A single link to the first track to allow the export script to build the search page
  • Undergraduate Poster Abstracts
  • Developmental Biology

    THU-835 FGF, BMP, SHH SIGNALING PATHWAYS REGULATE MORPHOGENESIS OF THE INNER EAR

    • Edgar Gutierrez ;
    • Suzanne Mansour ;
    • Lisa Urness ;

    THU-835

    FGF, BMP, SHH SIGNALING PATHWAYS REGULATE MORPHOGENESIS OF THE INNER EAR

    Edgar Gutierrez1, Suzanne Mansour2, Lisa Urness2.

    1University of California, Davis, Davis, CA, 2The University of Utah, Salt Lake City, UT.

    The vertebrate inner ear forms from a region of thickened epithelial cells during embryogenesis. This epithelium invaginates, forming a cup-like structure on either side of the developing head that deepens and pinches off from the overlying ectoderm to form a hollow sphere of cells called the otocyst. This simple structure gives rise to the 2 major components of the ear, the vestibular and auditory chambers that sense movement and sound, respectively. The otocyst provides a unique system for analyzing the morphogenetic events that transform a simple epithelial embryonic rudiment into a highly complex 3-dimensional organ such as the ear. Failure to undergo perfectly choreographed morphogenesis is a well-recognized cause of congenital hearing loss in humans. Bone morphogenetic protein (BMP), sonic hedgehog (SHH), and fibroblast growth factor (FGF)-mediated signaling are critical for many aspects of inner ear development. We hypothesize that these signaling pathways function both in parallel and via intersecting pathways to regulate a repertoire of epithelial cell behaviors including changes in cell shape, location, division rate, and survival, and these behaviors drive morphogenesis to ultimately sculpt the complex inner-ear labyrinth. We have found several useful probes for BMP and SHH signaling, and we are testing a BMP reporter mouse with which we will begin to examine the changes in BMP and SSH signaling in FGF-deficient otocysts. This work will provide insight into mechanisms underlying the morphogenesis of the inner ear and ultimately be applied toward improving the prospects for diagnosis and treatment of patients with inner-ear dysfunction.

    THU-834 THE TALLYHO MOUSE CARRIES AN OBESITY QTL, TABW3, ON CHROMOSOME 1 THAT EXAGGERATES HIGH-FAT-DIET-INDUCED OBESITY

    • Sofia Romero ;
    • Jacaline Parkman ;
    • Jung Han Kim ;

    THU-834

    THE TALLYHO MOUSE CARRIES AN OBESITY QTL, TABW3, ON CHROMOSOME 1 THAT EXAGGERATES HIGH-FAT-DIET-INDUCED OBESITY

    Sofia Romero1, Jacaline Parkman2, Jung Han Kim2.

    1University of California, Santa Cruz, Santa Cruz, CA, 2Marshall University, Huntington, WV.

    An estimated 30% of the world’s population is obese or overweight. Genetic factors are highly involved in the development of obesity, most likely in the form of interactions of multiple genes within obesity-promoting environments such as high fat diets. Previously, we mapped a quantitative trait locus (QTL) linked to obesity, named tabw3, on mouse chromosome 1 in obese and type 2 diabetic TALLYHO/Jng (TH) mice. Subsequently, we established a congenic mouse strain that carries the tabw3 locus derived from TH on a C57BL/6J (B6) background (B6.TH-tabw3). The purpose of this study was to characterize the B6.TH-tabw3 congenic mice. We also evaluated gene expression levels of interferon activated gene 202B (Ifi202b) to identify a positional candidate gene for the tabw3. At 4 weeks of age, the congenic and B6 mice were weaned onto chow or high fat diets and maintained. Body composition was measured by quantitative magnetic resonance imaging and indirect calorimetry conducted using the comprehensive laboratory animal monitoring system. The Ifi202b mRNA levels in subcutaneous adipose tissue were determined by qRT-PCR. On chow, congenic mice exhibited significantly larger body fat mass compared with B6. Both congenic and B6 mice gained more body fat when the animals were fed high fat diets than when fed chow, but the increase was greater in congenic than in B6 mice. Congenic mice showed significantly lower energy expenditure (kcal/kg/hr) than B6 on both diets, without differences in food intake. The Ifi202b mRNA levels were approximately 15-fold higher in the adipose tissue of congenic mice than B6.

    FRI-835 DEVELOPING A ROBUST APPETITIVE-CONDITIONING PARADIGM IN LARVAL ZEBRAFISH

    • Amber Simmons ;
    • Su Guo ;
    • Francesca Oltrabella ;
    • Adam Abate ;
    • Kristen Taylor ;
    • Emily Bryant ;

    FRI-835

    DEVELOPING A ROBUST APPETITIVE-CONDITIONING PARADIGM IN LARVAL ZEBRAFISH

    Amber Simmons1, Su Guo2, Francesca Oltrabella2, Adam Abate2, Kristen Taylor2, Emily Bryant2.

    1Hampton University, Hampton, VA, 2University of California, San Francisco, San Francisco, CA.

    The zebrafish (Danio rerio) is a widely used model organism in vertebrate biology, with its optical clarity, external development, and amenability to efficient genetic and chemical screening. These salient features allow for cellular and molecular mechanisms to be understood in relation to developmental and disease-oriented pathways. Avoidance-learning paradigms have been studied extensively in wild-type zebrafish with definitive results that show their ability to associate visual conditioned stimuli with aversive unconditioned stimuli as early as 7 days post fertilization (dpf). However, reward learning, a process implicated in mental disorders such as addiction, has not been explored with nearly the same depth. We are developing a robust appetitive conditioning paradigm that aims to teach larval zebrafish to associate neutral sensory cues (feeding tube) with a food reward (Paramecia). A computer automated microfluidic feeding system and video-recording device allow the larvae to be continuously observed and tested. Preliminary results showed an apprehension in approaching the food for larvae, which seemed to be caused by stress and lack of socialization. Following device optimization, recorded videos have begun to show routine feeding behavior. The next steps include optimization of the testing arena, statistical analysis of preliminary feeding-behavior data, and conditioning experiments organized and implemented using preliminary feeding data. Data collected will be used to uncover the neurobiology of reward learning and characterize genes and cell types involved in the process.

    THU-826 ANALYSIS OF THE OVER-EXPRESSION OF PORCN IN THE CHICK NEURAL TUBE

    • Jessica Magana ;
    • Laura Burrus ;
    • Lisa Galli ;

    THU-826

    ANALYSIS OF THE OVER-EXPRESSION OF PORCN IN THE CHICK NEURAL TUBE

    Jessica Magana1, Laura Burrus2, Lisa Galli2.

    1City College of San Francisco, San Francisco, CA, 2San Francisco State University, San Francisco, CA.

    Wnt proteins promote cell proliferation, specification, and differentiation. Porcupine (PORCN), an O-acyltransferase, promotes the palmitoylation of Wnt proteins and is required for Wnt secretion. In the chick embryo neural tube, Wnt proteins control the specification of interneurons and motor neurons. The proper specification of these neurons is critical for the development of the spinal cord of the chick embryo. It has previously been shown that overexpression of WNT1 and WNT3A in the chick neural tube causes an increase in the specification of dorsal interneurons and a decrease in the specification of motor neurons. We hypothesized that overexpression of PORCN in the chick neural tube would cause similar results, namely an increase in dorsal interneurons and a decrease in motor neurons. To test this hypothesis, we overexpressed pCIG-mPORCN in the chick neural tube through ovo electroporation. We then immunostained the neural tube with an Islet-1 antibody that binds to DI3 and motor neurons, allowing us to indirectly assess Wnt activity for both dorsal interneurons and motor neurons. Preliminary data, taken from 23 sections of just 1 chick embryo, show no significant difference in the specification of dorsal interneurons and motor neurons compared to the control side of the neural tube. More data is required to make a more definitive conclusion concerning how the overexpression of PORCN affects the specification of dorsal and motor neurons.

    THU-824 KRÜPPEL-LIKE FACTOR 4 GENE EXPRESSION IN DEVELOPING HUMAN FETAL SKIN

    • JaNiece Walker ;
    • Suzanne McConaghy ;
    • Robin Ohls ;

    THU-824

    KRÜPPEL-LIKE FACTOR 4 GENE EXPRESSION IN DEVELOPING HUMAN FETAL SKIN

    JaNiece Walker1, Suzanne McConaghy2, Robin Ohls2.

    1Xavier University of Louisiana, New Orleans, LA, 2The University of New Mexico, Albuquerque, NM.

    Preterm delivery abruptly alters the natural course of gene expression, forcing extremely low-birth-weight (ELBW) infants to continue development in a nonuterine, postnatal environment which is abundant in oxygen. In ELBW infants, the skin is not yet fully established as the primary barrier to prevent evaporation, nor as a critical component of the immune system resulting in susceptibility to bacterial infections and dehydration. Krüppel-like factor 4 (KLF4) is a transcription factor that regulates proteins such as keratohyalin and small proline-rich protein 2A, which are responsible for maturation in developing skin. We sought to determine changes in the KLF4 gene expression following ex utero exposure of fetal skin to a postnatal environment. We hypothesized that gene expression of KLF4 in human fetal skin would increase with exposure to ambient oxygen. Fetal skin samples (10.4 to 19.2 weeks gestation) were collected. Samples were triturated and incubated in DMEM with 10% fetal bovine serum and 1% antimicrobials at 21% oxygen, 5% CO2 in a humidified incubator for 0, 24, 48, and 72 hours. RNA was extracted and reverse transcription polymerase chain reaction (RT- PCR) performed with primers and a probe specific for KLF4. β-actin was used as a control in duplex PCR reactions. An increase in KLF4 expression occurred between baseline and 24 hours, and between baseline and 48 hours of incubation (p < 0.05). KLF4 gene expression increased with increasing exposure to air. We speculate that postpartum conditions up regulate gene expression of KLF4 and promote skin maturation.

    FRI-825 ACETYLCHOLINESTERASE LOCALIZATION AND FUNCTION DURING NEURODEVELOPMENT IN THE PLANARIAN DUGESIA JAPONICA

    • Karla Fernandez ;
    • Eva-Maria Schoetz Collins ;
    • Danielle Hagstrom ;

    FRI-825

    ACETYLCHOLINESTERASE LOCALIZATION AND FUNCTION DURING NEURODEVELOPMENT IN THE PLANARIAN DUGESIA JAPONICA

    Karla Fernandez, Eva-Maria Schoetz Collins, Danielle Hagstrom.

    University of California, San Diego, La Jolla, CA.

    Acetylcholinesterase (AChE) is an enzyme that breaks down the neurotransmitter acetylcholine (ACh) to regulate cholinergic neurotransmission which is used in motor activity and cognition. Studies suggest that AChE also plays an important role in neurodevelopment which may be completely independent of ACh regulation. However, it remains largely unknown what the balance between these 2 functions is during the course of neurodevelopment because existing data comes primarily from cell culture experiments. Our objective is therefore to close this knowledge gap and examine the role of AChE in neuro development in vivo. We use the freshwater planarian Dugesia japonica for these studies because it has a relatively simple brain that remains molecularly and structurally homologous to the human brain, and its fast brain development makes it experimentally tractable. We found 5 potential AChE candidates and will determine their expression profile through in situ hybridization. Using RNA interference (RNAi), we can further study the function of these candidates in adult and regenerating planarians. RNAi phenotypes will be analyzed both on the cellular and behavioral level. The results from these studies will help determine if AChE is essential in neurodevelopment in planarians. Since little is known about the role of AChE in neurodevelopment in vivo, the results from this study will bring us closer to understanding how AChE is involved in neurodevelopment.

    FRI-824 EXPRESSION PATTERN ANALYSIS OF THE SECRETED TYROSINE KINASE (VLK) AND ITS BIOLOGICAL FUNCTION IN THE FROG XENOPUS LAEVIS

    • Maria Benitez ;
    • Gabriele Colozza ;
    • Edward De Robertis ;

    FRI-824

    EXPRESSION PATTERN ANALYSIS OF THE SECRETED TYROSINE KINASE (VLK) AND ITS BIOLOGICAL FUNCTION IN THE FROG XENOPUS LAEVIS

    Maria Benitez, Gabriele Colozza, Edward De Robertis.

    University of California, Los Angeles, Los Angeles, CA.

    Vertebrate lonesome kinase (Vlk) is a secreted tyrosine kinase that phosphorylates proteins in the secretory pathway and the extracellular environment. Knockout of Vlk in mouse embryos leads to defects in skeletal and craniofacial development, as well as death only a few hours after birth due to problems with the respiratory system. Vlk is expressed in the organizer regions of both mouse and zebrafish embryos. The frog Xenopus laevis has 2 homologs of this kinase, Vlk1 and Vlk2, but a detailed description of their expression pattern and biological function is missing. First, reverse-transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization were used to describe the temporal and spatial expression pattern of Vlk1 and Vlk2. RT-PCR showed that Vlk1 and Vlk2 are first expressed at stage 10. Similarly, in situ hybridization of Vlk1 and Vlk2 showed that the expression of these kinases is localized in the frog organizer region during gastrulation. At stage 13, expression of both genes was detected in the prechordal plate, an embryonic region essential for head development. At later stages, strong expression was found in the optic vesicle and the pineal gland suggesting a possible role for Vlks in the development of these organs. In addition, we observed whether canonical Wnt affects Vlk1 and Vlk2 transcription by injection of Wnt8 mRNA or β-catenin morpholino into frog embryos. Changes in Vlk1 and Vlk2 transcript levels were observed using semiquantitative and quantitative RT-PCR, indicating that the expression of these kinases is under the control of the canonical Wnt pathway.

    THU-825 INVESTIGATING A ROLE FOR FGF SIGNALING IN INTEGRATING PROLIFERATION, MIGRATION, AND ASYMMETRIC HEART MORPHOGENESIS IN ZEBRAFISH

    • Briana Christophers ;
    • Meagan Grant ;
    • Rebecca Burdine ;

    THU-825

    INVESTIGATING A ROLE FOR FGF SIGNALING IN INTEGRATING PROLIFERATION, MIGRATION, AND ASYMMETRIC HEART MORPHOGENESIS IN ZEBRAFISH

    Briana Christophers, Meagan Grant, Rebecca Burdine.

    Princeton University, Princeton, NJ.

    Three of the most common human congenital heart defects, the leading cause of all infant mortalities arising from birth defects, result from aberrant asymmetric cardiac morphogenesis. Considering the conservation of morphogenetic behaviors in vertebrate heart development, understanding the mechanisms underlying asymmetric cardiac morphogenesis in zebrafish will provide insight into how defects occur in the developing human heart. Zebrafish heart morphogenesis is characterized by 2 asymmetric events: jogging and looping. During jogging, atrial cells are displaced to the left and anterior of ventricular cells. The heart tube bends during cardiac looping, and the ventricle is positioned to the right and anterior of the atrium, while cells from the second heart field (SHF) are added to the poles of the tube. Microarray analysis reveals upregulation of fibroblast growth factor (FGF) receptors and transcriptional targets due to Nodal signaling. FGF signaling is known to couple morphogenesis to cell migration events in development and is required for SHF cell addition to the arterial pole. We hypothesize that FGF signaling influences cardiac looping by promoting SHF addition to and rotation of the arterial pole, which allows it to undergo the torsion necessary for bending of the linear heart tube. We found that inhibition of FGF signaling during cardiac jogging results in aberrant looping. Embryos treated with SU5402, an FGFR inhibitor, exhibited a delay in the onset of tube bending followed by chamber curvature malformation. Also, our results show that the level of receptor inhibition negatively correlates with tube length and positively correlates with looping angle.

    FRI-834 EXAMINING THE ROLE OF THE SUPERFICIAL ENDODERMAL EPITHELIUM ON SOMITOGENESIS IN XENOPUS LEAVIS

    • Marika Deferrari ;
    • Carmen Domingo ;

    FRI-834

    EXAMINING THE ROLE OF THE SUPERFICIAL ENDODERMAL EPITHELIUM ON SOMITOGENESIS IN XENOPUS LEAVIS

    Marika Deferrari, Carmen Domingo.

    San Francisco State University, San Francisco, CA.

    Somites are groups of paraxial mesoderm cells consisting of elongated myotome fibers running parallel to the notochord that will give rise to the axial skeleton, muscle tissue, and the dermis in vertebrates. During somitogenesis, a specific sequence of cell behaviors takes place and causes cells to undergo a mediolateral elongation and rotation to form properly aligned muscle fibers. Disruptions in this process have been linked to scoliosis and other congenital defects and spinal deformities. Previous studies done in our lab using the African clawed frog Xenopus laevis as a model system have shown that tissue interactions between the overlying endodermal epithelium and the underlying mesoderm may be important for normal somite formation. However, it remains unclear as to when this critical signal occurs between these 2 tissues. In this study, we examined whether removal of the endodermal epithelium from a Xenopus embryo at the start of gastrulation disrupted somite formation. Gastrulation is a large-scale cell migration where the cells begin to involute and form the 3 germ layers. To conduct this experiment, we surgically removed the endodermal epithelium from Xenopus embryos at the onset of gastrulation. These embryos were then cultured to an early tailbud stage and then fixed and stained for muscle tissue. The effects that removing the endodermal epithelium had on somitogenesis were then evaluated using confocal imaging. Our results show that surgically removing the endodermal epithelium at the start of gastrulation had little to no effect on somitogenesis.

    FRI-823 DETERMINING ROLES OF HISTONE VARIANTS DURING SPERMATOGENESIS IN C. ELEGANS

    • Monet Jimenez ;
    • Diana Chu ;

    FRI-823

    DETERMINING ROLES OF HISTONE VARIANTS DURING SPERMATOGENESIS IN C. ELEGANS

    Monet Jimenez, Diana Chu.

    San Francisco State University, San Francisco, CA.

    During spermatogenesis, it is imperative that the right genes are accessible at a precise time and place; thus, regulation of chromatin accessibility is a highly complex process. DNA is packaged into nucleosomes composed of the core histones H2A, H2B, H3, and H4, which play an important role in maintaining chromatin accessibility. Furthermore, histone variants replace core histones to induce an additional layer of chromatin complexity. In C. elegans, we are focusing on 2 key variants: the evolutionarily conserved HTZ-1 and sperm-specific HTAS-1. Because mutants lacking their expression results in sterility or sub-fertility, we are curious about what distinct function each contributes during spermatogenesis. Comparing their protein sequences, these histone variants are vastly similar to core H2A, and differ most in their N- and C-terminal domains, sites where histone modification typically occurs. We hypothesize that these variable domains account for unique interactions to chromatin regulating proteins. In C. elegans, HTZ-1 localizes to 23% of all developmental promoters, suggesting a role in making chromatin more accessible. Conversely, HTAS-1 localizes to sperm chromatin, suggestive of inducing chromatin compaction. Using CRISPR/Cas-9, we are creating chimeric histone variants such that only one domain is expressed at a time. We expect that the N-term and C-term domains of HTZ-1 and HTAS-1 will be key, since these regions are most accessible to cell-type specific players involved in regulating chromatin during development.

    THU-812 SARCOMERE DISASSEMBLY DURING TAIL REGENERATION IN THE ADULT FISH STERNOPYGUS MACRURUS

    • Chiann-Ling Yeh ;
    • Robert Gueth ;
    • Graciela Unguez ;

    THU-812

    SARCOMERE DISASSEMBLY DURING TAIL REGENERATION IN THE ADULT FISH STERNOPYGUS MACRURUS

    Chiann-Ling Yeh, Robert Gueth, Graciela Unguez.

    New Mexico State University, Las Cruces, NM.

    The contractile apparatus, or sarcomere, is essential for skeletal muscle to generate force and movement. Severe muscle wasting that accompanies diseases is often due to the disassembly and degeneration of sarcomeres. Divided into highly organized subdomains or regions, a sarcomere includes the Z-disk, M-region, and A- and I-bands, with different proteins in each region. To date, in vitro studies on the formation of sarcomeres have proposed models of sarcomere development and assembly. In contrast, little is known about the process of sarcomere disassembly. The weakly electric fish Sternopygus macrurus has a remarkable capacity to regenerate all tissues in its tail (i.e., spinal cord, vertebrae, skeletal muscle, and the myogenic electric organ) after amputation. During tail regeneration, myofibers fuse and sarcomeres disassemble naturally to form electrocytes, the electric organ (EO) cells. We have studied the spatial and temporal expression patterns of 9 sarcomeric proteins during tail regeneration (n = 12 tails) to characterize this process of disassembly. Immunolabeling studies were informed by electron microscope studies (n = 2 tails) for higher resolution of sarcomere disassembly during the muscle-to-EO transdifferentiation. Our data show that the widening of inter-Z disks is first detected as Z-disks detach from each other prior to the disappearance of M-region proteins and subsequent inability to detect A-bands. Finally, clusters of I-Z-I-bands disappear as I-band components disassemble from the Z-disks and are dispersed throughout the electrocyte. In vivo analyses of sarcomere assembly in zebrafish embryos and in regenerating S. macrurus tails will prompt comparative and mechanistic insights to sarcomere stability.

    FRI-812 NONMUSCLE MYOSIN II-A PLAYS A ROLE IN SPERM DEVELOPMENT

    • Connie Lerma Cervantes ;
    • Keizo Tokuhiro ;
    • Neal Billington ;
    • Aibing Wang ;
    • Yingfan Zhang ;
    • Mary Anne Conti ;
    • Michael Kelley ;
    • Matthew Daniels ;
    • James Sellers ;
    • Jurrien Dean ;
    • Robert S. Adelstein ;

    FRI-812

    NONMUSCLE MYOSIN II-A PLAYS A ROLE IN SPERM DEVELOPMENT

    Connie Lerma Cervantes1, Keizo Tokuhiro1, Neal Billington1, Aibing Wang1, Yingfan Zhang1, Mary Anne Conti1, Michael Kelley2, Matthew Daniels1, James Sellers1, Jurrien Dean1, Robert S. Adelstein1.

    1National Heart, Lung, and Blood Institute, Bethesda, MD, 2Duke University, Durham, NC.

    Sperm head shaping is dependent upon the constriction of F-actin found in the Sertoli cells and a cytoskeletal plate known as the acroplaxome and its marginal ring. Furthermore, the presence of the acroplaxome is necessary for the anchoring of the acrosomal vesicle to the nuclear lamina. These differentiation processes as well as the coupling of the tail to the spermatid head are known as spermiogenesis. We have studied a mouse line with a mutation, E1841K, found in human MYH9-related disease. In addition to modeling macrothrombocytopenia, glomerulosclerosis, cataracts, and deafness (MYH9 RD), male mice homozygous for the mutation (AE1841K/AE1841K) are infertile. Histological analyses reveal severe sperm defects during spermiogenesis. Importantly, transmission electron microscopy uncovers aberrant spermatid elongation whereby spermatids fail to correctly extend and condense the acrosome. The acroplaxome shows an irregular wavy-like appearance while the elongated spermatids fail to couple the developing tail to the spermatid. Immunofluorescence confocal microscopy of developing spermatids shows localization of nonmuscle myosin II-A (NM II-A) to the marginal ring of the acroplaxome. In vitro experiments using baculovirus-expressed NM II show abnormal filament formation of the AE1841K/AE1841K myosin. The mutant filaments formed by the AE1841K/AE1841K myosin are longer and tend to form aggregates (A+/A+ = 314 +/- 28 nm, AEK/AEK = 372 +/- 94 nm length). The results suggest that the abnormal NM II-A filaments may form a debilitating marginal ring, which leads to abnormal sperm head shaping. Collectively, these observations suggest a previously unknown role for NM II-A in male fertility.

    THU-823 IDENTIFYING THE ROLES OF CCN1 AND CCN2 IN EMBRYONIC SKELETAL DEVELOPMENT

    • Tien Phan ;
    • Karen Lyons ;

    THU-823

    IDENTIFYING THE ROLES OF CCN1 AND CCN2 IN EMBRYONIC SKELETAL DEVELOPMENT

    Tien Phan, Karen Lyons.

    University of California, Los Angeles, Los Angeles, CA.

    CCN proteins reside primarily in the extracellular matrix and serve regulatory rather than structural roles. They regulate various biological functions such as cell adhesion, migration, proliferation, senescence, apoptosis, and chondrogenesis. The absence of CCN2 results in a range of skeletal defects; however, the role of CCN1 has not been explored. To evaluate the roles of CCN1 and CCN2, we examined the skeletal phenotypes in CCN1, CCN2, and CCN1-CCN2 cartilage-specific conditional knock-out mice during development. Ablation of CCN2 is neonatal lethal because of severe skeletal dysplasia including misaligned spines and sterna, kinked ribs, and bends in long bones such as the radius, ulna, tibia, and fibula. CCN1 mutants, on the other hand, survive to adulthood and display very subtle skeletal phenotype. Cell proliferation and apoptosis assays showed that CCN1 inhibits proliferation and promotes apoptosis while CCN2 had the opposite functions. The phenotypes seen in both mutants were consistent with defects in extracellular matrix deposition which led to weakened cartilage structures. Due to the differential expressions of CCN1 and CCN2 in some parts of the skeletal system, the absence of both of these proteins resulted in augmented skeletal defects. Presently, the gene expression profiles of the mutants are being examined to characterize the pathways by which CCN1 and CCN2 act to mediate cartilage development. This study not only enhances our current understanding of cartilage homeostasis but also holds promise for therapeutic treatments of diseased bone conditions