Chapter 11 Germ cells, fertilization and sex

Determination of the sexual phenotypeSex chromosomes

Chapter 14— Sex determinationDevelopmental Biology by Scott Gilbert

The sex chromosome in humans

Fig. 11-16

Mammals : Y chromosomeAlligator : environmental temperatureFish: switch sexDrosophila: chromosome contentCompensation of chromosomal composition

Figure 14.1 Sex determination in mammals (Part 1)

Development of the gonads

Fig. 11-18

SRY--Testes—Mullerian-inhibiting substance—suppress female reproductive organand induce cells to be Leydig cells—secrets testosterone

Sex phenotypes controlled by hormone

Figure 14.1 Sex determination in mammals (Part 2)

Figure 14.2 Differentiation of human gonads shown in transverse section (Part 1)

Figure 14.2 Differentiation of human gonads shown in transverse section (Part 2)

Sertoli cells

Sperm

Figure 14.2 Differentiation of human gonads shown in transverse section (Part 3)

GC-ovaGranulosa and thecal cellsfollicle

Figure 14.4 Possible mechanism for the initiation of primary sex determination in mammals

1

2

3

Sox9/Fgf9

Wnt4/b-catenin

Sex reversal in humans

Fig. 11-17

Y chromosome—embryo’s gonads—develop into testesSingle gene—sex-determining region of the Y chromosome (SRY)

Klinefelter syndrome: XXY—males but infertile

Turner syndrome: XO—female but no eggs

XY femalesXX malesCorssing over

XX+SRY gene-infertile male

Figure 14.6 An XX mouse transgenic for Sry is male

Figure 14.7 Ability of Sox9 to generate testes

Figure 14.10 Model for the formation of external genitalia

Figure 14.14 Organization of brain development by hormones

Figure 14.15 Masculinization of the brain by hormones (Part 1)

Figure 14.15 Masculinization of the brain by hormones (Part 2)

GenitaliaSex combPigmentationSmall wing

Fig. 11-20

XX femaleXY maleXXY femaleX male

Sex determining signal--- Sex-lethal (X chromosome)Sex-specific RNA splicing

Transformer-spliced + transformer 2

transformer doublesex

Figure 14.17 Proposed regulatory cascade for Drosophila somatic sex determination (Part 1)

Figure 14.17 Proposed regulatory cascade for Drosophila somatic sex determination (Part 2)

Dosage compensation

Barr bodyXist-non-coding RNA

Male specific geneRepressed by Sxl

2X higher numerator—binding to Pe Repression by autosome

Autoregulatory loopPost-transcriptional levels

Figure 14.18 Sex-specific RNA splicing in four major Drosophila sex-determining genes

Figure 14.20 Roles of DsxM and DsxF proteins in Drosophila sexual development (Part 1)

Figure 14.20 Roles of DsxM and DsxF proteins in Drosophila sexual development (Part 2)

Mating in fruit flies

Figure 14.21 Subsets of neurons expressing the male-specific form of fruitless

2006 WINNER

• A cluster of Fruitless-expressing neurons in the Drosophila brain has been found to differ between male and females. This difference is produced by active elimination of neuronal precursor cells in females. The male-specific Fruitless protein inhibits programmed cell death in a cluster of neurons, allowing them to form a neural circuit that directs males to court females and not males. This research shows how a single gene can direct brain development and subsequently a sex-specific behavior. In this framework, sexual orientation can be understood in relation to an identified neuronal circuit and defined actions of a sex-determination gene.

• This figure shows the projection pattern of sexually dimorphic mAL (medially located, just above Antennal Lobe) neurons in the brain of a female (left) and a male (right).

• Kimura, K.-I., Ote. M, Tazawa, T and Yamamoto, D. Fruitless specifies sexually dimorphic neural circuitry in the Drosophila brain. Nature, vol. 438, 229-233 (2005).

C. elegans

Self-fertilizing-limited amount of spermXO lethal(xol-1)—repressed by SEX-1 on X chromosome

Somatic sex determination pathway in C elegans

Egl-1—death of neurons associated in the hermaphrodite with egg laying

Signals specify germ-cell sex in mammals

Determination of germ-cell sex in the hermaphrodite gonad

Tips: germ cell multiplyMeiosis--sperm

Adult: proliferative zone--oocytes

Figure 14.22 Temperature-dependent sex determination in three species of reptiles

Figure 14.24 the feminization of male frogs and the decline of frog populations in regions where atrazine has

been used to control weed populations Atrasine