Let-7 microRNAs are developmentally regulated in circulating human erythroid cells.
BACKGROUND
MicroRNAs are approximately 22nt-long small non-coding RNAs that negatively regulate protein expression through mRNA degradation or translational repression in eukaryotic cells. Based upon their importance in regulating development and terminal differentiation in model systems, erythrocyte microRNA profiles were examined at birth and in adults to determine if changes in their abundance coincide with the developmental phenomenon of hemoglobin switching.


METHODS
Expression profiling of microRNA was performed using total RNA from four adult peripheral blood samples compared to four cord blood samples after depletion of plasma, platelets, and nucleated cells. Labeled RNAs were hybridized to custom spotted arrays containing 474 human microRNA species (miRBase release 9.1). Total RNA from Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines provided a hybridization reference for all samples to generate microRNA abundance profile for each sample.


RESULTS
Among 206 detected miRNAs, 79% of the microRNAs were present at equivalent levels in both cord and adult cells. By comparison, 37 microRNAs were up-regulated and 4 microRNAs were down-regulated in adult erythroid cells (fold change > 2; p < 0.01). Among the up-regulated subset, the let-7 miRNA family consistently demonstrated increased abundance in the adult samples by array-based analyses that were confirmed by quantitative PCR (4.5 to 18.4 fold increases in 6 of 8 let-7 miRNA). Profiling studies of messenger RNA (mRNA) in these cells additionally demonstrated down-regulation of ten let-7 target genes in the adult cells.


CONCLUSIONS
These data suggest that a consistent pattern of up-regulation among let-7 miRNA in circulating erythroid cells occurs in association with hemoglobin switching during the fetal-to-adult developmental transition in humans.
Noh
Seung-Jae
SJ
Molecular Medicine Branch, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA. nohseung@niddk.nih.gov
Miller
Samuel H
SH
Lee
Y Terry
YT
Goh
Sung-Ho
SH
Marincola
Francesco M
FM
Stroncek
David F
DF
Reed
Christopher
C
Wang
Ena
E
Miller
Jeffery L
JL
D000328:Adult; D000818:Animals; D041905:Erythroid Cells; D005312:Fetal Blood / Q000166:cytology; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D006454:Hemoglobins / Q000235:genetics; D006801:Humans; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015203:Reproducibility of Results; D012156:Reticulocytes / Q000502:physiology*
D006454:Hemoglobins; D035683:MicroRNAs; D012333:RNA, Messenger; C487931:mirnlet7 microRNA, human