Linkage of a gene causing malaria refractoriness to Diphenol oxidase-A2 on chromosome 3 of Anopheles gambiae

• Published in: The American journal of tropical medicine and hygiene Vol. 60; no. 1; pp. 22 - 29
• Main Authors: Romans, P, Black WC, , 4th, Sakai, RK, Gwadz, RW
• Format: Journal Article
• Language: English
• Published: Lawrence, KS ASTMH 01.01.1999; Allen Press
• Subjects: Alleles; Animals; Anopheles - enzymology; Anopheles - genetics; Anopheles - parasitology; Anopheles gambiae; Biological and medical sciences; Catechol Oxidase - genetics; Crosses, Genetic; Culicidae; diphenol oxidase; Female; Fundamental and applied biological sciences. Psychology; Genetic Linkage; Genotype; Heterozygote; Homozygote; Insect Vectors - enzymology; Insect Vectors - genetics; Insect Vectors - parasitology; Macaca mulatta; Malaria - immunology; Malaria - transmission; Male; Medically important nuisances and vectors, pests of stored products and materials: population survey and control; Multigene Family; Plasmodium; Plasmodium cynomolgi - physiology; Random Allocation; Tropical medicine; Vectors. Intermediate hosts; Protozoa; Apicomplexa; Protozoal disease; Linkage; Malaria; Insecta; Monkey; Transmission; Parasitosis; Chromosome 3; Experimental study; Infection; Refractory; Vertebrata; Mammalia; Anopheles gambiae; Gene; Arthropoda; Animal; Culicidae; Primates; Plasmodium cynomolgi; Invertebrata; Diptera
• ISSN: 0002-9637; 1476-1645
• DOI: 10.4269/ajtmh.1999.60.22

An inbred line of the African malaria vector Anopheles gambiae is refractory to development of malaria parasites. It is homozygous for a 4.3-kb Sal I restriction fragment at the Dox-A2 locus, whereas the parent population is polymorphic at this locus, and a susceptible line is homozygous for an alternate 3.85-kb fragment. The Dox-A2 locus is located in the middle of chromosome 3R, in division 33B, and is tightly linked to a cluster of genes including Dopa decarboxylase that are involved in the production of melanin. Because the refractoriness phenotype, melanotic encapsulation of ookinete/oocysts, might involve activation of or alteration in one or more of these genes, we performed genetic crosses to determine whether a previously identified Plasmodium cynomolgi Ceylon refractoriness gene, Pif-C, is linked to Dox-A2. Backcross mosquitoes fed on one infected monkey developed infections of < or = 100 oocysts. About 50% of these mosquitoes appeared phenotypically refractory, as expected for the backcross performed, but gave slight evidence of linkage between a refractoriness gene and Dox-A2. In contrast, females fed on a monkey that yielded higher infection levels, up to > 300 oocysts, showed clear evidence of linkage between a refractoriness gene and Dox-A2. We conclude that this Dox-A2-linked refractoriness gene is expressed under conditions particular to the higher infection levels, or that environmental factors obscured the genetic effect of this gene at lower infection levels.