Identification of undescribed Relb expression domains in the murine brain by new Relb:cre-katushka reporter mice

Noncanonical NF-κB signaling through activation of the transcription factor RelB acts as key regulator of cell lineage determination and differentiation in various tissues including the immune system. To elucidate temporospatial aspects of Relb expression, we generated a BAC transgenic knock-in mouse expressing the fluorescent protein Katushka and the enzyme Cre recombinase under control of the murine Relb promoter (Relb^Cre-Kat mice).

Co-expression of Katushka and Relb in fibroblast cultures and tissues of transgenic mice revealed highly specific reporter functions of the transgene. Crossing Relb^Cre-Kat mice with ROSA26R reporter mice that allow for Cre-mediated consecutive β-galactosidase or YFP synthesis identified various Relb expression domains in perinatal and mature mice. Besides thymus and spleen, highly specific expression patterns were found in different neuronal domains, as well as in other nonimmune organs including skin, skeletal structures and kidney. De novo Relb expression in the mature brain was confirmed in conditional knockout mice with neuro-ectodermal Relb deletion.

Our results demonstrate the usability of Relb^Cre-Kat reporter mice for the detection of de novo and temporarily restricted Relb expression including cell and lineage tracing of Relb expressing cells. Relb expression during mouse embryogenesis and at adulthood suggests, beyond immunity, important functions of this transcription factor in neurodevelopment and CNS function.