Researchers have shown that the enzyme lysine demethylase 7a helps ensure the ordered axial development of the mouse embryo by modulating Hox genes which specify positional characteristics along the head-to-tail axis. Their findings suggest that the enzyme modulates Hox gene activation by regulating the repressive histone mark H3K9me2, an epigenetic modification of the DNA packaging protein Histone H3. This study opens avenues for further research into evolutionary developmental biology.
It is an astounding fact that the unicellular zygote formed at fertilization contains all the information needed for development into a multicellular organism of immense complexity organized in well-ordered symmetry. How these data are encrypted and decoded is an escalating mystery as emerging answers only unearth further questions. Hox genes allocate regions along the head-tail axis of the developing embryo for development of appropriate structures; in vertebrates they specify the numbers and sequential shapes of the spinal bones.
Some histone-modifying enzymes have been implicated in normal morphogenesis as well as in disease. Using CRISPR-Cas9 gene editing technology, the research team first developed knockout mice (Kdm7a?/?) by introducing frameshift mutation. As a result, they obtained mice carrying the mutations for truncated Kdm7a proteins lacking demethylase activity.
The researchers analyzed postnatal skeletal preparations of both wild-type and Kdm7a-/-mice. Dr Yasuharu Kanki, senior author, describes the findings. «As expected, all wild-type mice showed a normal axial skeleton. Interestingly, all Kdm7a?/? mice and some heterozygous mutants exhibited vertebral transformation; some vertebrae assumed the characteristics and appendages of their anterior neighbors.»
The researchers next used RNA sequencing to examine the expression of Hox genes during embryogenesis. Their findings support a functional role of Kdm7a-mediated transcriptional control, especially of the posteriorly situated Hox genes, and suggest that regulation of the repressive histone mark H3K9me2 might be involved.
«Our data help explain morphogenesis along the anterior/posterior axis in the mouse embryo and, by extension, in all vertebrates including humans,» says Dr Kanki. «Deciphering the interplay of various genetic and epigenetic determinants of embryonal morphogenesis as well as the underlying molecular mechanisms increases our knowledge of evolutionary developmental biology and may help in the understanding of disease.»
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