Prx1andPrx2are upstream regulators of sonic hedgehog and control cell proliferation during mandibular arch morphogenesis

Abstract

The aristaless-related homeobox genes Prx1 and Prx2 are required for correct skeletogenesis in many structures. Mice that lack both Prx1 and Prx2 functions display reduction or absence of skeletal elements in the skull, face, limbs and vertebral column. A striking phenotype is found in the lower jaw, which shows loss of midline structures, and the presence of a single, medially located incisor. We investigated development of the mandibular arch of Prx1−/−Prx2−/− mutants to obtain insight into the molecular basis of the lower jaw abnormalities. We observed in mutant embryos a local decrease in proliferation of mandibular arch mesenchyme in a medial area. Interestingly, in the oral epithelium adjacent to this mesenchyme, sonic hedgehog (Shh) expression was strongly reduced, indicative of a function for Prx genes in indirect regulation of Shh. Wild-type embryos that were exposed to the hedgehog-pathway inhibitor, jervine, partially phenocopied the lower jaw defects of Prx1−/−Prx2−/− mutants. In addition, this treatment led to loss of the mandibular incisors. We present a model that describes how loss of Shh expression in Prx1−/−Prx2−/− mutants leads to abnormal morphogenesis of the mandibular arch.

Development of an Enzyme-Linked Immunosorbent Assay for the Veratrum Plant Teratogens: Cyclopamine and Jervine

“…Checkerboard assays using the antiserum raised against the CYCLO-SA-FET immunogen with CYCLO-SA-BSA coating conjugate resulted in an optimum dilution of antisera of 1/12000 with the coating conjugate at 250 ng/well for a CI-ELISA assay. Inhibition curves for rubijervine (10), estradiol (11), and diosgenin (13) showed no cross-reactivity with the antibodies over the concentration range studied in this assay.…”

“…Cross-reactivity. Ten steroidal alkaloids (Figure 1) were selected for cross-reactivity studies: jervine (2), N-methylcyclopamine (3), dihydrojervine (4), tetrahydrojervine (5), cyclopamine-4-ene-3-one (6), veratramine (7), muldamine (8), solanidine (9), rubijervine (10), and solasodine (12). In addition, the steroids estradiol (11) and diosgenin (13) were tested for cross-reactivity.…”

“…Cyclopamine (1), jervine (2), N-methylcyclopamine (3), dihydrojervine (4), tetrahydrojervine (5), cyclopamine-4-ene-3-one (6), veratramine (7), muldamine (8), solanidine (9), rubijervine (10), and solasidine (12) (Figure 1) were obtained from the sample collection of one of the authors (W.G.). Diosgenin (13) was purchased from Steraloids, Inc. (Newport, RI).…”

“…Several applications of cyclopamine (1) to inhibit mammalian Sonic hedgehog have correlated with the observations of terata in sheep. For example, the rapid, extensive expansion of the developing chick midbrain and forebrain have been retarded and overall head size was reduced following treatment with cyclopamine (8); treatment of regenerating fins in zebrafish with cyclopamine (1) leads to a reduction in fin outgrowth (9); and, mouse embryos exposed to jervine (2) partially phenocopied the lower jaw defects of Prx null mutants and further suffered loss of mandibular incisors (10).…”

Biomedical Applications of Poisonous Plant Research

“…They further suggest that Sonic hedgehog expression might be controlled by regulatory feedback mechanisms that define the region of bone secretion in the outgrowing fin (39). Finally, mouse embryos exposed to the Hedgehogpathway inhibitor jervine partially phenocopied the lower jaw defects of Prx1 and Prx2 null mutants and further suffered loss of the mandibular incisors (40). In the latter study, a novel molecular pathway has been proposed that identifies a mechanism that links the Prx genes to Hedgehog signaling in order to shape the developing mandibular arch (40).…”