Proliferation Reactivation and Dedifferentiation

Terminally differentiated postmitotic mammalian cells are thought to have little or no regenerative capacity, because they are already committed to their final specialized form and function, and they have permanently exited the cell cycle. Their inability to regenerate (i.e., to divide and replace damaged tissue) may constitute a biomedical problem. Consequently, the stimulation of adult postmitotic cells to reenter the cell cycle and proliferate may provide new therapeutic approaches for...

Epigenetic Control Of Imprinted Gene Expression

The parent of origin-specific bias in the expression of imprinted genes offers another notable example of epigenetic regulation. The existence of imprinted genes violates classical Mendelian genetic theory, which postulates the equal inheritance of and predictable segregation of genetic characteristics among the progeny. Animal breeders have long known, however, that the reciprocal mating of some animals yields phenotypically different progeny. One well-known example is the interspecific cross...

Lineage Specific Differentiation

The most commonly used method for inducing the differentiation of ESCs involves growing them in suspension (in the presence of serum and the absence of supplemented LIF) to form aggregates called embryoid bodies (EBs), which begin to differentiate into various cell lineages, including hematopoietic, endothelial, neuronal, and cardiac muscle cells. However, such uncontrolled differentiation is a poorly defined, inefficient, and relatively nonselective process, and it therefore leads to...

Heterogeneous Population Of Cells Defines The Anterior Pole

Markers of the Anterior Visceral Endoderm Numerous markers are now used to define the AVE. Originally the AVE was characterized by the expression of the homeobox gene Hesx1 on embryonic day 6.5 as well as by its ability to induce anterior ectoderm and neurectoderm during later stages (Thomas and Beddington, 1996). Markers of the AVE have a dynamic expression pattern that follows the migration of these cells. Some markers are detected early (in the DVE on embryonic day 5.5), including the...

Pharyngeal Gills And Cartilage Development

Pax 1 9 Expression and Hox Expression in Deuterostome Gill Slits Pharyngeal gill slits in hemichordates were originally used as a morphologic character uniting the hemichordate enteropneust worms with chordates (Figures 6.2 and 6.4 Romer, 1967 Schaeffer, 1987 Rychel et al., 2006). tionships are shown from morphologic and molecular data summarized by Zeng and Swalla (2005). Pax 1 and Pax 9 are expressed in the developing and adult pharyngeal gill slits of all of the vertebrate gnathostomes...

Comparison Of Dorsalventral Pattering In Drosophila And Vertebrates

Tl Signaling May Contribute to the Specification of the Vertebrate Dorsal-Ventral Axis The Tl signaling pathway has at least two functions in the life of the fruit fly. In addition to its role in embryonic DV patterning, this pathway is also required for the Drosophila immune response (Anderson, 2000 Imler and Hoffmann, 2001). In insects, immunity means innate immunity, because insects lack the systems required for adaptive immunity (e.g., B and T lymphocytes). The innate immune response is...

The Anterior Visceral Endoderm Domain Is Restricted By The Extraembryonic Ectoderm

The trophectoderm is required for implantation of the embryo into the uterus. Factors such as the homeodomain transcription factor Cdx2, the T-box transcription factor Eomes, and Fgf signaling via the Fgfr2 receptor regulate the correct differentiation of trophectodermal cells. After implantation, trophectoderm derivatives such as the ExE are also required for correct AP patterning of the mouse embryo. This has been demonstrated by genetic approaches. Ets2 (Georgiades and Rossant, 2006) and...

Subdivision Of The Embryo Into Multiple Developmental Domains By The Dorsal Nuclear Concentration Gradient

As discussed previously, the blastoderm embryo contains three DV developmental domains the mesoderm, the neurogenic ectoderm, and the dorsal ectoderm (Figure 11.3, A). DL establishes these domains by functioning as both a transcriptional activator and a repressor to direct the spatially restricted expression of zygotically active DV patterning genes (reviewed in Stathopoulos and Levine, 2002). In general, DL activates the genes that are required for the mesodermal and neurogenic ectodermal...

Specification Of Epidermis And Neural Tissue

During the late blastula stages, presumptive ectoderm develops into epidermis and neural tissue. This process is closely associated with dorsoventral patterning, because the epidermal tissue is derived from ventral ectoderm, whereas neural tissue forms dorsally (see Figure 12.1). Dorsoventral polarity is generated by the cytoskeletal reorganization (also known as the cortical-cytoplasmic rotation), which occurs soon after fertilization (Harland and Gerhart, 1997). Dorsoventral polarization...

Epigenetic Control Of Xchromosome Inactivation

XCI is characterized by an ordered series of epigenetic events (Figure 5.2). Both imprinted and random XCI are prefaced by the expression of the X-linked nonprotein coding X (inactive)-specific transcript (Xist) RNA from the prospective Xi (Heard, 2005). Xist transcription in cis is required to initiate silencing along the X chromosome. During imprinted XCI, Xist is expressed as early as the two-cell stage, and the RNA visibly begins to coat the Xp at the four-cell stage, preceding the...

Specification Of Ectoderm And Mesendoderm By Mutually Antagonistic Factors

Maternal Vegt

The animal-vegetal axis of the amphibian oocyte forms as a result of the differential deposition of maternal proteins and mRNAs. Embryonic ectoderm is specified in the animal hemisphere, which contains a set of maternally derived factors that differs from the one in the vegetal hemisphere King et al., 2005 . Cell progeny derived from the animal and the vegetal regions of the egg interact via secreted signaling factors to pattern the early embryo and to generate the basic body plan. Molecular...

Echinodermate Larvae Introduction

Phylogeny Hemichordates

History of Hypotheses of Chordate Origins Principles of Developmental Genetics 2007, Elsevier Inc. All rights reserved. FIGURE 6.1 Deuterostome phylogeny. There are five distinct adult body plans seen among the deuterostomes. Echinodermata and Hemichordata have distinctly different body plans, but similar tricoelomic feeding larvae. Xenoturbellids are a newly described deuterostome phylum, and little is known about their development. The fourth group exhibiting a distinct adult body plan is...