Timing of embryonic quiescence determines viability of embryos from the calanoid copepod, Acartia tonsa (Dana)

Abstract

Like 41 other calanoid copepods, Acartia tonsa, are capable of inducing embryonic quiescence when experiencing unfavorable environmental conditions. The ecdysone-signaling cascade is known to have a key function in developmental processes like embryogenesis and molting of arthropods, including copepods. We examined the role of ecdysteroid-phosphate phosphatase (EPPase), ecdysone receptor (EcR), ß fushi tarazu transcription factor 1 (ßFTZ-F1), and the ecdysteroid-regulated early gene E74 (E74), which represent different levels of the ecdysone-signaling cascade in our calanoid model organism. Progression of embryogenesis was monitored and hatching success determined to evaluate viability. Embryos that were induced quiescence before the gastrulation stage would stay in gastrulation during the rest of quiescence and exhibited a slower pace of hatching as compared to subitaneous embryos. In contrast, embryos developed further than gastrulation would stay in gastrulation or later stages during quiescence and showed a rapid pace in hatching after quiescence termination. Expression patterns suggested two peaks of the biological active ecdysteroids, 20-hydroxyecdysone (20E). The first peak of 20E was expressed in concert with the beginning of embryogenesis originating from yolk-conjugated ecdysteroids, based on EPPase expression. The second peak is suggested to originate from de novo synthesized 20E around the limb bud stage. During quiescence, the expression patterns of EPPase, EcR, ßFTZ-F1, and E74 were either decreasing or not changing over time. This suggests that the ecdysone-signaling pathway play a key role in the subitaneous development of A. tonsa embryogenesis, but not during quiescence. The observation is of profound ecological and practical relevance for the dynamics of egg banks.

Copepod Embryonic Dormancy: “An Egg Is Not Just an Egg”

“…This revealed that embryos that were entering quiescence before the gastrulation stage would stay in gastrulation during the rest of quiescence, and that they exhibited a slower pace of hatching compared to subitaneous embryos. In contrast, embryos entering quiescence after gastrulation would stay in later embryonic stages during quiescence, and they showed a rapid pace of hatching after quiescence termination (Nilsson and Hansen, 2018).…”

“…5), which traits create resistant individuals that can survive periods of adversity, and how the answers to these questions relate to species distribution. Understanding of the epigenetic and genetic mechanisms underlying embryonic dormancy is also limited (Nilsson, 2017). Therefore, I ask the following questions: (1) What are the physical-chemical-biological cues (day length, light intensity, temperature, crowding stress, food shortage, etc.…”

“…However, lately, a toolbox of molecular techniques has become widely available (e.g., beyond health science applications). Implementing a suite of these techniques-for example, genomics, transcriptomics, and metabolomics-to support standard physiological techniques in copepod molecular physiology seems promising (see Nilsson, 2017;Amato and Carotenuto, 2018;Tarrant et al, 2019).…”

“…Based on transcriptomic analysis throughout embryogenesis, several hormonal profiles were investigated for Acartia tonsa (Nilsson et al, 2018). The roles of ecdysteroidphosphatephosphatase (EPPase), ecdysone receptor (EcR), û fushi tarazu transcription factor 1 (ûFTZ-F1), and the ecdysteroid-regulated early gene E74 (E74), which represent different levels of the ecdysone-signaling cascade, were examined.…”

The genome and mRNA transcriptome of the cosmopolitan calanoid copepod Acartia tonsa Dana improve the understanding of copepod genome size evolution

“…RNA was extracted using the RNeasy mini Blood and Tissue kit from Qiagen (Hilden, Germany) according to protocol with the following modifications: sample tissue was kept on ice and ground in a 1.5 ml Eppendorf tube using a pestle and electric motor for two minutes and incubated with proteinase K for 4 hours with periodic mixing. The embryo RNA sample consisted of eggs from a few and up to 50 hours old to ensure that all stages in A. tonsa embryogenesis were present [45]. An overview of the libraries was constructed, and more details on indexes, insert sizes, biological materials, and SRA accession numbers can be found in Supplementary Material 1.…”