Environmental and genetic control of differentiation in Neurospora 



tyrosinase-melanin intermediates have a morphogenetic capacity in the protoperi- 

 thecial system. These observations, together with the evidence already presented, 

 suggest that our working hypothesis of a connexion between differentiation of 

 protoperithecia and synthesis of melanin in Neurospora is a sound one. To these 

 observations should be added a rather interesting preliminary observation on a 

 sterile mutant (93/54) which never forms protoperithecia on the standard P-minimal 

 medium, whereas it does form many protoperithecia on a low-sulphur P-minimal 

 medium. This suggests that in this mutant the tyrosinase inhibitor of Horowitz and 

 Shen, which normally is inactive on the standard P-minimal medium, is involved. 



It is quite obvious that our technique for feeding precursors in this system is much 

 too crude. The various assumed intermediates in melanin metabolism will have to 

 be synthesized and fed individually to the mutants before we can get much further. 

 What we want to present here is a morphogenetic system, namely the formation of 

 protoperithecia, which offers promising opportunities for studying the genetics and 

 biochemistry of morphogenesis on a synthetic substrate; and we hope to have 

 presented convincing evidence for our working hypothesis that at least one of 

 the keys to the biochemistry of this problem is tyrosinase activity and melanin 

 synthesis. 



Before finishing this presentation it may be worth while to discuss some of the 

 more general aspects of this work. As pointed out already by Dr. Horowitz, melanin 

 problems present one of the few fields where biochemistry, embryology, and genetics 

 meet, and, as Dr. Horowitz has also pointed out, with respect to tyrosinase activity 

 Neurospora behaves like the Siamese cat or the Himalayan rabbit. To this we want 

 to add that in Neurospora this enzyme system is involved in sexuality. We now also 

 have Neurospora mutants lacking tyrosinase and unable to form melanin, thus behav- 

 ing like many albino animals. In other mutants melanin formation is inhibited, just 

 as we have albinos in animals due to epistatic suppressors. We have certain mutant 

 strains in Neurospora where the melanin seems to agglutinate, bringing the dilution 

 gene (D-gene) in rabbits to mind. This investigation might also be discussed in rela- 

 tion to the older work of Goldschmidt on the effect of temperature upon the differ- 

 entiation of the wing pattern in butterflies (see Goldschmidt, 1938). It should also be 

 remembered that we are dealing with the very first system from which biochemical 

 genetics emerged: the work of Garrod on inborn errors of metabolism in man (Garrod 

 1923; Haldane 1954). Although we may not expect to find Neurospora strains with 

 alcaptonuria, hydroxyphenyluria, etc., we may nevertheless have a system which 

 can be of importance for studying some of the biochemical blocks which in man are 

 so often connected with mental disorders. 



A second aspect of this investigation is its relationship to the possible occurrence 

 of sex hormones in fungi, a subject recently reviewed by Raper (1952). In Neurospora 

 the earlier claims on the occurrence of diffusible sex hormones (Moreau and Moruzzi, 

 1 931) have been refuted (Aronescu, 1933; Hirsch, 1954). As far as the higher fungi 

 are concerned, it seems a good idea to look for the intermediates in melanin synthesis 

 in future work. Also the work of Moewus on sexuality in Chlamydomonas which, if 

 taken at its face value, represents a system far better worked out in detail than any 

 other, should be kept in mind. As will be remembered Moewus claims that two quite 

 unrelated groups of chemicals, carotenoids and anthocyanins, play a role in sex 



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