Neural tube development requires the cooperation of p53- and Gadd45a-associated pathways.
BACKGROUND
Numerous genetically engineered mouse models for neural tube defects (NTDs) exist, and some of the implicated proteins are functionally related. For example, the growth arrest and DNA damage-inducible protein Gadd45a and tumor suppressor p53 are functionally similar, and both are involved in neural tube development (Gadd45a- and Trp53-null embryos show low levels of exencephaly). To assess their roles in neural tube development, we generated double-null mice from Gadd45a- and Trp53-null mice, as well as from cyclin-dependent kinase inhibitor (Cdkn1a) (p21)-null and xeroderma pigmentosum group C (XPC)-null mice that do not show spontaneous exencephaly.


METHODS
Gadd45a-, Trp53-, Cdkn1a-, and XPC-null mice were crossed to generate several double-null mouse models. Embryos (embryonic day [ED] 16-18) from the single- and double-null crosses were scored for NTDs.


RESULTS
Deletion of both Gadd45a and Trp53 in mice increased exencephaly frequencies compared to the deletion of either single gene (34.0% in Gadd45a/Trp53-null compared to 8.4% and 9.1% in the Gadd45a- and Trp53-null embryos, respectively). Furthermore, although deletion of another p53-regulated gene, Cdkn1a, is not associated with exencephaly, in conjunction with Gadd45a deletion, the exencephaly frequencies are increased (30.5% in the Gadd45a/Cdkn1a-null embryos) and are similar to those in the Gadd45a/Trp53-null embryos. Although XPC deletion increased exencephaly frequencies in Trp53-null embryos, XPC deletion did not increase the exencephaly frequencies in Gadd45a-null embryos.


CONCLUSIONS
The increased genetic liability to exencephaly in the Gadd45a/Trp53- and Gadd45a/Cdkn1a-null embryos may be related to the disruption of multiple cellular pathways associated with Gadd45a and p53.
National Institutes of Health-George Washington University Graduate Partnerships Program in Genetics, National Cancer Institute, National Institutes of Health, Bethesda, MD 20889, USA.
Andrew D
AD
Patterson
Jeffrey
J
Hildesheim
Albert J
AJ
Fornace
M Christine
MC
Hollander
D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics / Q000502:physiology*; D002490:Central Nervous System / Q000196:embryology* / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D005260:Female; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009436:Neural Tube Defects / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000235:genetics* / Q000502:physiology; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000502:physiology*; D000097642:GADD45 Proteins
D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D016159:Tumor Suppressor Protein p53; C493957:Cdkn1a protein, mouse; C439070:GADD45A protein, human; D000097642:GADD45 Proteins; C501002:Xpc protein, mouse