POU-domain sequences from the flatworm Dugesia tigrina

Expression of AmphiPOU-IV in the developing neural tube and epidermal sensory neural precursors in amphioxus supports a conserved role of class IV POU genes in the sensory cells development

POU genes play a prominent role in the nervous system differentiation of several organism models, and in particular, they are involved in the differentiation of sensory neurons in numerous invertebrate and vertebrate species. In the present report, cloning and expression profile of a class IV POU gene in amphioxus was assessed for understanding its role in the sensory systems development. A single class IV gene, AmphiPOU-IV was isolated from the amphioxus Branchiostoma floridae. From a phylogenetic point of view, AmphiPOU-IV appears to be strictly related to the vertebrate one, sharing a high homology ratio especially with all vertebrate POU-IV proteins Brn-3a, Brn-3b, and Brn-3c. AmphiPOU-IV was found in the most anterior neural plate and in scattered ectodermic cells on the flanks of neurula, such ectodermic cells resemble the characteristic morphology and position of AmphiCoe and AmphiTrk developing sensory cells. Later on, the expression was confined in some motoneurons at level of the PMC and in some segmental arranged motoneurons in the hindbrain. Such expression is also maintained in larvae, and a new site of AmphiPOU-IV expression was also found in rostrum and mouth edge epidermal sensory cells of the larva. In conclusion, our data suggest an evolutionary conserved role of POU-IV transcription factors in the specification and differentiation of the sensory system in both vertebrates and invertebrates and underline the importance of amphioxus as linking step between them.

POU genes in metazoans: homologs in sea anemones, snails, and earthworms

Previously undescribed POU genes were detected in several invertebrate phyla using redundant primers in a polymerase chain reaction (PCR) that targeted highly conserved sequences encoding known POU-domains. A class IV gene and a gene tentatively assigned to class VI were identified in sea anemones (Condylactis), two distinct class III genes were identified in snails (Biomphalaria), and a single class IV gene was identified in earthworms (Lumbricus). The identification of POU genes in cnidarians, mollusks, and annelids completes a survey of the major metozoan phyla. As POU genes exist in all of these organisms, they appear to be a fundamental characteristic of the metazoan lineage, and may have played a major role in the diversification of these organisms.

Characterization of platyhelminth POU domain genes: ubiquitous and specific anterior nerve cell expression of different epitopes of GtPOU-1

POU domain proteins are a large family of transcription factors that have been identified in a variety of metazoans, from freshwater sponges, planarians and nematodes to arthropods, echinoderms and vertebrates. Many of these proteins are implicated in the development and establishment of the nervous system. In this paper we describe the identification of the planarian genes GtPOU-1, GtPOU-3 and GtPOU-4, which belong to the subclasses III and IV of POU-domain genes. Their similarity with other members of the POU family is restricted to the POU and homeo domains, plus some peptide sequences scattered in the linker and flanking regions. As with other subclass III POU genes, GtPOU-1 is devoid of introns. Axial transcript distribution by RT-PCR and immunohistochemical assays, performed with a polyclonal antibody raised against the GtPOU-1 fusion protein, indicate that both the GtPOU-1 transcript and protein are continuously expressed along the antero-posterior axis. A monoclonal antibody raised against the same fusion protein indicates that a GtPOU-1-specific epitope, probably obtained by post-translational modification, is present in neural cells from both the central and peripheral nerve systems of the adult planarian's anterior third. Moreover, the GtPOU-1-specific epitope shows a dynamic expression pattern during regeneration, always marking the most anterior region of the planarian nervous system. Both the rapid and general GtPOU-1-specific epitope modification, during posterior regeneration, indicate that regeneration is a global process involving all planarian regions, including those that are far from the wound, by a combination of morphallactic and epimorphic mechanisms.

Comparison of sequence and function of the Oct-6 genes in zebrafish, chicken and mouse

To examine the role of the Oct-6 gene in Schwann cell differentiation we have cloned and characterized the chicken and zebrafish homologues of the mouse Oct-6 gene. While highly homologous in the Pit1-Oct1/2-Unc86 (POU) domain, sequence similarities are limited outside this domain. Both genes are intronless and both proteins lack the amino acid repeats that are a characteristic feature of the mammalian Oct-6 proteins. However as in mammals, the aminoterminal parts of the chicken and zebrafish Oct-6 proteins are essential for transactivation of octamer containing promoters. By immunohistochemistry we have found that the chicken Oct-6 protein is expressed in late embryonic ensheathing Schwann cells of the sciatic nerve and is rapidly downregulated when myelination proceeds. This expression profile in glial cells is identical to that in the mouse and rat. Furthermore the zebrafish Oct-6 homolog is expressed in the posterior lateral nerve at a time when it contains actively myelinating Schwann cells. Thus despite extensive primary sequence divergence among the vertebrate Oct-6 proteins, the expression of the chicken and zebrafish Oct-6 proteins is consistent with the notion that Oct-6 functions as a 'competence factor' in promyelin cells to execute the myelination program.

Class III POU genes of zebrafish are predominantly expressed in the central nervous system

POU genes encode a family of transcription factors involved in a wide variety of cell fate decisions and in the regulation of differentiation pathways. We have searched for POU genes in the zebrafish, a popular model organism for the study of early development of vertebrates. Besides five putative pseudogenes we have identified five POU genes that are expressed during embryogenesis. Probes obtained by PCR were used to isolate full-length cDNAs. Four of the isolated genes encode proteins with class III POU domains. Analysis of genomic clones suggests that the fish genes in general do not contain introns, similar to class III genes of mammals. However, the C-termini of two of the encoded proteins vary due to facultative splicing of a short intervening sequence. These two genes show very strong similarities in their sequence. They have probably arisen by gene duplication, possibly as part of a larger scale duplication of part of the zebrafish genome. Analysis of the expression of the class III genes shows that they are predominantly expressed in the central nervous system and that they may play important roles in patterning the embryonic brain.