Developmental expression of mRNAs encoding thymosins β4 and β10 in rat brain and other tissues

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Abstract
In the course of screening a fetal rat cerebellum cDNA library for developmentally regulated sequences, we have identified a cDNA clone identical in sequence to that encoding a protein originally isolated from thymus, thymosin β10. Based on northern hybridization analyses with gene-specific oligonucleotide probes derived from the 3′-untranslated regions of thymosin β10 mRNA and the closely related β4 mRNA, we showed that both thymosin mRNAs were present at highest levels in fetal cortex and cerebellum but also were present at varying levels in all other fetal tissues examined (thymus, spleen, lung, kidney, adrenal, heart, and liver). Steady-state levels of thymosin β10 mRNA in cerebellum declined to negligible levels after day 14 of postnatal development. Its levels exhibited a similar pattern in developing cortex, although the adult cortex had slightly higher thymosin β10 mRNA levels. These results suggest that thymosin β10 mRNA is subject to strong developmental regulation in the rat central nervous system. Reduction of thymosin β10 mRNA levels also was seen during development of kidney, heart, and liver. Levels of both thymosin β10 and β4 mRNAs remained relatively constant during development of thymus, spleen, and lung. Thymosin β4 mRNA levels dropped much less sharply during brain development than did levels of the β10 mRNA. Testis and ovary contained the highest relative levels of thymosin β10 mRNA among adult tissues, but little thymosin β4 mRNA. A novel thymosin β10 mRNA species unique to adult testis was detected. These results indicate that both thymosins must function in the development of brain and many other organs, as well as in different subsets of organs in the adult.