GAMETOGENESIS AND FERTILIZATION 



717 



(a) Gametogenesis and fertilization 



The mechanics of fertihzation are a perennially active field of inquiry. Several 

 features of the process (approach of the sperm, attachment and penetration, 

 responses of the egg) have been reviewed by Tyler (1955). He discusses four 

 categories of substances related to the process of fertilization: fertilizins, anti- 

 fertilizins from eggs, antifertilizins from sperm and lytic agents from sperm. 

 Evidence is presented for the glycoprotein nature of fertilizin of Strongylocentrotus 

 purpuratus, and for protein structure of antifertilizins of egg and sperm. Related 

 to the gelatinous covering of fresh water and marine eggs and the cellular corona 

 radiata of mammalian eggs is the presence of a lytic agent in the sperm. That too, 

 both in aquatic forms, where investigated, and in mammalian sperm is protein 

 in nature. The latter, because of its ability to effect the breakdown of hyaluronic 

 acid is a hyaluronidase, one of a group of enzymes which act on intercellular 

 binding materials in other situations as well (see Meyer and Rapport, 1952). 

 Riinnstrom (1952) discusses the problem of fertilization principally from the point 

 of view of the response of the egg. 



Though it is known that sperm penetration is a trigger for completion of the 



— — r— -""^^ I—- — — 



MAMJ JASONDJFMAMJ JASONDJFMAM J JASON DJF 



let i.^a^r^ O^^ . ,« -l-J . 



1st year 



2nd year 



3rd year 



Fig. I . The cytological pattern for the seasonal growth of the oocyte of Rana temporaria, 

 a European species of frog which requires three years to reach sexual maturity. During 

 the first two years, the oocytes increase from 50 fx to 300 ]x in diameter (A-E) ; synthetic 

 activity occurs in the region of the nucleus but the newly formed products, lipid granules 

 and mitochondria, move to the cortical area. During the third year (F, G) synthesis of 

 yolk granules predominates; synthesis occurs principally in the cortical region and the 

 products migrate toward the interior. Early provision of cytoplasm with mitochondria and 

 RNA may point to their role in yolk synthesis, although other studies {e.g. Cooper, 1946, 

 1948, 1950) indicate incorporation of maternal proteins as well. (From Grant, 1953.) 



Literature p. 744 



