Expression of Mcl-1 in cerebellar granule neurons is regulated by IGF-I in a developmentally specific fashion.
Transgenic (Tg) mice that overexpress IGF-I during postnatal brain development exhibit remarkable cerebellar overgrowth characterized by significant increases in granule cell number that is predominantly due to IGF-I anti-apoptotic actions. Using these mice as a model to define the gene expression profile underlying the pro-survival actions of IGF-I, we screened 243 apoptosis-related genes by cDNA arrays and found that Mcl-1 was down-regulated in cerebella of IGF-I Tg mice. Contrary to the results obtained by cDNA array, Northern blot analyses showed that the Mcl-1 mRNA abundance in the cerebella of IGF-I Tg mice at postnatal day 14 (P14) was five times more than that of wild-type (Wt) controls. The increase in Mcl-1 mRNA expression in IGF-I Tg mice was detected as early as P8, peaked at P14, and remained detectable at P20. Both IGF-I Tg and Wt mice showed a similar expression pattern of Mcl-1 mRNA which coincided with the post-mitotic migration and the post-migratory maturation of granule cells. We measured the relative abundance of Mcl-1 protein in the cerebellum by immunoblots and found that anti-apoptotic Mcl-1L was the predominant form, while pro-apoptotic Mcl-1S was minimally detectable. Cerebellar Mcl-1L was 2.6-fold more abundant in IGF-I Tg mice compared with that in their Wt littermates. Using laser capture microdissection followed by RT-PCR, we determined that Mcl-1 mRNA was expressed in granule cells, but not in Purkinje cells. In summary, these findings show that the anti-apoptotic Mcl-1 isoform is expressed in cerebellar granule neurons, which undergo apoptosis during postnatal cerebellar cortical lamination, and Mcl-1 expression is up-regulated by IGF-I overexpression in a developmentally specific manner. These data suggest that anti-apoptotic Mcl-1 may mediate IGF-I pro-survival actions on granule neurons during the development of cerebellar cortex. They also point out pitfalls of cDNA array analyses.
Zhang
Jihui
J
Department of Pediatrics, Division of Endocrinology, CB# 7039, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7039, United States.
D'Ercole
A Joseph
AJ
D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000502:physiology; D002454:Cell Differentiation / Q000235:genetics; D002470:Cell Survival / Q000502:physiology; D002525:Cerebellar Cortex / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism*; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000235:genetics*; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D020033:Protein Isoforms / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics*; D011689:Purkinje Cells / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D015854:Up-Regulation / Q000502:physiology
C579094:Mcl1 protein, mouse; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D020033:Protein Isoforms; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I