Myf5, one of the basic helix-loop-helix transcription factors, controls muscle differentiation and is expressed in somites during early embryogenesis. However, the transcription factors bound to the cis-elements of myf5 are poorly understood. In this study, we used the yeast one-hybrid assay and found that Forkhead box d3 (Foxd3) interacted specifically with the -82/-62 cassette, a key element directing somite-specific expression of myf5. The dual-luciferase assay revealed that the expression of Foxd3 potently transactivated the myf5 promoter. Knocking down foxd3 with morpholino oligonucleotide (MO) resulted in a dramatic down-regulation of myf5 in somites and adaxial cells but not in the presomitic mesoderm. On the other hand, myod expression remained unchanged in foxd3 morphants. Foxd3 mediation of myf5 expression is stage-dependent, maintaining myf5 expression in the somites and adaxial cells during the 7- to 18-somite stage. Furthermore, in the pax3 morphant, the expression of foxd3 was down-regulated greatly and the expression of myf5 was similar to that of the foxd3 morphant. Co-injection of foxd3 mRNA and pax3-MO1 greatly restored the expression of myf5 in the somites and adaxial cells, suggesting that pax3 induces foxd3 expression, which then induces the expression of myf5. This report is the first study to show that Foxd3, a well-known regulator in neural crest development, is also involved in myf5 regulation.

ADP-ribosylation factor-like 6 (Arl6) mutation is linked to human disease and Arl6 interacts with Arl6 interacting protein (Arl6ip). However, the expression pattern and function of Arl6ip during embryogenesis are unknown. To confirm whether abnormal Arl6ip function might result in embryonic defects in zebrafish, we examined the expression patterns of arl6ip during embryogenesis, and they were maternally expressed and exhibited in the brain, optic primordia, hypochord, spinal cord, myotome, heart, fin-bud, kidney, trunk, and retina. Knockdown of Arl6ip revealed the following phenotypic defects: microphthalmia, disorganized pigment pattern, flat head, defective tectum, deficient pectoral fins, abnormal pneumatic duct, pericardial edema, and deformed trunk. Particularly, histological dissection of the retinae of arl6ip-morphants revealed that neuronal differentiation is severely delayed, resulting in no formation of retinal layers. We further confirmed that opsins of arl6ip-morphants were not transcribed. Based on this evidence, Arl6ip may play important roles in zebrafish ocular, heart, and fin-bud development. Developmental Dynamics 238: 232-240, 2009.

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BackgroundAlthough the embryonic expression pattern of ADP ribosylation factor-like 6 interacting protein 1 (Arl6ip1) has been reported, its function in neural crest development is unclear.Methods/Principal FindingsWe found that knockdown of Arl6ip1 caused defective embryonic neural crest derivatives that were particularly severe in craniofacial cartilages. Expressions of the ectodermal patterning factors msxb, dlx3b, and pax3 were normal, but the expressions of the neural crest specifier genes foxd3, snai1b, and sox10 were greatly reduced. These findings suggest that arl6ip1 is essential for specification of neural crest derivatives, but not neural crest induction. Furthermore, we revealed that the streams of crestin- and sox10-expressing neural crest cells, which migrate ventrally from neural tube into trunk, were disrupted in arl6ip1 morphants. This migration defect was not only in the trunk neural crest, but also in the enteric tract where the vagal-derived neural crest cells failed to populate the enteric nervous system. We found that this migration defect was induced by dampened Shh signaling, which may have resulted from defective cilia. These data further suggested that arl6ip1 is required for neural crest migration. Finally, by double-staining of TUNEL and crestin, we confirmed that the loss of neural crest cells could not be attributed to apoptosis.Conclusions/SignificanceTherefore, we concluded that arl6ip1 is required for neural crest migration and sublineage specification.