Masatsugu was active around Tensho, July 1573 - December 1592.  The meaning of Dotanuki is (胴太貫) torso–thick–penetrate, a testament to its cutting ability.  The Dotanuki school  is from Higo province, and in the linage of the Higo Enju school.  The Enju school was founded in 1305 by Enju Kunimura (延寿 国村), and was a student of Rai Kuyniyuki (来国行).  Following the decline of the Enju school, the Dotanuki school rmerged in the small Higo village of Dotanuki in the mid 16th century.  Masakuni (胴太貫正国) is said to have been the founder of the school. 

Although there are references to the Dotanuki working in Bizen tradition, this example clearly demonstrates the characteristics  coming out of Higo Enju.  It is unfortunate tat the nakago is so compromised, but the blade itself remains healthy, a minor tateware and small carbon pockets in the kissaki as shown below.   This is a seriously good collector's sword.