The painted sea urchin, Lytechinus pictus, as a genetically-enabled developmental model

Abstract

Although sea urchins are one of the oldest and most widely used marine model systems, few species have been routinely kept in culture through multiple generations. The workhorse of the field is the purple urchin Strongylocentrotus purpuratus. However, one disadvantage of S. purpuratus is its long generation time, making it impractical as a model for generating and maintaining transgenic lines. In an effort to develop a sea urchin that is suitable for transgenerational experiments and the generation of transgenic lines, we have focused on development of updated culturing methods and genomic resources for the painted sea urchin, Lytechinus pictus. Compared to S. purpuratus, L. pictus have relatively large eggs, develop into optically clear embryos, and the smaller adults can become gravid in under a year. Fifty years ago, Hinegardner developed culturing methods for raising L. pictus through metamorphosis. Here, we provide an updated protocol for establishing and maintaining L. pictus in the laboratory, and describe a new genome resource for this urchin. In our hands, L. pictus reach the 4-armed pluteus stage at 4 days; become competent to metamorphosis at 24 days; and are gravid by 6 months. Plutei and juveniles are fed on a diet of algae and di-atoms, and adults are fed on kelp. We also make available a L. pictus transcriptome generated from developmental stages (eggs to 2-day-old plutei) to support the annotation of our genome sequencing project, and to enhance the utility of this species for molecular studies and transgenesis.

Embryo, larval, and juvenile staging of Lytechinus pictus from fertilization through sexual maturation

“…The growing collection of community resources for working with L. pictus also make targeted molecular and genetic studies achievable. This includes a transcriptome and fully sequenced genome that will soon be publicly available 77 . This would provide a pathway to target ubiquitous genes in specific cell types, or to study longer‐term consequences of the environment through action on development.…”

“…Eggs were checked for fertilization success, where only batches of eggs with >98% successful fertilization were used. Embryos were grown with agitation at room temperature (20°C) as previously described 77 . Briefly, embryos were grown in FSW at a concentration of 1 embryo per mL until hatching from the fertilization envelope.…”

“…This includes a transcriptome and fully sequenced genome that will soon be publicly available. 77 This would provide a pathway to target ubiquitous genes in specific cell types, or to study longer-term consequences of the environment through action on development. Understanding of ecological and evolutionary development of L. pictus could strengthen our understanding of the processes that control development across echinoderms.…”

“…Embryos were grown with agitation at room temperature (20 C) as previously described. 77 Briefly, embryos were grown in FSW at a concentration of 1 embryo per mL until hatching from the fertilization envelope. Upon hatching, embryos were further diluted to a concentration of 1 embryo per 3 mL.…”

Generation of a homozygous mutant drug transporter (ABCB1) knockout line in the sea urchinLytechinus pictus

“…The painted sea urchin Lytechinus pictus represents an ideal candidate for the establishment of a genetically enabled sea urchin. Most notably, L. pictus has a relatively short generation time (4-6 months), that enables breeding in captivity ( Hinegardner, 1969 ; Nesbit et al, 2019 ; Nesbit and Hamdoun, 2020 ), and a recently published genome ( Warner et al, 2021 ), which together open the door to targeted stable mutagenesis. The contributions made using this species range from the seminal discovery of cyclins ( Evans et al, 1983 ) to the first characterizations of echinoderm cis -regulatory elements ( Xiang et al, 1991 ), the cytoskeletal controls of cell division ( Pal et al, 2022 ) and axis formation ( Henson et al, 2021 ), and modeling embryonic adaptations against ocean pollution and acidification ( Cserjesi et al, 1992 ; Wu et al, 2015 ; Smith et al, 2019 ).…”