DEVELOPMENTAL AND CELLULAR FUNCTIONS OF DELTA-CATENIN

Catenins have diverse and powerful roles in embryogenesis, homeostasis or disease progression, as best exemplified by the well-known beta-catenin. The less studied delta-catenin likewise contains a central Armadillo-domain. In common with other p120 sub-class members, it acts in a variety of intracellular compartments and modulates cadherin stability, small GTPase activities and gene transcription. In mammals, delta-catenin exhibits neural specific expression, with its knock-out in mice correspondingly producing cognitive defects and synaptic dysfunctions. My work instead employed the amphibian, Xenopus laevis, to explore delta-catenin’s physiological functions in a distinct vertebrate system. Initial isolation and characterization indicated delta-catenin’s expression in Xenopus. Unlike the pattern observed for mammals, delta-catenin was detected in most adult Xenopus tissues, although enriched in embryonic structures of neural fate as visualized using RNA in-situ hybridization. To determine delta-catenin’s requirement in amphibian development, I employed anti-sense morpholinos to knock-down gene products, finding that delta-catenin depletion results in developmental defects in gastrulation, neural crest migration and kidney tubulogenesis, phenotypes that were specific based upon rescue experiments. In biochemical and cellular assays, delta-catenin knock-down reduced cadherin levels and cell adhesion, and impaired activation of RhoA and Rac1, small GTPases that regulate actin dynamics and morphogenetic movements. Indeed, exogenous C-cadherin, or dominant-negative RhoA or dominant-active Rac1, significantly rescued delta-catenin depletion. Thus, my results indicate delta-catenin’s essential roles in Xenopus development, with contributing functional links to cadherins and Rho family small G proteins. In examining delta-catenin’s nuclear roles, I identified delta-catenin as an interacting partner and substrate of the caspase-3 protease, which plays critical roles in apoptotic as well as non-apoptotic processes. Delta-catenin’s interaction with and sensitivity to caspase-3 was confirmed using assays involving its cleavage in vitro, as well as within Xenopus apoptotic extracts or mammalian cell lines. The cleavage site, a highly conserved caspase consensus motif (DELD) within Armadillo-repeat 6 of delta-catenin, was identified through peptide sequencing. Cleavage thus generates an amino- (1-816) and carboxyl-terminal (817-1314) fragment each containing about half of the central Armadillo-domain. I found that cleavage of delta-catenin both abolishes its association with cadherins, and impairs its ability to modulate small GTPases. Interestingly, the carboxyl-terminal fragment (817-1314) possesses a conserved putative nuclear localization signal that I found is needed to facilitate delta-catenin’s nuclear targeting. To probe for novel nuclear roles of delta-catenin, I performed yeast two-hybrid screening of a mouse brain cDNA library, resolving and then validating its interaction with an uncharacterized KRAB family zinc finger protein I named ZIFCAT. My results indicate that ZIFCAT is nuclear, and suggest that it may associate with DNA as a transcriptional repressor. I further determined that other p120 sub-class catenins are similarly cleaved by caspase-3, and likewise bind ZIFCAT. These findings potentially reveal a simple yet novel signaling pathway based upon caspase-3 cleavage of p120 sub-family members, facilitating the coordinate modulation of cadherins, small GTPases and nuclear functions. Together, my work suggested delta-catenin’s essential roles in Xenopus development, and has revealed its novel contributions to cell junctions (via cadherins), cytoskeleton (via small G proteins), and nucleus (via ZIFCAT). Future questions include the larger role and gene targets of delta-catenin in nucleus, and identification of upstream signaling events controlling delta-catenin’s activities in development or disease progression.

Institutionalizing Intensive Family Preservation Services: A Strategy for Creating Staffing Standards Based on Projections of At-Risk Children from Referral Sources

In spite of new legislation and much public and professional interest, intensive family preservation service (IFPS) remains in a vulnerable position as compared to other child welfare services. This article details a method to project ideal IFPS caseloads as a function of children who are at-risk for placement by various referral sources. Using this approach, resource allocation for IFPS can be more nearly on equal ground with the traditional child welfare functions and help IFPS to assume its needed place as a core service in the child welfare continuum.

Familial aggregation, candidate genes and genome scans: Analyzing the role of genetics in stroke

The genetic etiology of stroke likely reflects the influence of multiple loci with small effects, each modulating different pathophysiological processes. This research project utilized three analytical strategies to address the paucity of information related to the identification and characterization of genetic variation associated with stroke in the general population. ^ First, the general contribution of familial factors to stroke susceptibility was evaluated in a population-based sample of unrelated individuals. Increased risk of subclinical cerebral infarction was observed among individuals with a positive parental history of stroke. This association did not appear to be mediated by established stroke risk factors, specifically blood pressure levels or hypertension status. ^ The need to identify specific gene variation associated with stroke in the general population was addressed by evaluating seven candidate gene polymorphisms in a population-based sample of unrelated individuals. Three polymorphisms were significantly associated with increased subclinical cerebral infarction or incident clinical ischemic stroke risk. These relationships include the G-protein β3 subunit 825C/T polymorphism and clinical stroke in Whites, the lipoprotein lipase S/X447 polymorphism and subclinical and clinical stroke in men, and the angiotensin I-converting enzyme Ins/Del polymorphism and subclinical stroke in White men. These associations did not appear to be obfuscated by the stroke risk factors adjusted for in the analysis models specifically blood pressure levels or anti-hypertensive medication use. ^ The final research strategy considered, on a genome-wide scale, the idea that genetic variation may contribute to the occurrence of hypertension or stroke through a common etiologic pathway. Genomic regions were identified for which significant evidence of heterogeneity was observed among hypertensive sibpairs stratified by family history of stroke information. Regions identified on chromosome 15 in African Americans, and chromosome 13 in Whites and African Americans, suggest the presence of genes influencing hypertension and stroke susceptibility. ^ Insight into the role of genetics in stroke is useful for the potential early identification of individuals at increased risk for stroke and improved understanding of the etiology of the disease. The ultimate goal of these endeavors is to guide the development of therapeutic intervention and informed prevention to provide a lasting and positive impact on public health. ^

DISTRIBUTION FUNCTIONS, MEAN SQUARED ERRORS, AND CONFIDENCE LIMITS FOR RIDGE REGRESSION ESTIMATORS

A large number of ridge regression estimators have been proposed and used with little knowledge of their true distributions. Because of this lack of knowledge, these estimators cannot be used to test hypotheses or to form confidence intervals.^ This paper presents a basic technique for deriving the exact distribution functions for a class of generalized ridge estimators. The technique is applied to five prominent generalized ridge estimators. Graphs of the resulting distribution functions are presented. The actual behavior of these estimators is found to be considerably different than the behavior which is generally assumed for ridge estimators.^ This paper also uses the derived distributions to examine the mean squared error properties of the estimators. A technique for developing confidence intervals based on the generalized ridge estimators is also presented. ^