Mammalian chimaeras / Anne McLaren.

  • McLaren, Anne.
Date:
[1976]
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Mammalian chimaeras / Anne McLaren. Source: Wellcome Collection.

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    Musculature and neural system 73 Fig. 27. Section of the retina of a C57BL<->C3H chimaera, showing an area (to the left) in which photoreceptor cells have degenerated so that only one or two rows of photoreceptor nuclei (PN) remain. The number of rows increases to the normal 8-10 on the right. The rod outer segments (OS) decrease in length along with the reduction in nuclei. From Wegmann, LaVail & Sidman (19716). structure of a bone that develops from a cartilaginous blastema, is to focus attention on a character several steps away from the underlying tissue patch¬ work. To throw light on cell lineage a gene is required with effects that can be identified in individual cells, and that acts strictly intracellularly. Few such genes are known for the mammalian nervous system. A possible candidate is the recessive gene for retinal degeneration (ri/), homozygous in the C3H strain, that causes partial or complete blindness through postnatal degenera¬ tion of the neural retina. Chimaeras between C3H and C57BL or other genetically normal embryos showed areas of degeneration in the retina (Fig. 27), interspersed with areas of partially affected or normal tissue (Mintz & Sanyal, 1970; Mintz, 1971c; Wegmann e/ a!., 19716). The existence of inter¬ mediate areas raises the suspicion that rd may not act strictly intracellularly, or alternatively that cell migration occurs to a significant degree (West, 1976öi). Mintz & Sanyal report that the normal and degenerating patches conform to a basic plan involving ten radiating sectors per retina; they identify each sector as a single clone. When chimaeras were made involving differences in the pigmented retina as well as in the neural retina, no correspondence was seen in the quantitative proportions and location of the areas of albinism and of degeneration in a single eye, suggesting that, as would seem plausible on embryological grounds, the two layers involve separate cell lineages.