Mechanisms in Fertilization^ 



CHARLES B. METZ 



Oceanographic Institute, Florida State University, Tallahassee, Florida 



FERTILIZATION LEADiNc; to biparcntal inheritance is a well nigh universal 

 phenomenon among animals and plants, both unicellular and multicellular. 

 Wherever it is studied it is seen to consist of a series of morphological, cytologi- 

 cal and physiological events, specific for the species, which under favorable 

 conditions proceed in a very precise and orderly fashion. The orderly nature 

 of these events suggests that they are interrelated and that they all proceed 

 from a few or even a single 'trigger-like' reaction between the interacting cells. 

 This presumed trigger reaction, frequently called the 'activation initiating 

 reaction,' and the physiological events which proceed from it, have been the 

 subject of intensive investigation over a period of many years. But in spite 

 of this effort, relatively little positive information concerning the activation 

 initiating reaction of fertilization is available. In fact some recent work indi- 

 cates that the activation initiating mechanism may be more complicated than 

 previously believed and that the concept of a simple trigger reaction may need 

 revision in so far as it applies to metazoan fertilization. 



This review will be confined to certain aspects of the recent work, namely 

 fertilization in the ciliate, Paramecium; possible trigger action on the sper- 

 matozoan as a prerequisite for fertilization; and some features of the activation 

 of the egg. A broader treatment of the subject of fertilization may be found in 

 several recent reviews (15, 62, 85, 86, 97, 99, 115, 116, 119). 



FERTILIZATION IN PARAMECIUM 



The physiology of fertilization has been studied more thoroughly in Para- 

 mecium than in any other protozoan (see ref. 62 for detailed review). Indeed, 

 some aspects of fertilization, particularly the activation initiating mechanism, 

 are more thoroughly understood in this form than in any metazoan. 



Mating or conjugation in Paramecium occurs only under certain physio- 

 logical conditions and these conditions are specific for the species or even for 

 particular varieties within a species. Furthermore, mating occurs only between 

 definite sexes or mating types, and is characterized by a very high order of 



1 The writer's studies have been aided by grants from the National Institutes of Health, 

 the American Cancer Society and the National Science Foundation. 



2 Contribution No. 72 from the Oceanographic Institute, Florida State University. 



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