CONTRIBUTIONS TO THE PROBLEM OF EYE 



PIGMENTATION IN INSECTS: STUDIED 



BY MEANS OF INTERGENERIC ORGAN 



TRANSPLANTATIONS IN DIPTERA 



By DIETRICH BODENSTEIN 



Gerontology Branch, National Institutes of Health 

 Baltimore City Hospitals 

 Baltimore, Md. 



(With One Plate) 

 INTRODUCTION 



The biosynthesis of the brown eye pigment in insects has been duci- 

 dated especially by the well-known studies of Beadle, Ephrussi, and 

 Tatum on Drosophila (see Wagner and Mitchell, 1955), and of Kiihn 

 and his school on Ephestia (see Kiihn, 1955). One of the essential 

 facts revealed by these investigations is the occurrence of "diffusible 

 substances" in the blood of the immature insect. These substances are 

 pigment precursors, which are produced not only by the prospective 

 eye tissue but also by other organ tissues. Because of these findings 

 it has been possible to introduce by organ transplantation pigment pre- 

 cursor substances into the organic environment of the developing in- 

 sect. Eye mutants lacking the brown eye pigment could thus be pro- 

 vided with appropriate pigment precursors and the differentiation of 

 the brown eye color analyzed. By the use of this and other methods it 

 was finally shown that the diffusible substances were intermediate 

 compounds of tryptophane metabolism. A metabolic map for the 

 formation of the brown eye pigment could be constructed, showmg 

 that the metabolic events led from tryptophane to formylkynurenine, 

 kynurenine, 3-hydroxykynurenine to the brown pigment. In the many 

 eye-color mutants investigated, genes have been found which block 

 this biosynthetic chain at different points. The responsible genes most 

 interesting in this connection are those that block the formation of 

 diffusible intermediates. One gene prevents the transformation of 

 tryptophane into kynurenine, and one other renders impossible the 

 conversion of kynurenine into 3-hydroxykynurenine. Thus, in a mu- 

 tant lacking the brown eye color because of the genetic block involving 

 the first gene, color development can be restored by the transplanta- 

 tion of an eye'primordium from a normal wild-type donor. The trans- 



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