Expression of the Sonic hedgehog (SHH) Gene during Early Human Development and Phenotypic Expression of New Mutations Causing Holoprosencephaly

Abstract

Holoprosencephaly (HPE), the most common developmental defect of the forebrain and the face, is genetically heterogeneous. One of the genes involved, Sonic hedgehog ( SHH ), on 7q36, has been identified as the first HPE-causing gene both in mouse and humans. In order to delineate the phenotype of specific SHH mutations, we described the expression of the SHH gene during early human embryogenesis and investigated the phenotype of novel SHH mutations. In situ hybridization studies were performed on paraffin-embedded human embryo sections at three different development stages. These studies show that SHH is expressed in the notochord, the floorplate, the brain, the zone of polarizing activity and the gut. We also report on the phenotype of four novel mutations identified in 40 HPE families (two in isolated HPE and two in familial HPE). Expressivity ranged from alobar HPE to microcephaly and hypoplasia of the pituitary gland in one family, and from HPE to an asymptomatic form in another family. No SHH mutation was found in six polymalformed cases combining HPE with other defects, such as skeletal, limb, cardiac, anal and/or renal anomalies. This study confirms the genetic heterogeneity of HPE, and further demonstrates that SHH mutations are associated with a broad spectrum of cerebral midline defects.

A new mutation in the six-domain of SIX3 gene causes holoprosencephaly

“…5 The identification of this SIX3 mutation made genetic counselling more reassuring for the normal male (II3), who was not a carrier. This SIX3 mutation, found in a panel of 56 unrelated HPE patients, confirms the well-known genetic heterogeneity of the disease, as five mutations were found in SHH, 9,12 three in ZIC2 and a missense mutation in SIX3 (data not shown). Similar frequencies were described by the previous reports.…”

“…We have performed a mutational analysis of SIX3 in 56 HPE patients including those already tested for SHH 9 and ZIC2. We found a mutation located for the first time in the SIX domain in a family with severe ophthalmologic symptoms.…”

Mutational analyses of UPIIIA, SHH, EFNB2, and HNF1β in persistent cloaca and associated kidney malformations

“…SHH is a secreted morphogen that signals through complex pathways involving membrane-associated molecules, patched and smoothened, and intracellular proteins, glioma-associated oncogenes 1-3 (GLI13) (8,36). SHH is expressed in the cloaca, hindgut, ureter and metanephros (17,21,22). The urothelium acts as a signalling centre, orchestrating the differentiation of associated smooth muscle through SHH secretion (22); down-regulation of SHH expression by retinoic acid administration (17) and nullmutation of the gene (23) in rodents cause anorectal malformations including persistent cloaca.…”

“…In addition, we screened three other genes, Sonic Hedgehog (SHH: 7q36), Ephrin B2 (EFNB2: 13q33) and Hepatocyte Nuclear Factor 1 β(HNF1β: 17cen-q21.3). As detailed in the Discussion, SHH (8,17,(21)(22)(23), EFNB2 (24) and HNF1β (25)(26)(27)(28)(29) are expressed in the developing renal, genital and alimentary tracts, and have been functionally implicated in the normal development of these structures.…”

Assessing Signaling Properties of Ectodermal Epithelia During Craniofacial Development

“…The similarity of outcomes when using quail or mouse ectoderm, and the conservation of molecular signals in this tissue among many species 6,11 indicates that this is a highly conserved signaling center among vertebrates. Furthermore, other investigators have used similar techniques to test the signaling properties of different regions of surface cephalic ectoderm and have uncovered the presence of multiple signaling centers located in the ectoderm that contribute to morphogenesis of the face 12 .…”