Browsing by Author "Merzdorf, Christa"

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Are the "wings" of zic1 expression a part of the pre-migratory neural crest?
(2013-03) Hutson, Carla; Merzdorf, Christa
The transcription factor Zic1 has several important functions during early embryonic development. zic1 regulates several of the genes that contribute to neural crest development in addition to roles it plays in development of the neural tube. The expression pattern of zic1 in Xenopus laevis can be described as a “horseshoe” with “wings” on either side. Although the “horseshoe” part of zic1 expression is along the edges of the neural plate, the “wings” lie outside this area. It has been suggested that these wings” are migrating neural crest cells, but this contradicts the fact that, in Xenopus laevis, neural crest cells do not begin to migrate until after neural tube closure is completed. In situ hybridization is a process used to observe gene expression in an embryo. A RNA probe is introduced into the embryo, and, through a series of reactions, produces a color stain only in the area of the embryo that the gene of interest is active. A double in situ hybridization follows the same basic protocol, but the expression of two genes are detected in the same embryo so that comparisons can be made. en-2, which defines the midbrain-hindbrain boundary, and slug, which is expressed only in the premigratory neural crest, will be used to in double in situ hybridizations with zic1. Using single- and double in situ hybridizations, this project will address the question of what the “wings” of zic1 expression are.
Distal spinal nerve development and divergence of avian groups
(2020-04) Rashid, Dana J.; Bradley, Roger S.; Bailleul, Alida; Surya, Kevin; Woodward, Holly; Wu, Ping; Wu, Yun-Hsin; Menke, Douglas; Minchey, Sergio; Parrott, Ben; Bock, Samantha; Merzdorf, Christa; Narotzky, Emma; Burke, Nathan; Horner, John R.; Chapman, Susan
The avian transition from long to short, distally fused tails during the Mesozoic ushered in the Pygostylian group, which includes modern birds. The avian tail embodies a bipartite anatomy, with the proximal separate caudal vertebrae region, and the distal pygostyle, formed by vertebral fusion. This study investigates developmental features of the two tail domains in different bird groups, and analyzes them in reference to evolutionary origins. We first defined the early developmental boundary between the two tail halves in the chicken, then followed major developmental structures from early embryo to post-hatching stages. Differences between regions were observed in sclerotome anterior/posterior polarity and peripheral nervous system development, and these were consistent in other neognathous birds. However, in the paleognathous emu, the neognathous pattern was not observed, such that spinal nerve development extends through the pygostyle region. Disparities between the neognaths and paleognaths studied were also reflected in the morphology of their pygostyles. The ancestral long-tailed spinal nerve configuration was hypothesized from brown anole and alligator, which unexpectedly more resembles the neognathous birds. This study shows that tail anatomy is not universal in avians, and suggests several possible scenarios regarding bird evolution, including an independent paleognathous long-tailed ancestor.
From dinosaurs to birds: a tail of evolution
(2014-05) Rashid, Dana J.; Chapman, Susan C.; Larsson, Hans C. E.; Organ, Chris L.; Merzdorf, Christa; Bradley, Roger S.; Horner, John R.
A particularly critical event in avian evolution was the transition from long- to short-tailed birds. Primitive bird tails underwent significant alteration, most notably reduction of the number of caudal vertebrae and fusion of the distal caudal vertebrae into an ossified pygostyle. These changes, among others, occurred over a very short evolutionary interval, which brings into focus the underlying mechanisms behind those changes. Despite the wealth of studies delving into avian evolution, virtually nothing is understood about the genetic and developmental events responsible for the emergence of short, fused tails. In this review, we summarize the current understanding of the signaling pathways and morphological events that contribute to tail extension and termination and examine how mutations affecting the genes that control these pathways might influence the evolution of the avian tail. To generate a list of candidate genes that may have been modulated in the transition to short-tailed birds, we analyzed a comprehensive set of mouse mutants. Interestingly, a prevalent pleiotropic effect of mutations that cause fused caudal vertebral bodies (as in the pygostyles of birds) is tail truncation. We identified 23 mutations in this class, and these were primarily restricted to genes involved in axial extension. At least half of the mutations that cause short, fused tails lie in the Notch/Wnt pathway of somite boundary formation or differentiation, leading to changes in somite number or size. Several of the mutations also cause additional bone fusions in the trunk skeleton, reminiscent of those observed in primitive and modern birds. All of our findings were correlated to the fossil record. An open question is whether the relatively sudden appearance of short-tailed birds in the fossil record could be accounted for, at least in part, by the pleiotropic effects generated by a relatively small number of mutational events.
Isolation and Cloning of zic Genes in Chick
(2013-03) Brewer, Justin; Merzdorf, Christa; Van Antwerp, Dan
Deficiencies or mutations of various genes, particularly those of the zic family, lead to a number of birth defects, including anencephaly and spina bifida. Currently, research into the role that zic genes play during embryonic development has primarily been done using Xenopus laevis and mouse; however, the use of chick embryos offers new possibilities and methods of researching zic genes. Since only zic1 has been isolated from chick, it has not been possible to use chick for zic gene research. The objective of my research is to isolate and clone the other zic genes in chick (zic2-4). I am using a phage chick cDNA library containing phages carrying the genes. Phage has been arrayed in liquid culture and screened using PCR. Positive wells are diluted, arrayed, and screened again. This process is then repeated a third time to further reduce the number of phage in the pool. The phage is then plated on solid medium and plaques will be screened using PCR. Positive plaques will be isolated and undergo excision to convert to useable plasmids. Currently, we have isolated liquid pools of zic3-containing phages and have begun isolating zic3-containing phages in solid medium.
Role of Zic Family of Transcription Factors in Early Neural Development
(2013-03) Kingston, Kyler; Merzdorf, Christa; Kalinina-Turner, Elena
A screen for genes that are regulated by Zic transcription factors identified a gene that proved to be an aquaporin (aqp-3b) (Cornish et al., 2009). Inhibition of this aquaporin suggests that it is required for proper neural tube closure. Neural tube closure defects are seen in 1 in every 500 births (Gilbert et al., 2006), and are due to such improper neural tube closures. Since mutations in Zic2 or Zic3 genes in mouse and humans are known to cause neural tube defects (Merzdorf, 2007), our hypothesis stated that either Zic2 or Zic3 regulates the aquaporin that aids in closing the neural tube. Morpholino oligonucleotides (MOs) were used to address which Zic gene regulates aqp-3b, starting with Zic3. Contingently, other genes in the Zic family would have been tested if Zic3 proved not to regulate aqp-3b. In this case, Zic1, Zic2, Zic4, and Zic5 would have been researched. Additionally, direct target genes of Zic transcription factors, including tnrc4, Xl.25952, and Xl.8933 (Cornish et al., 2009), could have been tested. However, during the summer time only allowed for the testing of Zic3.