Abstract
Piwi proteins and their small non-coding RNA partners are involved in the maintenance of stem cell character and genome integrity in the male germ cells of mammals. MIWI2, one of the mouse Piwi-like proteins, is expressed in the prepachytene phase of spermatogenesis during the period of de novo methylation. Absence of this protein leads to meiotic defects and a progressive loss of germ cells. There is an accumulation of evidence that Piwi proteins may be active in hematopoietic tissues. Thus, MIWI2 may have a role in hematopoietic stem and/or progenitor cell self-renewal and differentiation, and defects in MIWI2 may lead to abnormal hematopoiesis. MIWI2 mRNA can be detected in a mouse erythroblast cell line by RNA-seq, and shRNA-mediated knockdown of this mRNA causes the cells to take on characteristics of differentiated erythroid precursors. However, there are no detectable hematopoietic abnormalities in a MIWI2-deficient mouse model. While subtle, non-statistically significant changes were noted in the hematopoietic function of mice without a functional MIWI2 gene when compared to wild type mice, our results show that MIWI2 is not solely necessary for hematopoiesis within the normal life span of a mouse.
Highlights
Small, single-stranded RNA molecules of approximately 20–30 nucleotides have been discovered in a wide spectrum of species [1,2,3,4,5]
Given the parallels between male germ cells and HSCs with respect to selfrenewal and differentiation, and based on evidence that the Piwi and its associated RNAs (piRNAs) pathway is active in somatic cells, we sought to identify abnormalities of blood cells deficient in MIWI2
MIWI2 mRNA is transcribed in mouse erythroleukemia (MEL) cells, and knockdown of MIWI2 in this hematopoietic cell line causes the same characteristic changes seen in dimethyl sulfoxide (DMSO)-induced differentiation, indicating that MIWI2 has a functional role in hematopoiesis in vitro
Summary
Single-stranded RNA molecules of approximately 20–30 nucleotides (nt) have been discovered in a wide spectrum of species [1,2,3,4,5]. In association with specific proteins, small non-coding RNAs (ncRNAs) have been shown to be involved in transcriptional regulation, chromatin structural organization and mRNA stability. Several classes of small ncRNAs act as sequence guides that direct members of the Argonaute protein family, and their associated protein complexes, to partially or fully complementary nucleic acids. Micro RNAs (miRNAs) and small inhibiting (siRNAs) associate with Ago proteins to target mRNAs or viral genomes [1,2,7]. Piwi and its associated RNAs (piRNAs) have less well-defined functions [1,2]. They are linked to the maintenance of stem cell character and genome integrity [5], but the mechanisms by which they mediate these effects are not completely understood
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