Pax8, a murine paired box gene expressed in the developing excretory system and thyroid gland.

Several mouse genes designated 'Pax genes' contain a highly conserved DNA sequence homologous to the paired box of Drosophila. Here we describe the isolation of Pax8, a novel paired box containing clone from an 8.5 day p.c. mouse embryo cDNA library. An open reading frame of 457 amino acids (aa) contains the 128 aa paired domain near the amino terminus. Another conserved region present in some other paired box genes, the octapeptide Tyr-Ser-Ile-Asn-Gly-Leu-Leu-Gly, is located 43 aa C-terminal to the paired domain. Using an interspecies backcross system, we have mapped the Pax8 gene within the proximal portion of mouse chromosome 2 in a close linkage to the surf locus. Several developmental mutations are located in this region. In situ hybridization was used to determine the pattern of Pax8 expression during mouse embryogenesis. Pax8 is expressed transiently between 11.5 and 12.5 days of gestation along the rostrocaudal axis extending from the myelencephalon throughout the length of the neural tube, predominantly in two parallel regions on either side of the basal plate. We also detected Pax8 expression in the developing thyroid gland beginning at 10.5 days of gestation, during the thyroid evagination. In the mesonephros and metanephros the expression of Pax8 was localized to the mesenchymal condensations, which are induced by the nephric duct and ureter, respectively. These condensations develop to functional units, the nephrons, of the kidney. These data are consistent with a role for Pax8 in the induction of kidney epithelium. The embryonic expression pattern of Pax8 is compared with that of Pax2, another recently described paired box gene expressed in the developing excretory system.     

Gsh-2, a murine homeobox gene expressed in the developing brain

A novel murine dispersed homeobox gene, designated Gsh-2, is described. Analysis of cDNA sequence, including the full open reading frame, reveals an encoded homeodomain that is surprisingly similar to those of the Antennapedia-type clustered Hox genes. In addition, the encoded protein includes polyhistidine and polyalanine tracts, as observed for several other genes of developmental significance. In situ hybridizations showed Gsh-2 expression in the developing central nervous system, including the ganglionic eminences of the forebrain, the diencephalon, which gives rise to the thalamus and hypothalamus, and in the hindbrain. Furthermore, a random oligonucleotide selection and PCR amplification procedure was used to define a target DNA binding sequence, CNAATTAG, as a first step towards the identification of downstream target genes.     

The murine fork head gene Foxn2 is expressed in craniofacial,limb, CNS and somitic tissues during embryogenesis

The fork head domain-containing gene family (Fox) comprises over 20 members in mammals and is defined by a conserved 110 amino-acid motif containing a winged helix structure DNA-binding domain. The members of this gene family have been implicated as key regulators of embryogenesis, cell cycling, cell lineage restriction and cancer. The Foxn2 gene (Ches1) is expressed in postgastrulation embryos in multiple tissues that serve as important signaling centers as well as end-stage-differentiated cell types that arise from different germ layers of the developing embryo. The dynamic and specific expression of Foxn2 during embryonic development suggest multiple independent roles for Foxn2 function during gestation.     

Pax-5 is expressed at the midbrain-hindbrain boundary during mouse development.

The murine paired-box-containing gene 5, Pax-5, is highly homologous to two other Pax genes, Pax-2 and Pax-8. The expression pattern of Pax-5 during mouse embryogenesis was examined by in situ RNA hybridization and compared to those of Pax-2 and Pax-8. Beginning at day 9.5 postcoitum (p.c.), Pax-5 was expressed in the developing brain, predominantly at the midbrain-hindbrain boundary, and in the neural tube. While the neural tube expression pattern overlapped completely with Pax-2 and Pax-8, the expression pattern in the brain was only partially overlapping. Unlike Pax-2 and Pax-8, Pax-5 was not expressed in the developing excretory system, thyroid, eye or ear. Our data suggest that Pax-5 has a role in the development of the central nervous system.     

Characterization of quail Pax-6 (Pax-QNR) proteins expressed in the neuroretina.

After differential screening of a cDNA library constructed from quail neuroretina cells (QNR) infected with the v-myc-containing avian retrovirus MC29, we have isolated a cDNA clone, Pax-QNR, homologous to the murine Pax-6, which is mutated in the autosomal dominant mutation small eye of mice and in the disorder aniridia in humans. Here we report the characterization of the Pax-QNR proteins expressed in the avian neuroretina. From bacterially expressed Pax-QNR peptides, we obtained rabbit antisera directed against different domains of the protein: paired domain (serum 11), domain between the paired domain and homeodomain (serum 12), homeodomain (serum 13), and carboxyl-terminal part (serum 14). Sera 12, 13, and 14 were able to specifically recognize five proteins (48, 46, 43, 33, and 32 kDa) in the neuroretina. In contrast to proteins of 48, 46, and 43 kDa, proteins of 33 and 32 kDa were not recognized by the paired antiserum (serum 11). Paired-less and paired-containing proteins exhibited the same half-life (6 h) and were phosphorylated mostly on serine residues. Immunoprecipitations performed with subcellular fractions of neuroretinas showed that the paired-containing proteins were located in the nucleus, whereas the 33- and 32-kDa proteins were found essentially in the cytoplasmic compartment. However, immunofluorescence experiments performed after transient transfections showed that p46 and p33/32 were also located in vivo into the nucleus. Thus, the Pax-QNR/Pax-6 gene can produce proteins with two DNA-binding domains as well as proteins containing only the DNA-binding homeodomain.     

Hole is a novel gene product expressed in the developing heart and brain

Hole is a novel gene product isolated from a chick heart subtractive hybridization. Hole is a six-transmembrane protein (predicted size 311 and 317 amino acids in chick and mouse) expressed in the cardiac crescent and later in the myocardium of the developing chick heart, as well as in the fusing neural tube and ganglia. Mouse hole is not expressed in the developing heart, although it does share neural expression seen in the chick.     

The amphioxus FoxQ1 gene is expressed in the developing endostyle

The FoxQ1 genes form a distinct group within the Fox (also known as forkhead) gene family. We have isolated a gene from the amphioxus Branchiostoma floridae that encodes a forkhead domain with high identity to FoxQ1 genes in other chordates. Molecular phylogenetic analysis places AmphiFoxQ1 in a robust grouping with vertebrate FoxQ1 genes and with Ciona intestinalis Ci-FoxQ1. This group is separate from that containing AmphiFoxQ2, which instead groups with other invertebrate Fox genes. The expression of AmphiFoxQ1 was analysed by whole mount in situ hybridisation. The results show that AmphiFoxQ1 expression is confined to the developing endoderm, and specifically marks the endostyle and associated peripharyngeal bands of amphioxus larvae. Ci-FoxQ1 is also expressed in the endostyle, highlighting this as a conserved site of FoxQ1 gene expression in basal chordates.     

CaMADS1, a MADS box gene expressed in the carpel of hazelnut

Hazelnut (Corylus avellana L.) is a species of economic interest that shows a peculiar floral biology. Unlike most of the angiosperms, which produce ovules during floral development such that they are ready for pollen at anthesis, hazelnut ovary development is delayed and triggered by compatible pollination. In order to elucidate the mechanisms regulating this unusual process and the role of the MADS box genes in ovary development, a cDNA library from pollinated styles of hazelnut was screened with a mixture of MADS box genes from different plant species. CaMADS1 (Corylus avellana MADS box), a floral-specific MADS box gene, was isolated, and characterized as belonging to the sub-family of the AGAMOUS genes. Northern blot, RT-PCR analyses and in situ hybridization experiments show a precise correlation between ovary development and CaMADS1 expression, indicating a role of this MADS box gene in the processes of floral organogenesis.     

Ezrin gene, coding for a membrane-cytoskeleton linker protein, is regionally expressed in the developing mouse neuroepithelium

Ezrin is a member of the Ezrin, Radixin, Moesin (ERM) proteins family that are proposed to act as linkers between the cytoskeleton and plasma membrane. Ezrin regulates cell-cell and cell-matrix interactions playing a role in the regulation of cellular adhesion, movement and morphology in epithelia. Alterations in the expression of Ezrin and other members of ERM family have also been observed in brain tumours. Here we report the expression pattern of Ezrin during mouse neural development, from early stages to postnatal stages. In young and middle gestation embryos, Ezrin is expressed in the roof plate of the neural tube, in the presumptive domain of the choroidal plexus, and in some precise domains of ventricular epithelium. These domains are distributed in basal and alar neuroepithelial regions, some of them in relation to the expression of cadherins. At later gestation and postnatal stages, Ezrin expression is maintained on the mature choroidal plexus and is weakly detected in the proliferative regions of the mature brain.