Manifestation Mechanism of Yellow Larval Color in the Silkworm, with Special Regard to <i>d-lem</i> Gene

Abstract

1. A silkworm strain showing dilute yellow larval color was found and the genetic constitution of this strain was confirmed to be lem/lem; d-lem/d-lem, whereas that of lemon strain was lem/lem; +d-lem/+d-lem. The d-lem gene belongs to the 2nd linkage group, and is allelic to the i-lem gene.2. For the purpose of studying the manifestation mechanism of dilute lemon gene (d-lem) experiments were carried out.3. The amounts of yellow pigment obtained from lemon larvae is about three times as large as that from dilute lemon larvae.4. The amount of isoxanthopterin obtained from lemon larvae as well as from dilute lemon larvae is much smaller than that obtained from the normals. Furthermore, it was found that the hypodermis of dilute lemon larvae contains a smaller amount of isoxanthopterin than that of lemon larvae.5. None or very weak pterine reductase activity could be detected in dilute lemon larvae like in lemon larvae. Thus, no significant difference has been found in the activity of pterine reductase between lemon and dilute lemon strains.6. To test whether or not inhibition occurs at the step from a precursor to yellow pigment, a cross between normal and dilute lemon strains was carried out and the amount of isoxanthopterin contained in normal larvae which segregated in the F2 generation was determined by single measuring method. No clear-cut evidence of inhibition of pteridine metabolism by d-lem gene could be obtained.7. It is inferred from the experimental results that the following explanation is most plausible. Though the yellow pigment is normally produced, a large part of it is lost from the hypodermal cells owing to a defect caused by the d-lem gene in the system which keeps this compound within the cells. It is inferred that a certain protein is an important factor in combining with yellow pigments and keeping them within hypodermal cells.