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Developmental Regulation of β‐Thymosins in the Rat Central Nervous System
Author(s) -
Lugo Delia Ines,
Chen ShuCheng,
Hall Alan K.,
Ziai Reza,
Hempstead James L.,
Morgan James I.
Publication year - 1991
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1991.tb08172.x
Subject(s) - thymosin , central nervous system , biology , messenger rna , edman degradation , endocrinology , medicine , fetus , nervous system , biochemistry , peptide sequence , gene , pregnancy , genetics , neuroscience
HPLC analysis of guanidinium hydrochloride extracts of neonatal and adult rat brain revealed a polypeptide that is present in high concentration in the immature nervous system, but whose levels decline dramatically in the adult. This polypeptide has been isolated and its complete amino acid sequence determined by gas‐phase Edman degradation following specific chemical and enzymatic cleavages. The molecule is identified as thymosin β10, a member of a multigene family that encodes a structurally conserved series of small acidic polypeptides of uncertain function. Thymosin β10 is present in the developing nervous system as early as embryonic day 9. Levels subsequently increase to peak values between embryonic day 15 and postpartum day 3, before falling to adult values (about a 20‐fold reduction) by postpartum day 14. The elevated levels of thymosin β10 in fetal and neonatal brain correlate with high levels of thymosin β10 mRNA, whereas the low values of the polypeptide in the adult and juvenile are mirrored by an approximate 15‐fold reduction in specific mRNA. In comparison, the levels of thymosin β4 polypeptide, a homologue of thymosin β10, only decline by about 20% during the same developmental period. However, the mRNA encoding thymosin β4 is elevated in fetal brain, and its levels decrease approximately four‐fold to a stable value around the time of birth. The reason for this discrepancy between thymosin β4 protein and mRNA levels is unknown. Thymosin β10 can also be detected by HPLC in fetal liver, where levels are approximately 5% of those in brain. In liver, thymosin β10 also declines following birth. It is concluded that β‐thymosin expression (as measured by steady‐state mRNA and polypeptide levels) is both up‐and down‐regulated during different phases of maturation of the mammalian nervous system.