Ultrastructural Comparison of Processing of Protein and Pigment in the Ink Gland of Four Species of Sea Hares

Jeffrey S Prince,Paul Micah Johnson

doi:10.1155/2015/847961

Abstract

The ink glands of four sea hare species (Aplysia californica,A. parvula,A. juliana, andDolabrifera dolabrifera) were compared to determine where ink protein is synthesized, how it is incorporated into protein storage vesicles, and the degree of variation in the structure of the ink gland. Ink protein was synthesized in RER cells and stored in amber and white vesicles. Lack of competent RER cells in the ink gland ofD. dolabriferawas correlated with the absence of ink protein. Ink protein had similar characteristics in all threeAplysiaspecies but, again, it was absent inD. dolabrifera. Its uptake involved pinocytosis by protein vesicle cell membranes. Granulate cells showed little variation in structure among the four species, the opposite was the case for RER cells. The conversion of the red algal pigment, phycoerythrin, to phycoerythrobilin (PEB) occurs in the digestive gland but the change of PEB to aplysioviolin (APV), the form of pigment released by the ink gland, occurs in the ink gland itself by both granulate cells and pigment vesicles. The literature describes five types of vesicles based upon color and contents in the ink gland of these four species. We report only three types of vesicle: colored (purple), protein (white and amber), and transparent (includes clear vesicles).

Highlights

All species of sea hares (Gastropoda: Euopisthobranchia: Anaspidea) have an ink gland and release white ink, purple ink, both colors together, or none at all [1,2,3,4]
The general ultrastructural architecture of the ink gland and the cell and vesicle types found in this gland are described below first for Aplysia californica and for the other species of sea hares
In A. californica the RER and granulate cell types and vesicles make up the ink gland [9]

Summary

Introduction

All species of sea hares (Gastropoda: Euopisthobranchia: Anaspidea) have an ink gland and release white ink, purple ink, both colors together, or none at all [1,2,3,4]. Ink of the beststudied-ink-producing sea hare species, Aplysia californica Cooper, 1863, consists largely of two components; 65% is phycoerythrobilin (PEB), the red algal photosynthetic pigment, r-phycoerythrin, minus its low molecular mass protein [2, 5,6,7,8,9] while 35% is high molecular weight protein. The second component of ink, the high molecular mass ink protein, is synthesized by the sea hare itself [3, 9]. This ink protein has been isolated and sequenced for several sea hares.

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Conclusion