The single flagellum of the protozoan parasite Trypanosoma brucei is attached along the length of the cell body by a complex structure that requires the FLA1 protein. We show here that inhibition of FLA1 expression by RNA interference in procyclic trypanosomes causes flagellar detachment and prevents cytokinesis. Despite being unable to divide, these cells undergo mitosis and develop a multinucleated phenotype. The Trypanosoma cruzi FLA1 homolog, GP72, is unable to complement either the flagellar detachment or cytokinesis defects in procyclic T. brucei that have been depleted of FLA1 by RNA interference. Instead, GP72 itself caused flagellar detachment when expressed in T. brucei. In contrast to T. brucei cells depleted of FLA1, procyclic T. brucei expressing GP72 continued to divide despite having detached flagella, demonstrating that flagellar attachment is not absolutely necessary for cytokinesis. We have also identified a FLA1-related gene (FLA2) whose sequence is similar but not identical to FLA1. Inhibition of FLA1 and FLA2 expression in bloodstream T. brucei caused flagellar detachment and blocked cytokinesis but did not inhibit mitosis. These experiments demonstrate that the FLA proteins are essential and suggest that in procyclic T. brucei, the FLA1 protein has separable functions in flagellar attachment and cytokinesis.Trypanosoma brucei is an extracellular protozoan parasite that relies on a single flagellum for motility. This critical structure emerges from the flagellar pocket, a specialized secretory organelle near the posterior end of the cell, and extends along the cell body to the anterior tip. The flagellum contains an axoneme with the classical 9 ϩ 2 bundle of microtubules and a paraflagellar rod (PFR) 1 that is comprised primarily of two proteins, PFR-A and PFR-C (1, 2). The axoneme extends from the kinetoplast-linked basal body to the anterior tip of the flagellum. The PFR lies adjacent to the axoneme in the flagellum and is slightly shorter; it extends from the point where the flagellum exits the flagellar pocket to the tip. The PFR is required for motility; inhibition of PFR-A expression by RNA interference (RNAi) ablates the PFR and paralyzes procyclic trypanosomes (3).The flagellum is attached to the cell body via the flagellar attachment zone (FAZ), a complex but largely uncharacterized structure (4, 5). The FAZ is made up of an electron-dense cytoplasmic filament and a specialized set of four microtubules that are associated with the smooth endoplasmic reticulum (for a recent review of the T. brucei cytoskeleton, see Ref. 6). The filament is invariably located in a unique gap between two microtubules in the subpelicular cortex with the four microtubules always found immediately to the left when viewed from the posterior end. Cross-links extend from the filament across the cell and flagellum membranes and into the PFR.During cell division, the flagellum and FAZ must be duplicated and segregated to the daughter cells. Synthesis of the new flagellum begins with duplication of the basal ...

Chicken ovalbumin upstream promoter transcription factor (COUP-TF)-interacting protein 2 (CTIP2), also known as Bcl11b, is a transcriptional repressor that functions by direct, sequence-specific DNA binding activity or by recruitment to the promoter template by interaction with COUP-TF family members. CTIP2 is essential for both T cell development and axonal projections of corticospinal motor neurons in the central nervous system. However, little is known regarding the molecular mechanism(s) by which CTIP2 contributes to either process. CTIP2 complexes that were isolated from SK-N-MC neuroblastoma cells were found to harbor substantial histone deacetylase activity, which was likely conferred by the nucleosome remodeling and deacetylation (NuRD) complex. CTIP2 was found to associate with the NuRD complex through direct interaction with both RbAp46 and RbAp48, and components of the NuRD complex were found to be recruited to an artificial promoter template in a CTIP2-dependent manner in transfected cells. Finally, the NuRD complex and CTIP2 were found to co-occupy the promoter template of p57KIP2, a gene encoding a cyclin-dependent kinase inhibitor, and identified herein as a novel transcriptional target of CTIP2 in SK-N-MC cells. Therefore, it seems likely that the NuRD complex may be involved in transcriptional repression of CTIP2 target genes and contribute to the function(s) of CTIP2 within a neuronal context.

We surveyed 492 recent studies in the fields of ecology, evolution, and behavior (EEB) to evaluate potential for observer bias and the need for blind experimentation in each study. While 248 articles included experiments that could have been influenced by observer bias, only 13.3% of these articles indicated that experiments were blinded. The use of blind observation therefore was either grossly underreported in the surveyed articles, or many EEB studies were not blinded. We hope that a concerted effort of the field of EEB-including researchers, peer-reviewers, and journal editors-will help promote and institute routine, blind observation as an essential standard that should be practiced by all sciences.

A chromosome inversion can spread when it captures locally adapted alleles or when it is introduced into a species by hybridization with adapted alleles that were previously absent. We present a model that shows how both processes can cause a species range to expand. Introgression of an inversion that carries novel, locally adapted alleles is a particularly powerful mechanism for range expansion. The model supports the earlier proposal that introgression of an inversion triggered a large range expansion of a malaria mosquito. These results suggest a role for inversions as cassettes of genes that can accelerate adaptation by crossing species boundaries, rather than protecting genomes from introgression.

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