Sarah K. Szwed

Bio: Sarah K. Szwed is an academic researcher from Rockefeller University. The author has contributed to research in topics: Adipose tissue & microRNA. The author has an hindex of 2, co-authored 4 publications receiving 35 citations. Previous affiliations of Sarah K. Szwed include Kettering University.

Human mutant huntingtin disrupts vocal learning in transgenic songbirds

Abstract: Speech and vocal impairments characterize many neurological disorders. However, the neurogenetic mechanisms of these disorders are not well understood, and current animal models do not have the necessary circuitry to recapitulate vocal learning deficits. We developed germline transgenic songbirds, zebra finches (Taneiopygia guttata) expressing human mutant huntingtin (mHTT), a protein responsible for the progressive deterioration of motor and cognitive function in Huntington's disease (HD). Although generally healthy, the mutant songbirds had severe vocal disorders, including poor vocal imitation, stuttering, and progressive syntax and syllable degradation. Their song abnormalities were associated with HD-related neuropathology and dysfunction of the cortical-basal ganglia (CBG) song circuit. These transgenics are, to the best of our knowledge, the first experimentally created, functional mutant songbirds. Their progressive and quantifiable vocal disorder, combined with circuit dysfunction in the CBG song system, offers a model for genetic manipulation and the development of therapeutic strategies for CBG-related vocal and motor disorders.

AGO HITS-CLIP reveals distinct miRNA regulation of white and brown adipose tissue identity

Abstract: MicroRNAs (miRNAs) are short, noncoding RNAs that associate with Argonaute (AGO) to influence mRNA stability and translation, thereby regulating cellular determination and phenotype While several individual miRNAs have been shown to control adipocyte function, including energy storage in white fat and energy dissipation in brown fat, a comprehensive analysis of miRNA activity in these tissues has not been performed We used high-throughput sequencing of RNA isolated by cross-linking immunoprecipitation (HITS-CLIP) to comprehensively characterize the network of high-confidence, in vivo mRNA:miRNA interactions across white and brown fat, revealing >20,000 unique AGO binding sites When coupled with miRNA and mRNA sequencing, we found an inverse correlation between depot-enriched miRNAs and their targets To illustrate the functionality of our HITS-CLIP data set in identifying specific miRNA:mRNA interactions, we show that miR-29 is a novel regulator of leptin, an adipocyte-derived hormone that coordinates food intake and energy homeostasis Two independent miR-29 binding sites in the leptin 3' UTR were validated using luciferase assays, and miR-29 gain and loss of function modulated leptin mRNA and protein secretion in primary adipocytes This work represents the only experimentally generated miRNA targetome in adipose tissue and identifies multiple regulatory pathways that may specify the unique identities of white and brown fat

AGO HITS-CLIP in Adipose Tissue Reveals miR-29 as a Post-Transcriptional Regulator of Leptin

Abstract: MicroRNAs (miRNAs) are short, non-coding RNAs that associate with Argonaute (AGO) to regulate mRNA stability and translation. While individual miRNAs have been shown to play important roles in white and brown adipose tissue in normal physiology and disease1,2,3, a comprehensive analysis of miRNA activity in these tissues has not been performed. We used high-throughput sequencing of RNA isolated by crosslinking immunoprecipitation (HITS-CLIP) to comprehensively characterize the network of high-confidence, in vivo mRNA:miRNA interactions across white and brown fat, revealing over 100,000 unique miRNA binding sites. Targets for each miRNA were ranked to generate a catalog of miRNA binding activity, and the miR-29 family emerged as a top regulator of adipose tissue gene expression. Among the top targets of miR-29 was leptin, an adipocyte-derived hormone that acts on the brain to regulate food intake and energy expenditure4. Two independent miR-29 binding sites in the leptin 3’-UTR were validated using luciferase assays, and miR-29 gain and loss-of-function modulated leptin mRNA and protein secretion in primary adipocytes. In mice, miR-29 abundance inversely correlated with leptin levels in two independent models of obesity. This work represents the only experimentally generated miRNA targetome in adipose tissue and identifies the first known post-transcriptional regulator of leptin. Future work aimed at manipulating miR-29:leptin binding may provide a therapeutic opportunity to treat obesity and its sequelae.

Gene editing in birds takes flight.

Abstract: The application of gene editing (GE) technology to create precise changes to the genome of bird species will provide new and exciting opportunities for the biomedical, agricultural and biotechnology industries, as well as providing new approaches for producing research models. Recent advances in modifying both the somatic and germ cell lineages in chicken indicate that this species, and conceivably soon other avian species, has joined a growing number of model organisms in the gene editing revolution.

Primordial germ cell-mediated transgenesis and genome editing in birds.

Abstract: Transgenesis and genome editing in birds are based on a unique germline transmission system using primordial germ cells (PGCs), which is quite different from the mammalian transgenic and genome editing system. PGCs are progenitor cells of gametes that can deliver genetic information to the next generation. Since avian PGCs were first discovered in nineteenth century, there have been numerous efforts to reveal their origin, specification, and unique migration pattern, and to improve germline transmission efficiency. Recent advances in the isolation and in vitro culture of avian PGCs with genetic manipulation and genome editing tools enable the development of valuable avian models that were unavailable before. However, many challenges remain in the production of transgenic and genome-edited birds, including the precise control of germline transmission, introduction of exogenous genes, and genome editing in PGCs. Therefore, establishing reliable germline-competent PGCs and applying precise genome editing systems are critical current issues in the production of avian models. Here, we introduce a historical overview of avian PGCs and their application, including improved techniques and methodologies in the production of transgenic and genome-edited birds, and we discuss the future potential applications of transgenic and genome-edited birds to provide opportunities and benefits for humans.

Focal expression of mutant huntingtin in the songbird basal ganglia disrupts cortico-basal ganglia networks and vocal sequences

Abstract: The basal ganglia (BG) promote complex sequential movements by helping to select elementary motor gestures appropriate to a given behavioral context. Indeed, Huntington’s disease (HD), which causes striatal atrophy in the BG, is characterized by hyperkinesia and chorea. How striatal cell loss alters activity in the BG and downstream motor cortical regions to cause these disorganized movements remains unknown. Here, we show that expressing the genetic mutation that causes HD in a song-related region of the songbird BG destabilizes syllable sequences and increases overall vocal activity, but leave the structure of individual syllables intact. These behavioral changes are paralleled by the selective loss of striatal neurons and reduction of inhibitory synapses on pallidal neurons that serve as the BG output. Chronic recordings in singing birds revealed disrupted temporal patterns of activity in pallidal neurons and downstream cortical neurons. Moreover, reversible inactivation of the cortical neurons rescued the disorganized vocal sequences in transfected birds. These findings shed light on a key role of temporal patterns of cortico-BG activity in the regulation of complex motor sequences and show how a genetic mutation alters cortico-BG networks to cause disorganized movements.