[
Novartis Found Symp,
2005]
The C. elegans genome encodes a single lamin protein (Ce-lamin), three LEM domain proteins (Ce-emerin, Ce-MAN1 and LEM-3) and a single BAF protein (Ce-BAF). Down-regulation of Ce-lamin causes embryonic lethality. Abnormalities include rapid changes in nuclear morphology during interphase, inability of cells to complete mitosis, abnormal condensation of chromatin, clustering of nuclear pore complexes (NPCs), and missing or abnormal germ cells. Ce-emerin and Ce-MAN1 are both embedded in the inner nuclear membrane, and both bind Ce-lamin and Ce-BAF; in addition, both require Ce-lamin for their localization. Mutations in human emerin cause X-linked recessive Emery-Dreifuss muscular dystrophy. In C. elegans, loss of Ce-emerin alone has no detectable phenotype, while loss of 90% Ce-MAN1 causes approximately 15% embryonic lethality. However in worms that lack Ce-emerin, a approximately 90% reduction of Ce-MAN1 is lethal to all embryos by the 100-cell stage, with a phenotype involving chromatin condensation and repeated cycles of anaphase chromosome bridging and cytokinesis. The anaphase-bridged chromatin retained a mitosis-specific phosphohistone H3 epitope, and failed to recruit detectable Ce-lamin or Ce-BAF. Down-regulation of Ce-BAF showed similar phenotypes. These findings suggest that lamin, LEM-domain proteins and BAF are part of a lamina network essential for chromatin organization and cell division, and that Ce-emerin and Ce-MAN1 share at least one and possibly multiple overlapping functions, which may be relevant to Emery-Dreifuss muscular dystrophy.
[
Cell,
1996]
Across the animal kingdom, fertilization requires the encounter between a large stationary egg and small motile sperm. To maximize their likelihood of reaching the egg before their competition, sperm are extraordinarily specialized cells, generally consisting of little more than a haploid nucleus, mitochondria to generate energy, and a highly efficient movement engine. Almost all animal sperm are flagellated and seek the egg by swimming quickly through a liquid environment. Nematodes, however, produce sperm that move by crawling along solid substrates. These roundworm sperm extend pseudopods that look and behave like the actin-rich pseudopods of a wide variety of cells ranging from free-living soil amoebae to human white blood cells. The crawling sperm appear by most criteria to be exploiting classic actin-based cell motility, with one important difference: the sperm contain practically no actin (Nelson et al., 1982).