Biochemical differentiation and hormonal regulation of the developing testes in Tenebrio molitor

Abstract

During differentiation, the testes of Tenebrio molitor have been found to exhibit increases in biosynthetic capacity reflected in alterations in testicular protein and RNA. This biochemical differentiation was influenced by endogenous and/or exogenous hormones. The testes underwent dramatic increases in size and weight during the prepupal stage that were continued through later developmental stages. Histological analysis revealed that the maturation process of the germ cells to produce spermatozoa proceeded from the distal end of the follicles and toward the basal region to form a "differentiation wave." Spermatozoa were found in the prepupal testes. The underlying biochemical machinery of the developmental process was found to be accelerated in manufacturing different elements for germ cell differentiation at certain stages and particularly when the endogenous level of ecdysterone rose during the late prepupal and at mid-pupal stages. Gradual increases in testicular protein and RNA content were observed during the prepupal stage. The observed increases were more dramatic for both protein and RNA content in the pupal stage. The testicular protein and RNA content reached their maximum levels between days 4 and 7 of the pupal stage as did the rate of 3H-leucine incorporation. During the adult stage, the biosynthetic processes for producing protein and RNA were apparently reduced following the first few days after adult emergence. The protein products of the mealworm testes were shown by gel electrophoresis to be many and diverse. The 27 protein products were of various molecular weights, ranging from 12,000 to 127,000 daltons. These products were present at different ages of development and persisted for various times indicating that some of these proteins may be necessary for the formation of specific germ cell types. In addition, a variety of these testicular protein components incorporated leucine at measurable levels throughout development, particularly during the pupal stage. It was ascertained that the rate of incorporation of radioactive leucine into TCA -precipitable testicular protein was not affected by the administration of exogenous juvenile hormone alone (JHI, 1 µg/animal) during the pupal stage. However, the administration of exogenous ecdysterone (0. 5 µg/animal) to pupal Tenebrio resulted in an increase in the rate of radioactive leucine incorporation into TCA -precipitable testicular proteins, particularly during the first six days after pupal ecdysis. The amount of ecdysterone injected appeared to stimulate the production of the same testicular protein components that were present during normal pupal development. Injection of a higher dose of ecdysterone (1.5 µg/animal) during some of the pupal ages appeared to alter the testicular differentiation program by enhancing the incorporation of leucine into not only the age -specific testicular protein components but also into new protein components which did not normally appear at these specific ages. Simultaneous administration of both JH and ecdysterone on mealworm pupae at specific ages indicated that there was no apparent interaction, synergistic nor antagonistic, between these two hormones. Furthermore, the incorporation rate of leucine closely resembled that rate obtained following injection of ecdysterone alone in all the pupal ages studied.