ABSTRACT: Signaling pathways controlling vasculogenesis and angiogenesis are still poorly understood. Zebrafish Ets1-related protein (Etsrp) which encodes an ETS domain transcription factor, evolutionary related to the mammalian ER71 protein subfamily, has been identified as a major regulator of vasculogenesis and myelopoiesis and functions at the hemangioblast stage affecting the formation of both lineages. In the absence of Etsrp, angioblasts do not migrate or differentiate while overexpression of Etsrp results in the expansion of vascular endothelial and myeloid lineages. To identify genes functioning downstream of Etsrp we performed microarray analysis of etsrp-overexpressing embryos. Etsrp RNA injected embryos and control uninjected embryos were frozen at the tailbud stage and analyzed for expression of more than 30,000 genes using Nimblegen expression arrays. Approximately 300 genes showed greater than two-fold induction in etsrp-overexpressing embryos. Scl, crl, egfl7, aqp8, fli1a, fli1b, lmo2, cdh5 were among the previously known hemangioblast or vasculature-specific genes which were strongly upregulated in Etsrp-overexpressing embryos. We isolated and characterized a number of genes that were novel or previously unassociated with the zebrafish vasculature formation. Eight of them which include angiotensin II type 2 receptor (agtr2), src homology 2 domain containing E (she), similar to mannose receptor C1 (mrc1), endothelial cell-specific adhesion molecule (esam), cdc42 guanine nucleotide exchange factor 9 (arhgef9), yes-related kinase (yrk), zinc finger protein, multitype 2b (zfpm2b/fog2b) and stabilin 2 (stab2) were specifically expressed in vascular endothelial cells during early embryonic development while keratin18 expression was localized to the myeloid cells among others. Identification of novel vasculature and myeloid-specific genes that are regulated by Etsrp will be important for dissecting molecular mechanisms that regulate vasculogenesis / angiogenesis and myelopoiesis. Approximately 50 pg of etsrp RNA was microinjected into zebrafish embryos at the 1-4 cell stages. Three separate batches of approximately 150 microinjected embryos and uninjected controls were frozen on dry ice at the tailbud stage. Total RNA was purified using the RNAquous-4PCR kit (Ambion). Approximately 10-20 µg RNA from each batch was sent to the NimbleGen facility, were it was processed, labeled and hybridized to standard NimbleGen 385K gene expression array. Briefly, RNA was converted into cDNA using the SuperScript II cDNA Conversion Kit (Invitrogen, Carlsbad, CA). Double-stranded cDNA was random-prime labeled with Cy3-nonamers and hybridized to the microarrays for 16 hours at 42°C. The zebrafish microarray was based on Zv6 genome assembly and contained approximately 32,000 genes with approximately 12 probes of 60mer oligonucleotides per each gene. The arrays were washed, dried, and scanned at 5μm resolution using a GenePix 4000B microarray scanner (Molecular Devices, Sunnyvale, CA). Data were extracted from scanned images using NimbleScan software (Roche NimbleGen). Quantile normalization was performed across replicate arrays, and RMA (Robust Multichip Average) analysis was performed to generate gene expression values. Average ratios of expression values of etsrp-injected vs. control were calculated from three experiments. Results were sorted by the fold change from the highest to the lowest. Genes that displayed values of p>0.05 or showed expression levels less than 2-fold above the background level in both control and experimental samples were eliminated from further analysis.
