Xenopus endo B is a keratin preferentially expressed in the embryonic notochord.
Screening of a cDNA library from neurula stage Xenopus laevis for notochord-specific sequences led to the isolation of a cDNA clone, XK endo B (Xenopus keratin endo B), which encodes a nonepidermal type I keratin. In situ and Northern blot hybridizations indicate that expression of XK endo B RNA is concentrated in the notochord, whereas expression in the endoderm is 5-10 times lower. XK endo B mRNA is present in the oocyte and increases from late gastrula. Accumulation peaks by late neurula and is greatly reduced by the tadpole stage; in the adult, a low level of XK endo B RNA is present in the liver. XK endo B shows sequence homology to mouse endo B; genomic Southern blots show that XK endo B is the most similar sequence to mouse endo B in the Xenopus genome, and vice versa, indicating that XK endo B and mouse endo B are homologs. The use of endo B as a marker and the germ layer derivation of the notochord are discussed in light of these results.
LaFlamme
S E
SE
Laboratory of Molecular Genetics, National Institutes of Health, Bethesda, Maryland 20892.
Jamrich
M
M
Richter
K
K
Sargent
T D
TD
Dawid
I B
IB
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D004622:Embryo, Mammalian / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000502:physiology; D005796:Genes; D007633:Keratins / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D009672:Notochord / Q000378:metabolism*; D013045:Species Specificity; D014158:Transcription, Genetic; D014982:Xenopus laevis / Q000196:embryology*
D007633:Keratins; D004247:DNA