Multifunctional BAF-1

Nuclear assembly happens every cell division. So it's no surprise that nuclear assembly factors are overworked during embryogenesis, when proliferation is maximal. But there's no rest for one weary factor, called BAF-1, who has many jobs left to do even when embryogenesis is over, report Margalit et al. on page 661.

BAF-1 is enriched at the nuclear periphery and is required for the capture of chromosomes in reforming nuclei. It binds to histones, DNA, and nuclear envelope proteins including lamin and emerin.

Mutations to lamin and emerin, which are also crucial for nuclear assembly, somehow cause human diseases that manifest later in life, when cell division has lagged. In previous studies, the group found that knocking down the activity of BAF-1 in worms leads to embryonic death. They wondered, however, whether BAF-1, like lamin and emerin, might have functions later in life.

To investigate this question, they used BAF-1–null worms that survived embryogenesis thanks to maternal BAF-1 supplies. These survivors displayed a diverse but reproducible array of tissue-specific defects. The defects suggested that BAF-1 promotes distal tip cell migration, muscle cell integrity, gonad and germline development, and the correct timing of epidermal seam cell fusion—a process that literally seals the worm's skin.

BAF-1 delayed seam cell fusion by binding to the promoter and repressing the expression of the gene for a fusion factor called EFF-1. This newly described transcriptional regulatory activity might also explain BAF-1's other tissue-specific functions.