Hes1 is required for the development of pharyngeal organs and survival of neural crest-derived mesenchymal cells in pharyngeal arches.

Hes genes are required to maintain diverse progenitor cell populations during embryonic development. Loss of Hes1 results in a spectrum of malformations of pharyngeal endoderm-derived organs, including the ultimobranchial body (progenitor of C cells), parathyroid, thymus and thyroid glands, together with highly penetrant C-cell aplasia (81%) and parathyroid aplasia (28%). The hypoplastic parathyroid and thymus are mostly located around the pharyngeal cavity, even at embryonic day (E) 15.5 to E18.5, indicating the failure of migration of the organs. To clarify the relationship between these phenotypes and neural crest cells, we examine fate mapping of neural crest cells colonized in pharyngeal arches in Hes1 null mutants by using the Wnt1-Cre/R26R reporter system. In null mutants, the number of neural crest cells labeled by X-gal staining is markedly decreased in the pharyngeal mesenchyme at E12.5 when the primordia of the thymus, parathyroid and ultimobranchial body migrate toward their destinations. Furthermore, phospho-Histone-H3-positive proliferating cells are reduced in number in the pharyngeal mesenchyme at this stage. Our data indicate that the development of pharyngeal organs and survival of neural-crest-derived mesenchyme in pharyngeal arches are critically dependent on Hes1. We propose that the defective survival of neural-crest-derived mesenchymal cells in pharyngeal arches directly or indirectly leads to deficiencies of pharyngeal organs.

Pulmonary TCR γδ T cells induce the early inflammation of granuloma formation by a glycolipid trehalose 6,6'-dimycolate (TDM) isolated from Mycobacterium tuberculosis.

We previously showed that formation of pulmonary granulomas in mice in response to a mycobacterial glycolipid, trehalose 6,6'-dimycolate (TDM) is due to the action of TNF-α and not of IFN-γ. However, the mechanisms of formation and maintenance of pulmonary granulomas are not yet clear. The purpose of the present study is to evaluate the mechanisms of granuloma formation by TDM at the early phase. Histological analysis showed that inflammatory cells infiltrated the murine pulmonary interstitium on day 2 after an intravenous injection with TDM as a w/o/w emulsion. Clear granuloma formation was observed on day 7 after the injection. The mRNA expression of IL-17, IFN-γ and macrophage inflammatory protein 2 was found in lung mononuclear cells at the day after TDM injection. The major IL-17-producing cells were T-cell receptor (TCR) γδ T cells expressing Vγ6. In mice depleted of γδ T cells by treatment with anti-TCR γδ monoclonal antibody, the number of TDM-induced granuloma was decreased, but the size of granuloma was not affected. Our results suggest that the mycobacterial glycolipid TDM causes activation of IL-17-producing TCR γδ T cells and stimulates chemotaxis of inflammatory cells including neutrophils in to lung.

Hes1 is required for the development of the superior cervical ganglion of sympathetic trunk and the carotid body.

Hes1 gene represses the expression of proneural basic helix-loop-helix (bHLH) factor Mash1, which is essential for the differentiation of the sympathetic ganglia and carotid body glomus cells. The sympathetic ganglia, carotid body, and common carotid artery in Wnt1-Cre/R26R double transgenic mice were intensely labeled by X-gal staining, i.e., the neural crest origin. The deficiency of Hes1 caused severe hypoplasia of the superior cervical ganglion (SCG). At embryonic day (E) 17.5-E18.5, the volume of the SCG in Hes1 null mutants was reduced to 26.4% of the value in wild-type mice. In 4 of 30 cases (13.3%), the common carotid artery derived from the third arch artery was absent in the null mutants, and the carotid body was not formed. When the common carotid artery was retained, the organ grew in the wall of the third arch artery and glomus cell precursors were provided from the SCG in the null mutants as well as in wild-types. However, the volume of carotid body in the null mutants was only 52.5% of the value in wild-types at E17.5-E18.5. These results suggest that Hes1 plays a critical role in regulating the development of neural crest derivatives in the mouse cervical region.

Hes1 regulates the number and anterior-posterior patterning of mesencephalic dopaminergic neurons at the mid/hindbrain boundary (isthmus).

The lack of the Hes1 gene leads to the failure of cranial neurulation due to the premature onset of neural differentiation. Hes1 homozygous null mutant mice displayed a neural tube closure defect, and exencephaly was induced at the mid/hindbrain boundary. In the mutant mesencephalon, the roof plate was not formed and therefore the ventricular zone showing cell proliferation was displaced to the brain surface. Furthermore, the telencephalon and ventral diencephalon were defective. Despite the severe defects of neurogenesis in null mutants, the mesencephalic dopaminergic (mesDA) neurons were specified at the midline of the ventral mesencephalon in close proximity to two important signal centers - floor plate and mid/hindbrain boundary (i.e., the isthmic organizer). Using mesDA neuronal markers, tyrosine hydroxylase (TH) and Pitx3, the development of mesDA neurons was studied in Hes1 null mice and compared with that in the wild type. At early stages, between embryonic day (E) 11.5 and E12.5, mesDA neurons were more numerous in null mutants than in the wild type. From E13.5 onward, however, the cell number and fiber density of mesDA neurons were decreased in the mutants. Their distribution pattern was also different from that of the wild type. In particular, mesDA neurons grew dorsally and invaded the rostral hindbrain. 5-HT neurons were also ectopically located in the mutant midbrain. Thus, the loss of Hes1 resulted in disturbances in the inductive and repulsive activities of the isthmic organizer. It is proposed that Hes1 plays a role in regulating the location and density of mesDA neurons.