Knock-in and knock-out: the use of reverse genetics in somatic cells to dissect mitotic pathways

Werner complex deficiency in cells disrupts the Nuclear Pore Complex and the distribution of lamin B1

From the surrounding shell to the inner machinery, nuclear proteins provide the functional plasticity of the nucleus. This study highlights the nuclear association of Pore membrane (POM) protein NDC1 and Werner protein (WRN), a RecQ helicase responsible for the DNA instability progeria disorder, Werner Syndrome. In our previous publication, we connected the DNA damage sensor Werner's Helicase Interacting Protein (WHIP), a binding partner of WRN, to the NPC. Here, we confirm the association of the WRN/WHIP complex and NDC1. In established WRN/WHIP knockout cell lines, we further demonstrate the interdependence of WRN/WHIP and Nucleoporins (Nups). These changes do not completely abrogate the barrier of the Nuclear Envelope (NE) but do affect the distribution of FG Nups and the RAN gradient, which are necessary for nuclear transport. Evidence from WRN/WHIP knockout cell lines demonstrates changes in the processing and nucleolar localization of lamin B1. The appearance of "RAN holes" void of RAN corresponds to regions within the nucleolus filled with condensed pools of lamin B1. From WRN/WHIP knockout cell line extracts, we found three forms of lamin B1 that correspond to mature holoprotein and two potential post-translationally modified forms of the protein. Upon treatment with topoisomerase inhibitors lamin B1 cleavage occurs only in WRN/WHIP knockout cells. Our data suggest the link of the NDC1 and WRN as one facet of the network between the nuclear periphery and genome stability. Loss of WRN complex leads to multiple alterations at the NPC and the nucleolus.

Molecular and cellular evidence for the alternative lengthening of telomeres (ALT) mechanism in chicken

Telomere maintenance is an important genetic mechanism controlling cellular proliferation. Normally, telomeres are maintained by telomerase which is downregulated upon cellular differentiation in most somatic cell lineages. Telomerase activity is upregulated in immortalized cells and cancers to support an infinite lifespan and uncontrolled cell growth; however, some immortalized and transformed cells lack telomerase activity. Telomerase-negative tumors and immortalized cells utilize an alternative mechanism for maintaining telomeres termed alternative lengthening of telomeres (ALT). This research explored evidence for the ALT pathway in chicken cell lines by studying nontransformed immortalized cell lines (DF-1 and OU2) and comparing them to a normal (mortal) cell line and a transformed cell line (DT40). The research consisted of molecular and cellular analyses including profiling of telomeric DNA (array sizing and total content), telomerase activity, and expression of genes involved in the telomerase, recombination, and ALT pathways. In addition, an immunofluorescence analysis for an ALT marker, i.e. ALT-associated promyelocytic leukemia bodies (APBs), was conducted. Evidence for ALT was observed in the telomerase-negative immortalized cell lines. Additionally, the APB marker was also found in the other cell systems. The attributes of the chicken provide an additional vertebrate model for investigation of the ALT pathway.