Mammalian and Drosophila Sex Determination & Developmental Biology

What is the default phenotypic sex in mammals?

Female

What determines male sex in mammals?

Presence of a Y chromosome carrying SRY

What is the default phenotypic sex in Drosophila?

Male

What determines sex in Drosophila?

The X:A ratio

What is the phenotypic sex for XX genotype in mammals?

Female

What is the phenotypic sex for XY genotype in mammals?

Male

What is the phenotypic sex for XXY genotype in mammals?

Typically male (Klinefelter syndrome)

What is the phenotypic sex for XO genotype in mammals?

Typically female (Turner syndrome)

What is the phenotypic sex for XX genotype in Drosophila?

Female

What is the phenotypic sex for XY genotype in Drosophila?

Male

What is the phenotypic sex for XXY genotype in Drosophila?

Female

What is the phenotypic sex for XX genotype in C. elegans?

Hermaphrodite

What is the phenotypic sex for XO genotype in C. elegans?

Male

How is phenotypic sex regulated in mammals?

SRY initiates testis formation; absence leads to ovary development.

How is phenotypic sex regulated in Drosophila?

X:A ratio activates Sxl, leading to female differentiation.

What is dosage compensation in mammals?

X-inactivation (Lyonization) in XX females.

How do Drosophila achieve dosage compensation?

Male X hypertranscription via the MSL complex.

What are intrinsic factors in growth regulation?

Cell-autonomous gene programs, lineage growth rates, metabolism.

What are extrinsic factors in growth regulation?

Growth factors, hormones, nutrient availability, mechanical forces.

Why do cancer biologists study developmental biology?

Cancer re-uses developmental programs and key signaling pathways.

What is the effect of prolonged telomerase activity in adults?

Increased cancer risk and delayed replicative senescence.

How do Hox genes determine positional identity?

Combinatorial expression creates a positional code for tissues.

What does the AER do in chick limb development?

Secretes FGFs to promote limb outgrowth.

What does the ZPA do in chick limb development?

Secretes SHH for anterior-posterior positional information.

What happens if the AER is removed from a chick limb?

Limb truncation occurs, showing AER is necessary for distal outgrowth.

What does grafting ZPA to the anterior margin of a limb bud cause?

Mirror-image duplications of digits.

What happens if a limb bud is rotated 180°?

Dorsoventral changes occur due to ectodermal signals.

What does limb formation depend on?

Local organizers and inductive signals.

What are the roles of HoxA and HoxD clusters in limb development?

They help specify proximal-distal segments and identity of structures.

What happens when Hox expression is altered?

It shifts segment identity or causes malformations.

What are the two main models of proximo-distal development?

Progress zone model and early specification model.

What does the progress zone model propose?

Cells acquire positional identity by the time spent in the distal progress zone.

What does the early specification model suggest?

Proximal vs distal fates are specified early by opposing signals.

How can the progress zone model be tested experimentally?

By removing AER at different times and observing segment loss.

What is the significance of transplanting distal cells to proximal locations?

It helps determine if fate is specified early or if they adopt new fate.

What regulates somite formation?

The segmentation clock and wavefront model.

How does the segmentation clock and wavefront model work?

Oscillatory gene expression interacts with a moving determination front.

What factors influence somite size and number?

Embryo growth, temperature, and experimental perturbations.

How does cyclic gene expression regulate somite formation?

Oscillating expression of clock genes creates a temporal rhythm.

What is the role of SHH signaling in neuronal identity?

SHH forms a gradient that influences progenitor domain identity.

What regulates endodermal development in Xenopus?

Maternal determinants and localized cytoplasmic factors activate Nodal/Activin signaling.

How does mesoderm develop different identities?

It depends on position relative to organizer and signals received during gastrulation.

What types of cellular movement occur during gastrulation?

Invagination, involution, ingression, epiboly, convergent extension, and delamination.

What movements characterize gastrulation in Xenopus?

Large-scale involution, convergent extension, and bottle-cell-driven invagination.

What movements characterize gastrulation in chick/mammal?

Ingression through a primitive streak and convergent extension during elongation.

What are the cell adhesion changes during epithelial-to-mesenchymal transition (EMT)?

Downregulate E-cadherin and upregulate N-cadherin and integrins.

What is the shape of the mouse epiblast during early development?

Forms an egg-cylinder structure.

What is the shape of the human epiblast during early development?

Forms a flat bilaminar embryonic disc.

How do differences in epiblast geometry affect development?

They influence primitive streak formation and spatial patterning.

What are the three germ layers?

Ectoderm, Endoderm, Mesoderm

What model is used for fate mapping in germ layer development?

Xenopus model

What is the role of the Spemann organizer?

Required for proper germ layer development

What are some maternal factors involved in germ layer development?

VegT, Vg-1, XWnt-11

What does FoxI1e activate in the Xenopus blastula?

Ectoderm formation and controls cell position

What is the hypothesis regarding FoxI1e?

Whether FoxI1e participates in ectodermal specification

What does ectodermin inhibit?

VegT

What is the effect of FoxI1e on Smad4?

Ubiquinates Smad4

Is mesoderm dependent on maternal factors?

No, it is not dependent

What induces mesoderm from prospective ectoderm?

Signal from the endoderm

What is the significance of differential BMP activation?

BMP is expressed across the blastula, influencing development

What inhibits BMP around the Spemann organizer?

Chordin and noggin

What are the conditions for dorsal and ventral differentiation in mesoderm?

High Nodal + low BMP/Wnt → dorsal (notochord); Low Nodal + high BMP/Wnt → ventral (blood)

What are the conditions for neural and epithelial differentiation in ectoderm?

Low BMP + Foxl1E → neural; High BMP + Foxl1E → epithelial

Ectoderm

The outermost layer of cells in an embryo, which develops into the skin, nervous system, and other structures.

Ectodermin

A protein that plays a role in the inhibition of VegT, influencing cell fate during embryonic development.

VegT

A transcription factor that is crucial for mesoderm and endoderm formation in early embryonic development.

Ubiquitination of Smad4

A process where a ubiquitin molecule is attached to Smad4, marking it for degradation and regulating signaling pathways.

Mesoderm

The middle layer of cells in an embryo, which develops into muscles, bones, and the circulatory system.

Spemann organizer

A group of cells in the developing embryo that plays a key role in organizing the body plan and inducing the formation of the nervous system.

Differential Wnt-11 signaling

A process involving the Wnt signaling pathway that helps establish mesoderm identity along the dorsal/ventral axis in embryonic development.

BMP (Bone Morphogenetic Protein)

A group of growth factors known to play a role in bone and cartilage development, as well as in embryonic patterning.

Differential mesoderm identities

The specification of mesodermal tissues based on varying levels of signaling molecules, such as Nodal and BMP/Wnt.

Dorsal mesoderm

Characterized by high Nodal and low BMP/Wnt signaling, leading to the formation of the notochord.

Ventral mesoderm

Characterized by low Nodal and high BMP/Wnt signaling, leading to the formation of blood.

Differential ectoderm

The specification of ectodermal tissues based on BMP signaling and the presence of transcription factors like Foxl1E.

Neurulation

The process following gastrulation during which the neural tube forms from the ectoderm.

Spemann Organizer

A region in the developing embryo that plays a crucial role in organizing the development of the nervous system.

BMP-4

A signaling molecule from the ectoderm that inhibits neural development.

Noggin and Chordin

Proteins that inhibit BMP-4, promoting neural development.

Neural tube formation

The process by which the neural plate folds and fuses to form the neural tube, which will develop into the central nervous system.

Ingression

The process by which neural crest cells migrate away from the neural tube during development.

Convergent extension

A morphogenetic process where cells intercalate to narrow and elongate the tissue, typically occurring in the anterior-posterior direction.

Primitive streak

Structure that forms during early embryonic development.

Notochord

A rod-like structure that provides support in embryonic development.

Neural tube formation

Process by which the neural plate folds to form the neural tube.

Involution

Movement of cells inward during development.

Cell adhesion change

Alterations in how cells stick to each other, involving L-CAM, N-cadherin, N-CAM, and E-cadherin.

Convergent extension

Process that narrows and elongates the tissue to seal the epidermis.

Ingression

Process where neural crest cells migrate into the embryo.

CNS differentiation

Development of the central nervous system from the neural tube.

Anterior/posterior axis of neural tube

Orientation of the neural tube regulated by the notochord.

Neurogenesis

The process of generating new neurons.

Morphogen

Substance that governs the pattern of tissue development.

Hox genes

Transcription factors that regulate segmentation in development.

What is somitogenesis?

The creation of somites.

What is the equivalent of somitogenesis in Drosophila?

Segmentation.

What are somites derived from?

Discrete portions of mesoderm.

What structures do somites contribute to?

Ribs, skeletal muscle, spinal column, dermis.

What is the direction of primitive streak regression?

Anterior to posterior (A→P).

What is regulated by Hensen's node?

Mesenchymal-to-epithelial transition.