Hormonal regulation of sequential larval cuticular gene expression

Abstract

As the tobacco hornworm (Manduca sexta) larva feeds and grows, the abdominal epidermis synthesizes larval endocuticular proteins. During a molt this synthesis temporarily ceases while the cells deposit a new epicuticle; then these proteins reappear in a sequential manner, some before ecdysis, others after ecdysis. At the time of metamorphosis, the epidermis becomes pupally committed and ceases synthesizing these endocuticular proteins. Northern and dot blot hybridization analysis using cDNA clones for three different low-molecular-weight larval cuticular proteins showed that RNA transcription of all three ceased by the time of head cap slippage during the molt, then begins again just before ecdysis, one showing a different time course from the other two. All responded to the commitment peak of ecdysteroid in the absence of juvenile hormone OH) by a permanent cessation of transcription.During the final day of feeding (day 3) of the 5th instar the cuticular lamellae become 5-10 times thinner coincidentally with a change in cuticular protein synthesis involving a cessation of synthesis of many of the endocuticular proteins and the appearance of at least three new proteins -14.5,15, and 27 kd (kilodaltons). Incubation of day 1 5th instar epidermis with 10-100 ng/ml 20-hydroxyecdysone (20HE) induced the synthesis of the 27-kd protein and the transcription of the mRNAs for the 14.5-and 15-kd proteins. Incubation in the absence of hormones or with 20HE in the presence of JH prevented the appearance of these new proteins and the deposition of thin lamellae. The mRNAs for three endocuticular proteins whose synthesis ceases on day 3 showed differing responses to 20HE and JH. Thus, the sequential program of larval endocuticular gene expression is controlled primarily by hormonal titers in both the molt and the intermolt periods.

Characterization of a cDNA clone encoding a glycine‐rich cuticular protein of Tenebrio molitor: developmental expression and effect of a juvenile hormone analogue

“…the fall of the pupal ecdysteroid titre (Delbecque et a/., 1978). This time correlation is in agreement with previous experiments on Drosophila Doctor et a/., 1985; Fristrom 8, Liebrich, 1986) and on Manduca (Riddiford, 1986), which show that cuticular secretion needs a decrease in the ecdysteroid titre following an initial pulse. Recently, Apple & Fristrom (1991), using nuclear run-on experiments with Drosophila EDG cuticular genes, demonstrated that this regulation was at the transcriptional level.…”

Insect Juvenile Hormone Binding Protein Shows Ancestral Fold Present in Human Lipid-Binding Proteins

“…4,5 JH has profound influence on the insect life cycle by hindering larva metamorphosis and by regulating embryogenesis, stimulating reproductive maturation, and controlling the metabolism and migratory behavior of adults. [6][7][8] In insect hemolymph, three separate groups 2,9,10 of high-affinity proteins bind JH, namely, the most abundant high molecular weight lipophorins with up to 50% lipid content, the hexameric high molecular weight proteins with 15% lipid content, and the low molecular weight (LMW; molecular weight 25,000-30,000) proteins so far detected in Lepidopetra and Diptera. The third group is of special interest as these proteins bind 99% of JH in the hemolymph despite their low abundance-below 1% of total protein content.…”

Transferrin in a cockroach: molecular cloning, characterization, and suppression by juvenile hormone.

“…This paper represents a dovetail of our interests in iron metabolism and hormonal control of gene expression in insects. It originated with isolation of an anonymous cDNA to a cockroach (Blaberus discoidalis) fat body mRNA that was, in the adult female, markedly suppressed by the sesquiterpenoid juvenile hormone (H), a principal regulator of insect development and reproduction (22,23). DNA sequence analysis indicated that the JH-regulated cockroach message codes for a protein homologous to the vertebrate transferrins and transferrin from M. sexta, a distantly related insect.…”