Pink-eyed dilution (p) gene in rodents: Increased pigmentation in tissue culture

[摘要] Eyetissuesoftan-hooded,pink-eyedratswereshowninapreviousreporttobecomepigmentedinshort-termtissuecultures,andthephenomenonhasnowbeenanalyzedinmoredetail.Therats,inbredandnamedtheRCSstrain,arehomozygousfortherecessivegenepink-eyeddilution,p,oranallelewithsimilarproperties.Eyetissuesofpostnatalppratsandpp,p1p,andp1p1miceareminimallypigmentedinvivo,andmadelittlepigmentwhenculturedinsyntheticmedialackingtyrosine.Pigmentationwasstrongwhentyrosinewaspresentinthemedium,andthepigmentwasidentifiedasmelaninonthebasisofcolor,stainingproperties,intracellularlocation,appearanceinelectronmicrographs,andrestrictiontothecellsoftheiris,ciliarybody,pigmentepithelium,andchoroidthatcontainmelanininpigmentedanimals.Pigmentationwasobtainedinprimaryculturesoncollagen-coatedcoverslipsandinorgancultures,inroomairandinanatmosphereof95%O2-5%CO2.Aninductivemechanismfortheresponseisunlikelybecausetyrosine-mediatedpigmentationwasnotpreventedbypuromycin(upto150μg/ml)oractinomycinD(upto10μg/ml)intheculturemedium.Failureofmelanin-synthesizingenzymeactivitybecauseofmembranedisarraywithinmutantmelanosomeswasruledoutbecausedisorderedgranules,liketheregularones,appearedpigmentedinelectronmicrographs.Competitiveinhibitionbyexcessphenylalaninewasruledoutbyphenylalaninemeasurementsinvivoandbyvaryingphenylalanine:tyrosineratiosinculture.Tyrosinasecontainscopper,andagene-controlledcopperdeficitmightbecorrectedinvitrobycopperinordinaryculturemedia;however,tyrosine-mediatedpigmentationwasundiminishedbytheuseofcopper-freemedia.Thepgenesreducepigmentationdespitethepresenceofanapparentlyappropriatemelanin-synthesizingmachinery,possiblybycausingtyrosinetobeshuntedtootherpathways;exogenoustyrosineinvitrorestoredthenormalphenotype.

[学科分类] 生物科学（综合）