Texas Tech University

Lewis Irving Held

Associate Professor
Developmental Genetics

Email: See TTU Directory

Phone: (806) 834-3283

  • Ph.D., Molecular Biology, University of California Berkeley, 1977.
  • B.S., Life Sciences, Massachusetts Institute of  Technology, 1973.

Teaching Awards

Book Awards

  • 2nd Place Medal, TTU University-wide Book Competition, 2004.
  • 2nd Place Medal, TTU University-wide Book Competition, 2011.
  • 3rd Place Medal, TTU University-wide Book Competition, 2016.
Dr. Held

Web Links:

Wall Street Journal interviews Prof. Held about Darwinian evolution

Cambridge Univ. Press interviews Prof. Held about Darwin's legacy

Daily Toreador interviews Prof. Held about life & a fly joint mutation

For student use only (BIOL 3302):  StemCells1; StemCells2; Organoids1Organoids2; Organoids3; RegrowArms?; MorphogenGradients; MovieTranscript.
For student use only (BIOL 4110):  EvoDevoVideo1; EvoDevoVideo2; EvoDevoSlideshow; EvoDevo1EvoDevo2EvoDevo3EvoDevo4; FlyArt.
For student use only (BIOL 1403):  EvolutionSlideshow.

Flies ≈ humans!OrganSystems; WhyFlies?Video1(Basic); WhyFlies?Video2(Advanced); WhyFlies1?WhyFlies2?WhyFlies3?WhyFlies4?; WhyFlies5?; WhyFlies6?; WhyFlies7?; WhyFlies8?; WhyFlies9?; WhyFlies10?; WhyFlies11?; WhyFlies12?; WhyFlies13?; WhyFlies14?; FlyWorld1; Links-to-Literature.

Wonderlands of Fly Genes InteractiveFly; FunWithFlies1; FunWithFlies2; FunWithFlies3; NobelPrizes.

Research Interests

Research in my lab has focused on pattern formation: how do cells construct anatomy? The model system we have used is the leg of the fruit fly and its exquisitely intricate patterns of bristles. Over the years we have probed how various signaling pathways (TGF-beta, Wnt, and EGFR) establish the axes, boundaries, and coordinates of the leg landscape.  Recently we solved (at least partially) an intriguing riddle in evolutionary developmental (evo-devo) biology: how did the 1st pair of legs become different from the 2nd pair in terms of its sex comb (on the male tarsus) and its transverse rows (on the tibiae of both sexes)?  We found that a master gene in the Hox complex (called Scr ) causes transverse row bristles to be yellow and bractless by direct intervention, whereas its other effects appear to be mediated indirectly by as-yet unidentified circuits.  Currently we are using RNAi to probe the role of cell movements (as controlled by Rac & Rho) in fine-tuning bristle alignments, which are astoundingly regular in transverse rows & elsewhere.

Selected Publications

  • Held, L. I., Jr. (2017) Deep Homology?  Uncanny Similarities of Humans and Flies Uncovered by Evo-Devo. Cambridge University Press.  272 pp.  [Comparison of the genomic "operating systems" of humans and flies in terms of how the very same algorithms can build wildly different anatomies.]  This book is the third volume in a trilogy of books about evo-devo:  Quirks = Vol.1; Snake = Vol.2; DH = Vol.3. book review 1.
    HomologyCover
  • Held, L. I., Jr. (2014) How the Snake Lost its Legs:  Curious Tales from the Frontier of Evo-devo.  Cambridge University Press.  285 pp.  [A factual homage to Rudyard Kipling's fanciful  Just So Stories .  How the leopard actually got its spots, the zebra its stripes, the camel its hump, etc., from a modern genetic perspective.] book review 1 , book review 2 , book review 3 , book review 4, book review 5
    SnakesCover
  • Held, L. I., Jr., Billingsley, S. A., Muñoz, J. O. (2014) Disabling Cdc42 disrupts bristle patterning.   Dros. Info. Serv. 97 , 45-51.  [Filopodia may mediate bristle-cell movements.]
  • Held, L. I., Jr. (2013) Rethinking butterfly eyespots. Evol. Biol. 40 , 158-168.  [A new evo-devo hypothesis for how butterflies got their spots.]
  • Held, L. I., Jr. (2011) When does the spiny legs1 allele of the prickle gene cause extra joints? Dros. Info. Serv.  94 , 47-52.  [Probing the etiology of a bizarre syndrome.]
  • Held, L. I., Jr. (2010) How does Scr cause first legs to deviate from second legs?  Dros. Info. Serv.  93 , 132-146.  [A "Sherlock Holmes" study of old clues left by a Master Gene.]
  • Held, L. I., Jr. (2010) The evolutionary geometry of human anatomy: Discovering our inner fly. Evol. Anthropol.  19 , 227-235.  [Applying insights from flies to the human genome.]
  • Held, L. I., Jr. (2010)  The evo-devo puzzle of human hair patterning. Evol. Biol.  37 , 113-122.  [Reflections on why humans are the only "naked" apes & why guys go bald.]
  • Held, L. I., Jr. (2009) Quirks of Human Anatomy:  An Evo-Devo Look at the Human Body .   Cambridge University Press.  260 pp.  [Musings on many flaws we inherited via evolution.] book review 1 , book review 2 , book review 3 , book review 4 , book review 5 .
    QuirksCover
  • Held, L. I., Jr. (2009) 101 Unsolved Puzzles in Evo-Devo . Ancillary Workbook (Problem Sets) for Quirks of Human Anatomy .  [Mental exercises for those curious about oddities.]
  • Held, L. I., Jr. (2005) Suppressing apoptosis fails to cure "extra-joint syndrome" or to stop sex-comb rotation. Drosophila Info. Serv. 88 , 9-10.  [The syndrome causes double joints.]
  • Held, L. I., Jr., Grimson, M. J., Du, Z. (2004) Proving an old prediction: The sex comb rotates at 16-24 hrs after pupariation. Drosophila Info. Serv. 87 , 76-78.  [A rare proof.]
  • Held, L. I., Jr. (2003) Tetraploid male mosaics induced by pressure. Drosophila Info. Serv. 86 , 50-53.  [The cells of tetraploids are twice the volume of diploids & look a bit odd.]
  • Held, L. I., Jr. (2002) Imaginal Discs: The Genetic and Cellular Logic of Pattern Formation .  Cambridge University Press.  460 pp.  [History of a century of fly genetics, which has succeeded in deciphering the process of metamorphosis that converts discs into legs, wings, eyes, etc.]

    Imaginal Discs
  • Held, L. I., Jr. (2002) Bristles induce bracts via the EGFR pathway on Drosophila legs. Mechanisms of Development  117 , 225-234.  [The smallest known inductive interaction.]
  • Held, L. I., Jr., Heup, M.A. (1996) Genetic mosaic analysis of decapentaplegic and wingless gene function in the Drosophila leg. Development, Genes and Evolution  206 , 180-194.  [A critical piece in the puzzle of how genes generate geometry in fly legs.]
  • Held, L. I., Jr. (1995) Axes, boundaries, and coordinates: the ABCs of fly leg development. BioEssays  17 , 721-732.   [Overview of geometry of leg development.]
  • Held, L. I., Jr., Heup, M.A., Sappington, J.M., and Peters, S.D. (1994) Interactions of decapentaplegic , wingless , and Distal-less in the Drosophila leg.   Rouxs Arch. Dev. Biol.  203 , 310-319.  [A paper I wrote with three talented undergraduate apprentices.]
  • Held, L. I., Jr. (1992) Models for Embryonic Periodicity.  Karger.  119 pp.  [Historical survey of theories for how embryos make spatially periodic patterns, such as fingers, phalanges, and fingerprints, tree branches, flower petals, body segments, vertebrae, teeth, etc.  An homage to William Bateson's classic monograph Materials for the Study of Variation published a century earlier.]
    Models Cover

Department of Biological Sciences

  • Address

    Department of Biological Sciences, Texas Tech University, Box 43131 Lubbock, TX 79409
  • Phone

    806.742.2715
  • Email

    biology@ttu.edu