Effects of alterations of cell size and number on the structure and function of the Xenopus laevis nervous system.

Abstract

The evolution of the vertebrate central nervous system has involved increasing cell numbers and overall relative size, allometric changes in different brain regions, and quantitative and qualitative alterations in the interactions between different regions of the nervous system. The importance of genetic changes which alter the metrics of interactions between developing organ systems for evolutionary change has been stressed by Gould (1977). Yet relatively little evidence is available from experimental studies to support the idea that allometric changes, such as changes in cell size, cell number or the relative sizes of different organs within the vertebrate nervous system can cause qualitative as well as quantitative changes in structure and function. Recent advances in the genetics of Xenopus laevis have permitted us to investigate some of these effects. The results support the hypothesis that relatively simple alterations in cell size and numbers can cause both qualitative and quantitative changes in morphology and function of the nervous system.