Spermiogenesis and spermatozoa in mammals.

This is a summarizing review about some aspects of the morphogenesis and characteristics of mammalian spermatozoon. The morphology, biogenesis and function of the different spermatozoon structures are analysed, as well as different aspects, like immunology and endocrine control. Comparative morphology, fate and function of the male gamete during its passage through the epididymis and female tract are commented. The fact, that the phenomenon of spermiogenesis continues with the maturative changes in the epididymis, and that modifications occur in the female genital tract is put forward; this idea seems to be basic for understanding the role of many spermatozoon structures, as well as many biochemical and molecular changes that take place in the gamete. On the other hand, all these changes (spermiogenesis, maturation, capacitation and acrosomal reaction in the female tract), as well as the interaction sperm/egg are sequentially dependent, and are focussed on the sperming capacity of reaching and fertilizing the egg. Many gaps exist in regard to the functional role of different spermatozoon structures, and three important questions are emphasized with a view to solving these problems: a) The importance of the comparative analysis of spermatozoon and egg structures in different mammalian species. b) The necessity to develop ample studies using in vivo situations, particularly in reference to the changes occurred in the female tract. In this regard, the majority of studies have been developed in the in vitro situation, which is very different from the natural environment. c) The importance of using and compiling the different data (morphological, biochemical, molecular, etc.) about spermiogenesis, spermatozoon and fertilization. In the future, the use of new technologies appears as a promising idea to clarify doubts about spermatozoa biogenesis and function in mammals.