Severe nasal clefting and abnormal embryonic apoptosis in Alx3/Alx4 double mutant mice

Endochondral ossification of the mouse nasal septum

Endochondral ossification at the caudal junctions of the cartilaginous nasal septum, in combination with interstitial expansion of the septum, is thought to displace the facial skeleton away from the neurocranium. However, the rate of endochondral ossification has not been measured or related to rates of septal enlargement. This study examined endochondral ossification at these junctions in mice from postnatal days 0-15, in the context of known cranial growth sites, the synchondroses. BrdU labeling was used to compare cell division at the septoethmoidal and septopresphenoidal junctions with cell division at the synchondroses, and double-fluorochrome labeling was used to measure mineralization rate. The results showed that the septoethmoidal and septopresphenoidal junctions develop the characteristic morphology of growth plates postnatally, and that the pattern of cell division is similar to that of synchondroses. Mineralization at these junctions occurred at rates that were not statistically different from those of the synchondroses. However, the cartilaginous septum increased in length much more rapidly than could be explained by caudal growth, implying that interstitial expansion is the more important contributor to septal growth.

Regional regulation of palatal growth and patterning along the anterior-posterior axis in mice

Cleft palate is a congenital disorder arising from a failure in the multistep process of palate development. In its mildest form the cleft affects only the posterior soft palate. In more severe cases the cleft includes the soft (posterior) and hard (anterior) palate. In mice a number of genes show differential expression along the anterior-posterior axis of the palate. Mesenchymal heterogeneity is established early, as evident from Bmp4-mediated induction of Msx1 and cell proliferation exclusively in the anterior and Fgf8-specific induction of Pax9 in the posterior palate alone. In addition, the anterior palatal epithelium has the unique ability to induce Shox2 expression in the anterior mesenchyme in vivo and the posterior mesenchyme in vitro. Therefore, the induction and competence potentials of the epithelium and mesenchyme in the anterior are clearly distinct from those in the posterior. Defective growth in the anterior palate of Msx1-/- and Fgf10-/- mice leads to a complete cleft palate and supports the anterior-to-posterior direction of palatal closure. By contrast, the Shox2-/- mice exhibit incomplete clefts in the anterior presumptive hard palate with an intact posterior palate. This phenotype cannot be explained by the prevailing model of palatal closure. The ability of the posterior palate to fuse independent of the anterior palate in Shox2-/- mice underscores the intrinsic differences along the anterior-posterior axis of the palate. We must hitherto consider the heterogeneity of gene expression and function in the palate to understand better the aetiology and pathogenesis of non-syndromic cleft palate and the mechanics of normal palatogenesis.

Function and regulation of Alx4 in limb development: complex genetic interactions with Gli3 and Shh

The role of the aristaless-related homeobox gene Alx4 in antero-posterior (AP-) patterning of the developing vertebrate limb has remained somewhat elusive. Polydactyly of Alx4 mutant mice is known to be accompanied by ectopic anterior expression of genes like Shh, Fgf4 and 5'Hoxd. We reported previously that polydactyly in Alx4 mutant mice requires SHH signaling, but we now show that in early Alx4-/- limb buds the anterior ectopic expression of Fgf4 and Hoxd13, and therefore disruption of AP-patterning, occurs independently of SHH signaling. To better understand how Alx4 functions in the pathways that regulate AP-patterning, we also studied genomic regulatory sequences that are capable of directing expression of a reporter gene in a pattern corresponding to endogenous Alx4 expression in anterior limb bud mesenchyme. We observed, as expected for authentic Alx4 expression, expansion of reporter construct expression in a Shh-/- background. Total lack of reporter expression in a Gli3-/- background confirms the existence of Gli3-dependent and -independent Alx4 expression in the limb bud. Apparently, these two modules of Alx4 expression are linked to dissimilar functions.

Congenital arhinia with de novo reciprocal translocation, t(3;12)(q13.2;p11.2)

A female newborn suffering from congenital arhinia with complete airway obstruction is reported. In addition, she had hypertelorism, microphthalmia, high-arched palate, and hypoplasia of the auditory canal and mastoid and facial bones, along with the absence of olfactory bulbs and tracts. She had a de novo reciprocal translocation between chromosomes 3q13.2 and 12p11.2. Certain gene(s) located at either of the breakpoints, 3q13.2 and 12p11.2, may be involved in the pathogenesis of her arhinia.

Opposing roles of two isoforms of the Prx1 homeobox gene in chondrogenesis

The Prx1 homeobox gene is critical for cartilage and bone development as suggested by previous expression studies and demonstrated by gene targeting. However, neither approach assessed the individual roles of the two isoforms Prx1a and Prx1b. In this study, Western blot analysis demonstrates that, in the early stages of chondrogenesis, during mesenchymal condensation, only Prx1a is expressed. Higher level Prx1b expression is concomitant with the formation of a defined perichondrium. Prx1a overexpression in limb micro mass cultures results in an increase in the number of prechondrogenic condensations and cartilage nodules, whereas overexpression of Prx1b results in a decrease. Prx1a increases the percentage of proliferating cells in micro mass cultures and decreases apoptosis. The Prx1b isoform does not alter proliferation, but it does increase apoptosis, which is opposite of Prx1a. These results suggest that the Prx1a:Prx1b ratio and the alternative splicing mechanism that generates these two isoforms are critical in controlling chondrogenesis.

Tibial aplasia, lower extremity mirror image polydactyly, brachyphalangy, craniofacial dysmorphism and genital hypoplasia: further delineation and mutational analysis

Congenital anomalies involving tibial aplasia are rare. Recently, four children with an unusual combination of limb anomalies, facial dysmorphism and genital hypoplasia have been reported. All affected children reported were male. One case noted father to son transmission, implying autosomal dominant inheritance. We report the first female patient with this syndrome. The patient had tibial aplasia, mirror image preaxial polydactyly involving her feet, brachyphalangy, genital hypoplasia as well as facial dysmorphism including telecanthus, blepharophimosis, a flat nasal bridge with a small nose and a small mouth. Consistent with reports in males of a micropenis and hypoplastic scrotum, our patient had absent labia minora and a very small clitoris. Her father had very minor anomalies suggestive of somatic mosaicism or marked variability. Mouse models affecting limb development are powerful tools in the study of human syndromes. The clinical phenotype of patients with this syndrome is reminiscent of some luxoid mouse mutants suggesting Alx4 and related members of the paired homeodomain class as candidate genes. ALX4 haploinsufficiency in humans causes parietal foramina, which one patient with this syndrome was reported to have. Sequencing of coding exons of ALX4 and its related homologue, ALX3, in the proband failed to reveal coding sequence alterations. Our father/daughter pair is the second family reported, supporting a dominant mode of inheritance. Moreover, the very mild phenotype in the father suggests the need for very careful attention to parental examination in such cases.

Apoptosis distribution in the first molar tooth germ of the field vole (Microtus agrestis)

Apoptosis represents an important process in organ and tissue morphogenesis and remodeling during embryonic development. A role for apoptosis in shape formation of developing teeth has been suggested. The field vole is a useful model for comparative studies in odontogenesis, particularly because of its contrasting molar morphogenesis when compared to the mouse. However, little is known concerning apoptosis in tooth development of this species. Morphological (cellular and nuclear alterations) and biochemical (specific DNA breaks--TUNEL staining) characteristics of apoptotic cells were used to evaluate the temporal and spatial occurrence of apoptosis in epithelial and mesenchymal tissues of the developing first molar tooth germs of the field vole. Apoptotic cells were found in non-proliferating areas (identified previously) throughout bud to bell stages, particularly in the epithelium, however, scattered also in the mesenchyme. A high concentration of TUNEL positive cells was evident in primary enamel knots at late bud stage with increasing density of apoptotic cells until ED 16 when the primary enamel knot in the field vole disappears and mesenchyme becomes protruded in the middle axes of the bell forming two shallow areas with zig-zag located secondary enamel knots. Distribution of TUNEL positive cells corresponded with localisation of secondary enamel knots as shown using histological and 3D analysis. Apoptosis was shown to be involved in the first molar development of the field vole, however, exact mechanisms and roles of this process in tooth morphogenesis require further investigation.

C677T mutation in the MTHFR gene was not found in patients with frontoethmoidal encephalocele in East Java, Indonesia

BACKGROUND

Frontoethmoidal encephalocele (FEE) is a neural tube defect (NTD) characterized by a congenital bone defect in the anterior cranium and herniation of the intracranial mass through the defect. The C677T mutation in the 5,10-methylenetetrahydrofolate reductase gene (MTHFR) has been reported as a genetic risk factor for spina bifida. However, the role of the MTHFR in the pathogenesis of FEE remains to be clarified.

METHODS

A hospital-based survey of FEE patients who were referred to the Department of Neurosurgery and Plastic Surgery, Malang General Hospital, East Java, Indonesia was conducted. Genetic screening of MTHFR substitutions in 13 patients and eight mothers from 11 affected families were performed using a combination of polymerase chain reaction (PCR), denaturing high-performance liquid chromatography (DHPLC), and direct sequencing.

RESULTS

In total, 130 patients with FEE among 138 NTD patients (94.2%) were identified. The ratios of cranial encephalomeningocele to spinal meningocele (32 : 1) and of FEE to occipital encephalomeningocele (32 : 1) were higher than those in other populations. Five substitutions were detected in the MTHFR: C121T, C677T, C1060T, A1298C, and G1793A. No significant differences were found in the frequency of each nucleotide substitution between patients or mothers and controls. In addition, none of the subjects in this study were homozygous for T at nucleotide position 677.

CONCLUSION

FEE is the most common form of NTD in East Java, Indonesia. Genetic analysis of 11 affected families suggests that the MTHFR gene is not associated with the development of FEE, although the number of FEE families analyzed in this study was very limited.

The homeoprotein Alx3 contains discrete functional domains and exhibits cell-specific and selective monomeric binding and transactivation

Alx3 is a paired class aristaless-like homeoprotein expressed during embryonic development. Transcriptional transactivation by aristaless-like proteins has been associated with cooperative dimerization upon binding to artificially generated DNA consensus sequences known as P3 sites, but natural target sites in genes regulated by Alx3 are unknown. We report the cloning of a cDNA encoding the rat homolog of Alx3, and we characterize the protein domains that are important for transactivation, dimerization, and binding to DNA. Two proline-rich domains located amino-terminal to the homeodomain (Pro1 and Pro2) are necessary for Alx3-dependent transactivation, whereas another one (Pro3) located in the carboxyl terminus is dispensable but contributes to enhance the magnitude of the response. We confirmed that transcriptional activity of Alx3 from a P3 site correlates with cooperative dimerization upon binding to DNA. However, Alx3 was found to bind selectively to non-P3-related TAAT-containing sites present in the promoter of the somatostatin gene in a specific manner that depends on the nuclear protein environment. Cell-specific transactivation elicited by Alx3 from these sites could not be predicted from in vitro DNA-binding experiments by using recombinant Alx3. In addition, transactivation did not depend on cooperative dimerization upon binding to cognate somatostatin DNA sites. Our data indicate that the paradigm according to which Alx3 must act homodimerically via cooperative binding to P3-like sites is insufficient to explain the mechanism of action of this homeoprotein to regulate transcription of natural target genes. Instead, Alx3 undergoes restrictive or permissive interactions with nuclear proteins that determine its binding to and transactivation from TAAT target sites selected in a cell-specific manner.

About face: signals and genes controlling jaw patterning and identity in vertebrates

The embryonic vertebrate face is composed of similarly sized buds of neural crest-derived mesenchyme encased in epithelium. These buds or facial prominences grow and fuse together to give the postnatal morphology characteristic of each species. Here we review the role of neural crest cells and foregut endoderm in differentiating facial features. We relate the developing facial prominences to the skeletal structure of the face and review the signals and genes that have been shown to play an important role in facial morphogenesis. We also examine two experiments one at the genetic level and one at the signal level in which transformation of facial prominences and subsequent change of jaw identity was induced. We propose that signals such as retinoids and BMPs and downstream transcription factors such as Distal-less related genes specify jaw identity.

Development of calcareous skeletal elements in invertebrates

Most metazoans require skeletal support systems. While the formation of bones and teeth in vertebrates has been well studied, endo- and exoskeleton development of non-vertebrates, especially calcification during terminal differentiation, has been neglected. Biomineralization of skeletons in invertebrates presents interesting research opportunities. We undertake here to survey some of the better understood examples of skeletal development in selected invertebrates. The differentiation of the skeletal spicules of euechinoid larvae and other non-vertebrate deuterostomes, the shells of molluscs, and the calcification of crustacean carapaces are surveyed. The diversity of these different kinds of animals and our present limited understanding make it difficult to identify unifying themes, but there certainly are unifying questions: How is the mineral precursor secreted? What is the nature of the interaction of mineral with the matrix proteins of the skeleton? Is there any conservation of protein domains in matrix proteins found in skeletal elements from different phyla? Are there common strategies in the development of organs that form mineralized structures?

Microform holoprosencephaly in mice that lack the Ig superfamily member Cdon

Holoprosencephaly (HPE), the most common developmental defect of the forebrain and midface, is caused by a failure to delineate the midline in these structures. Despite the identification of several HPE genes, its genetic basis is largely unknown. Furthermore, the phenotype of affected individuals is highly variable, even within pedigrees. Facial defects in HPE range from cyclopia and proboscis in severe cases to solitary median maxillary central incisor in individuals with microforms of HPE. Cdon (also known as Cdo), an Ig superfamily member, is a component of a cell surface receptor that positively regulates skeletal myogenesis. Cdon is also highly expressed in the frontonasal and maxillary processes (FNP and MXP, respectively) of the developing mouse embryo, structures that contain signaling centers that pattern the face. We report here that mice homozygous for targeted mutations of Cdon display the hallmark facial defects associated with microforms of HPE. This is the first example of a mouse mutant with this phenotype, and this finding implicates a new family of receptors in development of the facial midline and suggests a potential role for Cdon in the pathogenesis and expressivity of HPE in humans.

Teratogenic effects of suramin on the chick embryo

Suramin, a polysulfonated naphthylamine, has been used for the chemotherapy of trypanosomiasis and onchocerciasis since about the 1920s. Currently, it is also being tested as an anticancer agent. It is hoped that suramin might stop the progression of some kinds of cancer since it has been found to inhibit the proliferation and migration of cells and the formation of new blood vessels. These processes are not only essential for the development and progression of cancer, but also for normal embryonic development. Suramin might, therefore, be a potent teratogen. In the literature, however, we have found only scant information on this subject. In the present study, we demonstrate the teratogenic effects of suramin on chick embryos. Suramin was injected into the coelomic cavity of chick embryos on incubation day (ID) 3. Following reincubation until ID 8, suramin-treated embryos ( n=50) were examined for congenital malformations and compared with a control group ( n=30). The survival rate of suramin-treated embryos was markedly reduced compared with controls (50% vs 90%). Among the 25 survivors the following malformations were recorded: caudal dysgenesia (100%), median facial clefts with hypertelorism (92%), malformations of the aortic arch arteries (88%), hypo-/aplasia of the allantoic vesicle (84%), microphthalmia (52%), abnormalities of the great arterial trunks (44%), unilateral or bilateral cleft lips (40%), heart defects with juxtaposition of the right atrial appendage (36%), persistence of the lens vesicle (32%), median clefts of the lower beak (8%), omphalocele (4%), and cloacal exstrophy (4%). These results show that suramin is a potent teratogen. The possible implications of our findings for human beings and the possible teratogenic mechanisms of suramin are discussed. Use of suramin in experimental teratology might help to clarify the morphogenesis of median facial clefts and of some congenital heart defects.

The OAR/aristaless domain of the homeodomain protein Cart1 has an attenuating role in vivo

Aristaless-related genes encode a structurally defined group of homeoproteins that share a C-terminal stretch of amino acids known as the OAR- or aristaless domain. Many aristaless-related genes have been linked to major developmental functions, but the function of the aristaless domain itself is poorly understood. Expression and functional studies have shown that a subgroup of these genes, including Prx1, Prx2, Alx3, Alx4 and Cart1, is essential for correct morphogenesis of the limbs and cranium. We now demonstrate the function of the aristaless domain in vivo by ectopically expressing normal and mutated forms of Cart1 and Alx3. Ectopic expression of Cart1 in transgenic mice does not disturb development, whereas expression of a Cart1 form from which the aristaless domain has been deleted results in severe cranial and vertebral malformations. The Alx3 protein contains a divergent aristaless domain that appears not to be functional, as ectopic expression of Alx3 results in an altered phenotype irrespective of the presence of this aristaless domain. Linking the Cart1 aristaless domain to Alx3 extinguishes teratogenicity. We show that, at the molecular level, the most important consequence of deleting the aristaless domain is increased DNA binding to its palindromic target sequence. This demonstrates that the aristaless domain functions as an intra-molecular switch to contain the activity of the transcription factor that it is part of.

Isolation of differentially expressed genes from wild-type and Twist mutant mouse limb buds

In the mouse, Twist is required for normal limb and craniofacial development. We show that the aristaless-like transcription factors, Alx3 and Alx4 are downregulated in the Twist(-/-) mutant and may be potential targets of Twist. By suppression subtractive hybridization we isolated 31 and 18 unique clones representing mRNAs that are putatively downregulated and upregulated respectively in Twist(-/-) forelimb buds. These included genes encoding cytoskeletal components, metabolic enzymes, hemoglobin molecules, membrane transport proteins, components of transcription and translation complexes, protein modification enzymes and proteins related to cell proliferation and apoptosis. Differential expression of selected clones was validated by whole mount in situ hybridization to E10.5 wild-type and Twist(-/-) embryos. We show that four novel clones are expressed in the Twist-expressing craniofacial tissues and paraxial mesoderm and downregulated in Twist(-/-) embryos, raising the possibility that they are, in addition to genes of the Alx family, downstream targets of Twist.