3.9 – Hormonal Control of Reproductive Processes

Mating triggers a cascade of physiological and behavioural responses in females that persist after copulation. In insects, seminal fluid proteins contained within male ejaculates are known to initiate some responses, but our understanding of how females mediate these reactions remains limited. Few studies have examined postmating transcriptional changes within ejaculate-receiving organs within females or how these changes might depend on the identity of the male. Furthermore, whereas males of many insects transfer packaged ejaculates, transcriptional dynamics have mainly been examined in dipterans, in which males transfer a free ejaculate. To identify genes that may be important in mediating female physiological responses in a spermatophore-producing species, we sequenced the transcriptomes of the ejaculate-receiving organs and examined postmating gene expression within and between pheromone strains of the European corn borer (ECB) moth, Ostrinia nubilalis. After within-strain mating, significant differential expression of 978 transcripts occurred in the female bursa or its associated bursal gland, including peptidases, transmembrane transporters, and hormone processing genes; such genes may potentially play a role in postmating male-female interactions. We also identified 14 transcripts from the bursal gland that were differentially expressed after females mated with cross-strain males, representing candidates for previously observed postmating reproductive isolation between ECB strains.

Postmating transcriptional changes in the female reproductive tract of the European corn borer moth

Conserved molecular mechanism for the stage specificity of the mosquito vitellogenic response to ecdysone.

In response to a blood meal, the fat body of the female mosquito produces several yolk proteins (YP) which are accumulated by the developing oocytes. 20-hydroxyecdysone (20E) stimulates high levels of YP gene expression in fat bodies cultured in vitro, but initiation of this expression was eliminated with cycloheximide. In the 1.5 kb upstream region of the gene encoding vitellogenic carboxypeptidase, a mosquito YP, there are several putative regulatory sequences that resemble steroid response elements (SRE), but they do not match the ecdysteroid response element (EcRE) consensus. A cDNA encoding a mosquito ecdysteroid receptor (AaEcR) has recently been cloned and found to possess P-Box and D-Box domains nearly identical to those found in the Drosophila and Chironomus EcRs, indicating that its DNA binding sequence will likely match the EcRE consensus. Taken together, these results indicate that the control of YP genes in the vitellogenic mosquito fat body by 20E is indirect. It may involve several factors in a hierarchy, with a factor other than the AaEcR directly controlling the YP genes.In the mosquito fat body, lysosomal enzymes are involved in termination of YP secretion. The mRNA of a mosquito lysosomal aspartic protease (LAP) reaches its peak 12 hr before the peak of LAP protein and enzymatic activity. The level of LAP protein rises as the titer of 20E declines. This suggests a translational inhibition of LAP mRNA by a high titer of 20E. We obtained direct experimental confirmation of this novel function of 20E. In addition, the 5'-untranslated region of the LAP mRNA shares similarity with elements conferring negative translational control by steroids. The LAP gene is controlled by dual promoters, one of which is dominant during enhanced expression. The identification of putative regulatory elements should help in determining the regulation of the gene during both housekeeping and enhanced expression.

Regulation of gene expression by 20-hydroxyecdysone in the fat body of Aedes aegypti (Diptera: Culicidae)

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Regulation of gene expression by 20-hydroxyecdysone in the fat body of Aedes aegypti (Diptera: Culicidae)