Different thresholds of Notch signaling bias human precursor cells toward B-, NK-, monocytic/dendritic-, or T-cell lineage in thymus microenvironment

Notch Signaling During Human T cell Development

“…At this point in development, thymocytes start to express the necessary genes to allow gene recombination at the TCRD, -G and -B loci, such as IL7R and the RAG genes, as well as PTCRA to allow immediate induction of preTCR signaling and subsequent -selection upon the generation of an in-frame TCR- chain. Consistent with a clear requirement for Notch signaling to support human TCR- chain rearrangements (De Smedt et al, 2005), also PTCRA expression seems Notch dependent, although we could only observe a small reduction in PTCRA expression upon Notch inhibition in human thymocytes using GSI ( Van de Walle et al, 2009) or DNMAML1 overexpression (Figure 3). While a conserved CSL binding site has been detected in both human and mouse (Reizis and Leder, 2002), PTCRA expression in human seems at least equally dependent on other regulatory inputs since its expression drops 7-fold in conditions of excess Notch stimulation compared to ex vivo isolated cells ).…”

“…Understanding this should also help to explain their specific expression profile at this early stage of human T cell development. In each case, Notch does not seem to be essential to induce human T-cell commitment in previously T-lineage specified progenitors in the absence of exogenous, non T-lineage, cytokines that can drive alternative lineage potential (De Smedt et al, 2005;De Smedt et al, 2007;Taghon et al, 2009;Magri et al, 2009). Given that the only function of the thymus is to give rise to T cells, it rather seems that the high initial levels of Notch signaling in human are important to expand the initial pool of uncommitted T-lineage specified progenitors that are generated from the limited number of TSPs.…”

“…Whether or not Notch signaling is required for survival of the TCR rearranging cells during these stages has not been thoroughly investigated in humans. While it is clear that Notch signaling is critical for the long-term survival of human thymocytes, it is not well-established whether this is mediated directly through Notch signaling events that regulate glucose metabolism as shown for mouse DN3 thymocytes (Ciofani and ZunigaPflucker, 2005), or rather indirectly due to the lack of other critical survival signals such as for instance provided through TCR signaling (De Smedt et al, 2005). Expression of MYC, coding for an important transcriptional regulator of genes involved in cellular growth and survival, does seem to be Notch-dependent during these stages of human T cell development, suggesting that Notch at least partially regulates these cellular processes during early human thymocyte development.…”

Specific Notch receptor–ligand interactions control human TCR-ab/gd development by inducing differential Notch signal strength

“…In the case of ICN1, ICN3, and MSCV transduced cells, cells were harvested activated to induce TCR- rearrangements. Interestingly, the generation of a functional TCR- chain has been shown to be dependent on Notch1 signaling in the mouse (Wolfer et al, 2002) and presumably also in humans (De Smedt et al, 2005). Although our gene expression analysis only reveals quantitative and no qualitative differences between Notch1 and Notch3 in their potential to activate or repress Notch target genes, previous work has proposed that Notch3 can inhibit Notch1 function (Beatus et al, 1999), leaving the possibility that TCR- chain rearrangements are differentially affected by Notch1 and Notch3.…”

Notch ligands potentiate IL‐7‐driven proliferation and survival of human thymocyte precursors

“…In humans, the role of Notch in T-cell differentiation was evidenced by culturing cord blood or bone marrow CD34 1 progenitors on OP9 stromal cells manipulated to express the Notch ligand DL1 (OP9-DL1 system) [11,12]. The role of Notch in the differentiation of thymic precursors has been mostly addressed by culturing normal or manipulated CD34 1 thymic cells expressing NICD on fetal thymic organ cultures [13][14][15].…”