Molecular analysis of the human cytoglobin mRNA isoforms.

Multiple functions have been proposed for the ubiquitously expressed vertebrate globin cytoglobin (Cygb), including nitric oxide (NO) metabolism, lipid peroxidation/signalling, superoxide dismutase activity, reactive oxygen/nitrogen species (RONS) scavenging, regulation of blood pressure, antifibrosis, and both tumour suppressor and oncogenic effects. Since alternative splicing can expand the biological roles of a gene, we investigated whether this mechanism contributes to the functional diversity of Cygb. By mining of cDNA data and molecular analysis, we identified five alternative mRNA isoforms for the human CYGB gene (V-1 to V-5). Comprehensive RNA-seq analyses of public datasets from human tissues and cells confirmed that the canonical CYGB V-1 isoform is the primary CYGB transcript in the majority of analysed datasets. Interestingly, we revealed that isoform V-3 represented the predominant CYGB variant in hepatoblastoma (HB) cell lines and in the majority of analysed normal and HB liver tissues. CYGB V-3 mRNA is transcribed from an alternate upstream promoter and hypothetically encodes a N-terminally truncated CYGB protein, which is not recognized by some antibodies used in published studies. Little to no transcriptional evidence was found for the other CYGB isoforms. Comparative transcriptomics and flow cytometry on CYGB+/+ and gene-edited CYGB-/- HepG2 HB cells did not unveil a knockout phenotype and, thus, a potential function for CYGB V-3. Our study reveals that the CYGB gene is transcriptionally more complex than previously described as it expresses alternative mRNA isoforms of unknown function. Additional experimental data are needed to clarify the biological meaning of those alternative CYGB transcripts.

SPREDs (Sprouty related proteins with EVH1 domain) promote self-renewal and inhibit mesodermal differentiation in murine embryonic stem cells.

BACKGROUND: Pluripotency, self-renewal, and differentiation are special features of embryonic stem (ES) cells, thereby providing valuable perspectives in regenerative medicine. Developmental processes require a fine-tuned organization, mainly regulated by the well-known JAK/STAT, PI3K/AKT, and ERK/MAPK pathways. SPREDs (Sprouty related proteins with EVH1 domain) were discovered as inhibitors of the ERK/MAPK signaling pathway, whereas nothing was known about their functions in ES cells and during early differentiation, so far. RESULTS: We generated SPRED1 and SPRED2 overexpressing and SPRED2 knockout murine ES cells to analyze the functions of SPRED proteins in ES cells and during early differentiation. Overexpression of SPREDs increases significantly the self-renewal and clonogenicity of murine ES cells, whereas lack of SPRED2 reduces proliferation and increases apoptosis. During early differentiation in embryoid bodies, SPREDs promote the pluripotent state and inhibit differentiation whereby mesodermal differentiation into cardiomyocytes is considerably delayed and inhibited. LIF- and growth factor-stimulation revealed that SPREDs inhibit ERK/MAPK activation in murine ES cells. However, no effects were detectable on LIF-induced activation of the JAK/STAT3, or PI3K/AKT signaling pathway by SPRED proteins. CONCLUSIONS: We show that SPREDs promote self-renewal and inhibit mesodermal differentiation of murine ES cells by selective suppression of the ERK/MAPK signaling pathway in pluripotent cells.