The homeobox gene, Xanf-1, can control both neural differentiation and patterning in the presumptive anterior neurectoderm of the Xenopus laevis embryo.
From the onset of neurectoderm differentiation, homeobox genes of the Anf class are expressed within a region corresponding to the presumptive telencephalic and rostral diencephalic primordia. Here we investigate functions of the Xenopus member of Anf, Xanf-1, in the differentiation of the anterior neurectoderm. We demonstrate that ectopic Xanf-1 can expand the neural plate at expense of adjacent non-neural ectoderm. In tadpoles, the expanded regions of the plate developed into abnormal brain outgrowths. At the same time, Xanf-1 can inhibit terminal differentiation of primary neurones. We also show that, during gastrula/neurula stages, the exogenous Xanf-1 can downregulate four transcription regulators, XBF-1, Otx-2, Pax-6 and the endogenous Xanf-1, that are expressed in the anterior neurectoderm. However, during further development, when the exogenous Xanf-1 was presumably degraded, re-activation of XBF-1, Otx-2 and Pax-6 was observed in the abnormal outgrowths developed from blastomeres microinjected with Xanf-1 mRNA. Other effects of the ectopic Xanf-1 include cyclopic phenotype and inhibition of the cement gland, both by Otx-2-dependent and -independent mechanisms. Using fusions of Xanf-1 with the repressor domain of Drosophila engrailed or activator domain of herpes virus VP16 protein, we showed that most of the observed effects of Xanf-1 were probably elicited by its functioning as a transcription repressor. Altogether, our data indicate that the repressor function of Xanf-1 may be necessary for regulation of both neural differentiation and patterning in the presumptive anterior neurectoderm.
Ermakova
G V
GV
Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, ul. Mikluho-Maklaya 16/10, V-437 Moscow 117871, Russia.
Alexandrova
E M
EM
Kazanskaya
O V
OV
Vasiliev
O L
OL
Smith
M W
MW
Zaraisky
A G
AG
D000818:Animals; D019677:Artificial Gene Fusion; D001483:Base Sequence; D019521:Body Patterning / Q000235:genetics; D002454:Cell Differentiation / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D004475:Ectoderm / Q000166:cytology; D018507:Gene Expression Regulation, Developmental; D005801:Genes, Homeobox; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D017403:In Situ Hybridization; D008845:Microinjections; D009420:Nervous System / Q000166:cytology / Q000196:embryology* / Q000254:growth & development; D016548:Prosencephalon / Q000196:embryology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D013687:Telencephalon / Q000196:embryology; D029867:Xenopus Proteins; D014982:Xenopus laevis / Q000196:embryology* / Q000235:genetics* / Q000378:metabolism
D017931:DNA Primers; C098129:HESX1 protein, Xenopus; D018398:Homeodomain Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D029867:Xenopus Proteins