Absolute requirement for STAT3 function in small-intestine crypt stem cell survival

The transcription factor signal transducer and activator of transcription 3 (STAT3) is frequently activated in human cancers. Interestingly, STAT3 also maintains the pluripotency and self-renewal of murine embryonic stem cells, and several tissue stem cell types. To investigate whether STAT3 also maintains the small-intestine crypt stem cell, we conditionally inactivated a Floxed Stat3 allele ( Stat3 fl ) in murine small-intestine crypt stem cells. Following Cre recombinase expression, apoptosis increased in Stat3 fl /− experimental crypts relative to Stat3 wt /− controls before declining. Control Stat3 wt /− mice carrying a Flox-STOP LacZ reporter transgene stably expressed LacZ after Cre induction. In contrast, Stat3 fl /− intestine LacZ expression initially increased modestly, before declining to background levels. Quantitative PCRs revealed a similar transient in recombined Stat3 fl allele levels. Long-term bromodeoxyuridine labelling directly demonstrated that functional STAT3 is required for +4 to +6 region label-retaining small-intestine stem cell survival. Rapid clearance of recombined Stat3 fl /− cells involves apoptosis potentially induced by elevated c-Myc in non-recombined cells and involves elevated p53 expression and caspase 3 activation. Intriguingly, Stat3 fl /− intestine recombination triggered dramatically upregulated polycomb transcriptional repressor Bmi1 – potentially accelerating recombined crypt repopulation. In summary, STAT3 activity is absolutely required for small-intestine crypt stem cell survival at both the +4 to +6 label-retaining and crypt base columnar cell locations.