RESUMEN
When faced with extreme environmental conditions, the milk snail (Otala lactea) enters a state of dormancy known as estivation. This is characterized by a strong reduction in metabolic rate to <30% of normal resting rate that is facilitated by various behavioural, physiological, and molecular mechanisms. Herein, we investigated the regulation of microRNA in the induction of estivation. Changes in the expression levels of 75 highly conserved microRNAs were analysed in snail foot muscle, of which 26 were significantly upregulated during estivation compared with controls. These estivation-responsive microRNAs were linked to cell functions that are crucial for long-term survival in a hypometabolic state including anti-apoptosis, cell-cycle arrest, and maintenance of muscle functionality. Several of the microRNA responses by snail foot muscle also characterize hypometabolism in other species and support the existence of a conserved suite of miRNA responses that regulate environmental stress responsive metabolic rate depression across phylogeny.
RESUMEN
Lactate dehydrogenase (LDH) has a crucial role in maintaining ATP production as the terminal enzyme in anaerobic glycolysis. This study will determine the effect of posttranslational modifications (PTMs) on the activity of LDH in the foot muscle and hepatopancreas of an estivating snail, Otala lactea. LDH in foot muscle of O. lactea was purified to homogeneity and partially purified in hepatopancreas in a two-step and three-step process, respectively. The kinetic properties and stability of these isoforms were determined where there was a significant difference in Km and I50 values with pyruvate and urea separately in foot muscle; however, hepatopancreas exhibited significant differences in Km and I50 in salt between control and stress. Interestingly, hepatopancreas has a higher affinity for pyruvate in the control state whereas foot muscle has a higher affinity for its substrate in the estivated state. PTMs of each isoform were identified using immunoblotting and dot blots, which prove to be significantly higher in the control state. Overall, foot muscle LDH enters a low phosphorylation state during estivation allowing more efficiency in consuming pyruvate with higher thermal stability but less structural stability. Hepatopancreas LDH becomes dephosphorylated in the estivating snail that decreases the efficiency of the enzyme in the forward direction; however, the snail has an increased tolerance to the presence of salt when water becomes scarce. Such tissue-specific regulations indicate the organism's ability to reduce energy consumption when undergoing metabolic depression.