Neural tube closure depends on nitric oxide synthase activity.
Neural tube (NT) closure is a multifactorial process that involves yet unresolved molecular mechanisms. It had been shown previously that high levels of nitric oxide (NO) block the process of NT closure in the chick embryo by inhibiting methionine synthase (MS). The MS inhibition and its effect on NT closure could be alleviated by folic acid, suggesting the involvement of the folate-methionine pathway in the process. Here we test the hypothesis that endogenous nitric oxide synthase (NOS) activity regulates the MS activity required in the process of NT closure. The experiments described here reveal that NOS activity per se, is indeed critical for NT closure in the chick embryo. Inhibition of NOS activity with either 2,4-diamino-6-hydroxypyrimidine (DAHP), which blocks biosynthesis of the NOS co-factor tetrahydrobiopterin (BH4), or with calmidazolium, which blocks calcium-calmodulin binding to NOS, resulted in reduced MS activity and consequently ablated NT closure. Addition of BH4 or the calcium ionophore A23187 restored NOS and MS activities, resulting in NT closure. The results described here imply that NOS and MS activities can serve as functional markers in this developmental process as they are essential in the process of NT closure.
Nachmany
Amir
A
Department of Cell Research and Immunology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel.
Gold
Veronica
V
Tsur
Asaf
A
Arad
Dan
D
Weil
Miguel
M
D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase / Q000037:antagonists & inhibitors; D000818:Animals; D001708:Biopterins / Q000031:analogs & derivatives / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002642:Chick Embryo; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005227:Fatty Acids / Q000378:metabolism; D019793:Fluorescein; D005456:Fluorescent Dyes; D007093:Imidazoles / Q000494:pharmacology; D007202:Indicators and Reagents; D009436:Neural Tube Defects / Q000201:enzymology* / Q000235:genetics*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D052248:Nitric Oxide Synthase Type I / Q000037:antagonists & inhibitors / Q000502:physiology*; D009599:Nitroprusside / Q000494:pharmacology; D014805:Vitamin B 12 / Q000378:metabolism
C414689:4,5-diaminofluorescein diacetate; D002147:Calmodulin; D004791:Enzyme Inhibitors; D005227:Fatty Acids; D005456:Fluorescent Dyes; D007093:Imidazoles; D007202:Indicators and Reagents; D020030:Nitric Oxide Donors; D009599:Nitroprusside; D001708:Biopterins; D000001:Calcimycin; C031938:calmidazolium; D052248:Nitric Oxide Synthase Type I; D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; C003402:sapropterin; D014805:Vitamin B 12; D019793:Fluorescein