Mullins Lab Publications
BMC Genomics. 2021 Jun 26;22(1):477. doi: 10.1186/s12864-021-07782-0.
BACKGROUND: Glaucoma is a leading cause of visual disability and blindness. Release of iris pigment within the eye, pigment dispersion syndrome (PDS), can lead to one type of glaucoma known as pigmentary glaucoma. PDS has a genetic component, however, the genes involved with this condition are largely unknown. We sought to discover genes that cause PDS by testing cohorts of patients and controls for mutations using a tiered analysis of exome data.
RESULTS: Our primary analysis evaluated melanosome-related genes that cause dispersion of iris pigment in mice (TYRP1, GPNMB, LYST, DCT, and MITF). We identified rare mutations, but they were not statistically enriched in PDS patients. Our secondary analyses examined PMEL (previously linked with PDS), MRAP, and 19 other genes. Four MRAP mutations were identified in PDS cases but not in controls (p = 0.016). Immunohistochemical analysis of human donor eyes revealed abundant MRAP protein in the iris, the source of pigment in PDS. However, analysis of MRAP in additional cohorts (415 cases and 1645 controls) did not support an association with PDS. We also did not confirm a link between PMEL and PDS in our cohorts due to lack of reported mutations and similar frequency of the variants in PDS patients as in control subjects.
CONCLUSIONS: We did not detect a statistical enrichment of mutations in melanosome-related genes in human PDS patients and we found conflicting data about the likely pathogenicity of MRAP mutations. PDS may have a complex genetic basis that is not easily unraveled with exome analyses.
Automated segmentation of choroidal layers from 3-dimensional macular optical coherence tomography scans
J Neurosci Methods. 2021 Jun 19;360:109267. doi: 10.1016/j.jneumeth.2021.109267. Online ahead of print.
BACKGROUND: Changes in choroidal thickness are associated with various ocular diseases, and the choroid can be imaged using spectral-domain optical coherence tomography (SD-OCT) and enhanced depth imaging OCT (EDI-OCT).
NEW METHOD: Eighty macular SD-OCT volumes from 80 patients were obtained using the Zeiss Cirrus machine. Eleven additional control subjects had two Cirrus scans done in one visit along with enhanced depth imaging (EDI-OCT) using the Heidelberg Spectralis machine. To automatically segment choroidal layers from the OCT volumes, our graph-theoretic approach was utilized. The segmentation results were compared with reference standards from two independent graders, and the accuracy of automated segmentation was calculated using unsigned/signed border positioning/thickness errors and Dice similarity coefficient (DSC). The repeatability and reproducibility of our choroidal thicknesses were determined by intraclass correlation coefficient (ICC), coefficient of variation (CV), and repeatability coefficient (RC).
RESULTS: The mean unsigned/signed border positioning errors for the choroidal inner and outer surfaces are 3.39 ± 1.26 µm (mean ± standard deviation)/- 1.52 ± 1.63 µm and 16.09 ± 6.21 µm/4.73 ± 9.53 µm, respectively. The mean unsigned/signed choroidal thickness errors are 16.54 ± 6.47 µm/6.25 ± 9.91 µm, and the mean DSC is 0.949 ± 0.025. The ICC (95% confidence interval), CV, RC values are 0.991 (0.977-0.997), 2.48%, 14.25 µm for the repeatability and 0.991 (0.977-0.997), 2.49%, 14.30 µm for the reproducibility studies, respectively.
COMPARISON WITH EXISTING METHOD(S): The proposed method outperformed our previous method using choroidal vessel segmentation and inter-grader variability.
CONCLUSIONS: This automated segmentation method can reliably measure choroidal thickness using different OCT platforms.
Stem Cells Transl Med. 2021 Jun 22. doi: 10.1002/sctm.21-0080. Online ahead of print.
Autologous photoreceptor cell replacement is one of the most promising approaches currently under development for the treatment of inherited retinal degenerative blindness. Unlike endogenous stem cell populations, induced pluripotent stem cells (iPSCs) can be differentiated into both rod and cone photoreceptors in high numbers, making them ideal for this application. That said, in addition to photoreceptor cells, state of the art retinal differentiation protocols give rise to all of the different cell types of the normal retina, the majority of which are not required and may in fact hinder successful photoreceptor cell replacement. As such, following differentiation photoreceptor cell enrichment will likely be required. In addition, to prevent the newly generated photoreceptor cells from suffering the same fate as the patient's original cells, correction of the patient's disease-causing genetic mutations will be necessary. In this review we discuss literature pertaining to the use of different cell sorting and transfection approaches with a focus on the development and use of novel next generation microfluidic devices. We will discuss how gold standard strategies have been used, the advantages and disadvantages of each, and how novel microfluidic platforms can be incorporated into the clinical manufacturing pipeline to reduce the complexity, cost and regulatory burden associated with clinical grade production of photoreceptor cells for autologous cell replacement.
Hum Mol Genet. 2021 May 20:ddab140. doi: 10.1093/hmg/ddab140. Online ahead of print.
The human neural retina is a light sensitive tissue with remarkable spatial and cellular organization. Compared to the periphery, the central retina contains more densely packed cone photoreceptor cells with unique morphologies and synaptic wiring. Some regions of the central retina exhibit selective degeneration or preservation in response to retinal disease and the basis for this variation is unknown. In this study, we used both bulk and single-cell RNA sequencing to compare gene expression within concentric regions of the central retina. We identified unique gene expression patterns of foveal cone photoreceptor cells, including many foveal-enriched transcription factors. In addition, we found that the genes RORB1, PPFIA1, and KCNAB2 are differentially spliced in the foveal, parafoveal, and macular regions. These results provide a highly detailed spatial characterization of the retinal transcriptome and highlight unique molecular features of different retinal regions.
Ann Plast Surg. 2021 Jun 1;86(4S Suppl 4):S452-S453. doi: 10.1097/SAP.0000000000002787.
BACKGROUND: Growth and sustainability of burn practices can be impaired by irregular patterns of patient presentations, resulting in uneven utilization of facilities and staff. Burn care itself may not engage the full capacities of members of burn care teams. To address these problems, we organized a burn and reconstruction center to provide statewide acute care as Mississippi's only burn unit, to fully integrate reconstructive surgery into management of burn patients, and to diversify practice based on plastic surgery scope of practice. The first 10 years of this unit were reviewed to evaluate the performance of this scheme.
METHODS: Burn admissions to and surgical procedures at this unit between July 2009 and June 2019 were analyzed to quantify acute burn care, secondary reconstructive burn care, and categories of practice growth.
RESULTS: The unit admitted 5469 acute burn patients with a mortality rate of 1.49%. Comparing year 10 to year 1 of practice, acute burn admissions increased 58%. Total operations increased 276%. Acute burn procedures increased 176%. Secondary burn procedures increased 405%. Nonburn procedures increased 352%, with the subset of nonburn hand surgery increasing 1062%.
CONCLUSION: Acute burn admissions and procedures increased over this period, but greater growth was seen in secondary burn procedures and nonburn procedures, especially hand cases. Expansion of practice into areas within the overall skill sets of burn team members was an effective growth strategy.
Cells. 2021 Mar 20;10(3):687. doi: 10.3390/cells10030687.
The extracellular matrix (ECM) plays a crucial role in all parts of the eye, from maintaining clarity and hydration of the cornea and vitreous to regulating angiogenesis, intraocular pressure maintenance, and vascular signaling. This review focuses on the interactions of the ECM for homeostasis of normal physiologic functions of the cornea, vitreous, retina, retinal pigment epithelium, Bruch's membrane, and choroid as well as trabecular meshwork, optic nerve, conjunctiva and tenon's layer as it relates to glaucoma. A variety of pathways and key factors related to ECM in the eye are discussed, including but not limited to those related to transforming growth factor-β, vascular endothelial growth factor, basic-fibroblastic growth factor, connective tissue growth factor, matrix metalloproteinases (including MMP-2 and MMP-9, and MMP-14), collagen IV, fibronectin, elastin, canonical signaling, integrins, and endothelial morphogenesis consistent of cellular activation-tubulogenesis and cellular differentiation-stabilization. Alterations contributing to disease states such as wound healing, diabetes-related complications, Fuchs endothelial corneal dystrophy, angiogenesis, fibrosis, age-related macular degeneration, retinal detachment, and posteriorly inserted vitreous base are also reviewed.