Alx3-deficient mice exhibit folic acid-resistant craniofacial midline and neural tube closure defects

Abstract

Neural tube closure defects are among the most frequent congenital malformations in humans. Supplemental maternal intake of folic acid before and during pregnancy reduces their incidence significantly, but the mechanism underlying this preventive effect is unknown. As a number of genes that cause neural tube closure defects encode transcriptional regulators in mice, one possibility is that folic acid could induce the expression of transcription factors to compensate for the primary genetic defect. We report that folic acid is required in mouse embryos for the specific expression of the homeodomain gene Alx3 in the head mesenchyme, an important tissue for cranial neural tube closure. Alx3-deficient mice exhibit increased failure of cranial neural tube closure and increased cell death in the craniofacial region, two effects that are also observed in wild type embryos developing in the absence of folic acid. Folic acid cannot prevent these defects in Alx3-deficient embryos, indicating that one mechanism of folic acid action is through induced expression of Alx3. Thus, Alx3 emerges as a candidate gene for human neural tube defects and reveals the existence of induced transcription factor gene expression as a previously unknown mechanism by which folic acid prevents neural tube closure defects.

Alx3-deficient mice exhibit decreased insulin in beta cells, altered glucose homeostasis and increased apoptosis in pancreatic islets

“…Statistical analysis indicated that differences between wild-type and Alx3-deficient islets are significant (p<0.01; Mann-Whitney U test). Alx3 deficiency in the cranial mesenchyme of developing embryos [35], a major site of Alx3 expression during development [18]. The smaller size observed in Alx3-deficient pancreatic islets may be related to their relatively high proportion of apoptotic cells, and may contribute to impaired islet cell function.…”

LRP2 mediates folate uptake in the developing neural tube

“…4A,C). Interestingly, expression of the Alx3-related folate-independent transcription factor Alx4 (Lakhwani et al, 2010) was unchanged in LRP2-deficient embryos (Fig. 4B,C).…”

“…Recently, it was shown that expression of the gene Alx3 (aristaless-family homeobox transcription factor 3) is specifically dependent on folate, and that ALX3 is important for neural tube closure (Kessaris et al, 2006;Lakhwani et al, 2010).…”

Thearistaless-like homeobox protein Alx3 as an etiopathogenic factor for diabetes mellitus

“…23 Although Alx3-deficient mice were originally found to develop with apparent normality, 24 recent studies demonstrated that a significant proportion of them exhibit neural tube closure defects and alterations in craniofacial midline development. 17 Frontonasal dysplasia, a related type of developmental alteration, has been found in humans bearing mutations in the ALX3 gene. 25 In addition, we have observed that about 15% of viable Alx3-null mice exhibit preaxial polydactyly (Fig.…”

“…14 Overlapping functions among different members of this family are likely. [15][16][17] Therefore, it is possible that a defect in one of them may be compensated by the others, resulting in a relatively mild phenotype. In this regard, at least two other aristaless-related proteins have been associated directly or indirectly with pancreatic islet function.…”