Williams Thomas L.

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Williams
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Thomas L.
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  • Article
    Dynamic pigmentary and structural coloration within cephalopod chromatophore organs
    (Nature Research, 2019-03-01) Williams, Thomas L. ; Senft, Stephen L. ; Yeo, Jingjie ; Martín-Martínez, Francisco J. ; Kuzirian, Alan M. ; Martin, Camille A. ; DiBona, Christopher W. ; Chen, Chun-Teh ; Dinneen, Sean R. ; Nguyen, Hieu T. ; Gomes, Conor M. ; Rosenthal, Joshua J. C. ; MacManes, Matthew D. ; Chu, Feixia ; Buehler, Markus J. ; Hanlon, Roger T. ; Deravi, Leila F.
    Chromatophore organs in cephalopod skin are known to produce ultra-fast changes in appearance for camouflage and communication. Light-scattering pigment granules within chromatocytes have been presumed to be the sole source of coloration in these complex organs. We report the discovery of structural coloration emanating in precise register with expanded pigmented chromatocytes. Concurrently, using an annotated squid chromatophore proteome together with microscopy, we identify a likely biochemical component of this reflective coloration as reflectin proteins distributed in sheath cells that envelop each chromatocyte. Additionally, within the chromatocytes, where the pigment resides in nanostructured granules, we find the lens protein Ω- crystallin interfacing tightly with pigment molecules. These findings offer fresh perspectives on the intricate biophotonic interplay between pigmentary and structural coloration elements tightly co-located within the same dynamic flexible organ - a feature that may help inspire the development of new classes of engineered materials that change color and pattern.
  • Article
    Photoreceptor disc incisures form as an adaptive mechanism ensuring the completion of disc enclosure
    (eLife Sciences Publications, 2023-07-14) Lewis, Taylor R. ; Phan, Sebastien ; Castillo, Carson M. ; Kim, Keun-Young ; Coppenrath, Kelsey ; Williams, Thomas L. ; Hao, Ying ; Skiba, Nikolai P. ; Horb, Marko E. ; Ellisman, Mark H. ; Arshavsky, Vadim Y.
    The first steps of vision take place within a stack of tightly packed disc-shaped membranes, or ‘discs’, located in the outer segment compartment of photoreceptor cells. In rod photoreceptors, discs are enclosed inside the outer segment and contain deep indentations in their rims called ‘incisures’. The presence of incisures has been documented in a variety of species, yet their role remains elusive. In this study, we combined traditional electron microscopy with three-dimensional electron tomography to demonstrate that incisures are formed only after discs become completely enclosed. We also observed that, at the earliest stage of their formation, discs are not round as typically depicted but rather are highly irregular in shape and resemble expanding lamellipodia. Using genetically manipulated mice and frogs and measuring outer segment protein abundances by quantitative mass spectrometry, we further found that incisure size is determined by the molar ratio between peripherin-2, a disc rim protein critical for the process of disc enclosure, and rhodopsin, the major structural component of disc membranes. While a high perpherin-2 to rhodopsin ratio causes an increase in incisure size and structural complexity, a low ratio precludes incisure formation. Based on these data, we propose a model whereby normal rods express a modest excess of peripherin-2 over the amount required for complete disc enclosure in order to ensure that this important step of disc formation is accomplished. Once the disc is enclosed, the excess peripherin-2 incorporates into the rim to form an incisure.