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

Calmin expression in embryos and the adult brain, and its regulation by all-trans retinoic acid
Mark A. Marzinke, Elizabeth M. Henderson, Katherine S. Yang, Angela Wai-Man See, Danielle C. Knutson, Margaret Clagett-Dame Fri, 11 Dec 2009 14:14:00 -0000
The vitamin A metabolite, all-trans retinoic acid (atRA), is a regulator of nervous system development. Using a subtracted cDNA library constructed from neuroblastoma cells, the atRA-responsive gene calmin (Clmn) was identified (Merrill et al. [2004] Biol Chem 385:605-614). The Clmn transcript is detected very early in rat embryonic development and is sensitive to retinoid status. In vitamin A-deficient embryos, Clmn mRNA is dramatically down-regulated in the neuroepithelium adjacent to the somites, and this expression can be rescued with the addition of atRA. In embryonic day 18.5 embryos, CLMN is detected in regions where newly differentiated neurons are found, including the neural retina and the cortical plate; and in the adult brain, CLMN is most highly expressed in the neuron cell bodies of the hippocampus, cerebellum, and olfactory bulb. Thus, Clmn is sensitive to retinoid status during early gestational stages, and its expression is relegated to postmitotic neuronal cells in the adult rat brain. Developmental Dynamics, 2010. © 2009 Wiley-Liss, Inc.
The formation of the superior and jugular ganglia: Insights into the generation of sensory neurons by the neural crest
Hannah Thompson, Aida Blentic, Sheona Watson, Jo Begbie, Anthony Graham Fri, 11 Dec 2009 14:14:00 -0000
The superior and jugular ganglia (S/JG) are the proximal ganglia of the IXth and Xth cranial nerves and the sensory neurons of these ganglia are neural crest derived. However, it has been unclear the extent to which their differentiation resembles that of the Dorsal Root Ganglia (DRGs). In the DRGs, neural crest cells undergo neuronal differentiation just after the onset of migration and there is evidence suggesting that these cells are pre-specified towards a sensory fate. We have analysed sensory neuronal differentiation in the S/JG. We show, in keeping with previous studies, that neuronal differentiation initiates long after the cessation of neural crest migration. We also find no evidence for the existence of migratory neural crest cells pre-specified towards a sensory phenotype prior to ganglion formation. Rather our results suggest that sensory neuronal differentiation in the S/JG is the result of localised spatiotemporal cues. Developmental Dynamics, 2010. © 2009 Wiley-Liss, Inc.
The tight junction component Claudin E is required for zebrafish epiboly
Manal Siddiqui, Hasan Sheikh, Christopher Tran, Ashley E.E. Bruce Fri, 11 Dec 2009 14:13:00 -0000
Zebrafish epiboly results in the thinning and spreading of the blastoderm to cover the yolk cell and close the blastopore. The extra-embryonic yolk syncytial layer (YSL) tows the blastoderm vegetally during epiboly by means of its tight junction attachments to the enveloping layer (EVL). Claudins are the major transmembrane protein components of tight junctions. Here, we focus on the function of Claudin E (Cldne), which is expressed specifically in the EVL. Morpholino knock-down of cldne produced a highly penetrant epiboly delay. Our analysis suggested that the EVL margin, which is attached to the YSL, was under reduced tension in morphant embryos. We propose that local variation in the strength of EVL-YSL attachment in morphant embryos resulted in slow and uneven advancement of the EVL and blastoderm. Our work is the first to demonstrate that Claudins are important for zebrafish epiboly. Developmental Dynamics, 2010. © 2009 Wiley-Liss, Inc.
Wnt modulators in the biotech pipeline
Jean-Philippe Rey, Debra L. Ellies Fri, 11 Dec 2009 14:13:00 -0000
The purpose of this review is to provide a better understanding for the LRP co-receptor-mediated Wnt pathway signaling. Using proteomics, we have also subdivided the LRP receptor family into six sub-families, encompassing the twelve family members. This review includes a discussion of proteins containing a cystine-knot protein motif (i.e., Sclerostin, Dan, Sostdc1, Vwf, Norrin, Pdgf, Mucin) and discusses how this motif plays a role in mediating Wnt signaling through interactions with LRP. Developmental Dynamics, 2010. © 2009 Wiley-Liss, Inc.
Mouse ZAR1-like (XM_359149) colocalizes with mRNA processing components and its dominant-negative mutant caused two-cell-stage embryonic arrest
Jianjun Hu, Fengchao Wang, Xiaoquan Zhu, Ye Yuan, Mingxiao Ding, Shaorong Gao Fri, 11 Dec 2009 14:13:00 -0000
Maternal effect genes and encoding proteins are necessary for nuclear reprogramming and zygotic genome activation. However, the mechanisms that mediate these functions are largely unknown. Here we identified XM_359149, a Zar1-like gene that is predominantly expressed in oocytes and zygotes, which we designated Zar1-like (Zar1l). ZAR1L-EGFP formed multiple cytoplasmic foci in late two-cell-stage embryos. Expression of the ZAR1L C-terminus induced two-cell-stage embryonic arrest, accompanied with abnormal methylation of histone H3K4me2/3 and H3K9me2/3, and marked down-regulation of a group of chromatin modification factors including Dppa2, Dppa4, and Piwil2. When ectopically expressed in somatic cells, ZAR1L colocalized with P-body components including EIF2C1(AGO1), EIF2C2(AGO2), DDX6 and LSM14A, and germline-specific chromatoid body components including PIWIL1, PIWIL2, and LIN28. ZAR1L colocalized with ZAR1 and interacted with human LIN28. Our data suggest that ZAR1L and ZAR1 may comprise a novel family of processing-body/chromatoid-body components that potentially function as RNA regulators in early embryos. Developmental Dynamics, 2010. © 2009 Wiley-Liss, Inc.
Wnt signaling has different temporal roles during retinal development
Ana V. Sánchez-Sánchez, Esther Camp, Aránzazu Leal-Tassias, José L. Mullor Fri, 11 Dec 2009 14:13:00 -0000
Differentiation of neural retinal precursor (NRP) cells in vertebrates follows an established order of cell-fate determination associated with exit from the cell cycle. Wnt signaling regulates cell cycle in colon carcinoma cells and has been implicated in different aspects of retinal development in various species. To better understand the biological roles of Wnt in the developing retina, we have used a transgenic and pharmacological approach to manipulate the Wnt signaling pathway during retinal development in medaka embryos. With the use of both approaches, we observed that during the early phase of retinal development Wnt signaling regulated cell cycle progression, proliferation, apoptosis, and differentiation of NRP cells. However, during later phases of retinal development, proliferation and apoptosis were not affected by manipulation of Wnt signaling. Instead, Wnt regulated Vsx1 expression, but not the expression of other retinal cell markers tested. Thus, the response of NRP cells to Wnt signaling is stage-dependent. Developmental Dynamics, 2010. © 2009 Wiley-Liss, Inc.

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