Egg jelly (extracellular layer'', ''jelly coat) is a gelatinous layer that surrounds the

oocyte An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ...

s of many organisms and releases species-specific chemoattractants that activate and guide sperm to the oocyte. The release of chemoattractants is species dependent. For example, sperm in ''

Lytechinus variegatus ''Lytechinus variegatus'', commonly called the green sea urchin or the variegated sea urchin, is a species of sea urchin that can be found in the warm waters of the western Atlantic Ocean and Caribbean Sea. Subspecies There are four subspec ...

'', the green sea urchin, are not chemotactically attracted to the jelly or the egg. The egg jelly is located immediately surrounding the

vitelline envelope The insect vitelline envelope is the outer proteinaceous layer outside the oocyte and egg. The vitelline envelope, not being a cellular structure, is commonly referred to as a membrane. However, this is a technical misnomer as the structure is com ...

and consists primarily of a network of short peptides and sulfated fucan glycoproteins. These short peptides diffuse into the surrounding area and stimulate respiration and movement of the sperm to the egg. An example of such a peptide is resact, which has been studied as the primary means of attracting and orientating sperm to the eggs in sea urchins. The sulfated fucan glycoproteins play an important role in binding to sperm receptors and triggering the

acrosomal reaction During fertilization, a sperm must first fuse with the plasma membrane and then penetrate the female egg cell to fertilize it. Fusing to the egg cell usually causes little problem, whereas penetrating through the egg's hard shell or extracellula ...

. Many other functions for the egg jelly have been proposed including sperm agglomeration, protection from mechanical stress and

polyspermy In biology, polyspermy describes the fertilization of an egg by more than one sperm. Diploid organisms normally contain two copies of each chromosome, one from each parent. The cell resulting from polyspermy, on the other hand, contains three or ...

, and increasing the size of the egg to improve its chances of colliding with sperm. For echinoderms the jelly coat can increase the diameter of the egg by more than 100%, making it efficient in enhancing fertilization. In female ''P. shqipericus,'' the

Albanian water frog The Albanian water frog (''Pelophylax shqipericus'') is a species of true frog (family Ranidae) and is native to Albania and Montenegro. As its common name suggests, it prefers aquatic environments. The Albanian water frog is an endangered spec ...

, the jelly coat cause sperm to become motile and move faster. For this species of frog, the sperm must interact with the jelly coat for the egg to be successfully fertilized. Unlike the egg cell, jelly coats do not provide the embryo nutrients. In addition to the sea urchin, egg jelly appears in many species including invertebrates and mammals. Egg jelly can vary in composition and complexity from the relatively homogenous single layer sea urchin egg to the three layer egg jelly in starfish. There is an increasing concern in how

ocean acidification Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxid ...

will affect the fertilization of eggs. In ''H. tuberculate,'' low pH can damage the eggs chemical influence on sperm mobility and velocity.

References

Germ cell structures {{developmental-biology-stub

See also

References