Abstract
We have analyzed two variants of Drosophila melanogaster (RS and RE) which lead to the dual phenotype of elevated DDC activity and increased resistance to dietary alpha-methyldopa relative to Oregon-R controls. Both phenotypes show tight genetic linkage to the dopa decarboxylase, Ddc, and l(2)amd genes (i.e., less than 0.05 cM distant). We find that low (Oregon-R), medium (RS) and high (RE and Canton-S) levels of DDC activity seen at both pupariation and eclosion in these strains are completely accounted for by differences in accumulation of DDC protein as measured by immunoprecipitation. Genetic reconstruction experiments in which Ddc+ and amd+ gene doses are varied show that increasing DDC activity does not lead to a measurable increase in resistance to dietary alpha-methyldopa. This suggests that the increased resistance to dietary alpha-methyldopa is not the result of increased DDC activity but, rather, results from increased l(2)amd+ activity. Both cytogenetic and molecular analyses indicate that these overproduction variants are not the result of small duplications of the Ddc and amd genes, nor are they associated with small (greater than or equal to 100 bp) insertions or deletions. Measurements of DDC activity in wild-type strains of Drosophila reveal a unimodal distribution of activity levels with the Canton-S and RE strains at the high end of the scale, the Oregon-R control at the low end and RS near the modal value. We conclude that accumulated changes in a genetic element (or elements) in close proximity to the Ddc+ and amd+ genes lead to the coordinated changes in the expression of the Ddc and amd genes in these strains.
Highlights
E Abbrevidtions: DDC = Dopa decarboxylase en7yme; cM = centimorgan; C R M = Cross-reacting material
SHERALaDnd WRIGHT(1974) identified two strains which exhibit the dual phenotype of elevated resistance to dietary alpha MD and elevated DDC activity relative to a carefully constructed Oregon-R control strain
We have observed naturally occurring genetic variants which lead to both elevated DDC activity and increased resistance to dietary alpha MD
Summary
Medium and high activity variants of the Ddc and, possibly, amd genes to determine whether these changes might be due to altered gene regulation. We have observed natural activity variants that lead to both elevated dopa decarboxylase activity and to increased resistance to dietary alpha-methyldopa relative to Oregon-R controls. In this report we examine the possible regulatory nature of these variants and document their affects on the level of activity of the Drosophila Ddc and amd genes. Genetic reconstruction experiments suggest that the increased resistance to dietary alpha-methyldopa most likely results from increased expression of the amd+ gene product rather than from the increase in DDC activity. Cytogenetic and molecular analysis indicates that the altered regulation in these variants results from accumulated changes in a genetic element (or elements) which affect the expression of both the Ddc and amd genes
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