.350 BIOCHEMICAL GENETICS 



the mode of expression of other genes concerned with melanin formation will be 

 investigated along similar lines. 1044 



Transplantation to mammalian eye or spleen and to chick-embryo celom. — Other methods 

 for discriminating between those factors which act intrinsically within the melanocyte 

 and those which act via the follicular environment involves the transplantation of 

 embryonic melanoblast-containing tissues to the adult spleen, 1205, 1206 the anterior 

 chamber of the eye, 853 or to the celom of the chick embryo. 284, 881 The granular and 

 morphologic attributes of melanocytes which have differentiated in the foreign environ- 

 ment following their migration out of the grafts as melanoblasts, are compared with 

 those of the melanocytes which occur either within the implant or in adult animals of 

 the donor genotype. For example, it has been found that neural-crest cells from 

 genotypically yellow embryos of the mouse not only differentiate into eumelanin- 

 secreting melanocytes in the celom of the chick embryo or in the spleens of pheno- 

 typically different murine hosts, 1205 but also in those regions of yellow mice where 

 melanin pigment is normally found outside of the hair, for example, in the Harderian 

 gland or eye. 854 These results established that the intrinsically determined capacity 

 of melanoblasts of all genotypes is to produce eumelanin, and only in the local milieu of 

 physiologically appropriate hair bulbs do they produce phaeomelanin. 



Melanoblasts appear to migrate more extensively from grafts placed in the anterior 

 chamber of the eye or in the celom of the chick embryo than from those placed in the 

 spleen. 1205 In addition, the two former sites have the advantage in that grafts residing 

 within them do not stimulate the host immunologically and procure their own destruc- 

 tion. In the case of heterografts in chick embryos their acceptance is, of course, due 

 to the immaturity of the recipient. Homografts in the anterior chamber of the eye are 

 exempted from the consequences of any reaction because they usually remain without 

 vascularization and, therefore, cannot succumb to an immune reaction even if they 

 could elicit one. Grafts in the anterior chamber are rejected if they do become 

 vascularized. The conditions of an unvascularized graft in the anterior chamber of the 

 eye are similar to those within cell-impermeable diffusion chambers which make use 

 of membrane filters to separate grafted tissue from host cells. 5, 6 



It must be stressed that it is of utmost importance not to overlook nongenetic 

 influences in these transplantation studies, stemming, for example, from the purely 

 mechanical or other properties of the unnatural environment into which the donor 

 melanoblasts are introduced, which may affect the differentiation of the latter. That 

 these must sometimes be taken into consideration in interpreting the results has been 

 demonstrated in transplants to the anterior chamber of the eye 853 and in transplants to 

 the chick celom. 944 



White spotting and albinism. — Using appropriate genotypes these transplantation 

 methods have been employed to investigate problems of white spotting and albinism, 

 characters which have been recorded in a great variety of mammals 792 including man. 

 While it is beyond the scope of this paper to discuss these investigations in detail 10 ° 

 some information is required in order to illustrate the methodology. 



