Generation of mice harboring a Sox4 conditional null allele.

Sox4 belongs to the family of Sry-related HMG box transcription factors, which specify cell fate and differentiation in many lineages. Sox4 is widely expressed in the embryo and controls such processes as neuronal tissue, lymphocyte, heart, and bone development. Sox4-null mice die at embryonic day 14 from heart malformation. This early lethality has therefore limited studies on Sox4 functions. We show here that we have generated mice harboring a Sox4 conditional null allele (Sox4fl+) by flanking the entire coding region with loxP sites. Sox4fl+/fl+ mice are indistinguishable from wildtype mice and produce the wildtype Sox4 protein at a normal level. Sox4fl+ is efficiently converted into a null allele (Sox4fl-) by Cre recombinase in somatic and germ-line cells, and Sox4fl-/fl- embryos die from the same heart defects as Sox4-/- mice. This Sox4 conditional null allele will thus be a valuable tool to further uncovering Sox4 functions in various processes in vivo.