Cumulus oophorus

Function 

Cumulus oophorus consists of a cluster of granulosa cells that surround and support the oocyte (a female germ cell involved in reproduction) in an antral follicle (a developmental stage of a follicle, with a single fluid-filled cavity in the center, Pic. 1). These cells serve three primary functions:

1. Before ovulation, the cells of cumulus oophorus support oocyte maturation and coordinate follicle (a small sac-like structure which contains developing oocytes) development. Their roles include transport of nutrients to the oocyte, production of specific proteins and regulation of gene expression (production of proteins encoded by specific genes). 
2. During ovulation, these cells protect the oocyte and probably serve to direct it into the oviduct (Fallopian tube).
3. During fertilization, they also protect the oocyte and they participate in the complex regulation of fertilization. Cumulus cells are thought to have the ability, to some extent, to select viable sperm cells that enter the oocyte, entrap them and guide them towards the oocyte.
   

Structure 

Cumulus oophorus consists of a group of cells that are tightly packed together around the maturing oocyte. They originate from the cell population known as membrana granulosa, or granulosa cells, which form a solid layer around the oocyte in the early stages of follicle maturation (Pic. 2). As the follicle matures, small spaces start to appear among the granulosa cells. These spaces gradually fuse together until they form a single cavity in the center of the follicle, which is filled with fluid and is called a follicle antrum. One part of the granulosa cells then forms a layer lining the antrum, and the rest forms a cluster of cells that bulges into the antrum and contains a mature oocyte, which is called the cumulus oophorus (Pic. 3). The part that connects the cumulus itself to the rest of granulosa cells is sometimes called discus prodigerus. Furthermore, the innermost layer of the cumulus, that directly surrounds the oocyte, is called corona radiata, and it has important roles in protecting the oocyte during ovulation.

Gene expression profiling

Gene expression profiling is a procedure used to estimate oocyte quality in laboratory conditions. It can give hints whether the gene information contained in the oocyte have suffered mutations or hints about the embryo development and pregnancy outcomes. Such information is used to describe the competence of an oocyte. It is possible to determinate the competence of an oocyte according to the level of gene expression of specific genes of cumulus cells.

Pathological conditions

The exact role of cumulus cells in fertility and its disorders is still not fully understood. However, studies show that proteins produced by cumulus cells are indispensable for a healthy oocyte development and normal ovulation. Therefore, disorders of the cumulus oophorus functions may account for a portion of cases of unexplained infertility and ovulatory disorders.