Organelle Inheritance

The need to inherit those membranes that arise from the ER is much less clear. As an example, the integral *Imperial Cancer Research Fund Cell Biology Laboratory membrane proteins and lipids of the Golgi apparatus are derived entirely from the ER. If a daughter did not 44 Lincoln's Inn Fields London WC2A 3PX inherit a copy of the Golgi apparatus, it should be able to synthesize one de novo. Several experiments suggest United Kingdom † Department of Biochemistry that this is possible but slow (Zorn et al. of an inheritance mechanism. The time taken to grow a new Golgi apparatus de novo would put an organism, especially a unicellular organism, at a strong selective Introduction disadvantage in a competitive environment. Every membrane-bordered organelle in a particular cell type has a characteristic copy number, size, and position , which reflect its cellular function. Mitochondria, for Partitioning Strategies example, are often located near organelles that con-Studies on the inheritance of chloroplasts and mito-sume energy, and their number is determined by the chondria in the early part of this century laid the founda-magnitude of these energy needs. They are abundant tions for the study of organelle inheritance. Of particular in muscle cells, where they are interwoven with the myo-note are the pioneering studies on mitochondrial inheri-fibrils that generate mechanical force; in sperm cells, tance by E. B. Wilson (1925). These studies, which identi-they are tightly wrapped around the flagellum, providing fied the different inheritance strategies, were later the energy needed for movement; in ion-transporting placed on a more quantitative footing by Birky (1983b). epithelial cells, they are interdigitated with extensive Perhaps the most important early discovery was the infoldings of the plasma membrane, across which a high observation that the inheritance strategy adopted by a flux of ions is pumped; last, they are packed together particular organelle varied from cell type to cell type and in longitudinal arrays in the inner segments of retinal from organism to organism. Even within a particular cell rods and cones, where they provide energy for the pho-type, different organelles could use different strategies. totransduction process. The inheritance of cellular organelles therefore differs During the cell cycle, each organelle must double in fundamentally from the inheritance of chromosomes, size, divide, and be delivered to its proper location in where a single, universal strategy is used, based on the the daughter cells. This problem has fascinated cell biol-mitotic spindle …