Formation of the Micropyle in<i>Tilapia mossambica</i>Peters and<i>Stigmatogobius javanicus</i>(Blkr.)

Aravindan, C M; Padmanabhan, K.G.

doi:10.1111/j.1463-6395.1972.tb00572.x

Acta Zoologica

1972

DOI: 10.1111/j.1463-6395.1972.tb00572.x

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Formation of the Micropyle inTilapia mossambicaPeters andStigmatogobius javanicus(Blkr.)

C M Aravindan

K.G. Padmanabhan

Abstract: The formation of the micropyle in Tilapia mossambica and Stigmatogobius javanicus, two fresh water teleosts is described. In T. mossambica the micropyle is formed by a single modified follicular cell, while in S. javanicus it is formed by a cellular mass derived from the follicle.

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Fine structure of the micropylar apparatus of the chum salmon egg, with a discussion of the mechanism for blocking polyspermy

Kobayashi

Yamamoto

1981

J. Exp. Zool.

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The micropylar apparatus of the eggs of the chum salmon, Oncorhynchus keta, was examined by scanning and transmission electron microscopy. The apparatus consists of a funnel-shaped vestibule, from the bottom of which extends the micropylar canal, about 5 pm, in diameter. The canal traverses the entire zona pellucida interna of the egg envelope, about 30 pm in thickness. At its inner end, the diameter of the micropylar canal is the same as the width of the sperm head, about 2 pm. The lower portion of the canal is occupied by a conspicuous outgrowth of the ooplasmic surface, 3-10 pn in length.The first contact of the ooplasmic surface with a fertilizing spermatozoon occurs at the apex of the outgrowth in the micropylar canal. The surface of the outgrowth undergoes changes immediately after penetration by a fertilizing spermatozoon that prevent supernumerary spermatozoa from penetrating the ooplasm. As the formation of the perivitelline space takes place, the outgrowth withdraws from the micropylar canal. Supernumerary spermatozoa, however, cannot enter the perivitelline space and are eliminated from the canal lumen. In addition, the micropylar canal decreases in diameter at the region near its inner end and forms a mechanical barrier to the passage of supernumerary spermatozoa.

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Fine structure of the micropylar apparatus of the chum salmon egg, with a discussion of the mechanism for blocking polyspermy

Kobayashi

Yamamoto

1981

J. Exp. Zool.

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Fine structure of the micropylar cell and its change during oocyte maturation in the chum salmon, Oncorhynchus keta

Kobayashi

Yamamoto

1985

Journal of Morphology

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In the ovarian follicle, the micropylar cell (MPC) is distinguished from neighboring granulosa cells by its larger cell size and its thick cytoplasmic process. The micropylar cell body fits into a shallow depression (micropylar vestibule) on the outer surface of the egg envelope; its process extends through the micropylar canal, which extends from the bottom of the vestibule through the full thickness of the zona pellucida interna. At its distal end, the cell process expands into a bulb which fits into an indentation of the ooplasmic surface immediately beneath the inner opening of the micropylar canal. Intermediate and desmosomelike junctions establish an intimate association between MPC process and oocyte. Various kinds of organelles and inclusions in the MPC show a characteristic pattern of cytoplasmic distribution; rough endoplasmic reticulum with markedly dilated cisternae is found exclusively in the main cell body, while microtubules and thin filaments are observed in the cytoplasmic process. Immediately before or during the breakdown of the germinal vesicle in the intrafollicular oocyte, the cytoplasmic process of the MPC gradually decreases in length and begins to withdraw from the micropylar canal. At the same time, the ooplasmic surface protrudes outward to form a papilla in the canal. The intimate MPC-oocyte association disappears during formation of the ooplasmic papilla. Hydration of the oocyte apparently occurs at the final stage of maturation and probably participates in papilla formation. Although the MPC undergoes degenerative changes as ovulation draws near, it remains attached to the inner surface of the granulosa cell layer even after its association with the oocyte has completely disappeared. We speculate that the micropyle develops during fish oogenesis through the combined activity of the MPC and neighboring granulosa cells. It appears that the cell body of the micropylar cell and nearby granulosa cells exert mechanical pressure on the external surface of the growing oocyte and thus participate in formation of the micropylar vestibule. The cytoplasmic process of the MPC evidently forms a passive barrier to deposition of material for the egg envelope in the animal pole, thereby resulting in formation of the micropylar canal.

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A comparative analysis of the evolution of the egg envelopes and the origin of the yolk

Mazzini

Callaini

Mencarelli

1984

Bolletino di zoologia

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In this paper, the evolution of egg envelope is examined from a structural point of view. The structurally simplest eggs are found in Sponges and Cnidarians where reproduction is ensured by external fertilization. In these instances, the oocyte plasma membrane is protected by only a thin glycocalyx. A more structurally complex envelope is present in triblastic hletazoa where the vitelline membrane makes its first appearance. With the emergence of internal fertilization, the egg envelope is modified as to face the constraints imposed by the terrestrial environment. However the pursuit of such defensive strategy would have made eggs practically impermeable to spermatozoa. Eggs with a thick chorion are thus endowed with a proper micropyle to allow fertilization. With the acquisition of viviparity egg envelopes have undergone marked reduction. In this paper particular attention has also been paid to the relationship of the oocyte with accessory cells and to the nature and function of the reserve material stored in the oocyte. The role of cortical granules and of gamete interaction during fertilization is also discussed.

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Formation of the Micropyle inTilapia mossambicaPeters andStigmatogobius javanicus(Blkr.)

Abstract: The formation of the micropyle in Tilapia mossambica and Stigmatogobius javanicus, two fresh water teleosts is described. In T. mossambica the micropyle is formed by a single modified follicular cell, while in S. javanicus it is formed by a cellular mass derived from the follicle.

Cited by 5 publications

References 0 publications

Fine structure of the micropylar apparatus of the chum salmon egg, with a discussion of the mechanism for blocking polyspermy

Fine structure of the micropylar apparatus of the chum salmon egg, with a discussion of the mechanism for blocking polyspermy

Fine structure of the micropylar cell and its change during oocyte maturation in the chum salmon, Oncorhynchus keta

A comparative analysis of the evolution of the egg envelopes and the origin of the yolk

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