Parthenogenesis

Parthenogenesis is the process by which an egg can develop without being fertilized by the sperm and is a form of reproduction common to a variety of lower organisms such as ants, flies, lizards, snakes, fish, amphibia, and honeybees that may occasionally reproduce in this manner.

Although mammals are not spontaneously capable of this form of reproduction, mammalian ova can successfully undergo artificial parthenogenesis in vitro. Mimicking the calcium wave induced by the sperm at fertilization, with the use of a calcium ionophore or other stimuli, the mature oocyte is activated and begins to divide. Mammalian parthenotes can develop into different stages after oocyte activation, depending on the species, but never to term.

Parthenogenetic activation can be induced at diferent stages along oocyte meiosis, resulting in parthenotes with diferent chromosome complements.

When parthenogenetic activation is performed in oocytes at the secondmetaphase it results in the extrusion of the second polar body and leads to the formation of a haploid parthenote. This method is rarely used since, in this case, the developmental competence is reduced compared to normal embryos and to diploid parthenotes.

Diploid parthenotes can be obtained in two different ways. The most common consists in combining the activation of metaphase II oocytes with exposure to an actin polymerization inhibitor, usually cytochalasin B. Alternatively, a diploid parthenote can be generated by preventing the extrusion of the first polar body. This protocol leads to the formation of tetraploid oocytes and the diploid status is then re-established at the end of oocytematuration with the extrusion of the second polar body.