ENTOMOPHILOUS,INTRAFLORAL POLLINATION IN PHYLA INCISA

Experimental pollination studies indicate that probing into the corolla tube by insects is a requirement for autogamous reproduction in Phyla incisa. Insect-mediated self-fertilization combines the anthecology of allogamous reproduction with the genetic consequences of autogamy.     

Natural variation in Caenorhabditis briggsae mitochondrial form and function suggests a novel model of organelle dynamics

Mitochondrial functioning and morphology are known to be connected through cycles of organelle fusion and fission that depend upon the mitochondrial membrane potential (ΔΨM); however, we lack an understanding of the features and dynamics of natural mitochondrial populations. Using data from our recent study of univariate mitochondrial phenotypic variation in Caenorhabditis briggsae nematodes, we analyzed patterns of phenotypic correlation for 24 mitochondrial traits. Our findings support a role for ΔΨM in shaping mitochondrial dynamics, but no role for mitochondrial ROS. Further, our study suggests a novel model of mitochondrial population dynamics dependent upon cellular environmental context and with implications for mitochondrial genome integrity.     

Mechanisms controlling steroid receptor binding to specific DNA sequences.

Mammalian progesterone receptors activated by hormone binding in nuclei of intact cells exhibit substantially higher binding activity for specific DNA sequences than receptors bound with hormone and activated in cell-free cytosol. Differences in DNA-binding activity occur despite the fact that both activated receptor forms sediment at 4S on sucrose gradients and are apparently dissociated from the heat shock protein 90. This suggests that hormone-induced release of heat shock protein 90 from receptors is necessary, but not sufficient for maximal activation of DNA binding. This report is a review of studies from our laboratories that have examined the role of receptor interaction with other nuclear protein factor(s), and receptor dimerization in solution, as additional regulatory steps involved in the process of receptor activation and binding to specific gene sequences.     

Force Generation and Dynamics of Individual Cilia under External Loading

Motile cilia are unique multimotor systems that display coordination and periodicity while imparting forces to biological fluids. They play important roles in normal physiology, and ciliopathies are implicated in a growing number of human diseases. In this work we measure the response of individual human airway cilia to calibrated forces transmitted via spot-labeled magnetic microbeads. Cilia respond to applied forces by 1), a reduction in beat amplitude (up to an 85% reduction by 160-170 pN of force); 2), a decreased tip velocity proportionate to applied force; and 3), no significant change in beat frequency. Tip velocity reduction occurred in each beat direction, independently of the direction of applied force, indicating that the cilium is “driven” in both directions at all times. By applying a quasistatic force model, we deduce that axoneme stiffness is dominated by the rigidity of the microtubules, and that cilia can exert 62 ± 18 pN of force at the tip via the generation of 5.6 ± 1.6 pN/dynein head.