scholarly journals XXIII.—The Development of the Anterior Mesoderm, and Paired Fins with their Nerves, in Lepidosiren and Protopterus.

1907 ◽  
Vol 45 (3) ◽  
pp. 611-641 ◽  
Author(s):  
W. E. Agar

In a Lepidosiren embryo of stage 20 (Graham Kerr) the mesoderm stretches continuously through the head and trunk regions. In the trunk the dorsal mesoderm is segmented into myotomes, but the segmentation stops short some distance behind the auditory vesicle, leaving unsegmented mesoderm in front of this. In both head and trunk the lateral plate mesoderm is still connected with the dorsal, myotomic or somatic portion.

Development ◽  
1997 ◽  
Vol 124 (17) ◽  
pp. 3293-3302 ◽  
Author(s):  
K. Sampath ◽  
A.M. Cheng ◽  
A. Frisch ◽  
C.V. Wright

An association has been noted previously in chick, mouse and frog embryos between asymmetric nodal-related gene expression and embryonic situs, implying an evolutionarily conserved role in left-right specification. Of the four Xenopus nodal-related genes expressed during gastrulation, only Xnr-1 is re-expressed unilaterally in the left lateral plate mesoderm at neurula/tailbud stages. Here, we show that the asymmetric expression of Xnr-1 can be made bilaterally symmetric by right-sided microinjection of RNA encoding active Xenopus hedgehog proteins. Moreover, we provide the first evidence that Xnr-1 expression per se is a causal factor in left-right axis determination. When plasmids expressing Xnr-1 were delivered unilaterally to the right side of Xenopus embryos, a reversed laterality of both the heart and gut (homotaxic reversal) was induced in 40% of surviving embryos, while an additional 10–20% showed reversal of the heart or gut alone (heterotaxia). This effect on laterality was specific to Xnr-1, since neither Xnr-2 nor Xnr-3 plasmids had this activity. In addition, we find that Xnr-1 and Xnr-2, which have both been defined as mesoderm inducers from overexpression studies, show quantitative differences in their ability to induce dorsal mesoderm. Together, these findings suggest that the various Xnrs perform substantially different functions during Xenopus embryogenesis. Moreover, they strongly support the hypothesis that left lateral plate expression of nodal-related genes is a causative factor in the determination of asymmetry in vertebrate embryos.


2018 ◽  
Vol 10 (1) ◽  
pp. 87-100 ◽  
Author(s):  
Charles Yoon ◽  
Hannah Song ◽  
Ting Yin ◽  
Damaris Bausch-Fluck ◽  
Andreas P. Frei ◽  
...  

PLoS ONE ◽  
2012 ◽  
Vol 7 (7) ◽  
pp. e42228 ◽  
Author(s):  
Diana Eng ◽  
Hsiao-Yen Ma ◽  
Jun Xu ◽  
Hung-Ping Shih ◽  
Michael K. Gross ◽  
...  

2017 ◽  
Vol 145 ◽  
pp. S79-S80
Author(s):  
Karin Dorien Prummel ◽  
Christopher Hess ◽  
Eline Brombacher ◽  
Anastasia Felker ◽  
Christian Mosimann

2016 ◽  
Vol 371 (1710) ◽  
pp. 20150402 ◽  
Author(s):  
Rebecca D. Burdine ◽  
Daniel T. Grimes

Left–right (L-R) asymmetry of the internal organs of vertebrates is presaged by domains of asymmetric gene expression in the lateral plate mesoderm (LPM) during somitogenesis. Ciliated L-R coordinators (LRCs) are critical for biasing the initiation of asymmetrically expressed genes, such as nodal and pitx2 , to the left LPM. Other midline structures, including the notochord and floorplate, are then required to maintain these asymmetries. Here we report an unexpected role for the zebrafish EGF-CFC gene one-eyed pinhead ( oep ) in the midline to promote pitx2 expression in the LPM. Late zygotic oep (LZ oep ) mutants have strongly reduced or absent pitx2 expression in the LPM, but this expression can be rescued to strong levels by restoring oep in midline structures only. Furthermore, removing midline structures from LZ oep embryos can rescue pitx2 expression in the LPM, suggesting the midline is a source of an LPM pitx2 repressor that is itself inhibited by oep . Reducing lefty1 activity in LZ oep embryos mimics removal of the midline, implicating lefty1 in the midline-derived repression. Together, this suggests a model where Oep in the midline functions to overcome a midline-derived repressor, involving lefty1 , to allow for the expression of left side-specific genes in the LPM. This article is part of the themed issue ‘Provocative questions in left–right asymmetry’.


2018 ◽  
Author(s):  
Marco Regolini

In zebrafish inner ear, hair cell orientation in anterior and posterior maculae of the embryonic otic vesicle is different (about 30-40 degrees): this is rather unusual in planar polarity mechanism of action, instead suggests that kinocilia may be rotationally polarized. In mice node, the innermost monociliated cells generate a left-ward fluid flow sensed by the immotile primary cilia of Left peri-nodal cells: the Nodal signaling pathway is then expressed asymmetrically, in the Left lateral plate mesoderm, breaking symmetry in visceral organs (situs solitus); however, Right peri-nodal cells also, if artificially excited by a right-ward flow, break symmetry and activate the Nodal cascade, though inverting visceral organ asymmetry (situs inversus); surprisingly, peri-nodal cells prove to be adept at distinguishing flow directionality. Recently, in the Kupffer vesicle (the zebrafish laterality organ), chiral primary cilia orientation has been described: primary cilia, in the left and right side, are symmetrically oriented, showing a mirror average divergence of about 15-20 degrees from the midline. This finding, taken together with the mirror behavior of mouse perinodal cells and zebrafish hair cells, champions the idea of primary cilia enantiomerism.


Development ◽  
2010 ◽  
Vol 137 (17) ◽  
pp. 2961-2971 ◽  
Author(s):  
S. Theis ◽  
K. Patel ◽  
P. Valasek ◽  
A. Otto ◽  
Q. Pu ◽  
...  

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