Biomedical subjects

X B Shi

Publications and source records attributed to X B Shi.

20 records · Page 2Linked to original sources

PubMedDate not supplied

Morphology and development of mirror-image doublets of Stylonychia mytilus.

This paper describes the cortical anatomy and development of mirror-image doublets of Stylonychia mytilus, analyzed using the protargol technique. The reversed, or "left-handed" (LH) component of these doublets is a mirror image of the normal or "right handed" (RH) component with regard to the arrangement of cortical structures. The mirror-image patterning is imperfect, however, as the individual ciliary structures of the LH component all are of normal internal asymmetry, and the orientation of membranelles is inverted. Certain structures that would be expected to form near the line of symmetry are absent. During cell division and cortical reorganization, ciliary primordia arise and become arranged in a mirror-image pattern that is more perfect than that exhibited by the mature structures. Deviations from a mirror-image pattern appear at late stages when organelle sets differentiate within ciliary primordia: for example, the membranelle set differentiates within the oral primordium of the LH component in a sequence that is an inversion rather than a mirror image of the corresponding sequence of the RH component. This mixed control of oral development by different cortical "informational systems" accounts for some of the characteristic abnormalities of the mature oral structures of the LH component.

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PubMedDate not supplied

Morphology and development of left-handed singlets derived from mirror-image doublets of Stylonychia mytilus.

Mirror-image doublets of Stylonychia mytilus include 2 sets of cortical structures, one with the normal "right-handed" (RH) arrangement, the other with a reversed "left-handed" (LH) arrangement. These sets, however, are incomplete, with certain structures, most notably cirri of the right marginal type, missing near the line of symmetry. When a mirror-image doublet is bisected longitudinally to separate the RH and LH components physically, each fragment undergoes a regeneration process that restores a complete set of cortical structures, including the previously missing cirri of the right marginal type. In the resulting LH cell, all ciliary structures are present in an arrangement that is globally reversed in relation to that found in RH cells; in particular, marginal cirri of the left-marginal type are formed at the cell's right margin, and marginal cirri of the right-marginal type are produced at the cell's left margin. Whereas the regenerated RH fragment always divides and initiates a clone of normal singlets, the LH fragment, though structurally nearly complete, in all cases eventually dies without dividing. The cause of death is starvation due to the formation of an abnormal oral apparatus. In the Discussion, we consider the nature and consequences of a reversal of global positional information.

Animals↗