UC San Diego

Metamorphosis is a radical morphological and environmental transition from a larval phase to an adult. This process is utilized by ~80% of all animal species and is a particularly common life history strategy among marine invertebrates. It has been well established that across species developmentally competent marine larvae utilize bacterial cues to indicate a suitable habitat conducive to adult survival and reproduction. Despite the high incidence of bacterially induced metamorphosis, the underlying mechanisms of how animals directly sense these signals remain under-studied, especially in Echinoderms (e.g., sea urchins). This study aims to a investigate component of the innate immune system, antimicrobial peptides (AMPs), as a potential candidate for connecting bacterial presence to metamorphosis. To explore AMPs as a player in bacterially induced metamorphosis, I utilized the rapid and synchronously developing sea urchin Lytechnius pictus. I first identified a homolog of the Echinoderm specific AMP Strongylocin 2 in L. pictus. I found that LpStrongylocin 2 (LpS2l) is only transcribed in early larvae in the event of bacterial infection. In nascent late-stage larvae, LpS2l transcription is upregulated and accumulates within cells in developing adult structures, likely a subtype of blastocoelar cells. The spatiotemporal regulation of LpS2l transcription in L. pictus larvae suggests a role for AMPs in the development of new structures and recognizing metamorphosis-inducing bacterial cues. Future experiments will be aimed at assessing functional role of LpS2l in metamorphosis by disrupting transcription using CRISPR/Cas9 sgRNA guides designed in this study.