[Show abstract][Hide abstract] ABSTRACT: Despite progress in identifying the cellular composition of hematopoietic stem/progenitor cell (HSPC) niches, little is known about the molecular requirements of HSPC support. To address this issue, we used a panel of 6 recognized HSPC-‐supportive stromal lines and less-‐supportive counterparts originating from embryonic and adult hematopoietic sites. Through comprehensive transcriptomic meta-‐analyses, we identified 481 mRNAs and 17 microRNAs organized in a modular network implicated in paracrine signaling. Further inclusion of 18 additional cell strains demonstrated that this mRNA subset was predictive of HSPC support. Our gene set contains most known HSPC regulators but also a number of novel ones, such as Pax9 and Ccdc80, as validated by functional studies in zebrafish embryos. In sum, our approach has identified the core molecular network required for HSPC support. These cues together with a searchable web resource will inform ongoing efforts to instruct HSPC ex vivo amplification and formation from pluripotent precursors.
[Show abstract][Hide abstract] ABSTRACT: In humans and mice, the early development of αβ T cells is controlled by the pre-T-cell receptor α chain (pTα) that is covalently associated with the T-cell receptor β (TCRβ) chain to form the pre-T-cell receptor (pre-TCR) at the thymocyte surface. Pre-TCR functions in a ligand-independent manner through self-oligomerization mediated by pTα. Using in silico and gene synteny-based approaches, we identified the pTα gene (PTCRA) in four sauropsid (three birds and one reptile) genomes. We also identified 25 mammalian PTCRA sequences now covering all mammalian lineages. Gene synteny around PTCRA is remarkably conserved in mammals but differences upstream of PTCRA in sauropsids suggest chromosomal rearrangements. PTCRA organization is highly similar in sauropsids and mammals. However, comparative analyses of the pTα functional domains indicate that sauropsids, monotremes, marsupials, and lagomorphs display a short pTα cytoplasmic tail and lack most residues shown to be critical for human and murine pre-TCR self-oligomerization. Chicken PTCRA transcripts similar to those in mammals were detected in immature double-negative and double-positive thymocytes. These findings give clues about the evolution of this key molecule in amniotes and suggest that the ancestral function of pTα was exclusively to enable expression of the TCRβ chain at the thymocyte surface and to allow binding of pre-TCR to the CD3 complex. Together, our data provide arguments for revisiting the current model of pTα signaling.
Full-text · Article · Nov 2010 · Proceedings of the National Academy of Sciences