Juvenile hormone-stimulated polyploidy in adult locust fat body

Abstract

The relative DNA contents of adult fat body nuclei of Locusta migratoria have been assayed by scanning microspectrophotometry after Feulgen staining, spermatid and brain nuclei being used as haploid and diploid reference standards. In the fat body, several DNA classes were found, the mean ploidy increasing during the period of reproductive maturation. The extinction frequency peaks fall at values that are less than doublings of the diploid value, which suggests incomplete replication of the genome, although this interpretation requires confirmation by independent techniques. On Day 1 the female and male fat body nuclei are chiefly tetraploids. Elevation to octaploidy or higher, especially in the female is evident by Day 15. Allatectomy, removing the source of JH, prevents the increase in ploidy, and administration of the JH mimic, ZR-515, restores it in both sexes. Incorporation of [ 3H]thymidine in female fat body shows a broad peak, maximal at Day 6. After allatectomy, incorporation of [ 3H]thymidine is strongly stimulated by ZR-515 in both sexes. It is suggested that the JH-dependent polyploidy in female fat body permits accelerated production of mRNA for vitellogenin and possibly other proteins. The male fat body responds to JH by DNA replication but not by expression of the vitellogenin gene.