Wdr68 Mediates Dorsal and Ventral Patterning Events for Craniofacial Development.

Birth defects are among the leading causes of infant mortality and contribute substantially to illness and long-term disability. Defects in Bone Morphogenetic Protein (BMP) signaling are associated with cleft lip/palate. Many craniofacial syndromes are caused by defects in signaling pathways that pattern the cranial neural crest cells (CNCCs) along the dorsal-ventral axis. For example, auriculocondylar syndrome is caused by impaired Endothelin-1 (Edn1) signaling, and Alagille syndrome is caused by defects in Jagged-Notch signaling. The BMP, Edn1, and Jag1b pathways intersect because BMP signaling is required for ventral edn1 expression that, in turn, restricts jag1b to dorsal CNCC territory. In zebrafish, the scaffolding protein Wdr68 is required for edn1 expression and subsequent formation of the ventral Meckel's cartilage as well as the dorsal Palatoquadrate. Here we report that wdr68 activity is required between the 17-somites and prim-5 stages, that edn1 functions downstream of wdr68, and that wdr68 activity restricts jag1b, hey1, and grem2 expression from ventral CNCC territory. Expression of dlx1a and dlx2a was also severely reduced in anterior dorsal and ventral 1st arch CNCC territory in wdr68 mutants. We also found that the BMP agonist isoliquiritigenin (ISL) can partially rescue lower jaw formation and edn1 expression in wdr68 mutants. However, we found no significant defects in BMP reporter induction or pSmad1/5 accumulation in wdr68 mutant cells or zebrafish. The Transforming Growth Factor Beta (TGF-ß) signaling pathway is also known to be important for craniofacial development and can interfere with BMP signaling. Here we further report that TGF-ß interference with BMP signaling was greater in wdr68 mutant cells relative to control cells. To determine whether interference might also act in vivo, we treated wdr68 mutant zebrafish embryos with the TGF-ß signaling inhibitor SB431542 and found partial rescue of edn1 expression and craniofacial development. While ISL treatment failed, SB431542 partially rescued dlx2a expression in wdr68 mutants. Together these findings reveal an indirect role for Wdr68 in the BMP-Edn1-Jag1b signaling hierarchy and dorso-anterior expression of dlx1a/2a.

Expression of 72-kDa gelatinase (matrix metalloproteinase-2) in the developing mouse craniofacial complex.

Tissue remodelling is an important feature during embryogenesis. Although the matrix metalloproteinases are believed to participate in these processes, the relation between matrix metalloproteinases and tissue remodelling during craniofacial morphogenesis remains unclear. The purpose of the study was to look for the presence of enzymes involved in extracellular matrix degradation during craniofacial morphogenesis. Protein expression of the matrix metalloproteinase, 72-kDa gelatinase (matrix metalloproteinase-2, gelatinase A, 72-kDa type IV collagenase) was studied by gelatine zymography and by indirect immunofluorescence with conventional and confocal microscopy. In the anterior region of the developing mouse face, 72-kDa gelatinase was labelled mainly in the tips and peripheral regions of the nasal and facial prominences. Upon contact and fusion of the prominences, the staining was intensely localized to the zone of the fusion and the tips and peripheral regions of the nasal prominences and the maxilla. The labelling of 72-kDa gelatinase was also present in the peripheral regions of the mandible, second branchial arch, and the face around the developing eye. However, during lens vesicle formation, the staining of 72-kDa gelatinase was absent in the invaginated lens ectoderm. After the lens had completely detached from the surface ectoderm, the staining was resumed in the corneal epithelium and mesenchyme. Gelatine zymography was used to confirm the presence of active and latent 72-kDa gelatinase in the developing mouse craniofacial complex. Collectively, these data indicate that 72-kDa gelatinase may play a significant part in localized tissue remodelling during craniofacial morphogenesis and the aberrant expression or function of the enzyme could be involved in causing facial abnormalities.

Lactate dehydrogenase isoenzyme changes during facial development.

Lactate dehydrogenase activity (LDH) was demonstrated by a histochemical technique in free, dissected, facial processes of rats from the ninth embryonic day. Facial processes of embryonic rats aged 9-15 days were analysed by isoelectric focusing for their isoenzymic distribution of LDH. A dominance of LDH-5, LDH-4 and LDH-3 isoenzymes was observed. As a comparison, LDH isoenzymes from mandibular and maxillary processes of rat embryos aged 9-11 days revealed only LDH-5 and, to a smaller extent, LDH-4. These results constitute evidence for prominent anaerobic metabolism in these tissues during early facial development. Intense staining for LDH was seen in surface epithelium, respiratory epithelium and in myogenic and osteogenic areas.

Inactivation of type MM phosphoglycerate mutase by sulfhydryl group reagents during facial embryogenesis.

Type MM phosphoglycerate mutase from free dissected mandibular processes from embryonic rats was reversibly inactivated by tetrathionate, p-chloromercuribenzoate, and Hg2+. Titration with p-chloromercuribenzoate showed the existence of two sulfhydryl groups per enzyme subunit, the modification of which produced a progressive decline in enzyme activity. The apparent Km values for substrate and cofactor were not affected by tetrathionate treatment. Phosphoglycerate mutase inactivated by tetrathionate and by p-chloromercuribenzoate was unable to form the functionally active phosphorylenzyme when mixed with glycerate-2,3-P2. Glycerate-2,3-P2 protected against tetrathionate but failed to protect against Hg2+ and p-chloromercuribenzoate.

Isoenzyme changes during rat facial development.

A method is presented by which rat facial processes from different stages were obtained in pure fraction. The morphology, and protein and DNA contents in free dissected facial processes were determined. Facial processes of embryonic rats aged 9-15 days were analyzed by isoelectric focusing for their isoenzymic distribution of four enzymes: lactate dehydrogenase, creatine phosphokinase, fructose diphosphate aldolase and phosphoglycerate mutase. A dominance of LDH-5, LDH-4 and LDH-3 isoenzymes was observed. As a comparison, LDH isoenzymes from mandibular and maxillary processes of rat embryos aged 9-11 days only revealed LDH-5 and to a smaller extent LDH-4. The results support the presence of a prominent anaerobic metabolism in these tissues during early facial development. The change to LDH-3 development correlates well with the formation of new blood vessels. From the ninth embryonic day, isoenzyme BB of creatine phosphokinase was present and during days 10-15 MB and MM developed. Isoenzyme A4 of fructose diphosphate aldolase was present from the ninth embryonic day and isoenzymes A3C and A2C2 developed during days 10-15. From the tenth embryonic day, isoenzyme BB of phosphoglycerate mutase was present and during days 10-15 isoenzyme MB and MM developed. Isoenzyme development was first seen in mandibular processes, followed by maxillary, lateral nasal and medial nasal processes, and it preceded morphologic evidence of skeletal muscle formation.

Osteogenic response to hydroxyapatite-fibrin implants in maxillofacial bone defects.

Bone formation in hydroxyapatite-fibrin implants has been reported several times. However, available studies refer to experimental animals, or are limited to short periods after implantation. We report the results of histological, histochemical and ultrastructural studies carried out 2.5-8 yr after implantation of non-resorbable, porous hydroxyapatite (HA) and fibrin glue in human maxillofacial bones. Prominent ossification was found in all cases, with the presence of normally structured spongy bone. HA granules were embedded in the calcified bone matrix. They had not elicited inflammatory reactions and did not induce bone resorption. Ossification was preceded by the appearance of alkaline phosphatase activity on fibroblast-like cells, and by the formation of dense collagenous layers, similar to osteoid borders, on the surface of HA granules. The early phases of the calcification process occurred in these borders, with the appearance of calcification nodules adjacent to alkaline phosphatase-positive osteoblast-like cells. A remodeling process similar to that occurring in normal bones was found in the newly formed bone. These results justify the conclusion that HA-fibrin implants lead to the formation of long-lasting bone that does not differ from that of the normal maxillofacial skeleton. Mixing the HA granules with fibrin has the advantage of creating an easily mouldable material which can be adapted to any skeletal surface and stays in place after surgery.