Fertilization of the lamprey (<i>Lampetra japonica</i>) eggs: Implication of the presence of fast and permanent blocks against polyspermy

DOI Web Site Web Site 被引用文献3件

この論文をさがす

抄録

<jats:title>Abstract</jats:title><jats:p>We have carried out a morphological examination to analyze the mechanism of monospermic fertilization in the lamprey, <jats:italic>Lampetra japonica</jats:italic>. Upon insemination, many sperm passed through a “tuft” of jelly that is found only on the animal pole area of the egg and underwent the acrosome reaction after they came into contact with the outer surface of the two‐layered vitelline envelope. The acrosomal filaments were admitted into the envelope and their tips touched the ooplasmic surface. The Hoechst dye transfer method revealed that a single sperm showed intense fluorescence before its nucleus penetrated the vitelline envelope; this indicated the actual fusion of the gametes. No other sperm with acrosomal filaments fluoresced, however. These findings indicate that a fast block against polyspermy is established at the plasma membrane level and prevents additional sperm‐egg fusion.</jats:p><jats:p>The separation of the ooplasmic surface from the vitelline envelope (perivitelline space formation) was initiated beneath the margin of the animal pole region and progressed toward the animal and vegetal poles of the egg. At this stage, the head of a fertilizing sperm passed through the thickness of the vitelline envelope. The nuclei of supernumerary sperm were unable to enter the inner layer of the vitelline envelope. During the early phase of the perivitelline space formation at the animal pole region, many thin threads and one, or a small number, of the thick projection(s) of the ooplasm connected the envelope with the vitellus. A fertilizing sperm invariably moved along one of the thin threads and was embedded in the ooplasm at the animal pole region. Cytochalasin B inhibited sperm from passing through the inner layer of the vitelline envelope. When ionophore‐activated eggs were inseminated, the tips of the acrosomal filaments were prevented from touching the ooplasmic surface by the intervening presence of the perivitelline space. None of these sperm passed through the vitelline envelope. These findings suggest that the fusion of the acrosomal filament with the egg plasma membrane is a prerequisite for the passage of sperm through the inner layer of the vitelline envelope. Furthermore, actin‐mediated ooplasmic activity is probably involved in the passage. We conclude that the formation of the perivitelline space at the animal pole region contributes to the establishment of a permanent block against polyspermy in the lamprey egg. © 1994 Wiley‐Liss, Inc.</jats:p>

収録刊行物

被引用文献 (3)*注記

もっと見る

キーワード

詳細情報 詳細情報について

問題の指摘

ページトップへ