Biology Reference
In-Depth Information
development.
…
Consequently, the morphological simplicity of basal animals,
and the great differences in morphology between sponges and arthropods or
vertebrates, cannot be due to the absence of these protein-coding gene fami-
lies but instead must involve differences in the temporal and spatial deployment
of these genes and their regulation.” One possible mechanism is the “contin-
ual evolutionary addition of microRNAs, which code for 22-nucleotide regula-
tory RNAs that affect translation of target mRNAs, resulting in homeostasis and
cell identity. MicroRNAs have been continuously added to eumetazoan genomes
through time with very little loss in most taxa. When losses did occur, the loss
seems to be associated with morphological simplification.”
Dolgin (2012)
reported on three analyses of evolutionary biology based on
analyses of microRNAs.
Sempere et al. (2006)
,
Peterson et al. (2009)
, and
Janvier
(2010)
analyzed animal phylogeny using microRNA sequences. MicroRNAs “are
either there or they aren't,” and “once gained, microRNAs usually remain func-
tional, which means that their signal stays intact for hundreds of millions of
years” (
Dolgin 2012
). The hypothesis is that microRNAs hold the secret to mor-
phological complexity. The farther away from the base of the evolutionary tree
the animals are, the more microRNAs they have accumulated. This fact could pro-
vide “a brand new way to do phylogeny, using a set of rare genomic characters
that no one had ever considered before” (
Dolgin 2012
). According to an analysis
by
Peterson et al. (2009)
, “778 microRNA families have arisen during the 600 mil-
lion or so years of animal evolution, and only 48 have been lost. This pattern of
inheritance leaves an easy-to-follow evolutionary trail for phylogenetic sleuths.”
This approach to deep phylogeny is controversial and, in the case of mam-
malian evolution, contradicts the tree developed using other genetic data.
Campbell et al. (2011)
used microRNAs to analyze the relationships of the
Tardigrada and Arthropoda. Morphological data group Tardigrada (water bears)
and Onychophora (velvet worms) and Arthropoda into a monophyletic group
known as the Panarthropoda. Molecular data do not support the inclusion of
tardigrades within the Panarthropoda. However, analysis of microRNAs and ESTs
support a monophyletic Panarthropoda that includes tardigrades.
Rota-Stabelli et al. (2011)
used a combination of microRNAs and morphol-
ogy to support the monophyletic status of the Mandibulata. Morphology indi-
cates that myriapods, insects and crustaceans form a monophyletic group, the
Mandibulata, but other studies indicate other interpretations. They studied 198
protein-coding genes and microRNAs to indicate that the Mandibulata is mono-
phyletic. Two microRNAs are present and expressed in all mandibulates studied,
but not in chelicerates.
