BIOL 216 TOPIC 2.2-2.3

Motility, shape, adhesion

Gastrulation involves a major reorganizing of the blastula and key changes in cell ________, ________, and __________.

Migrate, differentiation

During gastrulation, cell motility changes as cells ______ and reposition during germ layer __________.

Cytoskeleton

During gastrulation, cell shape changes as the _________ remodels for folding and expansion.

Tissue, adhere, extracellular

During gastrulation, cell adhesion changes as _________ assembly guides which cells ______ to other cells and the _______ matrix.

Invagination

Cell movement in which cells fold inward to form a cavity/tube. The cells engaged in this movement are called an epithelial sheet.

Ingression

Cell movement in which individual cells exit the epithelial sheet and become freely moving mesenchyme cells.

Involution

Cell movement in which the epithelial sheet bends under a layer of pre-existing cells, forming a dual layer.

Epiboly

Cell movement in which a sheet of cells thins via spreading.

Intercalation

Cell movement in which a double layer of cells merges into one longer, thinner layer.

Convergent Extension

Cell movement in which rows of cells intercalate, highly directional.

Neurulation

The fundamental developmental process of neural tube formation in the embryo.

Invaginates, groove, folds

The first step in neurulation is primary neurulation. In this step, the neural plate, which is formed by ectoderm cells and was induced to thicken and differentiate due to mesoderm signaling, _______ and forms the neural ______. Elevated neural _______ form on each side of the groove until eventually they approach each other and fuse, forming the the top part of the neural tube.

Precursor, hollows, crest

The second step in neurulation is secondary neurulation. In this step, a _________ cell mass sinks into the embryo and _______ out, forming the bottom half of the neural tube. Neural _______ cells migrate and become many different kinds of tissue.

Closes, central nervous system

The third step in neurulation is neural tube closure. In this step, the neural tube _____ off, ensuring protection of the precursor __________.

Differentiate, primary nervous system

The fourth step in neurulation is differentiation and fate. In this step, regions of the tube ________ into ____________ organs.

Somites

Formed from mesoderm, segmented tissue blocks which will become vertebrae and skeletal muscle.

Notochord

Much of it disappears before birth, but some goes on to become inner vertebral disc.

Cadherin

Transmembrane proteins that play an important role in cell adhesion.

Migrate, associate, differentiate, gene expression, signaling

Cells fated to become different organs ______, _______, and _________. This leads to organ creation and is regulated by ____________ and cell _________.

Cadherins, organize

_________ help tissues _______ and separate during neurulation.

Divides, vertebrae, muscle, structure

The mesoderm _______ into somites to form _______ and ________ while the transient notochord provides critical ______ cues before birth.

Plate, tube, crest

The neural ______ folds to form the neural ______, and neural ______ cells disperse to build organ networks.

Internal, local, maternal, neighboring

Many stimuli affect a cell’s early development, including signals from the cell’s ______ and ______ environments, _______ substances, and signals released by _______ cells.

Tissues, organs, left, right

Even before ______ and _______ have developed, the relative positions of the head/tail, back/front, and _____/_____ are determined.

Anterior, posterior, gravity, dorsal, ventral

In a growing chick egg, the _____/______ axis is determined by ______ as the egg moves through the oviduct. pH differences between each side of the egg determine _____/_____ sides.

Morphogenic, axes

In a growing insect egg, _______ gradients guide precise cellular positioning and establish the body’s ______ early.

Morphogen

A substance governing the pattern of tissue development and the positions of cells within, gene products, or signaling molecules.

Bicoid

Two tailed maternal effect gene. Homeobox gene which encodes for a key transcription factor which leads to posterior organ development. An offspring whose mother had two mutant copies of the gene will grow a posterior tail at each end.

mRNA, protein, diffuses, enhancers, anterior

Bicoid specifies the anterior end because it’s ______ is concentrated at the egg’s anterior, and post fertilization, is transcribed into ______ which _______ towards the posterior end, creating a gradient. Bicoid binds to _______ of other pattern formation genes, directing ______ formation.

Maternal effect genes

____________ genes establish the anterior/posterior and dorsal/ventral axes but are destroyed as the embryo develops, allowing embryonic genome and proteins to take over and further differentiate.

Gap genes

Gene which affects the development of a contiguous block of embryonic segments.

Pair rule genes

Genes which affect the development of adjacent pairs.

Segment polarity genes

Genes which affect individual segments’ polarity and boundaries.

Hox genes

Genes which affect the development and characteristics of a particular segment, encode transcription factors, are crucial for limb and organ development, and specify the pre-limb field

Spatial colinearity

Hox genes express __________, which means that they are expressed from anterior to posterior in the same order that they are expressed 3 prime to 5 prime on the chromosome.

Hox proteins, activator, repressor, homeodomain

Hox genes produce transcription factors called _________. Each one is very versatile and can act as an _______ for one gene and a _______ for another. The _________ is one specific product of the hox genes and it is a 60 amino acid long DNA binding protein.

Limb buds, mesodermal, ectoderm, hox

Limbs start out as raised _______ before growing further. Composed of _______ tissue surrounded by ________ skin, differential ______ gene expression allows specific cells to develop appropriately.

Proximal/distal, FGF (fibroblast growth factor)

The Apical Ectodermal Ridge of the limb bud consists of thickened ectoderm at the tip and controls __________ organization of the limb. Cells secrete _____ protein which help limb grow.

Posterior, anterior/posterior, posterior, SHH (sonic hedgehog)

The Zone of Polarizing Activity of the limb bud is located where the _______ end of the bud connects to the body. It regulates the ___________ axis because cells closest to the ZPA form ________ structures due to secretion of the morphogenic signal _______.

SHH (sonic hedgehog)

________ is involved in the development of limbs, midline brain, eyes, teeth, and individual digits.

FGF (fibroblast growth factor)

______ is an important signaling molecule which supports AER limb outgrowth.

WNT7

_______ is an important signaling molecule which is found in the dorsal limb ectoderm and is involved in dorsal/ventral patterning and neural tube development.

BMP

_______ is an important signaling molecule which regulates FGF and apoptosis.

Microtubules, actin filaments

The cytoskeleton is crucial during neurulation. The neural tube’s ability to pinch off is dependent upon ______ extending in the neural plate and __________ at one end contracting.

Cell crawling

When cells expand/contract to navigate the embryo using the cytoskeleton

Actin, lamellipodium, myosin II, focal contacts

In cell crawling, _____ polymerization drives ________ extension, rear contracts according to ______ signaling, and the ______________ assemble and disassemble, allowing the cell to move.

Integrins, fibronectins

Cells use _____________ and __________ to move through the extracellular matrix.

Integrins

_______ are embedded in the plasma membrane, so they connect to both the extracellular matrix and the cytoplasm and are able to transmit signals between the two.

Cytoplasm, ECM

Integrins are crucial for _____-______ communication and for guiding cell migration through the extracellular matrix.

Apoptosis

Highly regulated, programmed cell death which removes specific cells to shape tissues. Examples include tadpole tails which are lost by the time the frog fully develops and the interdigital region between our fingers/toes.