Neural tube closure depends on expression of Grainyhead-like 3 in multiple tissues

Abstract

Failure of neural tube closure leads to neural tube defects (NTDs), common congenital abnormalities in humans. Among the genes whose loss of function causes NTDs in mice, Grainyhead-like3 (Grhl3) is essential for spinal neural tube closure, with null mutants exhibiting fully penetrant spina bifida. During spinal neurulation Grhl3 is initially expressed in the surface (non-neural) ectoderm, subsequently in the neuroepithelial component of the neural folds and at the node-streak border, and finally in the hindgut endoderm. Here, we show that endoderm-specific knockout of Grhl3 causes late-arising spinal NTDs, preceded by increased ventral curvature of the caudal region which was shown previously to suppress closure of the spinal neural folds. This finding supports the hypothesis that diminished Grhl3 expression in the hindgut is the cause of spinal NTDs in the curly tail, carrying a hypomorphic Grhl3 allele. Complete loss of Grhl3 function produces a more severe phenotype in which closure fails earlier in neurulation, before the stage of onset of expression in the hindgut of wild-type embryos. This implicates additional tissues and NTD mechanisms in Grhl3 null embryos. Conditional knockout of Grhl3 in the neural plate and node-streak border has minimal effect on closure, suggesting that abnormal function of surface ectoderm, where Grhl3 transcripts are first detected, is primarily responsible for early failure of spinal neurulation in Grhl3 null embryos.

Insights into the Etiology of Mammalian Neural Tube Closure Defects from Developmental, Genetic and Evolutionary Studies

“…A similar disruptive effect on the development of DLHPs or the bending to concave shape is suggested for the homolog, Grhl3 . In the caudal region Grhl3 , is expressed in surface ectoderm during neural tube closure, and lack of Grhl3 seems to cause delay of specification of surface ectoderm [ 73 ], a situation somewhat like the findings for Grhl2 [ 72 ]. Later, at the most caudal end of primary neurulation, a second mechanism is observed.…”

“…Later, at the most caudal end of primary neurulation, a second mechanism is observed. Grhl3 is expressed in the gut endoderm that underlies the neural tube, and lack of Grhl3 expression there is associated with defective hindgut cell proliferation that causes excessive axial bending that mechanically interferes with closure of the posterior neuropore [ 73 ].…”

An Injectable Reverse Thermal Gel for Minimally Invasive Coverage of Mouse Myelomeningocele

“…32 The Grhl family of transcription factors has proven to play critical roles in neural tube closure and epidermal development. [33][34][35][36] The Grhl3 Cre mutant strain carries a "knockin" of Cre-recombinase into the Grhl3 locus, causing a loss of function allele. Homozygous mutant fetuses fail to undergo spinal neural tube closure, leading to a neural tube defect that extends over the caudal spinal region.…”

Overexpression of Grainyhead-like 3 causes spina bifida and interacts genetically with mutant alleles of Grhl2 and Vangl2 in mice

“…Analysis of Grhl3 -null and tissue-specific knockout embryos indicates that the initial defect leading to failure of spinal neurulation is localized to the surface ectoderm component of the closing neural folds, corresponding with its prominent early expression in this cell layer ( 12 ). Grhl3 is also expressed in the node-streak border/caudo-lateral epiblast and, later and transiently, in the neuroepithelium as well as in the gut endoderm ( 9 , 11 , 12 ). Among these tissues, knockout of Grhl3 in the gut endoderm causes spinal NTDs, but with later onset than in null embryos.…”