1: Mol Biol Evol. 2005 Jul;22(7):1569-78. Epub 2005 Apr 27. 

The Trichoplax PaxB gene: a putative Proto-PaxA/B/C gene predating the origin of
nerve and sensory cells.

Hadrys T, DeSalle R, Sagasser S, Fischer N, Schierwater B.

ITZ, Ecology & Evolution, Hannover, Germany. thorsten.hadrys@uni-oldenburg.de

Pax genes play key regulatory roles in embryonic and sensory organ development
in metazoans but their evolution and ancestral functions remain widely
unresolved. We have isolated a Pax gene from Placozoa, beside Porifera the only
metazoan phylum that completely lacks nerve and sensory cells or organs. These
simplest known metazoans also lack any kind of symmetry, organs, extracellular
matrix, basal lamina, muscle cells, and main body axis. The isolated Pax gene
from Trichoplax adhaerens harbors a paired domain, an octapeptide, and a
full-length homeodomain. It displays structural features not only of PaxB and
Pax2/5/8-like genes but also of PaxC and Pax6 genes. Conserved splice sites
between Placozoa, Cnidaria, and triploblasts, mark the ancient origin of intron
structures. Phylogenetic analyses demonstrate that the Trichoplax PaxB gene,
TriPaxB, is basal not only to all other known PaxB genes but also to PaxA and
PaxC genes and their relatives in triploblasts (namely Pax2/5/8, Pax4/6, and
Poxneuro). TriPaxB is expressed in distinct cell patches near the outer edge of
the animal body, where undifferentiated and possibly multipotent cells are
found. This expression pattern indicates a developmental role in cell-type
specification and/or differentiation, probably in specifying-determining fiber
cells, which are regarded as proto-neural/muscle cells in Trichoplax. While
PaxB, Pax2/5/8, and Pax6 genes have been linked to nerve cell and sensory
system/organ development in virtually all animals investigated so far, our study
suggests that Pax genes predate the origin of nerve and sensory cells.

PMID: 15858210 [PubMed - in process]


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2: Gene. 1995 Sep 11;162(2):267-70. 

Identification of DNA recognition sequences for the Pax3 paired domain.

Chalepakis G, Gruss P.

Max-Planck Institute for Biophysical Chemistry, Gottingen, Germany.

The Pax gene family, encoding transcription factors, has been classified into
four subfamilies according to their genomic organization, the sequences of the
paired domains (PD) and the expression pattern. Pax1 and Pax9 constitute one
subfamily, Pax2, Pax5 and Pax8 another, Pax3 and Pax7 another one and Pax4 and
Pax6 the fourth subfamily. The PD exhibits DNA-binding activity, and is the most
conserved functional motif in all Pax proteins. A high-resolution analysis of a
PD structure has been performed [Xu et al., Cell 80 (1995) 639-650] and the
DNA-binding characteristics of members of two Pax subfamilies (Pax2, Pax5 and
Pax6) have been determined. Here, we have utilized a PCR-based selection
approach to identify the DNA-binding sequences of the Pax3/PD, a member of a
subfamily which has not yet been characterized. Comparison of the
Pax3/PD-binding sequences with those of other PD proteins revealed both
similarities and differences in the DNA-recognition sequence. This suggests that
different Pax proteins can regulate the expression of the same target gene, but
they can also regulate the expression of completely unrelated genes by binding
to their DNA regulatory regions.

PMID: 7557441 [PubMed - indexed for MEDLINE]


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