Embryology and Development Chapter 5

Vocabulary flashcards covering the developmental biology, genetics, and molecular mechanisms of the model organism C. elegans.

Hermaphrodite

A self-fertilizing sex in C. elegans that produces all its sperm ($150$ sperm per gonadal arm) during the L4 stage and subsequently produces only oocytes ($isolecithal$ eggs).

Amoeboid spermatozoa

Non-flagellated sperm cells in C. elegans stored in the spermatheca where fertilization occurs as eggs pass through.

P0

The name of the zygote formed after the sperm and egg pronuclei fuse; its posterior end is specified by the position of the sperm pronucleus.

Rotational holoblastic cleavage

The cleavage pattern seen in C. elegans and mammals where second cleavage mitotic orientations are equatorial for the AB cell and meridional for the P1 cell.

AB cell

The larger anterior founder cell resulting from the first unequal meridional cleavage of the P0 zygote.

P1 cell

The smaller posterior cell resulting from the first unequal meridional cleavage of the P0 zygote.

P granules

Large ribonucleoprotein (RNP) particles in C. elegans that migrate toward the P cell lineage and are associated with RNA metabolism and posttranscriptional regulation.

Autonomous specification

A type of cell specification based internally on cell lineage, exemplified by the P germ cell lineage in C. elegans.

Conditional specification

Specification that relies on interactions with neighboring cells, such as the EMS cell requiring signals from the P2 cell.

SKN-1

A maternal transcription factor necessary for the EMS cell lineage to produce gut and pharyngeal muscle; mutations lead to the production of skin tissue instead.

MOM-2

A maternal signal and Wnt homolog produced by the P2 cell that is necessary for gut development from the EMS cell lineage.

MOM-5

A maternal Frizzled homolog receptor on the EMS cell that is activated by the MOM-2 signal.

Rhabditin granules

A gut tissue-specific marker used to observe differentiation in the EMS cell lineage.

959

The exact number of somatic cells in a normal adult hermaphrodite C. elegans.

Space and Temporal Gradients

Spatial gradients involve unequal distribution of cytoplasmic morphogens (e.g., P-granules), while temporal gradients involve local morphogen concentration variations over time.

Heterochronic genes

Genes like lin-4 and lin-14 whose expression varies over time and whose abnormal expression causes structures to develop at incorrect times.

lin-14

A heterochronic gene whose translation is normally stopped at the L2 stage to halt the proliferation of the T blast cell lineage.

lin-4

A gene coding for a microRNA (miRNA) that is antisense to the $3'\,UTR$ of lin-14 mRNA, blocking its translation.

RNA interference (RNAi)

A cellular mechanism discovered by Andrew Fire and Craig Mello that recognizes and destroys invading double-stranded RNAs ($dsRNAs$) to silence gene function.

Dicer

A ribonuclease ($RNase$) that cleaves entering double-stranded RNA into short pieces called small interfering RNAs ($siRNAs$).

Argonaute (AGO)

A protein that separates $siRNA$ strands and remains bound to a single strand to form the RNA-induced silencing complex (Argonaute/RISC).

Equivalence group

A group of cells with the same potency but different fates, such as the six vulval precursor cells (VPCs).

Vulval precursor cells (VPCs)

Six blast cells (P3p, P4p, P5p, P6p, P7p, and P8p) derived from the ABp blastomere that have the potency to form the vulva.

Anchor cell

A cell in the gonad that provides the inductive signal (LIN-3) to specify the primary fate of the closest vulval precursor cell.

LIN-3

An inductive signal from the anchor cell that activates vulval genes; high amounts imprint the primary fate on P6p.

Delta

A lateral juxtacrine signal expressed by P6p that activates the lin-12 gene in P5p and P7p, inducing them to adopt the secondary fate.

Apoptosis

An active, energy-dependent series of programmed cellular events leading to cell death, distinct from accidental death (necrosis).

131

The number of cells eliminated by apoptosis during the normal embryonic development of C. elegans.

Ced-3

A pro-apoptotic protease in C. elegans that acts as the executioner of apoptosis; loss-of-function mutants show survival of cells that should die.

Ced-4

A protein required for the activation of the Ced-3 protease during the process of apoptosis.

Ced-9

An anti-apoptotic protein that inhibits Ced-4 to prevent cell death; null mutations lead to the death of the developing animal.