Developmental Dynamics

Harzsch, Steffen; Vilpoux, Kathia; Blackburn, David C.; Platchetzki, David; Brown, Nadean L.; Melzer, Roland; Kempler, Karen E.; Battelle, Barbara A.

doi: 10.1002/dvdy.20960pmid: N/A

Dorsal view of a larva of the horseshoe crab Limulus polyphemus (Chelicerata, Xiphosura) showing the paired lateral eyes and the median eyes. See Harzsch et al., Developmental Dynamics 235:2641–2655.

Sive, Hazel

doi: 10.1002/dvdy.20958pmid: 16972277

Muriel, Joaquin M.; Xu, Xuehong; Kramer, James M.; Vogel, Bruce E.

doi: 10.1002/dvdy.20888pmid: 16804890

Fibulin‐1C and fibulin‐1D splice variants have been conserved throughout metazoan evolution and have distinct functions in Caenorhabditis elegans development. Both splice variants are required for the assembly of hemidesmosome‐mediated mechanosensory neuron and uterine attachments, although the molecular associations that underlie their distinct functions at these locations are not known. Here, we show that the assembly of fibulin‐1C and fibulin‐1D splice variants at these anchorages is dependent upon distinct components of the extracellular matrix (ECM): Fibulin‐1D assembly at uterine and mechanosensory neurons attachments is dependent upon a perlecan/ UNC‐52 splice variant that includes alternately spliced IG8‐IG10, whereas the assembly of fibulin‐1C at mechanosensory neuron attachments is dependent upon laminin/ EPI‐1. These data not only indicate that fibulin‐1C and fibulin‐1D are components of distinct networks of ECM but also demonstrates a novel function for a major class of perlecan splice variants found in C. elegans and mouse. In addition, we demonstrate that overexpression of another ECM protein, collagen XVIII, can suppress gonad morphogenesis defects associated with loss of fibulin‐1C, suggesting that some genetic defects that result in a weakened basement membrane can be compensated by overexpression of genes for ECM components that stabilize basement membranes. Developmental Dynamics 235:2632–2640, 2006. © 2006 Wiley‐Liss, Inc.

Harzsch, Steffen; Vilpoux, Kathia; Blackburn, David C.; Platchetzki, David; Brown, Nadean L.; Melzer, Roland; Kempler, Karen E.; Battelle, Barbara A.

doi: 10.1002/dvdy.20866pmid: 16788994

Despite ongoing interest into the architecture, biochemistry, and physiology of the visual systems of the xiphosuran Limulus polyphemus, their ontogenetic aspects have received little attention. Thus, we explored the development of the lateral eyes and associated neuropils in late embryos and larvae of these animals. The first external evidence of the lateral eyes was the appearance of white pigment spots—guanophores associated with the rudimentary photoreceptors—on the dorsolateral side of the late embryos, suggesting that these embryos can perceive light. The first brown pigment emerges in the eyes during the last (third) embryonic molt to the trilobite stage. However, ommatidia develop from this field of pigment toward the end of the larval trilobite stage so that the young larvae at hatching do not have object recognition. Double staining with the proliferation marker bromodeoxyuridine (BrdU) and an antibody against L. polyphemus myosin III, which is concentrated in photoreceptors of this species, confirmed previous reports that, in the trilobite larvae, new cellular material is added to the eye field from an anteriorly located proliferation zone. Pulse–chase experiments indicated that these new cells differentiate into new ommatidia. Examining larval eyes labeled for opsin showed that the new ommatidia become organized into irregular rows that give the eye field a triangular appearance. Within the eye field, the ommatidia are arranged in an imperfect hexagonal array. Myosin III immunoreactivity in trilobite larvae also revealed the architecture of the central visual pathways associated with the median eye complex and the lateral eyes. Double labeling with myosin III and BrdU showed that neurogenesis persists in the larval brain and suggested that new neurons of both the lamina and the medulla originate from a single common proliferation zone. These data are compared with eye development in Drosophila melanogaster and are discussed with regard to new ideas on eye evolution in the Euarthropoda. Developmental Dynamics 235:2641–2655, 2006. © 2006 Wiley‐Liss, Inc.

Hayward, Penelope; Balayo, Tina; Martinez Arias, Alfonso

doi: 10.1002/dvdy.20902pmid: 16881048

Cell fate decisions require the integration of various signalling inputs at the level of transcription and signal transduction. Wnt and Notch signalling are two important signalling systems that operate in concert in a variety of systems in vertebrates and invertebrates. There is evidence that the Notch receptor can modulate Wnt signalling and that its target is the activity and levels of Armadillo/β‐catenin. Here, we characterize this function of Notch in relation to Axin, a key element in the regulation of Wnt signalling that acts as a scaffold for the Shaggy/GSK3β‐dependent phosphorylation of Armadillo/β‐catenin. While Notch can regulate ectopic Wingless signalling caused by loss of function of Shaggy, it can only partially regulate the ectopic Wnt signalling induced by the loss of Axin function. The same interactions are observed in tissue culture cells where we observe a synergy in between Axin and Notch in the regulation of Armadillo/β‐catenin. Our results provide evidence for a function of Axin in the regulation of Armadillo that is different from its role as a scaffold for GSK3β. Developmental Dynamics 235:2656–2666, 2006. © 2006 Wiley‐Liss, Inc.

Grow, Matthew; Neff, Anton W.; Mescher, Anthony L.; King, Michael W.

doi: 10.1002/dvdy.20897pmid: 16871633

Xenopus laevis tadpoles are capable of limb regeneration after amputation, in a process that initially involves the formation of a blastema. However, Xenopus has full regenerative capacity only through premetamorphic stages. We have used the Affymetrix Xenopus laevis Genome Genechip microarray to perform a large‐scale screen of gene expression in the regeneration‐complete, stage 53 (st53), and regeneration‐incomplete, stage 57 (st57), hindlimbs at 1 and 5 days postamputation. Through an exhaustive reannotation of the Genechip and a variety of comparative bioinformatic analyses, we have identified genes that are differentially expressed between the regeneration‐complete and ‐incomplete stages, detected the transcriptional changes associated with the regenerating blastema, and compared these results with those of other regeneration researchers. We focus particular attention on striking transcriptional activity observed in genes associated with patterning, stress response, and inflammation. Overall, this work provides the most comprehensive views yet of a regenerating limb and different transcriptional compositions of regeneration‐competent and deficient tissues. Developmental Dynamics 235:2667–2685, 2006. © 2006 Wiley‐Liss, Inc.

Shimada, Naoko; Moorman, Stephen J.

doi: 10.1002/dvdy.20901pmid: 16894605

Gravity has been a constant physical factor during the evolution and development of life on Earth. We have been studying effects of simulated microgravity on gene expression in transgenic zebrafish embryos expressing gfp under the influence of gene‐specific promoters. In this study, we assessed the effect of microgravity on the expression of the heat shock protein 70 (hsp70) gene in lens during development using transgenic zebrafish embryos expressing gfp under the control of hsp70 promoter/enhancer. Hsp70:gfp expression was up‐regulated (45%) compared with controls during the developmental period that included the lens differentiation stage. This increase was lens specific, because the entire embryo showed only a 4% increase in gfp expression. Northern blot and in situ hybridization analysis indicated that the hsp70:gfp expression recapitulated endogenous hsp70 mRNA expression. Hypergravity exposure also increased hsp70 expression during the same period. In situ hybridization analysis for two lens‐specific crystallin genes revealed that neither micro‐ nor hypergravity affected the expression level of βB1‐crystallin, a non‐hsp gene used as a marker for lens differentiation. However, hypergravity changed the expression level of αA‐crystallin, a member of the small hsp gene family. Terminal deoxynucleotidyl transferase–mediated deoxyuridinetriphosphate nick end‐labeling (TUNEL) assay analysis showed that altered‐gravity (Δg) decreased apoptosis in lens during the same period and the decrease correlated with the up‐regulation of hsp70 expression, suggesting that elimination of nuclei from differentiating lens fiber cells was suppressed probably through hsp70 up‐regulation. These results support the idea that Δg influences hsp70 expression and differentiation in lens‐specific and developmental period specific manners and that hsp family genes play a specific role in the response to Δg. Developmental Dynamics 235:2686–2694, 2006. © 2006 Wiley‐Liss, Inc.

Kopinke, Daniel; Sasine, Joshua; Swift, Jennifer; Stephens, W. Zac; Piotrowski, Tatjana

doi: 10.1002/dvdy.20905pmid: 16871626

Because tissues from all three germ layers contribute to the pharyngeal arches, it is not surprising that all major signaling pathways are involved in their development. We focus on the role of retinoic acid (RA) signaling because it has been recognized for quite some time that alterations in this pathway lead to craniofacial malformations. Several studies exist that describe phenotypes observed upon RA perturbations in pharyngeal arch development; however, these studies did not address whether RA plays multiple roles at distinct time points during development. Here, we report the resulting phenotypes in the hindbrain, the neural crest–derived tissues, and the pharyngeal endoderm when RA synthesis is disrupted during zebrafish gastrulation and pharyngeal arch morphogenesis. Our results demonstrate that RA is required for the post‐gastrulation morphogenesis and segmentation of endodermal pouches, and that loss of RA does not affect the length of the pharyngeal ectoderm or medial endoderm along the anterior‐posterior axis. We also provide evidence that RA is not required for the specification of pharyngeal pouch endoderm and that the pharyngeal endoderm consists of at least two different cell populations, of which the pouch endoderm is sensitive to RA and the more medial pharyngeal endoderm is not. These results demonstrate that the developmental processes underlying pharyngeal arch defects differ depending on when RA signaling is disturbed during development. Developmental Dynamics 235:2695–2709, 2006. © 2006 Wiley‐Liss, Inc.

Fujita, Hironori; Mochizuki, Atsushi

doi: 10.1002/dvdy.20908pmid: 16894601

The leaf venation pattern of plants shows remarkable diversity and species‐specificity. However, the mechanism underlying the pattern formation and pattern diversity remains unclear. We developed a mathematical model that is based on the positive feedback regulation between plant hormone auxin and its efflux carrier. This system can generate auxin flow pathways by self‐organization from an almost homogeneous state. This result explains a well‐known experimental phenomenon referred as to “polar auxin transport.” The model can produce diverse leaf venation patterns with spatial regularity under similar conditions to those of leaf development, that is, in the presence of leaf expansion and auxin sink. Final venation patterns are strikingly affected by leaf shape and leaf expansion. These results indicate that the positive feedback regulation between auxin and its efflux carrier is a central dynamic in leaf venation pattern formation. The diversity of leaf venation patterns in plant species is probably due to the differences of leaf shape and leaf expansion pattern. Developmental Dynamics 235:2710–2721, 2006. © 2006 Wiley‐Liss, Inc.

Eroglu, Binnur; Wang, Guanghu; Tu, Naxin; Sun, Xutong; Mivechi, Nahid F.

doi: 10.1002/dvdy.20911pmid: 16894598

Brg1 is a member of the SWI/SNF chromatin‐remodeling complex, and in some organisms Brg1 has been shown to interact with β‐catenin and positively control the TCF/LEF transcription factor that is located downstream of the Wnt signal transduction pathway. During development, TCF/LEF activity is critical during neurogenesis and head induction. In zebrafish, Brg1‐deficient embryos exhibit retinal cell differentiation and eye defects; however, the role of Brg1 in neurogenesis and neural crest cell induction remains elusive. We used zebrafish deficient in Brg1 (yng) or Brg1 specific‐morpholino oligonucleotide‐mediated knockdown to analyze the embryonic requirements of Brg1. Our results indicate that reduction in Brg1 expression leads to the expansion of the forebrain‐specific transcription factor, six3, and marked reduction in expression of the mid/hind‐brain boundary and hind‐brain genes, engrailed2 and krox20, respectively. At 12 hpf, the expression of neural crest specifiers are severely affected in Brg1‐morpholino‐injected embryos. These results suggest that Brg1 is involved in neural crest induction, which is critical for the development of neurons, glia, pigment cells, and craniofacial structures. Brg1 is a maternal factor, and brg1‐deficient embryos bearing the yng mutation derived from heterozygote intercrosses exhibit lesser effects on neural crest–specific gene expression, but show defects in neurogenesis and neural crest cell differentiation. This is exhibited by the aberrant brain patterning, a reduction in the sensory neurons, and craniofacial defects. These results further elucidate the critical role for Brg1 in neurogenesis, neural crest induction, and differentiation. Developmental Dynamics 235:2722–2735, 2006. © 2006 Wiley‐Liss, Inc.