Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis," which is the process that gives rise to tissues, organs and anatomy. Embryology is a subfield, the study of organisms between the one-cell stage (generally, the zygote) and the end of the embryonic stage, which is not necessarily the beginning of free living. Embryology was originally a more descriptive science until the 20th century. Embryology and developmental biology today deal with the various steps necessary for the correct and complete formation of the body of a living organism.

The related field of evolutionary developmental biology was formed largely in the 1990s and is a synthesis of findings from molecular developmental biology and evolutionary biology which considers the diversity of organismal form in an evolutionary context.

The findings of developmental biology can help to understand developmental malfunctions such as chromosomal aberrations, for example, Down syndrome. An understanding of the specialization of cells during embryogenesis may shield information on how to specialize stem cells to specific tissues and organs, which could lead to the specific cloning of organs for medical purposes. Another biologically important process that occurs during development is apoptosis - cell "suicide". For this reason, many developmental models are used to elucidate the physiology and molecular basis of this cellular process.

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Developmental Dynamics

Normal table of postembryonic zebrafish development: Staging by externally visible anatomy of the living fish
David M. Parichy, Michael R. Elizondo, Margaret G. Mills, Tiffany N. Gordon, Raymond E. Engeszer Wed, 04 Nov 2009 16:44:00 -0000
The zebrafish is a premier model organism yet lacks a system for assigning postembryonic fish to developmental stages. To provide such a staging series, we describe postembryonic changes in several traits that are visible under brightfield illumination or through vital staining and epiflourescent illumination. These include the swim bladder, median and pelvic fins, pigment pattern, scale formation, larval fin fold, and skeleton. We further identify milestones for placing postembryonic fish into discrete stages. We relate these milestones to changes in size and age and show that size is a better indicator of developmental progress than is age. We also examine how relationships between size and developmental progress vary with temperature and density, and we document the effects of histological processing on size. To facilitate postembryonic staging, we provide images of reference individuals that have attained specific developmental milestones and are of defined sizes. Finally, we provide guidelines for reporting stages that provide information on both discrete and continuous changes in growth and development. Developmental Dynamics, 2009. © 2009 Wiley-Liss, Inc.
Collagen type IV and Perlecan exhibit dynamic localization in the Allantoic Core Domain, a putative stem cell niche in the murine allantois
Maria M. Mikedis, Karen M. Downs Wed, 04 Nov 2009 16:44:00 -0000
A body of evidence suggests that the murine allantois contains a stem cell niche, the Allantoic Core Domain (ACD), that may contribute to a variety of allantoic and embryonic cell types. Given that extracellular matrix (ECM) regulates cell fate and function in niches, the allantois was systematically examined for Collagen type IV (ColIV) and Perlecan, both of which are associated with stem cell proliferation and differentiation. Not only was localization of ColIV and Perlecan more widespread during gastrulation than previously reported, but protein localization profiles were particularly robust and dynamic within the allantois and associated visceral endoderm as the ACD formed and matured. We propose that these data provide further evidence that the ACD is a stem cell niche whose activity is synchronized with associated visceral endoderm, possibly via ECM proteins. Developmental Dynamics, 2009. © 2009 Wiley-Liss, Inc.
Muscleblind-like 1 is a negative regulator of TGF-[beta]-dependent epithelial-mesenchymal transition of atrioventricular canal endocardial cells
Natalie A. Vajda, Kyle R. Brimacombe, Kathryn E. LeMasters, Andrea N. Ladd Tue, 03 Nov 2009 12:38:00 -0000
The development of the valves and septa of the heart depends on the formation and remodeling of endocardial cushions. Here, we report that the alternative splicing regulator muscleblind-like 1 (MBNL1) exhibits a regionally restricted pattern of expression in canal region endocardium and ventricular myocardium during endocardial cushion development in chicken. Knockdown of MBNL1 in atrioventricular explants leads to a transforming growth factor [beta]-dependent increase in epithelial-mesenchymal transition (EMT) of endocardial cells. This reveals a novel role for MBNL1 during embryonic development, and represents the first evidence that an alternative splicing regulator is a key player in endocardial cushion development. Developmental Dynamics, 2009. © 2009 Wiley-Liss, Inc.
Chondroitin sulfate expression is required for cardiac atrioventricular canal formation
David S. Peal, C. Geoffrey Burns, Calum A. Macrae, David Milan Tue, 03 Nov 2009 12:37:00 -0000
Defects in cardiac valvulogenesis are a common cause of congenital heart disease, and the study of this process promises to provide mechanistic insights and lead to novel therapeutics. Normal valve development involves multiple signaling pathways, and recently roles have been identified for extracellular matrix components, including glycosaminoglycans. We, therefore, explored the role of the glycosaminoglycan chondroitin sulfate during zebrafish cardiac development. Beginning at 33 hr, there is a distinct zone of chondroitin sulfate expression in the atrioventricular (AV) boundary, in the cardiac jelly between the endocardium and myocardium. This expression is both spatially and temporally restricted, and is undetectable after 48 hr. Chemical as well as genetic inhibition of chondroitin synthesis results in AV canal (AVC) defects, including loss of the atrioventricular constriction, blood regurgitation, and failure of circulation. Lack of chondroitin disrupts a marker of cell migration, results in a loss of myocardial and endothelial markers of valvulogenesis, and misregulates bone morphogenetic protein expression, supporting an early role in AVC development. In summary, we have defined a requirement for chondroitin sulfate expression in the normal patterning of the AV boundary, suggesting that this component of the cardiac jelly provides a necessary signal in this critical transition in vertebrate cardiogenesis. Developmental Dynamics, 2009. © 2009 Wiley-Liss, Inc.
Asator, a tau-tubulin kinase homolog in Drosophila localizes to the mitotic spindle
Hongying Qi, Changfu Yao, Weili Cai, Jack Girton, Kristen M. Johansen, Jørgen Johansen Tue, 03 Nov 2009 12:37:00 -0000
We have used a yeast two-hybrid interaction assay to identify Asator, a tau-tubulin kinase homolog in Drosophila that interacts directly with the spindle matrix protein Megator. Using immunocytochemical labeling by an Asator-specific mAb as well as by transgenic expression of a GFP-labeled Asator construct, we show that Asator is localized to the cytoplasm during interphase but redistributes to the spindle region during mitosis. Determination of transcript levels using qRT-PCR suggested that Asator is expressed throughout development but at relatively low levels. By P-element excision, we generated a null or strong hypomorphic Asatorexc allele that resulted in complete adult lethality when homozygous, indicating that Asator is an essential gene. That the observed lethality was caused by impaired Asator function was further supported by the partial restoration of viability by transgenic expression of Asator-GFP in the Asatorexc homozygous mutant background. The finding that Asator localizes to the spindle region during mitosis and directly can interact with Megator suggests that its kinase activity may be involved in regulating microtubule dynamics and microtubule spindle function. Developmental Dynamics, 2009. © 2009 Wiley-Liss, Inc.
Characterization of molecular markers to assess cardiac cushions formation in Xenopus
Young-Hoon Lee, Jean-Pierre Saint-Jeannet Tue, 03 Nov 2009 12:37:00 -0000
The valves and septa of the mature heart are derived from the cardiac cushions, which develop from discrete swellings in two regions of developing heart tube: the atrioventricular (AV) canal and the ventricular outflow tract (OFT). In higher vertebrates, three distinct lineages contribute to the heart valves and septa, the endocardium, the myocardium, and the cardiac neural crest that will populate the cardiac jelly of the OFT. Very little is known about cardiac cushions development in amphibians. Here, we describe the expression of eight genes during key stages of cardiac cushion development in Xenopus. Among these genes, the Wnt antagonist Frzb1 and the transcription factors Xl-Fli, Sox8, Sox9, and Sox10 are differentially expressed in the mesenchyme of the OFT and AV cushions. These genes can be used in combination with lineage-tracing experiments to determine the embryonic origin of the cardiac cushions mesenchyme in Xenopus. Developmental Dynamics, 2009. © 2009 Wiley-Liss, Inc.

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