Wooseok Seo | PubMed Health

PubMed2005

CD34 and CD43 inhibit mast cell adhesion and are required for optimal mast cell reconstitution.

CD34 is a cell-surface sialomucin expressed by hematopoietic stem cells (HSC), mast cells, and vascular endothelia. Despite its popularity as an HSC marker, the function of CD34 on hematopoietic cells remains enigmatic. Here, we have addressed this issue by examining the behavior of mutant mast cells lacking CD34, the related sialomucin, CD43, or both molecules. Loss of these molecules leads to a gene-dose-dependent increase in mast cell homotypic aggregation with CD34/CD43KOs > CD43KO > CD34KO > wild-type. Importantly, reexpression of CD34 or CD43 in these cells caused reversal of this phenotype. Furthermore, we find that loss of these sialomucins prevents mast cell repopulation and hematopoietic precursor reconstitution in vivo. Our data provide clear-cut evidence for a hematopoietic function for CD34 and suggest that it acts as a negative regulator of cell adhesion.

Animals↗

PubMed2002

Non-cognate template usage and alternative priming by a group II intron-encoded reverse transcriptase.

Group II introns are retroelements that site-specifically insert into DNA through homing. They are also implicated in related phenomena such as ectopic site insertions and precise intron deletions, but little is known about how group II intron reverse transcriptases (RTs) interact with non-cognate substrates. Here we show that wild-type aI2 RT readily reverse transcribes non-cognate RNAs in mitochondrial RNP particles when the aI2 intron structure is misfolded. In two closely related priming mutants, 1degree2(DeltaD5) and 1(+)2(DeltaD5), which contain wild-type RT but a disrupted intron structure, the RT has substantially lost specificity for aI2 RNA and copies multiple RNAs present in the RNP particles, using an alternative priming mechanism. The RT in 1degree2(DeltaD5) RNP particles can also copy exogenous RNAs but unlike the endogenous templates, a complementary primer is required, suggesting that the alternative priming event is specific to RT-RNA interactions formed in vivo. Alternatively primed cDNAs from strains 1degree2(DeltaD5), 1(+)2(DeltaD5) and 1degree2(P714T) (containing the mutation P714T in the RT) do not use homing site DNA as a primer, but appear to utilize a non-complementary DNA primer of approximately ten nucleotides. The alternative priming mechanism and reverse transcription of non-cognate templates has implications for in vivo reverse transcription of non-intronic RNAs, which is expected to occur during intron deletions and other retroprocessing events.

DNA Primers↗