New insights on ctenophore neural anatomy: immunofluorescence study in Pleurobrachia pileus (Müller, 1776).

Ctenophores are non-bilaterian animals sharing with cnidarians and bilaterians the presence of sensory receptors, nerve cells, and synapses, absent in placozoans and sponges. Although recent immunofluorescence studies have renewed our knowledge of cnidarian neuro-anatomy, ctenophores have been much less investigated despite their importance to understanding the origin and early evolution of the nervous system. In this study, the neuro-anatomy of the ctenophore Pleurobrachia pileus (Müller, 1776) was explored by whole-mount fluorescent antibody staining using antibodies against tyrosylated -tubulin, FMRFamide, and vasopressin.

Are Hox genes ancestrally involved in axial patterning? Evidence from the hydrozoan Clytia hemisphaerica (Cnidaria).

Background: The early evolution and diversification of Hox-related genes in eumetazoans has been the subject of conflicting hypotheses concerning the evolutionary conservation of their role in axial patterning and the pre-bilaterian origin of the Hox and ParaHox clusters. The diversification of Hox/ParaHox genes clearly predates the origin of bilaterians. However, the existence of a "Hox code" predating the cnidarian-bilaterian ancestor and supporting the deep homology of axes is more controversial.

Insights into the early evolution of SOX genes from expression analyses in a ctenophore.

SOX genes encode transcription factors acting in various developmental processes in bilaterian animals, such as stem cell maintenance and the control of specification and differentiation of cell types in a variety of contexts, notably in the developing nervous system. To gain insights into the early evolution of this important family of developmental regulators, we investigated the expression of one subgroup B, two subgroup E, one subgroup F and two divergent SOX genes in the cydippid larva and in the adult of the ctenophore Pleurobrachia pileus. Transcripts of the two unclassified SOX (PpiSOX2/12) were detected in the female germ line and in various populations of putative somatic stem cells/undifferentiated progenitors.