The Sperm Cell - Production, Maturation, Fertilization, Regeneration

Description

Eggs are made for sperm. Sperm are made for eggs. All other (body) cells are made to support, directly or indirectly, the development of eggs and sperm and the survival of their united product: the zygote – the next generation. he prime function of spermatozoa is to deliver the male genome safely into eggs. Any errors during sperm formation, maturation and union with eggs will result in serious problems in themale’s fertility and in the wellbeing of the ofspring. his book covers our current knowledge of (1) the formation of spermatozoa, (2) the preparation of spermatozoa for fertilization, (3) the union of spermatozoa with eggs, (4) the awakening of ‘sleeping’ eggs by spermatozoa leading to embryo development, (5) genomic and nongenomic (e.g. environmental) factors afecting the development and fertility of spermatozoa, and (6) the challenges of overcoming male (sperm) fertility problems. Information compiled in each chapter should be considered a stepping stone to better understanding and better control of male fertility and infertility. The very first chapter of this book mentions the possible production of ‘artificial human spermatozoa’ from pluripotent stem cells such as human iPSCs. Obviously, it is not appropriate to use live animals or get assistance from live animal cells to achieve this goal. To eliminate or minimize the stress and risks these cells would face during their transformation into haploid cells, we must learnmuchmore about what is really happening in the natural environment of spermatogenic cells, within the testes.he last chapter considers the value of the mouse as a model for the study of mammalian fertility and infertility. Is the mouse a perfect animal model to use for the study of fertility and infertility of all mammals, including humans? Although the mouse is certainly one of the most heavily used model animals for studying mammalian fertility and reproduction, we must remember that each animal uses species-speciic tactics to produce its ofspring. What is found in one species must be extrapolated to other species with caution. Today, it is theoretically possible to reproduce any mammals without males. In fact, hundreds of cows have already been produced by somatic cell nuclear transfer. Clearly, males are not essential for animal and human reproduction. Why are there males? At the beginning of life on Earth, there were no males. Females reproduced by themselves. During the course of evolution, a bisexual mode of reproduction emerged, and it has been maintained in most animals, including humans. Compared with animals propagating unisexually (females only), animals using a bisexual mode of reproduction seemto be less vulnerable to extinction in the face of constantly changing, competitive environments. Technically, human cloning (nonsexual reproduction) is possible today. In other words, humans can reproduce without males. Is this what we desire? A few years ater the birth of Dolly (a cloned sheep) andmany clonedmice, I gave talks to groups of people about animal and human cloning. At the end of my talk I asked the audience if they wanted to live in a world without men. With no exception, women did not want to live in the worldwithoutmen. ‘It would be boring. We cannot use men?hat would be horrible.’ Men are needed by women, and we will stay that way. When I started research as an undergraduate student, I thought everything written in books and research papers was a fact. I now know that what is written is authors’ interpretations or just a part of the whole story. Many things written in books and reported in original papers will be modiied and even discarded during the next 40–50 years. Science progresses that way. The comprehensive collection of topics that compose this new edition of he Sperm Cell provide readers with a map and compass to chart a course for future investigations. It is the readers’ task ater reading these highly topical research areas to determine what subjects are let unclear and compelling, what next courses might be important to follow and what burgeoning questions are yet to be studied. Ryuzo Yanagimachi, PhD Professor Emeritus, Department of Anatomy, Biochemistry and Physiology, Institute of Biogenesis Research, John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii