Different rate of protein granule formation in the larval fat body of Drosophila melanogaster

The concentration of protein granules was determined cytologically in different regions of the fat body during the latter half of the third larval instar of Drosophila melanogaster. The measurements made at 6 hr intervals from 72–96 hr larvae showed that the concentration of the granules was the highest in the posterior, lowest in the anterior and intermediate in the middle region of the fat body. From these measurements, it was shown that the rate of granule formation was different in each region. Furthermore, there is a strong indication that at any given stage, the rate increases gradually and continuously from the anterior to the posterior region. When the fat body from larvae prior to the time of granule formation was cultured for three days in ecdysterone-containing medium, protein granules were produced in the anterior, middle and posterior regions in the same concentration as that in 90 hr larvae. The same gradient of protein granule formation in vitro is found whether the fat body is cultured as an intact piece or as three separate, dissected regions. The putative adaptive advantage of region-dependent granule formation is discussed.