Despite being densely packed with chromatin, nuclear bodies and a nucleoskeletal 
network, the nucleus is a remarkably dynamic organelle. Chromatin loops form and 
relax, RNA transcripts and transcription factors move diffusively, and nuclear 
bodies move. We show here that RNA splicing speckled domains (splicing speckles) 
fluctuate in constrained nuclear volumes and remodel their shapes. Small 
speckles move in a directed way toward larger speckles with which they fuse. 
This directed movement is reduced upon decreasing cellular ATP levels or 
inhibiting RNA polymerase II activity. The random movement of speckles is 
reduced upon decreasing cellular ATP levels, moderately reduced after inhibition 
of SWI/SNF chromatin remodeling and modestly increased upon inhibiting RNA 
polymerase II activity. To define the paths through which speckles can 
translocate in the nucleus, we generated a pressure gradient to create flows in 
the nucleus. In response to the pressure gradient, speckles moved along 
curvilinear paths in the nucleus. Collectively, our results demonstrate a new 
type of ATP-dependent motion in the nucleus. We present a model where recycling 
splicing factors return as part of small sub-speckles from distal sites of RNA 
processing to larger splicing speckles by a directed ATP-driven mechanism 
through interchromatin spaces.