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.jpg): Failed to open stream: No such file or directory in C:\Inetpub\vhosts\kidney.de\httpdocs\pget.php on line 117 Evodevo
2018 ; 9
(ä): 16
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Formation of the initial kidney and mouth opening in larval amphioxus studied
with serial blockface scanning electron microscopy (SBSEM)
#MMPMID29977493
Holland ND
Evodevo
2018[]; 9
(ä): 16
PMID29977493
show ga
BACKGROUND: For early larvae of amphioxus, Kaji et al. (Zool Lett 2:2, 2016)
proposed that mesoderm cells are added to the rim of the forming mouth, giving it
the quality of a coelomoduct without homology to the oral openings of other
animals. They depended in part on non-serial transmission electron microscopic
(TEM) sections and could not readily put fine structural details into a broader
context. The present study of amphioxus larvae is based largely on serial
blockface scanning electron microscopy (SBSEM), a technique revealing TEM-level
details within an extensive anatomical volume that can be reconstructed in three
dimensions. RESULTS: In amphioxus larvae shortly before mouth formation, a
population of compact mesoderm cells is present at the posterior extremity of the
first left somite. As development continues, the more dorsal of these cells give
rise to the initial kidney (Hatschek's nephridium), while the more ventral cells
become interposed between the ectoderm and endoderm in a localized region where
the mouth will soon penetrate. SBSEM reveals that, after the mouth has opened, a
majority of these mesoderm cells can still be detected, sandwiched between the
ectoderm and endoderm; they are probably myoblasts destined to develop into the
perioral muscles. CONCLUSIONS: SBSEM has provided the most accurate and detailed
description to date of the tissues at the anterior end of amphioxus larvae. The
present study supports the finding of Kaji et al. (2016) that the more dorsal of
the cells in the posterior region of the first left somite give rise to the
initial kidney. In contrast, the fate of the more ventral cells (called here the
oral mesoderm) is less well understood. Although Kaji et al. (2016) implied that
all of the oral mesoderm cells joined the rim of the forming mouth, SBSEM reveals
that many of them are still present after mouth penetration. Even so, some of
those cells go missing during mouth penetration and their fate is unknown. It
cannot be ruled out that they were incorporated into the rim of the nascent mouth
as proposed by Kaji et al. (2016). On the other hand, they might have degenerated
or been shed from the larva during the morphogenetic interaction between the
ectoderm and endoderm to form the mouth. The present SBSEM study, like Kaji et
al. (2016), is based on static morphological data, and dynamic cell tracer
experiments would be needed to decide among these possibilities.