B-type lamins are essential nuclear scaffold proteins known to maintain peripheral heterochromatin through lamina-associated domains (LADs). Here, we identify an unexpected role for B-type lamins in preserving transcriptional output by regulating chromatin proximity to nuclear speckles, key hubs of transcription and RNA processing. Using TSA-Seq mapping and RNA-Seq in lamin-depleted human cells, we show that most differentially expressed genes are located in non-LAD, speckle-associated chromatin domains. Lamin depletion causes euchromatin to relocate away from nuclear speckles, resulting in global transcriptional repression accompanied by alterations in RNA processing and reduced cell viability. In contrast, heterochromatin gains speckle proximity and exhibits aberrant transcriptional activation. Integrative epigenomic analyses reveal that these spatial chromatin rearrangements precede disruption of speckle-associated domains (SPADs), including genes involved in cell viability and RNA metabolism. Together, our findings uncover a speckle-centered regulatory axis governed by B-type lamins and highlight chromatin-speckle proximity as a key spatial parameter in nuclear gene regulation.
Shin et al. (Wed,) studied this question.