Ubiquitously expressed genes participate in cell-specific functions via alternative promoter usage.

How do different cell types acquire their specific identities and functions is a fundamental question of biology. Previously significant efforts have been devoted to search for cell-type-specifically expressed genes, especially transcription factors, yet how do ubiquitously expressed genes participate in the formation or maintenance of cell-type-specific features remains largely unknown. Here, we have identified 110 mouse embryonic stem cell (mESC) specifically expressed transcripts with cell-stage-specific alternative transcription start sites (SATS isoforms) from 104 ubiquitously expressed genes, majority of which have active epigenetic modification- or stem cell-related functions. These SATS isoforms are specifically expressed in mESCs, and tend to be transcriptionally regulated by key pluripotency factors through direct promoter binding. Knocking down the SATS isoforms of Nmnat2 or Usp7 leads to differentiation-related phenotype in mESCs. These results demonstrate that cell-type-specific transcription factors are capable to produce cell-type-specific transcripts with alternative transcription start sites from ubiquitously expressed genes, which confer ubiquitously expressed genes novel functions involved in the establishment or maintenance of cell-type-specific features.

Genome-wide identification and functional analysis of genes expressed ubiquitously in rice.

Genes that are expressed ubiquitously throughout all developmental stages are thought to be necessary for basic biological or cellular functions. Therefore, determining their biological roles is a great challenge. We identified 4034 of these genes in rice after studying the results of Agilent 44K and Affymetrix meta-anatomical expression profiles. Among 105 genes that were characterized by loss-of-function analysis, 79 were classified as members of gene families, the majority of which were predominantly expressed. Using T-DNA insertional mutants, we examined 43 genes and found that loss of expression of six genes caused developing seed- or seedling-defective phenotypes. Of these, three are singletons without similar family members and defective phenotypes are expected from mutations. Phylogenomic analyses integrating genome-wide transcriptome data revealed the functional dominance of three ubiquitously expressed family genes. Among them, we investigated the function of Os03g19890, which is involved in ATP generation within the mitochondria during endosperm development. We also created and evaluated functional networks associated with this gene to understand the molecular mechanism. Our study provides a useful strategy for pheonome analysis of ubiquitously expressed genes in rice.

Genome-wide Identification and Functional Analysis of Genes Expressed Ubiquitously in Rice.

Genes that are expressed ubiquitously throughout all developmental stages are thought to be necessary for basic biological or cellular functions. Therefore, determining their biological roles is a great challenge. We identified 4,034 of these genes in rice after studying the results of Agilent 44K and Affymetrix meta-anatomical expression profiles. Among the 105 that were characterized by loss-of-function analysis, 79 were classified as members of gene families, with the majority of them being predominantly expressed. Using T-DNA insertional mutants, we examined 43 genes and found that loss-of-expression in six caused developing seed- or seedling-defective phenotypes. Of them, three are singletons without same family members and easily expect the defective phenotypes by the mutations. Phylogenomic analyses integrating genome-wide transcriptome data revealed the functional dominance of three ubiquitously expressed family genes. From them, we investigated the role of Os03g19890, which is involved in ATP generation within the mitochondria during endosperm development. We also created and evaluated functional networks associated with that gene to understand the molecular mechanism. Our study will provide useful strategy for pheonome analysis of ubiquitously expressed genes.