75ppt-24L:00D-0[Fe]). Multiple regression analyses indicated that in BNE, five genes (SGEG, artemin, Arp-CBP, p8, and BRCA1) and three environmental factors (DIE, SAL, and IC) were important predictor variables for the POE response variable given that all of them were included in the highest-ranking models. In SFB, only two genes (ArHsp21 and artemin) and one environmental factor (SAL) were important explanatory variables in the highest-ranking models. It was concluded that the BNE population presented a characteristic gene expression pattern that differed from that of the SFB population. This pattern might be related to the marked oviparous reproduction of the BNE population. This gene expression pattern could be useful for monitoring the reproductive mode leading to diapause in Artemia and to assist with intensive cyst production in pond systems.

Characteristics, dynamics and mechanisms of actions of some major stress-induced biomacromolecules; addressing Artemia as an excellent biological model

Stress tolerance is one of the most prominent and interesting topics in biology since many macro- and micro-adaptations have evolved in resistant organisms that are worth studying. When it comes to confronting various environmental stressors, the extremophile Artemia is unrivaled in the animal kingdom. In the present review, the evolved molecular and cellular basis of stress tolerance in resistant biological systems are described, focusing on Artemia cyst as an excellent biological model. The main purpose of the review is to discuss how the structure and physicochemical characteristics of protective factors such as late embryogenesis abundant proteins (LEAPs), small heat shock proteins (sHSPs) and trehalose are related to their functions and by which mechanisms, they exert their functions. In addition, some metabolic depressors in Artemia encysted embryos are also mentioned, indirectly playing important roles in stress tolerance. Importantly, a great deal of attention is given to the LEAPs, exhibiting distinctive folding behaviors and mechanisms of actions. For instance, molecular shield function, chaperone-like activity, moonlighting property, sponging and snorkeling capabilities of the LEAPs are delineated here. Moreover, the molecular interplay between some of these factors is mentioned, leading to their synergistic effects. Interestingly, Artemia life cycle adapts to environmental conditions. Diapause is the defense mode of this life cycle, safeguarding Artemia encysted embryos against various environmental stressors. Communicated by Ramaswamy H. Sarma.

Identification and characterization of a Masculinizer (Masc) gene involved in sex differentiation in Artemia

The sex of relatively primitive animals such as invertebrates is mostly determined by environmental factors and chromosome ploidy. Heteromorphic chromosomes may also play an important role, as in the ZW system in lepidopterans. However, the mechanisms of these various sex determination systems are still largely undefined. In the present study, a Masculinizer gene (Ar-Masc) was identified in the crustacean Artemia franciscana Kellogg 1906. Sequence analysis revealed that the 1140-bp full-length open reading frame of Ar-Masc encodes a 380-aa protein containing two CCCH-type zinc finger domains having a high degree of shared identities with the MASC protein characterized in the silkworm Bombyx mori, which has been determined to participate in the production of male-specific splice variants. Furthermore, although Ar-Masc could be detected in almost all stages in both sexual and parthenogenetic Artemia, there were significant variations in expression between these two reproductive modes. Firstly, qRT-PCR and Western blot analysis showed that levels of both Ar-Masc mRNA and protein in sexual nauplii were much higher than in parthenogenetic nauplii throughout the hatching process. Secondly, both sexual and parthenogenetic Artemia had decreased levels of Ar-Masc along with the embryonic developmental stages, while the sexual ones had a relatively higher and more stable expression than those of parthenogenetic ones. Thirdly, immunofluorescence analysis determined that sexual individuals had higher levels of Ar-MASC protein than parthenogenetic individuals during embryonic development. Lastly, RNA interference with dsRNA showed that gene silencing of Ar-Masc in sexual A. franciscana caused the female-male ratio of progeny to be 2.19:1. These data suggest that Ar-Masc participates in the process of sex determination in A. franciscana, and provide insight into the evolution of sex determination in sexual organisms.

Expression profiles of miRNAs and involvement of miR-100 and miR-34 in regulation of cell cycle arrest in Artemia

Regulation of the cell cycle is complex but critical for proper development, reproduction and stress resistance. To survive unfavourable environmental conditions, the crustacean Artemia produces diapause embryos whose metabolism is maintained at extremely low levels. In the present study, the expression profiles of miRNAs during Artemia diapause entry and termination were characterized using high-throughput sequencing. A total of 13 unclassified miRNAs and 370 miRNAs belonging to 87 families were identified; among them, 107 were differentially expressed during diapause entry and termination. We focused on the roles of two of these miRNAs, miR-100 and miR-34, in regulating cell cycle progression; during the various stages of diapause entry, these miRNAs displayed opposing patterns of expression. A functional analysis revealed that miR-100 and miR-34 regulate the cell cycle during diapause entry by targeting polo-like kinase 1 (PLK1), leading to activation of the mitogen-activated protein kinase kinase-extracellular signal-regulated kinase-ribosomal S6 kinase 2 (MEK-ERK-RSK2) pathway and cyclin K, leading to suppression of RNA polymerase II (RNAP II) activity respectively. The findings presented in the present study provide insights into the functions of miR-100 and miR-34 and suggest that the expression profiles of miRNAs in Artemia can be used to characterize their functions in cell cycle regulation.