Further Scutellarein analysis showed that some of the genes could be involved in regulation of cholesterol-dependent events in chemotaxis towards antigen. This study was initiated because of long-standing discrepancies in published data indicating that NTAL in mouse mast cells is a negative regulator of FceRI signaling, whereas in human or rat mast cells is a positive regulator. However, it was not clear whether these discrepancies reflect different methods/ strategies used for NTAL down-regulation and 12-O-Tiglylphorbol-13-isobutyrate developmental alterations in KO mice as described in other systems where absence of a given gene is compensated for by enhanced transcriptional activity of other genes. In attempt to understand the contribution of the compensatory mechanisms, we investigated for the first time the properties of mouse BMMCs with NTAL KD and compared them with BMMCs from mice with NTAL KO and well-matched controls. Several lines of evidence obtained in this study, indicate expressive similarities between the properties of BMMCs with NTAL KD or KO, and support the concept that NTAL is mostly a negative regulator of FceRI signaling, independently of possible compensatory developmental alterations. First, BMMCs with both NTAL KO and NTAL KD showed comparable increase in degranulation induced by FceRI triggering. Compared to WT cells, NTAL KDs showed the highest increase in degranulation at suboptimal concentrations of Ag, similarly to NTAL KOs. At optimal and supraoptimal Ag concentrations the differences were less pronounced. Interestingly, activation through KIT was not potentiated by the absence of NTAL, even though NTAL is tyrosine phosphorylated in KITactivated mast cells and activation through KIT enhances degranulation of FceRI-activated WT cells, and even more so of cells with NTAL KO or KD. Second, Ag-activated BMMCs with NTAL KD exhibited higher Ca2+ response when compared to WT pLKO cells, but lower when compared to NTAL KO cells. Similarly to degranulation, down-regulation of NTAL had no effect on Ca2+ response after KIT triggering, even though KIT activation enhanced Ca2+ response in Ag-activated WT cells, and even more so in NTALdeficient cells. Third, when compared to WT cells, Ag activation of cells with NTAL KD resulted in enhanced tyrosine phosphorylation of ERK and LAT.