The TTC is still working on upgrading its signal system, and you know what that means.
The TTC has really been on a roll with these things lately.
On Saturday, once again, a portion of the Yonge-University-Spadina subway line will be closed while the TTC does some work on its signal systems. This time, the affected part of the line is the bit between Bloor-Yonge and Union stations. Subways will turn back at both those stations. Frequent shuttle buses will be running as far north as Rosedale.
But of course, if you still want to take a subway downtown, you can always just walk over to the other side of the horseshoe. Trains will still be running between Spadina and Union stations.