“Lens Mitochondria” in the Retinal Cones of the Tree-shrew Tupaia belangeri

Knabe, Wolfgang; Skatchkov, Serguei N.; Kuhn, Hans-Jürg

doi:10.1016/s0042-6989(96)00199-x

Cited by 45 publications

(56 citation statements)

References 22 publications

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“…In many morphological aspects, these enlarged organelles are similar to those described by Samorajski et al (1966) in the cones of the common tree shrew (Tupaia glis), and by Foelix et al (1987), Knabe and Kuhn (1996), and Knabe et al (1997) in the northern tree shrew (Tupaia belangeri). According to 3D reconstruction by Knabe and Kuhn (1996), the apical and central portions of each cone ellipsoid in the adult Tupaia are filled with several megamitochondria.…”

Section: Discussionsupporting

confidence: 73%

“…Furthermore, according to Bereiter-Hahn (1990), the condensed conformation of cristae may represent the low-energy state of mitochondria (see Bereiter-Hahn, 1990, and references therein). In agreement with these observations, Knabe et al (1997) argued that many of the morphological traits of megamitochondria of the retina cone inner segment cannot be related to known metabolic functions. They proposed that these organelles have an optical function, and that the numerous and small mitochondria that surround them are responsible for the active metabolism of cones because of their more favorable surface-to-volume ratio.…”

Section: Discussionmentioning

confidence: 59%

“…Furthermore, because the giant mitochondria act on individual photoreceptors, they may have an advantage over the lens and cornea. As in Tupaia (Knabe et al, 1997), the nuclei of cones in Sorex are arranged in one row, the cone inner segments are wider than the outer segments, and the outer segments of the adjacent cone nuclei are widely separated. Consequently, the presence of a solid fusiform mass of megamitochondria may favor strong refraction of light falling upon the lateral sides of the inner segment toward discs of the outer segments.…”

Section: Discussionmentioning

confidence: 99%

“…The results of this study are compared from a morphological and functional viewpoint with those reported by Knabe et al (1997) for Tupaia.…”

mentioning

confidence: 95%

“…Although ellipsoid mitochondria show a wide range of shapes and sizes, unusual and modified forms have also been described (Ishikawa and Yamada, 1969). The characteristics of some of these modified mitochondria (like those of ellipsosomes in some teleost fish; oil droplets in several birds, reptiles, amphibians, and monotreme mammals; and megamitochondria in Tupaia) have been related to the improvement of photoreceptor optics (Walls, 1963;Ishikawa and Yamada, 1969;Nag and Bhattacharjee, 1995;Knabe et al, 1997;Douglas and Marshall, 1999). They may alter the spectral composition of transmitted light, by acting as short-wave filters or even as a microlenses to enhance the optical function of cones.…”

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confidence: 99%

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Giant mitochondria in the retina cone inner segments of shrews of genus Sorex (Insectivora, Soricidae)

2003

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The retinas of three species of shrews (Sorex araneus, S. coronatus, and S. minutus) were analyzed. Two kinds of photoreceptors were identified according to (among other characteristics) the traits of the mitochondria of their inner segments. The rod inner segments contained several round or oval mitochondria distributed longitudinally inside the ellipsoid. The cone inner segment showed a few mitochondria, which we classified as megamitochondria (maximum length ϭ 4.22 m in S. araneus, 5.68 m in S. coronatus, and 2.42 m in S. minutus). An analysis of serial thin sections in S. coronatus showed that these large organelles occurred in the apical and central portions of the ellipsoid. In the peripheral and basal regions of the ellipsoid, megamitochondria were frequently accompanied by smaller mitochondria. The giant mitochondria were irregular in form and densely packed, and a reduced cytosol was observed between each mitochondria. In general, they exhibited an electron-dense matrix and a complex system of cristae, which varied in length and array. In mammalian retina, megamitochondria have only been described in the ellipsoid of the tree shrews Tupaia glis and T. belangeri, two diurnal Scandentia with a rich-cone retina. In general terms, Sorex megamitochondria are morphologically very similar to those reported for Tupaia, especially in their arrangement in the cone ellipsoid. However, they differ in the orientation of the cristae. We propose that the ellipsoid of Sorex may serve two functions: as a source of energy for receptor cells, and as a device for improving the cone outer segment optics. Anat Rec Part A 272A: 484 -490, 2003.

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Section: Discussionsupporting

confidence: 73%

Section: Discussionmentioning

confidence: 59%

Section: Discussionmentioning

confidence: 99%

“…The results of this study are compared from a morphological and functional viewpoint with those reported by Knabe et al (1997) for Tupaia.…”

mentioning

confidence: 95%

mentioning

confidence: 99%

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Giant mitochondria in the retina cone inner segments of shrews of genus Sorex (Insectivora, Soricidae)

2003

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Pattern of cell death during optic cup formation in the tree shrewTupaia belangeri

Knabe

Kuhn

1998

J. Comp. Neurol.

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Developmental cell death during optic cup formation was investigated in the tree shrew Tupaia belangeri. Twenty-six embryos from days 12 to 16 of prenatal ontogenesis were studied by light microscopy. Prior to the optic vesicle stage, a dorsal area of cell death surrounded the lumen of the V-shaped optic evagination (phase 1). A ventral band of dead cells, found in the optic vesicle (phase 2), preceded a dorsal focus of cell death (phase 3) previously described as a characteristic avian feature. During further invagination (phase 4), a peak of cell death was represented by a ventrodorsal band extending from the diencephalon over the complete optic anlage. The main areas of cell death found in phases 2 to 4 were, topographically, segments of this band. Also, the distinct areas of cell death reported in the literature for the vertebrate species studied so far fit well into this ventrodorsal band found in Tupaia. Thus, most probably, a common spatio-temporal sequence of cell death exists in all of them. In Tupaia, dead cells concentrated at the diencephalic insertion of the optic stalk, the suboptic necrotic center (SONC) reported by several authors, were part of the early ventral band of cell death originating from the median floor of the prosencephalon (phase 2). During optic cup formation, the SONC was part of the ventrodorsal band and, thus, was not secondarily formed by the subdivision of a pre-existing distal ventral area of cell death as reported for several other vertebrates.

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Belief vs. scientific observation: The curious story of the precardiac mesoderm

Eisenberg

2002

Anat. Rec.

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The retinas of three species of shrews (Sorex araneus, S. coronatus, and S. minutus) were analyzed. Two kinds of photoreceptors were identified according to (among other characteristics) the traits of the mitochondria of their inner segments. The rod inner segments contained several round or oval mitochondria distributed longitudinally inside the ellipsoid. The cone inner segment showed a few mitochondria, which we classified as megamitochondria (maximum length = 4.22 μm in S. araneus, 5.68 μm in S. coronatus, and 2.42 μm in S. minutus). An analysis of serial thin sections in S. coronatus showed that these large organelles occurred in the apical and central portions of the ellipsoid. In the peripheral and basal regions of the ellipsoid, megamitochondria were frequently accompanied by smaller mitochondria. The giant mitochondria were irregular in form and densely packed, and a reduced cytosol was observed between each mitochondria. In general, they exhibited an electron‐dense matrix and a complex system of cristae, which varied in length and array. In mammalian retina, megamitochondria have only been described in the ellipsoid of the tree shrews Tupaia glis and T. belangeri, two diurnal Scandentia with a rich‐cone retina. In general terms, Sorex megamitochondria are morphologically very similar to those reported for Tupaia, especially in their arrangement in the cone ellipsoid. However, they differ in the orientation of the cristae. We propose that the ellipsoid of Sorex may serve two functions: as a source of energy for receptor cells, and as a device for improving the cone outer segment optics. Anat Rec Part A 272A:484–490, 2003. © 2003 Wiley‐Liss, Inc.

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“Lens Mitochondria” in the Retinal Cones of the Tree-shrew Tupaia belangeri

Cited by 45 publications

References 22 publications

Giant mitochondria in the retina cone inner segments of shrews of genus Sorex (Insectivora, Soricidae)

Giant mitochondria in the retina cone inner segments of shrews of genus Sorex (Insectivora, Soricidae)

Pattern of cell death during optic cup formation in the tree shrewTupaia belangeri

Belief vs. scientific observation: The curious story of the precardiac mesoderm

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