Chapter 11 Germ cells, fertilization and sex Determination of the sexual phenotype Sex chromosomes Chapter 14— Sex determination Developmental Biology by Scott Gilbert

The sex chromosome in humans Mammals : Y chromosome Alligator : environmental temperature Fish: switch sex Drosophila: chromosome content Compensation of chromosomal composition Fig. 11-16

Figure 14.1 Sex determination in mammals (Part 1) DevBio9e-Fig-14-01-1R.jpg

Development of the gonads SRY--Testes—Mullerian-inhibiting substance —suppress female reproductive organ and induce cells to be Leydig cells— secrets testosterone Sex phenotypes controlled by hormone Fig. 11-18

Figure 14.1 Sex determination in mammals (Part 2) DevBio9e-Fig-14-01-2R.jpg

Figure 14.2 Differentiation of human gonads shown in transverse section (Part 1) DevBio9e-Fig-14-02-1R.jpg

Figure 14.2 Differentiation of human gonads shown in transverse section (Part 2) Sertoli cells Sperm DevBio9e-Fig-14-02-2R.jpg

Figure 14.2 Differentiation of human gonads shown in transverse section (Part 3) DevBio9e-Fig-14-02-3R.jpg GC-ova Granulosa and thecal cells follicle

Figure 14.4 Possible mechanism for the initiation of primary sex determination in mammals Sox9/Fgf9 DevBio9e-Fig-14-04-0.jpg 3 1 2 Wnt4/b-catenin

Sex reversal in humans Y chromosome—embryo’s gonads —develop into testes Single gene—sex-determining region of the Y chromosome (SRY) Klinefelter syndrome: XXY —males but infertile Turner syndrome: XO—female but no eggs XY females XX males Corssing over XX+SRY gene-infertile male Fig. 11-17

Figure 14.6 An XX mouse transgenic for Sry is male DevBio9e-Fig-14-06-0.jpg

Figure 14.7 Ability of Sox9 to generate testes DevBio9e-Fig-14-07-0.jpg

Figure 14.10 Model for the formation of external genitalia DevBio9e-Fig-14-10-0.jpg

Figure 14.14 Organization of brain development by hormones DevBio9e-Fig-14-14-0.jpg

Figure 14.15 Masculinization of the brain by hormones (Part 1) DevBio9e-Fig-14-15-1R.jpg

Figure 14.15 Masculinization of the brain by hormones (Part 2) DevBio9e-Fig-14-15-2R.jpg

Genitalia Sex comb Pigmentation Small wing XX female XY male XXY female X male Fig. 11-20

Sex determining signal--- Sex-lethal (X chromosome) Sex-specific RNA splicing transformer doublesex Transformer-spliced + transformer 2

Figure 14.17 Proposed regulatory cascade for Drosophila somatic sex determination (Part 1) DevBio9e-Fig-14-17-1R.jpg

Figure 14.17 Proposed regulatory cascade for Drosophila somatic sex determination (Part 2) DevBio9e-Fig-14-17-2R.jpg

Dosage compensation Barr body Xist-non-coding RNA Male specific gene Repressed by Sxl

Repression by autosome 2X higher numerator—binding to Pe Autoregulatory loop Post-transcriptional levels

Figure 14.18 Sex-specific RNA splicing in four major Drosophila sex-determining genes DevBio9e-Fig-14-18-0.jpg

Figure 14.20 Roles of DsxM and DsxF proteins in Drosophila sexual development (Part 1) DevBio9e-Fig-14-20-1R.jpg

Figure 14.20 Roles of DsxM and DsxF proteins in Drosophila sexual development (Part 2) DevBio9e-Fig-14-20-2R.jpg

Mating in fruit flies

Figure 14.21 Subsets of neurons expressing the male-specific form of fruitless DevBio9e-Fig-14-21-0.jpg

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 sperm XO 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 multiply Meiosis--sperm Adult: proliferative zone--oocytes

Figure 14.22 Temperature-dependent sex determination in three species of reptiles DevBio9e-Fig-14-22-0.jpg

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 DevBio9e-Fig-14-24-2R.jpg