Outline

7.1 The Death of Many Cells Is a Normal Process in Development

7.2 The Extent of Death among Developing Motor Neurons Is Regulated by the Size of the Target

• RESEARCHERS AT WORK Adding to the Periphery Prevents Apoptosis of Motor Neurons

7.3 Nerve Growth Factor (NGF) Is Discovered to Regulate Apoptosis in Sensory Neurons

• RESEARCHERS AT WORK Screening for Nerve Growth Factor
• BOX 7.1 THE CONTROVERSY OVER THE NOBEL PRIZE FOR NGF

7.4 NGF Has Both Tropic and Trophic Effects on Selective Neuronal Populations

7.5 The Search for Relatives of NGF Reveals a Family of Neurotrophic Factors and Their Receptors

7.6 Studies in C. elegans Provide Crucial Information about the Process of Apoptosis

• BOX 7.2 KERFUFFLES IN LANGUAGE: PROGRAMMED CELL DEATH
• RESEARCHERS AT WORK It Was Suicide, Not Murder

7.7 Apoptosis Involves Active Self- Destruction through a Cascade of “Death Genes”

7.8 Do Motor Neurons Die in ALS for Lack of Neurotrophic Factor(s)?

7.9 Hormones Direct Sexual Differentiation of the Vertebrate Body and Behavior

• RESEARCHERS AT WORK Early Exposure to Androgens Organizes the Male Brain

7.10 The Brain Is Also Sexually Dimorphic

7.11 Hormones Can Regulate Apoptosis to Masculinize the Vertebrate Brain

• RESEARCHERS AT WORK Sometimes the Tail Wags the Dog

7.12 Sexual Differentiation in Flies Is a Cell- Autonomous Process

• RESEARCHERS AT WORK Fruitless Mutants Pursue Unrequited Love

7.13 The Controversy over Sexual Orientation in Flies, Rats, and People