Cardiac arterial pole alignment is sensitive to FGF8 signaling in the pharynx.

Morphogenesis of the cardiac arterial pole is dependent on addition of myocardium and smooth muscle from the secondary heart field and septation by cardiac neural crest cells. Cardiac neural crest ablation results in persistent truncus arteriosus and failure of addition of myocardium from the secondary heart field leading to malalignment of the arterial pole with the ventricles. Previously, we have shown that elevated FGF signaling after neural crest ablation causes depressed Ca2+ transients in the primary heart tube. We hypothesized that neural crest ablation results in elevated FGF8 signaling in the caudal pharynx that disrupts secondary heart field development. In this study, we show that FGF8 signaling is elevated in the caudal pharynx after cardiac neural crest ablation. In addition, treatment of cardiac neural crest-ablated embryos with FGF8b blocking antibody or an FGF receptor blocker rescues secondary heart field myocardial development in a time- and dose-dependent manner. Interestingly, reduction of FGF8 signaling in normal embryos disrupts myocardial secondary heart field development, resulting in arterial pole malalignment. These results indicate that the secondary heart field myocardium is particularly sensitive to FGF8 signaling for normal conotruncal development, and further, that cardiac neural crest cells modulate FGF8 signaling in the caudal pharynx.

Identification of negative regulator of interleukin-3 (NIL-3) in bone marrow.

We have reported that an inhibitor of interleukin-3 (NIL-3) is produced from murine bone marrow cells in response to excess stimulation of interleukin-3. In this report, we attempted the purification of the NIL-3 activity from bone marrow culture supernatant in the presence of interleukin-3. The purified NIL-3 activity was a protein with relative molecular weight of 54.5 kDa (SDS-PAGE), which inhibited the growth of IL-3 dependent DA-1 cell growth in a dose dependent manner. The N-terminal amino acid sequence of purified NIL-3 activity was determined to be homologous to beta-2 glycoprotein I (apolipoprotein H: APO-H). The gene expression of APO-H was detected by nested-PCR in STIL-3 C5-CM stimulated total bone marrow cells and STIL-3 C5-CM stimulated bone marrow fraction 2 (Fr. 2) which has been reported as a hematopoietic stem cell rich fraction. These observations indicate the possibility that the APO-H is the NIL-3 which was produced from bone marrow cells in response to excess IL-3 stimuli.