Gamete interactions and the fate of sperm organelles in fertilized echinoderm eggs

We demonstrate that complete sea urchin male pronuclear development in vitro is a two-step process involving membrane-independent chromatin decondensation and nuclear envelope-dependent pronuclear swelling. In the absence of cytoplasmic membrane vesicles (MVs), permeabilized sperm chromatin decondenses into a spherical nucleus of approximately 4 microns in diameter. Pronuclear swelling to approximately 7 microns requires an intact nuclear envelope, and the degree of swelling is limited by the amount of MVs assembled on the chromatin. Furthermore, after a nuclear envelope is formed, swelling can occur in the absence of additional cytoplasmic MVs. Nuclear swelling also requires ATP hydrolysis, Ca2+ and cytosolic factors, some of which are sensitive to heat and to the sulfhydryl alkylating agent, N-ethylmaleimide. The requirement for a nuclear envelope and the rate of pronuclear swelling are consistent with previous in vivo observations.

Section: Ne Growthmentioning

confidence: 88%

Formation of the sea urchin male pronucleus in vitro: Membrane‐independent chromatin decondensation and nuclear envelope‐dependent nuclear swelling

Collas

Poccia

1995

“…We only detected two sperm transients and no modified ACs at higher negative V c out of 98 experiments examined for MOs, suggesting that failure of sperm entry at more negative voltages seems to be quite few and different from that in sea urchin eggs. These results may account for involvement of CGE for the failure of sperm entry in sea urchin eggs voltage‐clamped at negative V c because a mature starfish oocyte seems to have less cortical granules located in a bit deeper position from the plasma membrane compared to a sea urchin egg (Ivonnet et al, 2017; Longo, 1991; Longo et al, 1995).…”

Section: Discussionmentioning

confidence: 97%

“…According to the report on L. variegatus , I on was supposed to indicate the electrical continuity between an attached sperm and the sperm attachment site or the vicinity of egg membrane (McCulloh & Chambers, 1992). Four or five times smaller or no I on in MOs compared to sea urchin eggs may be due to the morphological difference; a fertilizing starfish sperm has a long and skinny acrosomal process (15–25 µm for length [L], 20–30 nm in diameter [d]) to the oocyte whereas a sea urchin sperm has very short acrosome process (L = 0.5 µm, d = ~60 nm) bridged to the egg (Dan & Hagiwara, 1967; Longo, 1991). Thus the connection between two gametes with elongated acrosome in sea urchin is much shorter but thicker than that in starfish.…”

Section: Discussionmentioning

confidence: 99%

Starfish oocytes of A. pectinifera reveal marked differences in sperm‐induced electrical and intracellular calcium changes during oocyte maturation and at fertilization

Mohri

Kyozuka

2021

Although changes in membrane potential and intracellular Ca2+ (Cai) during fertilization in starfish oocytes have been known for long time, little is known precisely about how and what kind of channels are involved during oocyte maturation and in fertilization, and how the mechanisms of changes in Cai in oocytes develop during oocyte maturation. Since in starfish, oocyte maturation‐inducing hormone, 1‐methyladenine (1MA) is well known, we took advantage of it to investigate the developmental process of channel‐function and changes in Cai in three different developmental stages using 1MA. Sperm‐induced membrane current at voltage clamp and changes in Cai in starfish oocytes, Asterina pectinifera, were examined in stages of immature, partly mature (a state in 15–20 min after sufficient concentration, 1 µM of 1MA addition, or 30–40 min exposure to subthreshold concentration of 1MA), and mature oocytes (MO). We found some immature and many partly MOs showed fluctuating responses in membrane current, membrane potential, and corresponding changes in Cai, which are distinct from those in MOs. The responses in immature and partly MOs indicate physiologically characteristic responses of insufficient changes in Cai and its corresponding electrical responses at the partial developmental stage during maturation. Our data should shed light on the mechanism of egg activation and oocyte maturation in terms of examining membrane current and corresponding changes in Cai.

Sperm incorporation and pronuclear development during fertilization in the freshwater bivalve Dreissena polymorpha

Misamore

Stein

Lynn

2006

The invasive zebra mussel, Dreissena polymorpha (D. polymorpha), is proving to be a valuable model for understanding general mechanisms of fertilization, particularly regarding sperm incorporation. In the present study, we tracked the various components of the fertilizing sperm of D. polymorpha during sperm incorporation. During fertilization the sperm membrane remains associated with the egg surface as a distinct patch that disperses over time. This patch marked the site of sperm entry that occurs predominately on the CD blastomere. Taking advantage of the relatively unpigmented cytoplasm, real-time observations were made of the incorporated sperm nucleus as it decondensed and reformed as a developing pronucleus. Pronuclear enlargement occurred progressively and at rates comparable with previously reported fixed-time point observations. Sperm mitochondria were incorporated and separated from the sperm along the leading edge of the decondensing nucleus. Sperm mitochondria labeled with Mitotracker Green remained predominately associated with the CD blastomere following first cleavage and could be tracked to the 16-cell stage before the fluorescence was too faint to detect. Additionally, the demembranated sperm axoneme was incorporated, separated during nuclear decondensation, and remained visible in the egg cytoplasm up to 30 min postinsemination (PI). The present study provides one of the most complete descriptions of incorporation on multiple sperm components into the egg and coordinates fixed-time point observations with real-time observations of sperm within the remarkably transparent egg cytoplasm of zebra mussels.