Agenesis In Humans Research Articles

Rescue of cleft palate in Msx1-deficient mice by transgenic Bmp4 reveals a network of BMP and Shh signaling in the regulation of mammalian palatogenesis.

Cleft palate, the most frequent congenital craniofacial birth defects in humans, arises from genetic or environmental perturbations in the multi-step process of palate development. Mutations in the MSX1 homeobox gene are associated with non-syndromic cleft palate and tooth agenesis in humans. We have used Msx1-deficient mice as a model system that exhibits severe craniofacial abnormalities, including cleft secondary palate and lack of teeth, to study the genetic regulation of mammalian palatogenesis. We found that Msx1 expression was restricted to the anterior of the first upper molar site in the palatal mesenchyme and that Msx1 was required for the expression of Bmp4 and Bmp2 in the mesenchyme and Shh in the medial edge epithelium (MEE) in the same region of developing palate. In vivo and in vitro analyses indicated that the cleft palate seen in Msx1 mutants resulted from a defect in cell proliferation in the anterior palatal mesenchyme rather than a failure in palatal fusion. Transgenic expression of human Bmp4 driven by the mouse Msx1 promoter in the Msx1(-/-) palatal mesenchyme rescued the cleft palate phenotype and neonatal lethality. Associated with the rescue of the cleft palate was a restoration of Shh and Bmp2 expression, as well as a return of cell proliferation to the normal levels. Ectopic Bmp4 appears to bypass the requirement for Msx1 and functions upstream of Shh and Bmp2 to support palatal development. Further in vitro assays indicated that Shh (normally expressed in the MEE) activates Bmp2 expression in the palatal mesenchyme which in turn acts as a mitogen to stimulate cell division. Msx1 thus controls a genetic hierarchy involving BMP and Shh signals that regulates the growth of the anterior region of palate during mammalian palatogenesis. Our findings provide insights into the cellular and molecular etiology of the non-syndromic clefting associated with Msx1 mutations.

Absence of mutations involving the LIM homeobox domain gene LHX9 in 46,XY gonadal agenesis and dysgenesis.

The etiology of most cases of 46,XY gonadal dysgenesis in the absence of extragenital anomalies is not accounted for by mutations in the genes known to date to be involved in sex determination. We have investigated the possibility that mutations in the gene LHX9, whose murine ortholog causes isolated gonadal agenesis when inactivated, might be responsible for gonadal dysgenesis and agenesis in humans. We isolated a human LHX9 complementary DNA (cDNA), mapped the gene to the long arm of human chromosome 1, and determined its genomic structure. We found that LHX9 is highly conserved between species, sharing in particular over 98% amino acid identity. A mutational screen was performed in a sample of patients with a range of gonadal maldevelopment, including bilateral gonadal agenesis in two sisters with an opposite sex karyotype. We did not detect mutations in the open reading frame of LHX9 in the patients studied. However, the extent of between-species structural conservation suggests that LHX9 deserves further consideration as a determinant of gonadal function in humans.

Erratum to “MSX1 mutation is associated with orofacial clefting and tooth agenesis in humans”

Erratum to “MSX1 mutation is associated with orofacial clefting and tooth agenesis in humans”

MSX1 mutation is associated with orofacial clefting and tooth agenesis in humans.

A Dutch family with tooth agenesis and various combinations of cleft palate only and cleft lip and cleft palate showed a nonsense mutation (Ser104stop) in exon 1 of MSX1. The mutant phenotype of the family is similar to that of the Msx1-mutant mouse.

The LIM homeobox gene Lhx9 is essential for mouse gonad formation.

During mammalian embryonic development, the ovaries and testes develop from somatic cells of the urogenital ridges as indifferent gonads, harbouring primordial germ cells that have migrated there. After sex determination of the gonads, the testes produce testosterone and anti-Mullerian hormone which mediate male sexual differentiation, and the female developmental pathway ensues in their absence. Here we show that transcripts of the LIM homeobox gene Lhx9 are present in urogenital ridges of mice at embryonic day 9.5; later they localize to the interstitial region as morphological differentiation occurs. In mice lacking Lhx9 function, germ cells migrate normally, but somatic cells of the genital ridge fail to proliferate and a discrete gonad fails to form. In the absence of testosterone and anti-Mullerian hormone, genetically male mice are phenotypically female. The expression of steroidogenic factor 1 (Sf1), a nuclear receptor essential for gonadogenesis, is reduced to minimal levels in the Lhx9-deficient genital ridge, indicating that Lhx9 may lie upstream of Sf1 in a developmental cascade. Unlike mice lacking other genes that mediate early stages of gonadogenesis, Lhx9 mutants do not exhibit additional major developmental defects. Thus, LHX9 mutations may underlie certain forms of isolated gonadal agenesis in humans.