Members of the JAK/STAT proteins are expressed and regulated during development in the mammalian forebrain

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Abstract
The presence and activation of members of the Janus Kinases/ Signal Transducers and Activator of Transcription proteins in response to specific cytokines is currently the focus of intense investigation in the hematopoietic system. Although some evidence suggests that cytokines might play an important role in brain development and brain pathologies, very limited information is available on the presence of the JAK/ STAT proteins in the Central Nervous System. Here we provide Western blot and immunohystochemistry data on the presence of Jak2 in vivo in the immature brain, its expression being greater in early stages of the embryonic life and gradually diminishing towards adulthood. Conversely, Jak1 was found expressed at a lower level compared to Jak2 and not modulated during brain maturation. Western blot data also show that specific members of the STAT family, the cytoplasmic substrates of the Janus Kinases, are present in vivo and that the extent of their expression is modulated differently at various stages. In particular, Stat6 protein levels were markedly attenuated at advanced stages of differentiation, as well as in the adult brain, with respect to early embryonic life. On the contrary, Stat3 levels did not vary. Analysis of Stat1 and Stat5 proteins showed a more complex expression pattern. These data indicate that members of the JAK/ STAT proteins are present and modulated in vivo in the embryonic and postnatal brain, therefore supporting their role in the modulation of gene expression during the different stages of brain maturation. J. Neurosci. Res. 54:320–330, 1998.