Pseudopodia

2 Key excerpts on "Pseudopodia"

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  eBook - PDF

  The Biology of Amoeba

  • Kwang Jeon(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  256 EUGENE C. BOVEE AND THEODORE L. JAHN E. OTHER POSTULATES FOR PSEUDOPODIUM FORMATION AND FUNCTION Other assumptions for pseudopodium formation, extension and generation of motive force may, however, be required for one or another amoeba. Jepps (1956) remarked that an amoeba's Pseudopodia have to fit the circumstances, suggesting both adaptations of the Pseudopodia and the functional mechanisms. Seravin (1965, 1971) claims that pseudopodium formation and locomotion are due to multiple processes which follow one another in a coordinated sequence, with locomotion involving one major process occurring anteriorly and another occurring posteriorly (Seravin, 1966). Bovee (1964) and Seravin (1965) both note that ectoplasmic structures are quite different among various amoebae, resulting in visible evidence of diversity of species. In Vannella miroides an initially hemispheroid bulge lengthens to become a tubular pseudopodium filled with clear endoplasm. That solidifies and the pseudopodium twists into a tight spiral, then extends as a long conical, slightly spiral pseudopodium which rotates, at least at the tip, as it lengthens (Bovee, 1965). Jarosch (1971a,b) assumes that spiral fibrils of different periods may be present in the gel, interacting to bring about lengthening of the pseudo-podium. What all this amounts to is that each species of amoeba has its own variant of the basic actomyosinoid, ATP-using polymeric machinery. Generalizing about amoeboid movement may neither describe nor explain what happens in more than one amoeba. Even for the most-studied variety of amoeboid move-ment and locomotion, that of A. proteus, there is as yet no agreement on how the mechanism functions. Hence, there is much left to observe and examine experimentally about movement and locomotion in amoebae. Each species must be considered a special problem with the answers to be sought, rather than to be explained by modifying any p e t theory at the expense of the search.

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  eBook - PDF

  Cells and Their Component Parts

  Biochemistry, Physiology, Morphology

  • Jean Brachet, Alfred E. Mirsky(Authors)
  • 2014(Publication Date)
  • Academic Press

    (Publisher)

  The essential features of the two processes are quite similar. A possible exception to this statement is the role of the hyaloplasmic veils or ruffles on many tissue cells, which, while similar in some ways to the ameba's hyaline cap, are much more active in movement, phagocytosis, and pinocytosis than their counterpart in the ameba (Robineaux, 1954, 1959). Although the embryological literature contains many accounts of the ameboid activity of dissociated embryonic cells and many cases of ameboid activity inferred from changes in cellular distribution, there have until recently been few direct observations to show the long sus-pected importance of ameboid movement in embryonic development. Recently, Dan and Okazaki (1956) and Gustaf son and Kinnander (1956) have demonstrated the importance of contracting Pseudopodia (some of 190 ROBERT D. ALLEN which resemble fllopodia) of both primary and secondary mesenchyme cells of the sea urchin embryo during gastrulation. The observations of Dan and Okazaki were demonstrated by physiological experiments and those of Gustafson and Kinnander by a remarkable time-lapse film. There will doubtless be found many other examples of the performance of physical work by Pseudopodia in developmental processes. Not only embryonic and some adult tissue cells, but also some neo-plastic cells have been studied. Enterline and Coman (1950) have re-viewed the observations, some of which were made almost a hundred years ago, on ameboid movements in neoplastic cells. It has been con-sidered virtually certain for some time that the invasiveness of neoplastic cells is due largely to the migration of unattached cells into interstitial spaces by ameboid movement. While the rate of locomotion of cancer cells appears not to be very rapid, it has been calculated that movement from the mammary gland to the axillary lymph nodes would take only about a month by ameboid movement alone.

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