Fertilization Studies and Assisted Fertilization in Mammals: Their Development and Future

Abstract

Abstract. Studies of mammalian fertilization progressed very slowly in the beginning because of difficulties in obtaining a large quantity of fully mature eggs at one time. With progression of techniques to collect and handle eggs and spermatozoa, research in mammalian fertilization advanced rapidly. Today, far more papers are published on mammalian gametes and fertilization than those of all other animals combined. The development of assisted fertilization and related technologies revolutionized basic research as well as human reproductive medicine and animal husbandry. Reproduction is fundamental to human and animal lives. The author lists a few subjects of his personal interest for further development of basic and applied research of gametes and fertilization. Each reader will probably have more exciting subjects of future investigation. Key words: Assisted fertilization, Egg, Fertilization, ICSI, Sperm Discovery of Mammalian Eggs, Spermatozoa and Fertilization Although it was known from ancient times that the eggs of birds and frogs were the start of new life, no one was certain whether this was true for mammals until Karl von Bare 1792-1876 (1827) discovered tiny eggs within dog and human ovaries. Interestingly, spermatozoa had been discovered 150 years earlier by Anton van Leeuwenhoek 1632-1723 (~1676)* and a medical student of Leiden, Johan Ham who saw many tiny tadpole-like creatures ("animacules") within human seminal plasma. Leewenhoek later saw same creatures in the semen of the rabbit, dog and fish. He thought that they were normal components of semen originating from the testis. Obviously, Leeuwenhoek saw spermatozoa without knowing their exact biological role. It was not until 1840s-1870s when it became clear that spermatozoa and eggs of all animals, large or small, are cells [Albert von Koelliker 1817-1905 (1840) ; Karl Gegenbaur (1861)] and that sperm entry into the egg -in particular the union of sperm and egg nuclei (sygamy) -is the essence of fertilization and provides cytological evidence of biparental inheritance [Edouard van Beneden 1846-1910 (1875) Studies of Mammalian FertilizationThe analysis of animal fertilization began from the start of the 20 th century. Because invertebrate animals such as sea urchins and starfish produce millions of mature eggs at one time and their fertilization and embryo development can be followed readily in a dish of seawater, most of the early and important investigations of fertilization were done using gametes of aquatic invertebrate animals. In mammals, even after induction of superovulation, only a few eggs (usually up to 40-50) can be obtained from a single female. Furthermore, eggs are normally fertilized and develop within the female's body, which makes observations and experiments of eggs cumbersome. Because most investigators of mammalian eggs and fertilization used fixed and stained materials, the study of mammalian fertilization progressed very slowly. It was Colin "Bunny" Austin who disclosed many details of mammalian fertilization using the...

Artificial activation of mature unfertilized eggs in the malaria vector mosquito, Anopheles stephensi (Diptera, Culicidae)

“…As long as sperm are injected directly into eggs, similar to ICSI performed in mammals, the quality of sperm does not seem to be an issue. A spermatid can be used for ICSI in mammals (Yanagimachi, 2012). Elongated spermatids can be used for ICSI in A. rosae as well as mammals (Hatakeyama et al, 2000).…”

“…Artificial fertilization, such as intracytoplasmic sperm injection (ICSI) using cryopreserved sperm, is one of the most general methods for the storage of strains in mammals (Yanagimachi, 2012). The cryopreservation of sperm is a very simple and efficient method that is an alternative to the cryopreservation of larval gonads or embryos.…”

The pioneering of intracytoplasmic sperm injection: historical perspectives

“…Early studies of fertilization were conducted in invertebrate animals such as the sea urchin and starfish (Yanagimachi 2012). These animals generally produced millions of mature oocytes at one time, with fertilization and subsequent embryo development occurring outside the body (Yanagimachi 2012).…”

“…These animals generally produced millions of mature oocytes at one time, with fertilization and subsequent embryo development occurring outside the body (Yanagimachi 2012). Furthermore, the early stages of development could be observed in a simple dish of sea water under laboratory conditions (Yanagimachi 2012).…”

“…These animals generally produced millions of mature oocytes at one time, with fertilization and subsequent embryo development occurring outside the body (Yanagimachi 2012). Furthermore, the early stages of development could be observed in a simple dish of sea water under laboratory conditions (Yanagimachi 2012). Although 40-50 mammalian oocytes could be obtained from mice or rabbits using superovulation, the process of fertilization occurred inside the body of a female (Yanagimachi 2012).…”