Fertilization in ascidians: Studies on the egg envelope, sperm and gamete interactions in Phallusia mammillata

Honegger, Thomas G.

doi:10.1016/0012-1606(86)90079-5

Cited by 64 publications

(41 citation statements)

References 30 publications

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“…Foreign spermatozoa initially interacting with the follicle cell layer remain on its surface, leaving the interfollicular clefts empty; however, other functions are performed, such as mucus secretion, sperm attraction, entrapment and phagocytosis and, to a lesser extent, sperm mitochondrion translocation. Therefore, even if the species-specific block is ensured by the vitelline coat (Rosati and De Santis, 1978;Honegger, 1986;Lambert, 1986) the follicle cells undoubtedly act as the first obstacle to heterospecific sperm penetration.…”

Section: Discussionmentioning

confidence: 99%

The Follicle Cells of Styela Plicata (Ascidiacea, Tunicata): A Sem Study

Villa¹,

Patricolo²

2000

Zoological Science

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Section: Discussionmentioning

confidence: 99%

The Follicle Cells of Styela Plicata (Ascidiacea, Tunicata): A Sem Study

Villa¹,

Patricolo²

2000

Zoological Science

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“…At their base follicle cells are attached to the OFL. Cell-cell contact between FCs is established by several filopodia which contain actin filaments (Honegger, 1986). Typical junctions cannot be recognized at contact site of the filopodia.…”

Section: Tg Honegger and R Koyanagimentioning

confidence: 99%

“…This is also the case if conventional preparation is applied for transmission electron microscopy (TEM). Due to dehydration the VC appears as a relatively thin bi-or tripartite filamentous structure of about 400 to 900 nm (Honegger, 1986;Xie and Honegger, 1993;Cloney, 1995;Burighel and Cloney, 1997). Especially the filamentous structure of the inner VC layer mostly appears compressed and its different appearance in diverse species may be an artifact.…”

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confidence: 99%

The ascidian egg envelope in fertilization: structural and molecular features

Honegger¹,

Koyanagi²

2008

Int. J. Dev. Biol.

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In this report, unpublished and recent findings concerning the structure and function of the ascidian egg coat are compiled in context with fertilization. In the initial stage of ascidian fertilization, sperm interact with a complex egg investment that consists of a layer of follicle cells attached to an acellular vitelline coat. Increasing evidence exists that ascidian sperm are activated at their encounter with the follicle cells. The molecular basis of sperm-follicle cell interactions is discussed in context with sperm binding, membrane proteins and sperm bound glycosidase. The model that suggests a block to polyspermy established by glycosidase released from the follicle cells on fertilization is evaluated and compared with assured facts. Although a number of questions remain to be answered, our recent findings that a cloned β-hexosaminidase from P. mammillata binds exclusively to the follicle cells of unfertilized but not fertilized eggs, indicates that the follicle cells participate in the block to polyspermy. A dual function, mediating sperm activation and a block to polyspermy attributes to the ascidian follicle cells a key position in fertilization. KEY WORDS: fertilization, ascidian, egg coat, follicle cellThe ascidian egg envelope: a survey of the structural features Ascidian eggs are surrounded by an acellular envelope called chorion or vitelline coat (VC) to which follicle cells (FCs) adhere externally and test cells (TC) internally. Multitudinous functions have been attributed to the egg envelope as entity and to each of its structural components. In the present paper we focus on the role of the egg envelope in fertilization particularly the function of FCs in sperm egg-interaction.The pictures of Phallusia mammillata eggs ( Fig. 1 A,B) give a view of the egg and egg envelope representative for solitary and colonial ascidians with external fertilization. The egg of about 130 µm in diameter exhibits a relatively smooth plasma membrane with only few short microvilli. It is surrounded by an acellular VC with test cells attached to the inner and follicle cells to the outer surface. In most solitary species, the follicle cells are cubical or columnar or rarely tall cone-shaped as in Ciona. Test cells typically adhere to the inner matrix of the VC not to the egg surface. In some species, they form an almost closed sheet in others they are loosely arranged in groups. Although scanning electron microscopy (SEM) pictures reveal a good 3D impression, Int. J. Dev. Biol. 52: 527-533 (2008) the real dimension of the highly hydrated VC layers is never preserved and the highly vacuolated follicle cells are shriveled. This is also the case if conventional preparation is applied for transmission electron microscopy (TEM). Due to dehydration the VC appears as a relatively thin bi-or tripartite filamentous structure of about 400 to 900 nm (Honegger, 1986;Xie and Honegger, 1993;Cloney, 1995;Burighel and Cloney, 1997). Especially the filamentous structure of the inner VC layer mostly appears compressed and...

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“…They suggested that sperm binding could be mediated by an enzymesubstrate complex established between a sperm surface glycosidase and glycoside moieties on the egg coat. Because glycosidases usually have a low activity at neutral and alkaline conditions, a transitory stable lectin-like enzyme-substrate binding would be established in sea water (Hoshi 1984;Honegger 1986;Lambert 1989b;Godknecht & Honegger 1991;Godknecht & Honegger 1995). The currently favored model of ascidian fertilization claims that sperm ␤ -hexosaminidase participates in transient spermegg binding and that ␤ -hexosaminidase released from the egg contributes to the block against polyspermy (Lambert 1989a,b;Lambert et al .…”

Section: Introductionmentioning

confidence: 99%

Molecular cloning and sequence analysis of an ascidian egg β‐N‐acetylhexosaminidase with a potential role in fertilization

Koyanagi

Honegger²

2003

Dev Growth Differ

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␤ -N-Acetylhexosaminidase, which is found almost ubiquitously in sperm of invertebrates and vertebrates, supposedly mediates a carbohydrate-based transient sperm-egg coat binding. In ascidians and mammals, ␤ -hexosaminidase released at fertilization from eggs has been proposed to modify sperm receptor glycoproteins of the egg envelope, thus setting up a block to polyspermy. Previously, it was shown that in potential sperm receptor glycoproteins of the ascidian Phallusia mammillata , N-acetylglucosamine is the prevailing glycoside residue and that the egg harbors three active molecular forms of ␤ -hexosaminidase. In the present study, P. mammillata ␤ -hexosaminidase cDNA was isolated from an ovarian cDNA library and characterized. The deduced amino acid sequence showed a high similarity with other known ␤ -hexosaminidases; however, P. mammillata ␤ -hexosaminidase had a unique potential N-glycosylation site. A phylogenetic analysis suggested that P. mammillata ␤ -hexosaminidase developed independently after having branched off from the common ancestor gene of the chordate enzyme before two isoforms of the mammalian enzyme appeared. In situ hybridization revealed stage-specific expression of ␤ -hexosaminidase mRNA during oogenesis in the oocyte and in the accessory test and follicle cells. This suggests that the three egg ␤ -hexosaminidase forms are specific for the oocyte, test cells and follicle cells.

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Fertilization in ascidians: Studies on the egg envelope, sperm and gamete interactions in Phallusia mammillata

Cited by 64 publications

References 30 publications

The Follicle Cells of Styela Plicata (Ascidiacea, Tunicata): A Sem Study

The Follicle Cells of Styela Plicata (Ascidiacea, Tunicata): A Sem Study

The ascidian egg envelope in fertilization: structural and molecular features

Molecular cloning and sequence analysis of an ascidian egg β‐N‐acetylhexosaminidase with a potential role in fertilization

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