RAD51 paralogs: Expanding roles in replication stress responses and repair.

Mammalian RAD51 paralogs are essential for cell survival and are critical for RAD51-mediated repair of DNA double-strand breaks (DSBs) by homologous recombination (HR). However, the molecular mechanism by which RAD51 paralogs participate in HR is largely unclear. Germline mutations in RAD51 paralogs are associated with breast and ovarian cancers and Fanconi anemia-like disorder, underscoring the crucial roles of RAD51 paralogs in genome maintenance and tumor suppression. Despite their discovery over three decades ago, the essential functions of RAD51 paralogs in cell survival and genome stability remain obscure. Recent studies unravel DSB repair independent functions of RAD51 paralogs in replication stress responses. Here, we highlight the recent findings that uncovered the novel functions of RAD51 paralogs in replication fork progression, its stability, and restart and discuss RAD51 paralogs as a potential therapeutic target for cancer treatment.

The cytoplasmic tyrosine kinase Arg regulates gastrulation via control of actin organization.

Coordinated cell movements are crucial for vertebrate gastrulation and are controlled by multiple signals. Although many factors are shown to mediate non-canonical Wnt pathways to regulate cell polarity and intercalation during gastrulation, signaling molecules acting in other pathways are less investigated and the connections between various signals and cytoskeleton are not well understood. In this study, we show that the cytoplasmic tyrosine kinase Arg modulates gastrulation movements through control of actin remodeling. Arg is expressed in the dorsal mesoderm at the onset of gastrulation, and both gain- and loss-of-function of Arg disrupted axial development in Xenopus embryos. Arg controlled migration of anterior mesendoderm, influenced cell decision on individual versus collective migration, and modulated spreading and protrusive activities of anterior mesendodermal cells. Arg also regulated convergent extension of the trunk mesoderm by influencing cell intercalation behaviors. Arg modulated actin organization to control dynamic F-actin distribution at the cell-cell contact or in membrane protrusions. The functions of Arg required an intact tyrosine kinase domain but not the actin-binding motifs in its carboxyl terminus. Arg acted downstream of receptor tyrosine kinases to regulate phosphorylation of endogenous CrkII and paxillin, adaptor proteins involved in activation of Rho family GTPases and actin reorganization. Our data demonstrate that Arg is a crucial cytoplasmic signaling molecule that controls dynamic actin remodeling and mesodermal cell behaviors during Xenopus gastrulation.

A Simple PCR-RFLP Method for Genetic Phase Determination in Compound Heterozygotes.

When susceptibility to diseases is caused by cis-effects of multiple alleles at adjacent polymorphic sites, it may be difficult to assess with confidence the genetic phase and identify individuals carrying the risk haplotype. Experimental assessment of genetic phase is still challenging and most population studies use statistical approaches to infer haplotypes given the observed genotypes. While these statistical approaches are powerful and have been proven very useful in large scale genetic population studies, they may be prone to errors in studies with small sample size, especially in the presence of compound heterozygotes. Here, we describe a simple and novel approach using the popular PCR-RFLP based strategy to assess the genetic phase in compound heterozygotes. We apply this method to two extensively studied SNPs in two clustered immune-related genes: The -308 (G > A) and the +252 (A > G) SNPs of the tumor necrosis factor (TNF) alpha and the lymphotoxin alpha (LTA) genes, respectively. Using this method, we successfully determined the genetic phase of these two SNPs in known compound heterozygous individuals and in every sample tested. We show that the A allele of TNF -308 is carried on the same chromosome as the LTA +252(G) allele.