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From the Latest Results
“Oxygen shapes arms and legs: origins of a new developmental mechanism called 'interdigital cell death'”
Ingrid Rosenburg Cordeiro
, Kaori Kabashima, Haruki Ochi, Keijiro Munakata, Chika Nishimori, Mara Laslo, James Hanken, and Mikiko Tanaka (2019).
Developmental Cell DOI：https://doi.org/10.1016/j.devcel.2019.05.025
The webbing between the fingers of some animals ? the interdigital membranes ? is formed in different ways across species.
We found that the removal of the interdigital membrane by cell death depends on the production of reactive oxygen species (ROS),
which only occurs in embryos exposed to sufficient oxygen levels during development.
In chicken, an amniote with interdigital cell death, modulating oxygen or ROS levels directly affected the amount of dying cells.
Surprisingly, increasing the amount of environmental oxygen induced interdigital cell death in amphibian that typically lacks it,
the African clawed frog (Xenopus laevis). Increasing the density of blood vessels in the limbs of these frogs also induced cell death. Moreover,
the oxygen tension in the interdigital regions was distinct between chicken and frog. Atmospheric oxygen could modulate the local oxygen tension in the interdigital region in both species.
To gain an evolutionary perspective, we also investigated other two amphibian species. While the African clawed frog and Japanese fire-bellied newt had no interdigital cell death,
the coqui frogs had dying cells in their interdigital regions. Importantly, unlike the other two amphibians, the coqui frogs grow without a tadpole stage in terrestrial eggs,
a process called direct-development, and breathe oxygen from the air. This data revealed that ecological features ? where the embryos are and how much oxygen surrounds it ?
can have a direct effect on the presence of cell death in the limbs during development.
“Basis of Development of Vertebrate Limb Muscles has been established in Cartilaginous Fishes”
, Rie Kusakabe, Shigehiro Kuraku, Susumu Hyodo, Alexandre Robert-Moreno, Koh Onimaru, James Sharpe, Shigeru Kuratani and Mikiko Tanaka (2017)
Nature Ecology & Evolution DOI: 10.1038/s41559-017-0330-4 http://www.nature.com/articles/s41559-017-0330-4
The development of limb muscle has been well studied in most land dwelling vertebrates such as humans and modern research models.
In these species, muscle precursors travel to the limb bud, where they multiply and form muscle tissue under the control of genes
that coordinate limb- muscle formation, such as Lbx1.
It has been shown that this mechanism of development is shared with bony but not with cartilaginous fish.
Using catshark embryos, we confirmed that Lbx1-positive cells are found in cartilaginous fish fin as well as in hypobranchial muscle precursors,
and that these are formed via the mechanism that has been established in land dwelling vertebrates as well as in bony fish.
"Key genetic event underlying fin-to-limb evolution"
, Kuraku, Takagi, Hyodo, Sharpe and Tanaka (2015) eLife DOI: 10.7554/eLife.07048: http://dx.doi.org/10.7554/eLife.07048
The forelimbs of tetrapod evolved from the pectoral fins of the ancestral fish. These fins contain three or more basal bones connected to the pectoral girdle. However, the most of basal bones located in the anterior side (i.e. the thumb side in the human limb) were lost in early tetrapods, and only the most posterior bone remained as the “humerus (i.e. the upper arm of humans)”.
Pectoral fins of catsharks also contain three basal bones (Figure 1a, left) as seen in the ancestral fish. Thus, we examined the fin development of catsharks, and revealed that there was a shift in the balance of anterior (thumb side) and posterior (pinky side) filelds in their fin buds compared to that in mouse limb buds (Figure 1b).
A key regulator protein controlling the balance of anterior and posterior fields of limb buds of tetrapods is Gli3. Gli3 is expressed in the anterior part of limb buds, and regulates the expression of a number of genes providing cells with information about their position along the anterior-posterior axis. In this study, we found that the catshark genome lacked a sequence found in mice and other tetrapods, which is responsible for preventing Gli3 expression in the posterior part of tetrapod limb buds. When we deliberately “posteriorised” pectoral fin buds of catsharks, the fins lost anterior skeletal elements, and showed a single bone connected to the pectoral girdle, as seen in fossil Tiktaalik pectoral fins.
These results suggest that a one of the key genetic events during the fin-to-limb evolution was a shift of the balance of the anterior and posterior fields (a “posteriorisation”) and loss of anterior skeletal elements.
“Mechanism determining survival-and-death fate of cells in limb formation”
We show that MafB was specifically expressed in apoptotic regions of chick limb buds, and MafB/cFos
heterodimers repressed apoptosis, whereas MafB/cJun heterodimers promoted apoptosis for sculpting
the shape of the limbs via activation of p63 and p73.
Suda et al. (2014) Development
141, 2885-2894 (original article).