Ultrastructure of the oocyte envelopes of some Eurasian acipenserids

Abstract

The cellular and acellular envelopes of oocytes and follicles at the ultrastructural level are described for some acipenserids. The objective was to identify whether morphological features exist that can assist in discrimination of caviar products in trade originating from various species. The follicular envelopes include one thecal and one follicular cell layer separated by a basal lamina. The oocyte is surrounded by four acellular layers: (i) the internal zona radiata directly in contact with the oocyte plasma membrane; (ii) the external zona radiata; (iii) a layer of alveolar material; and (iv) a thin adhesive layer probably secreted by the follicular cells. These structures are similar in the eggs of genus Acipenser and Huso. Comparison of descriptions and definitions from different authors reveal a confusing terminology and sometimes different terms are used for similar structures. A terminology for the envelopes of Acipenseriform eggs is proposed. The authors conclude that morphological characters of sturgeon eggs are less valuable for discrimination of caviar.

Formation and structure of egg envelopes in Russian sturgeon Acipenser gueldenstaedtii (Acipenseriformes: Acipenseridae)

“…(e) , Vacuoles containing material for the vitelline envelope in the peripheral ooplasm; er, endoplasmic reticulum; m, mitochondria; ld, lipid droplets. (f) Vitelline envelope: FL, the filamentous layer; t, trabecules; t1 (zre), trabecular layer t1 = zona radiata externa (Debus et al , 2008); , fibrils; ch, alveolar chorion; , the canals; O, oocyte; mv, oocyte microvilli.…”

“…During their formation in ovarian follicles, the egg envelopes develop numerous canals. Due to this process, either all the envelopes or only the vitelline envelope are referred to as zona radiata (Le Menn & Pelissero, 1991; Riehl, 1999; Debus et al , 2008). The main functions of egg envelopes include the fixation of a deposited egg to the substratum, sperm attraction, prevention of polyspermy and antibacterial and mechanical protection.…”

“…Eggs of Acipenseriformes (sturgeons and paddlefishes) are sticky, smooth and equipped with so‐called multiple micropyles, i.e. numerous micropylar openings located in a small area at the animal region of the egg (Cherr & Clark, 1982, 1985; Dettlaff et al , 1993; Linhart & Kudo 1997; Debus et al , 2008). In Acipenseridae, the number of micropylar openings varies not only among species but also among different females of the same species [white sturgeon Acipenser transmontanus Richardson: average seven micropylar openings (Cherr & Clark, 1982); shortnose sturgeon Acipenser brevirostrum Lesueur: several (Flynn & Benfey, 2007); beluga Huso huso (L.): up to 52 micropyles (Ginsburg, 1972)].…”

Ultrastructure and Histochemistry of the Periplasm in Oocytes of Sturgeons during Egg Envelope Formation

“…Eggs of sturgeons including the investigated species, Acipenser gueldenstaedtii and Acipenser baerii, are equipped with multiple micropyles lo-cated at the animal region that allow entry of numerous spermatozoa (CHERR & CLARK 1982;DEBUS et al 2008;PSENICKA et al 2010;¯ELAZOWSKA 2010). Observation of egg surfaces in A. transmontanus and in A. baerii during gamete fusion revealed that after incorporation of a spermatozoon, the contents of cortical granules was released into the space between the oocyte and egg envelope.…”

“…In oocytes of the investigated species, the layer of egg envelope located most externally to the oolemma slightly thickens. In A. baerii this layer is called the adhesive layer or jelly coat (DEBUS et al 2008;PSENICKA et al 2010). In A. gueldenstaedtii this layer is referred to as the extrachorion (¯ELAZOWSKA 2010).…”