Embryonic expression of the human 40-kD keratin: evidence from a processed pseudogene sequence.
Analysis of the cytoskeletal components of early murine embryos has detected expression of two keratin proteins, K#8 and K#18, at the 4-8-cell stage. Comparable data for human embryos do not exist, although several processed pseudogenes corresponding to K#8 and K#18 have been discovered in the human genome. Because only genes that are expressed in pre-germ-line and germ-line cells can give rise to processed pseudogenes, the existence of human K#8 and K#18 processed pseudogenes is prima facie evidence for expression of keratins K#8 and K#18 in the early human embryo. We have cloned and determined the complete sequence of a processed pseudogene corresponding to another acidic human keratin. Comparison of its sequence with known sequences of other mammalian keratins indicates that the pseudogene arose from a reverse transcript of a correctly initiated and terminated functional human K#19 gene. This implies expression of K#19 keratin in addition to K#8 and K#18 in the early human embryo. We have proposed previously that K#19 evolved specifically to redress unbalanced production of various basic keratins, and our current evidence, that it is expressed at an early stage of development, implies that K#19 may fulfill this same role during human embryogenesis.
Savtchenko
E S
ES
Department of Dermatology, New York University Medical Center, NY 10016.
Schiff
T A
TA
Jiang
C K
CK
Freedberg
I M
IM
Blumenberg
M
M
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004622:Embryo, Mammalian; D005786:Gene Expression Regulation; D006801:Humans; D007633:Keratins / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011544:Pseudogenes; D015183:Restriction Mapping
D007633:Keratins