Cellular autonomy
Hake S and Freeling M
Analysis of genetic mosaics show that the extra epidermal cell divisions in Knotted mutant maize plants are induced by adjacent mesophiyll cells.
Nature 320: 621-623, 1986

This is the first class of this year's Developmental Biology course.

While many courses are designed to "provide knowledge" to the participants, the primary objective of this course is to nurture the ability to "think critically". The class will be run by using primary literature as a course material and discussing on the topic. The lecturers (or rather, the discussion leader) of each session are not necessarily experts in the topic covered by the paper, but have chosen the topic and the paper because they have identified some interesting aspect that they would like to share and discuss with the participants.

The topic of this session is "Cellular autonomy (細胞自律性)". In studying developmental events we often employ genetic manipulations (e.g. mutants) to disrupt or alter gene activity, and infer the role of such gene activity in a particular developmental process by examining the consequence of such manipulation (e.g. the phenotype of a mutation). "Cellular autonomy" is the correlation between the genotype of the cell and the phenotype that the cell exhibits. The presence or absence of cellular autonomy can provide useful information on the mode of action of the gene, even when we do not know what the gene actually encodes.

The paper that we are going to discuss on October 22 deals with the morphogenesis of the plant leaf, which consists of three layers; the inner mesophyll (葉肉) layer sandwiched by upper and lower epidermis (上皮). (For the anatomy of the leaf see the following URL: http://en.wikipedia.org/wiki/Mesophyll_tissue#Anatomy). The authors study the phenotype of a maize (トウモロコシ) mutant called Knotted, whose leaf produces hollow outpockets of tissues, or "knots". This is caused by extra cell devisions in the leaf, both in the epidermis and the mesophill. The authors are trying to analyze how this cell division phenotype is caused, by examining "genetic mosaics", i.e. plants that consists of a mixture of Knotted mutant and normal cells. Knotted is a dominant mutation, so here the mutant allele is designated "Kn", and the normal allele is designated "kn". In mosaics, the genotype of the mutant cell is Kn/kn, and the that of normal cells is -/kn, i.e. the Kn mutant allele is lost by chromosomal breakage. To identify the genotype of each cell, the lw mutation, which causes the loss of chlorophill, is used, because it is tightly linked to the Kn mutation.

Many of you may not be familiar with "fate-mapping" or "gynandromorph studies" mentioned in the first paragraph. We will explain these terms in class.

See you next Monday, either in class or through the remote lecture system!