Human stem and progenitor cells offer an innovative way to study early events in development. An exciting new opportunity for these cells is their application to study the underlying developmental consequences of genetic diseases. Because many diseases, ranging from leukemias to developmental disorders, are caused by single-gene defects, stem and progenitor cells that carry disease-causing genetic mutations are invaluable in understanding and treating disease. We have characterized human neural progenitor (hNPCs) cells that carry a single-gene defect that leads to the neurodevelopmental disorder Fragile X syndrome (FX). A loss-of-function mutation in the FMR1 gene leads to subtle changes in neural development and subsequent mental impairment characteristic of FX. hNPCs were isolated from fetal cortex carrying the FMR1 mutation to determine whether aberrations occur in their proliferation and differentiation. As expected, FX hNPCs have reduced expression of the FMR1 gene product Fragile X mental retardation protein (FMRP), and this decrease is maintained in culture and following differentiation. In contrast to a previously published report, the proliferation of FX hNPCs and their differentiation into neurons is not different from unaffected controls. Although the early development of FX hNPCs is essentially normal, microarray analysis reveals novel changes in the expression of signal transduction genes in FX hNPCs. Therefore, hNPCs have intrinsic characteristics that can be investigated to further our understanding and potential treatment of developmental disorders such as FX.

CREB-responsive transcription has an important role in adaptive responses in all cells and tissue. In the nervous system, it has an essential and well established role in long-term memory formation throughout a diverse set of organisms. Activation of this transcription factor correlates with long-term memory formation and disruption of its activity interferes with this process. Most convincingly, aug-menting CREB activity in a number of different systems enhances memory formation. In Drosophila, a sequence rearrangement in the original transgene used to enhance memory formation has been a source of confusion. This rearrangement prematurely terminates translation of the full-length protein, leaving the identity of the “enhancing molecule” unclear. In this report, we show that a naturally occurring, downstream, in-frame initiation codon is used to make a dCREB2 protein off of both transgenic and chromosomal substrates. This protein is a transcriptional activator and is responsible for memory enhancement. A number of parameters can affect enhancement, including the short-lived activity of the activator protein, and the time-of-day when induction and behavioral training occur. Our results reaffirm that overexpression of a dCREB2 activator can enhance memory formation and illustrate the complexity of this behavioral enhancement.

The transcription factor CREB is an important regulator of many adaptive processes in neurons, including sleep, cellular homeostasis, and memory formation. The Drosophila dCREB2 family includes multiple protein isoforms generated from a single gene. Overexpression of an activator or blocker isoform has been shown to enhance or block memory formation, but the molecular mechanisms underlying these phenomena remain unclear. In the present study, we generate isoform-specific antibodies and new transgenic flies to track and manipulate the activity of different dCREB2 isoforms during memory formation. We find that nuclear accumulation of a dCREB2 activator-related species, p35+, is dynamically regulated during memory formation. Furthermore, various dCREB2 genetic manipulations that enhance or block memory formation correspondingly increase or decrease p35+ levels in the nucleus. Finally, we show that overexpression of S6K can enhance memory formation and increase p35+ nuclear abundance. Taken together, these results suggest that regulation of dCREB2 localization may be a key molecular convergence point in the coordinated host of events that lead to memory formation.