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Beside its unique nutritional content breast milk also contains live cells from the mother. Fate of these cells in the offspring has not been adequately described. In this study, we aimed to detect and identify maternal cells in the suckling’s blood and the brain. Green fluorescent protein expressing transgenic female mice (GFP+) were used as foster mothers to breastfeed wildtype newborn pups. One week and two months after the birth, blood samples and brains of the sucklings were analyzed to detect presence of GFP+ cells by fluorescence activated cell sorting, polymerase chain reaction and immunohistochemistry on the brain sections and optically cleared brains. The tests confirmed that maternal cells were detectable in the blood and the brain of the pups and that they differentiated into both neuronal and glial cell types in the brain. This phenomenon represents breastfeeding – induced microchimerism in the brain with functional implications remain to be understood.

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Elk-1 belongs to the ternary complex factors (TCFs) subfamily of the ETS domain proteins, and plays a critical role in the expression of immediate-early genes (IEGs) upon mitogen stimulation and activation of the mitogen-activated protein kinase (MAPK) cascade. The association of TCFs with serum response elements (SREs) on IEG promoters has been widely studied and a role for Elk-1 in promoting cell cycle entry has been determined. However, the presence of the ETS domain transcription factor Elk-1 in axons and dendrites of post-mitotic adult brain neurons has implications for an alternative function for Elk-1 in neurons other than controlling proliferation. In this study, possible alternative roles for Elk-1 in neurons were investigated, and it was demonstrated that blocking TCF-mediated transactivation in neuronal cells leads to apoptosis through a caspase-dependent mechanism. Indeed RNAi-mediated depletion of endogenous Elk-1 results in increased caspase activity. Conversely, overexpression of either Elk-1 or Elk-VP16 fusion proteins was shown to rescue PC12 cells from chemically-induced apoptosis, and that higher levels of endogenous Elk-1 correlated with longer survival of DRGs in culture. It was shown that Elk-1 regulated the Mcl-1 gene expression required for survival, and that RNAi-mediated degradation of endogenous Elk-1 resulted in elimination of the mcl-1 message. We have further identified the survival-of-motor neuron-1 (SMN1) gene as a novel target of Elk-1, and show that the ets motifs in the SMN1 promoter are involved in this regulation.

No abstract