The Draft Genome and Transcriptome of the Atlantic Horseshoe Crab, Limulus polyphemus.

Stephen D Simpson,Winsor H Watson Iii,Christopher C Chabot,Jordan S Ramsdell

doi:10.1155/2017/7636513

Stephen D Simpson, Winsor H Watson Iii + Show 2 more

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https://doi.org/10.1155/2017/7636513

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Abstract

The horseshoe crab, Limulus polyphemus, exhibits robust circadian and circatidal rhythms, but little is known about the molecular mechanisms underlying those rhythms. In this study, horseshoe crabs were collected during the day and night as well as high and low tides, and their muscle and central nervous system tissues were processed for genome and transcriptome sequencing, respectively. The genome assembly resulted in 7.4 × 105 contigs with N50 of 4,736, while the transcriptome assembly resulted in 9.3 × 104 contigs and N50 of 3,497. Analysis of functional completeness by the identification of putative universal orthologs suggests that the transcriptome has three times more total expected orthologs than the genome. Interestingly, RNA-Seq analysis indicated no statistically significant changes in expression level for any circadian core or accessory gene, but there was significant cycling of several noncircadian transcripts. Overall, these assemblies provide a resource to investigate the Limulus clock systems and provide a large dataset for further exploration into the taxonomy and biology of the Atlantic horseshoe crab.

Highlights

The Atlantic horseshoe crab, Limulus polyphemus, is an important species for a variety of reasons
Lateral inhibition, one of the underlying principles of visual physiology, was first demonstrated in Limulus by Haldan Keffer Hartline, and as a result he won the Nobel Prize in Physiology or Medicine in 1967 [7]. This species has been used as a model for the investigation biological rhythms, for instance, circadian rhythms of visual sensitivity [8,9,10]
Because no clear differences in the expression of putative circadian genes were apparent, we further examined some of the transcripts that did exhibit significant day/night or high/low tide differences as a first step towards the identification of potential proteins involved in the temporal control of the behavior and physiology in this species

Summary

Introduction

The Atlantic horseshoe crab, Limulus polyphemus, is an important species for a variety of reasons. In these habitats their foraging behavior releases trapped nutrients into their local environment [1, 2] Their eggs are a source of food for endemic and endangered long distance avian migrants. Lateral inhibition, one of the underlying principles of visual physiology, was first demonstrated in Limulus by Haldan Keffer Hartline, and as a result he won the Nobel Prize in Physiology or Medicine in 1967 [7] This species has been used as a model for the investigation biological rhythms, for instance, circadian rhythms of visual sensitivity [8,9,10]

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