Abstract
Platelets, while anucleate, contain RNA, some of which is translated into protein upon activation. Hypothesising that the platelet proteome is reflected in the transcriptome, we identified 82 proteins secreted from activated platelets and compared these, as well as published proteomic data, to the transcriptional profile. We also compared the transcriptome of platelets to other tissues to identify platelet-specific genes and used ontology to determine gene categories over-represented in platelets. RNA was isolated from highly pure platelet preparations for hybridization to Affymetrix oligonucleotide arrays. We identified 2,928 distinct messages as being present in platelets. The platelet transcriptome was compared with the proteome by relating both to UniGene clusters. Platelet proteomic data correlated well with the transcriptome, with 69% of secreted proteins detectable at the mRNA level, and similar concordance was obtained using two published datasets. While many of the most abundant mRNAs are for known platelet proteins, messages were detected for proteins not previously reported in platelets. Some of these may represent residual megakaryocyte messages; however, proteomic analysis confirmed the expression of many previously unreported genes in platelets. Transcripts for well-described platelet proteins are among the most platelet-specific messages. Ontological categories related to signal transduction, receptors, ion channels, and membranes are over-represented in platelets, while categories involved in protein synthesis are depleted. Despite the absence of gene transcription, the platelet proteome is mirrored in the transcriptome. Conversely, transcriptional analysis predicts the presence of novel proteins in the platelet. Transcriptional analysis is relevant to platelet biology, providing insights into platelet function and the mechanisms of platelet disorders.
Highlights
IntroductionWhile anucleate, contain RNA, some of which is translated into protein upon activation
Platelets, while anucleate, contain RNA, some of which is translated into protein upon activation
Platelet RNA—In preliminary investigations, we examined isolated platelet RNA for the presence of full-length messages
Summary
While anucleate, contain RNA, some of which is translated into protein upon activation. Hypothesising that the platelet proteome is reflected in the transcriptome, we identified 82 proteins secreted from activated platelets and compared these, as well as published proteomic data, to the transcriptional profile. While many of the most abundant mRNAs are for known platelet proteins, messages were detected for proteins not previously reported in platelets Some of these may represent residual megakaryocyte messages; proteomic analysis confirmed the expression of many previously unreported genes in platelets. We have interrogated gene arrays with platelet RNA and compared the results with a proteomic analysis of proteins secreted from platelets, as well as data from two previously published platelet proteomic studies [12, 13], to address whether the profile of platelet mRNA correlates with protein expression. We have identified individual messages that are relatively and absolutely platelet-specific as well as ontological categories overrepresented in platelets
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