The fat body transcriptomes of the yellow fever mosquito Aedes aegypti, pre- and post- blood meal

Abstract

Background: The fat body is the main organ of intermediary metabolism in insects and the principal source of hemolymph proteins. As part of our ongoing efforts to understand mosquito fat body physiology and to identify novel targets for insect control, we have conducted a transcriptome analysis of the fat body of Aedes aegypti before and in response to blood feeding.

Results: We created two fat body non-normalized EST libraries, one from mosquito fat bodies non-blood fed (NBF) and another from mosquitoes 24 hrs post-blood meal (PBM). 454 pyrosequencing of the non-normalized libraries resulted in 204,578 useable reads from the NBF sample and 323,474 useable reads from the PBM sample. Alignment of reads to the existing reference Ae. aegypti transcript libraries for analysis of differential expression between NBF and PBM samples revealed 116,912 and 115,051 matches, respectively. De novo assembly of the reads from the NBF sample resulted in 15,456 contigs, and assembly of the reads from the PBM sample resulted in 15,010 contigs. Collectively, 123 novel transcripts were identified within these contigs. Prominently expressed transcripts in the NBF fat body library were represented by transcripts encoding ribosomal proteins. Thirty-five point four percent of all reads in the PBM library were represented by transcripts that encode yolk proteins. The most highly expressed were transcripts encoding members of the cathepsin b, vitellogenin, vitellogenic carboxypeptidase, and vitelline membrane protein families.

Conclusion: The two fat body transcriptomes were considerably different from each other in terms of transcript expression in terms of abundances of transcripts and genes expressed. They reflect the physiological shift of the pre-feeding fat body from a resting state to vitellogenic gene expression after feeding.

Figure 1. Gene Ontology of the Aedes aegypti fat body.

Pre-and Post-Bloodmeal Level 2 GO functions for de novo assembled contigs. The x-axis represents the total number of contigs with the given level 2 GO term.

Figure 2. The VCB family of Aedes aegypti.

A. Neighbor joining tree showing evolutionary relationships of Ae. aegypti VCBs. B. Number of VCB reads identified in the NBF and PBM libraries. All cathepsins identified in Ae. aegypti which had reads align using the methods used for sequence alignment and data analysis, are represented. C. Domain structure of Ae. aegypti VCB proteins. Cy - Cystatin-like domain, Pept_C1 - Papain family cysteine protease domain, I29 - Cathepsin propeptide inhibitor domain, SO - Somatomedin B -like domain. Signal peptides are labeled red.

Figure 3. Transporters identified in the Aedes aegypti fat body.

Number of reads in the NBF and PBM samples by transporter type. Transporters were identified as described in the text and the number of reads aligned were pulled from the aligned reads generated for our EST expression in the fat body overview.