Biomedical subjects
M B Godward
Publications and source records attributed to M B Godward.
Ultrastructural studies in the Rhodophyta. I. Development of mitotic spindle poles in Apoglossum ruscifolium, Kylin.
The ultrastructure of somatic mitosis in the germlings of Apoglossum ruscifolium, Kylin, fixed from its natural habitat, was examined to investigate spindle-pole development and the role of the 'polar ring'. It was found that the polar ring originates from a special nuclear pore raised above a small projection of the nuclear envelope. The initiation of mitotic polarity takes the form of changes in the nuclear envelope. These are: close crowding of pores, heavy deposition of electron-opaque material and attachment of microtubules. No such phenomena are to be observed in the equatorial regions of the nuclear envelope, which persists throughout mitosis. The next stage is the development of 'clear zones', which become filled with microtubules excluding all other structures, notably ribosomes, at both poles. At pre-metaphase, microtubules begin to be extended from the clear zones through polar fenestrae in the nuclear envelope into the nucleus itself. With subsequent development of the intranuclear spindle, the microtubules in the clear zones show signs of degeneration. At metaphase, the polar regions of the nuclear envelope begin to return to their normal condition. After metaphase, the polar rings degenerate. Thus it is primarily the nuclear envelope, via its polar modifications, which begins the organization of the mitotic spindle. The capabilities of nuclear pores are summarized. In the Discussion, the polar rings are compared with procentrioles; since they appear to have a passive role in spindle-pole organization, it is suggested that they may represent an evolutionary stage prior to the procentriole. The origin of the centriole ultimately from a nuclear pore is presented as an hypothesis. It is concluded to be unlikely that the polar ring is a degenerate centriole, and therefore it is proposed that the red algae never had centrioles in the course of their evolution. Thus the view of the non-flagellate ancestry of the red algae is supported.
The nucleolus in telophase, interphase and prophase.
The ultrastructure of telophase to interphase has been followed in a green alga, Spirogyra submargaritata. A series of changes transitional between the late anaphase chromatid, the decondensing chromatid of telophase, and the 'pale fibrillar material' occupying channels in the nucleolus at interphase have been demonstrated. Early stages in the regeneration of the nucleolus are described. It has been shown that the pale fibrillar material in the nucleolus is attached to, and continuous with, the fully condensed (chromocentric) part of the nucleolar-organizing chromosome at interphase. It is also shown that in early prophase, the channels in the nucleolonema of the nucleolus are no longer occupied by pale fibrillar material, but instead a long section of condensed chromosome is present, traversing the nucleolonema. It is contended that these observations taken together constitute evidence that the pale fibrillar material of the nucleolus is the chromatin of the nucleolar-organizing region of the chromosome, expanded for transcription. A model of the nucleolus as it is seen in most electron-microscope sections, and as it can be interpreted in the light of present-day knowledge about it, is presented. A brief review of the relevant literature considers the views supporting the mode, and the contrary views, implicating the use of the term 'nucleolar organizer', that are still current at the present time.
Tubular elements - a new structure in blue-green algal cells.
New cell inclusions, 'tubular elements' are described from the blue-green alga Calothrix marchica. These structures are found in about 20% of all cells observed. They are 18-22 nm in diameter, apparently composed of sub-units of which the estimated number, as seen in transverse section, is 8-10.
Some observations on the nucleolus in Spirogyra.
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Cytological studies in the genus Zygnema.
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Mitotic peaks and mitotic time in the Desmidiaceae.
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Electron microscopy of the nucleolus of Spirogyra britannica and Spirogyra ellipsospora.
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