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Mechanobiology of Erythrocytes from Adult Mice Homozygous for a Targeted Disruption of the E-Tmod Gene at Exon 1

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Abstract

The erythrocyte membrane skeleton is a protein network that provides deformability and stability to erythrocytes. Defects in the network lead to dysfunction and diseases. Erythrocyte tropomodulin (E-Tmod) of 41 kDa is an actin-capping protein at the slow-growing end, and together with tropomyosin 5 or 5b, has been proposed to form a “molecular ruler” dictating the length of actin protofilament of 37 nm in the network. We have previously created an E-Tmod knockout mouse model by targeted disruption of exon 1, which contains the AUG initiation codon. In this study, we showed that the embryonic lethality of the E-Tmod −/− mice was rescued by breeding with transgenic mice overexpressing E-Tmod in the heart and investigated the biomechanics of erythrocytes and its network topology. Western blot analysis revealed that a cytosolic E-Tmod29 isoform, which lacks the N-terminal F-actin binding domain, remains intact in the E-Tmod −/− erythrocytes, but is highly dimerized by oxidation. Micropipette aspiration indicated a higher elastic shear modulus and ektacytometry showed a lower average integrated elongation index. E-Tmod −/− mice had more microcytic erythrocytes with more compacted network on transmission electron microscopy. These results demonstrated the importance of E-Tmod41, the membrane-bound long isoform, in the network organization and mechanobiology of erythrocytes.

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Abbreviations

E-Tmod:

Erythrocyte tropomodulin

TM:

Tropomyosin

TOT:

Tropomodulin overexpressing transgenic

μRBC:

Microcytic RBC or erythrocyte

JC:

Junctional complex

SC:

Suspension complex

WBC:

White blood cell

MCV:

Mean cell volume

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Acknowledgments

We thank Dr. Shu Chien for inspiration, encouragement, and serving on Terrell Green’s Ph.D. dissertation committee. Terrell Green was supported by the Ford Foundation, Eugene Cota-Robles Fellowship, NIH Training Grant T32 HL007089, and the Siebel Scholars Foundation. Reagents were partially supported by the NIH Grant ARRA 23102A. Dr. Mark Sussman's work was supported by 2R01HL067245. We used the Biotech Core of the Bioengineering Department, animal facilities at UCSD (for breeding and whole blood count analyses), and the micropipette aspiration system established by Dr. Shu Chien and Dr. Kuo-Li Paul Sung.

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Authors and Affiliations

  1. Department of Bioengineering, University of California, San Diego, PFBH Room 333, La Jolla, CA, 92093-0412, USA

    Terrell Green, Carlos Vera & Lanping Amy Sung

  2. Department of Biology, San Diego State University, San Diego, CA, 92182-4614, USA

    Mark A. Sussman

  3. National Center for Microscopy and Imaging Research, University of California, San Diego, La Jolla, CA, 92093-0412, USA

    Maryann Martone

Authors
  1. Terrell Green
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  2. Carlos Vera
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  3. Mark A. Sussman
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  5. Lanping Amy Sung
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Correspondence to Lanping Amy Sung.

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Associate Editor John Shyy and Yingxiao Wang oversaw the review of this article.

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Green, T., Vera, C., Sussman, M.A. et al. Mechanobiology of Erythrocytes from Adult Mice Homozygous for a Targeted Disruption of the E-Tmod Gene at Exon 1. Cel. Mol. Bioeng. 4, 637–647 (2011). https://doi.org/10.1007/s12195-011-0203-x

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