MiR-10 Represses HoxB1a and HoxB3a in Zebrafish

BACKGROUND: The Hox genes are involved in patterning the anterior-posterior axis. In addition to the protein coding Hox genes, the miR-10, miR-196 and miR-615 families of microRNA genes are conserved within the vertebrate Hox clusters. The members of the miR-10 family are located at positions associated with Hox-4 paralogues. No function is yet known for this microRNA family but the genomic positions of its members suggest a role in anterior-posterior patterning. METHODOLOGY/PRINCIPAL FINDINGS: Using sensor constructs, overexpression and morpholino knockdown, we show in Zebrafish that miR-10 targets HoxB1a and HoxB3a and synergizes with HoxB4 in the repression of these target genes. Overexpression of miR-10 also induces specific phenotypes related to the loss of function of these targets. HoxB1a and HoxB3a have a dominant hindbrain expression domain anterior to that of miR-10 but overlap in a weaker expression domain in the spinal cord. In this latter domain, miR-10 knockdown results in upregulation of the target genes. In the case of a HoxB3a splice variant that includes miR-10c within its primary transcript, we show that the microRNA acts in an autoregulatory fashion. CONCLUSIONS/SIGNIFICANCE: We find that miR-10 acts to repress HoxB1a and HoxB3a within the spinal cord and show that this repression works cooperatively with HoxB4. As with the previously described interactions between miR-196 and HoxA7 and Hox-8 paralogues, the target genes are located in close proximity to the microRNA. We present a model in which we postulate a link between the clustering of Hox genes and post-transcriptional gene regulation. We speculate that the high density of transcription units and enhancers within the Hox clusters places constraints on the precision of the transcriptional control that can be achieved within these clusters and requires the involvement of post-transcriptional gene silencing to define functional domains of genes appropriately

cDNA array analysis of stress-induced gene expression in barley androgenesis

Different aspects of androgenesis induction have been studied in detail, but little is known about the molecular mechanisms associated with this developmental switch. We have employed macroarrays containing 1421 expressed sequence tags covering the early stages of barley zygotic embryogenesis to compare the gene expression profiles of stress-induced androgenic microspores with those of uninucleate microspores as they progressed into binucleate stage during pollen development. Principal component analysis defined distinct sets of gene expression profiles that were associated with androgenesis induction and pollen development. During pollen development, uninucleate microspores were characterized by the expression of cell division-related genes and transcripts involved in lipid biosynthesis. Progress into binucleate stage resulted in the significant increase in the level of transcripts associated with starch biosynthesis and energy production. These transcripts were downregulated in androgenic microspores. These results indicate that stress blocks the expression of pollen-related genes. The induction of androgenesis by stress was marked by the upregulation of transcripts involved in sugar and starch hydrolysis, proteolysis, stress response, inhibition of programmed cell death, and signaling. Further expression analysis revealed that the induction of genes encoding alcohol dehydrogenase 3, metalloprotease FtsH, cysteine protease 1 precursor, phytepsin precursor (aspartic protease), and a 26S proteasome regulatory subunit was associated with the androgenic potential of microspores, whereas the induction of transcripts involved in signaling and cytoprotection was associated with stress responses. Taken together, these expression profiles represent 'bio-markers' associated with the androgenic switch in microspores, providing a substantial contribution toward understanding the molecular events underlying stress-induced androgenesis. Copyright © Physiologia Plantarum 2006

Genomic annotation and transcriptome analysis of the zebrafish (<i>Danio rerio</i>) hox complex with description of a novel member, <i>hoxb13a</i>

The zebrafish (Danio rerio) is an important model in evolutionary developmental biology, and its study is being revolutionized by the zebrafish genome project. Sequencing is at an advanced stage, but annotation is largely the result of in silico analyses. We have performed genomic annotation, comparative genomics, and transcriptional analysis using microarrays of the hox homeobox-containing transcription factors. These genes have important roles in specifying the body plan. Candidate sequences were located in version Zv4 of the Ensembl genome database by TBLASTN searching with Danio and other vertebrate published Hox protein sequences. Homologies were confirmed by alignment with reference sequences, and by the relative position of genes along each cluster. RT-PCR using adult Tubingen cDNA was used to confirm annotations, to check the genomic sequence and to confirm expression in vivo. Our RT-PCR and microarray data show that all 49 hox genes are expressed in adult zebrafish. Significant expression for all known hox genes could be detected in our microarray analysis. We also find significant expression of hox8 paralogs and hoxb7a in the anti-sense direction. A novel gene, D. rerio hoxb13a, was identified, and a preliminary characterization by in situ hybridization showed expression at 24 hpf at the tip of the developing tail. We are currently characterizing this gene at the functional level. We argue that the oligo design for microarrays can be greatly enhanced by the availability of genomic sequences