Early expression of Pax2 and Pax8 compared. This image shows the earliest expression of Pax8 (A) and Pax2 (B) in 7 somite (S1, S7) mouse embryos of approximately 8 embryonic days. Note that at this stage Pax8 is more profoundly expressed throughout the area of the future otic placode (OP) just anterior to the first somite (S1). In contrast, Pax2 is more prominently expressed in the brain with only very limited expression in the area of the otic placode (OP). At this stage the heart is anterior to the future otic placode. Bar indicates 100 um.