Enteral glutamine supplementation for very-low-birth-weight infants decreases hospital costs

Vertebrate Pax-6 and its Drosophila homolog eyeless play central roles in eye specification, although it is not clear if this represents the ancestral role of this gene class. As the most "primitive" animals with true nervous systems, the Cnidaria may be informative in terms of the evolution of the Pax gene family. For this reason we surveyed the Pax gene complement of a representative of the basal cnidarian class (the Anthozoa), the coral Acropora millepora. cDNAs encoding two coral Pax proteins were isolated. Pax-Aam encoded a protein containing only a paired domain, whereas Pax-Cam also contained a homeodomain clearly related to those in the Pax-6 family. The paired domains in both proteins most resembled the vertebrate Pax-2/5/8 class, but shared several distinctive substitutions. As in most Pax-6 homologs and orthologs, an intron was present in the Pax-Cam locus at a position corresponding to residues 46/47 in the homeodomain. We propose a model for evolution of the Pax family, in which the ancestor of all of the vertebrate Pax genes most resembled Pax-6, and arose via fusion of a Pax-Aam-like gene (encoding only a paired domain) with an anteriorly-expressed homeobox gene resembling the paired-like class.     

Posterior patterning by the Caenorhabditis elegans even-skipped homolog vab-7

Patterning of the posterior end in animals is not well understood. Homologs of Drosophila even-skipped (eve) have a similar posterior expression pattern in many animals, and in vertebrates they are linked physically to the "posterior" ends of homeotic clusters (HOM-C), suggesting a conserved role in posterior development. However, the function of this posterior expression is not known. Here I show that the Caenorhabditis elegans gene vab-7 encodes an eve homolog that is required for posterior development and expressed in a pattern strikingly similar to that of vertebrate eve genes. Using a four-dimensional recording system, I found that posterior body muscles and the posterior epidermis are patterned abnormally in vab-7 mutants, but commitment to muscle and epidermal fates is normal. Furthermore, vab-7 activity is required for the complete expression of the most posterior HOM-C gene egl-5 in muscle cells, supporting the idea that eve homologs may act with the HOM-C to determine posterior cell fates. The conservation of sequence and expression pattern between vab-7 and eve homologs in other animals argues that most eve genes have posterior mesodermal and ectodermal patterning functions.     

Murine Otx1 and Drosophila otd genes share conserved genetic functions required in invertebrate and vertebrate brain development

Despite the obvious differences in anatomy between invertebrate and vertebrate brains, several genes involved in the development of both brain types belong to the same family and share similarities in expression patterns. Drosophila orthodenticle (otd) and murine Otx genes exemplify this, both in terms of expression patterns and mutant phenotypes. In contrast, sequence comparison of OTD and OTX gene products indicates that homology is restricted to the homeodomain suggesting that protein divergence outside the homeodomain might account for functional differences acquired during brain evolution. In order to gain insight into this possibility, we replaced the murine Otx1 gene with a Drosophila otd cDNA. Strikingly, epilepsy and corticogenesis defects due to the absence of Otx1 were fully rescued in homozygous otd mice. A partial rescue was also observed for the impairments of mesencephalon, eye and lachrymal gland. In contrast, defects of the inner ear were not improved suggesting a vertebrate Otx1-specific function involved in morphogenesis of this structure. Furthermore, otd, like Otx1, was able to cooperate genetically with Otx2 in brain patterning, although with reduced efficiency. These data favour an extended functional conservation between Drosophila otd and murine Otx1 genes and support the idea that conserved genetic functions required in mammalian brain development evolved in a primitive ancestor of both flies and mice.     

Multiple roles of the eyes absent gene in Drosophila

The eyes absent (eya) gene plays an essential role in the events that lead to formation of the Drosophila eye; without expression of eya in retinal progenitor cells, they undergo programmed cell death just prior to the morphogenetic furrow, leading to an eyeless or reduced eye phenotype. The eya gene has recently been found to be highly conserved to humans, defining a new gene family. Insights into the gene's function in the fly, therefore, are likely to be relevant to the role of its homologs in vertebrates. Detailed studies at the subcellular level indicate that the Eya protein is localized to the nucleoplasm, suggesting a role in control of nuclear events. The eya gene shows expression and roles in tissues other than the eye, including subsets of cells of the adult visual system, brain, and ovary, as well as an elaborate expression pattern in the embryo. Various mutations in the eya gene cause loss of ocelli, female sterility, or lethality. Analysis of the embryonic lethal phenotype indicates that mutant alleles show defects in head morphogenesis. These data indicate that eya has critical roles in morphogenesis of a number of tissues in the animal, in addition to its role in early eye formation. Despite multiple roles at multiple stages of development of the fly, both the type I and type II forms of the protein, when expressed ectopically during larval development, can direct eye formation.     

Specification of anteroposterior cell fates in Caenorhabditis elegans by Drosophila Hox proteins

Antennapedia class homeobox (Hox) genes specify cell fates in successive anteroposterior body domains in vertebrates, insects and nematodes. The DNA-binding homeodomain sequences are very similar between vertebrate and Drosophila Hox proteins, and this similarity allows vertebrate Hox proteins to function in Drosophila. In contrast, the Caenorhabditis elegans homeodomains are substantially divergent. Further, C. elegans differs from both insects and vertebrates in having a non-segmented body as well as a distinctive mode of development that involves asymmetric early cleavages and invariant cell lineages. Here we report that, despite these differences, Drosophila Hox proteins expressed in C. elegans can substitute for C. elegans Hox proteins in the control of three different cell-fate decisions: the regulation of cell migration, the specification of serotonergic neurons, and the specification of a sensory structure. We also show that the specificity of one C. elegans Hox protein is partly determined by two amino acids that have been implicated in sequence-specific DNA binding. Together these findings suggest that factors important for target recognition by specific Hox proteins have been conserved throughout much of the animal kingdom.     

Rescue of Caenorhabditis elegans pharyngeal development by a vertebrate heart specification gene

Development of pharyngeal muscle in nematodes and cardiac muscle in vertebrates and insects involves the related homeobox genes ceh-22, nkx2.5, and tinman, respectively. To determine whether the nematode and vertebrate genes perform similar functions, we examined activity of the zebrafish nkx2.5 gene in transgenic Caenorhabditis elegans. Here, we report that ectopic expression of nkx2.5 in C. elegans body wall muscle can directly activate expression of both the endogenous myo-2 gene, a ceh-22 target normally expressed only in pharyngeal muscle, and a synthetic reporter construct controlled by a multimerized CEH-22 binding site. nkx2.5 also efficiently rescues a ceh-22 mutant when expressed in pharyngeal muscle. Together, these results indicate that nkx2.5 and ceh-22 provide a single conserved molecular function. Further, they suggest that an evolutionarily conserved mechanism underlies heart development in vertebrates and insects and pharyngeal development in nematodes.     

Tolerance, compliance and psychological consequences of post-exposure prophylaxis in health-care workers

We have cloned, from an oribatid mite, a gene homologous to the zerknült (zen) genes of insects and the Hox 3 genes of vertebrates. Hox genes specify cell fates in specific regions of the body in all metazoans studied and are expressed in antero-posteriorly restricted regions of the embryo. This is true of the vertebrate Hox 3 but not of the zen genes, the insect homologs, and it has been proposed that the zen genes have lost their Hox-like function in the ancestor of the insects. We studied expression of a mite Hox 3/zen homolog and found that it is expressed in a discrete antero-posterior region of the body with an anterior boundary coinciding with that of the chelicerate homolog of the Drosophila Hox gene, proboscipedia, and propose that its loss of Hox function in insects is due to functional redundancy due to this overlap with another Hox gene.     

The lunatic fringe gene is a target of the molecular clock linked to somite segmentation in avian embryos

The most obvious segments of the vertebrate embryo are the trunk mesodermal somites which give rise to the segmented vertebral column and the skeletal muscles of the body. Mechanistic insights into vertebrate somitogenesis have recently been gained from observations of rhythmic expression of the avian hairy-related gene (c-hairy1) in chick presomitic mesoderm (PSM), suggesting the existence of a molecular clock linked to somite segmentation ([1]; reviewed in [2]). Here, we show that lunatic Fringe (IFng), a vertebrate homolog of the Drosophila Fringe gene, is also expressed rhythmically in PSM. The PSM expression of IFng was observed as coordinated pulses of mRNA resembling the expression of c-hairy1. We show that c-hairy1 and IFng expression in the PSM are coincident, indicating that both genes are responding to the same segmentation clock. The genes were found to differ in their regulation, however; in contrast to c-hairy1, IFng mRNA oscillations required continued protein synthesis, suggesting that IFng could be acting downstream of c-hairy1 in the clock mechanism. In Drosophila, Fringe has been shown to play a role in modulating Notch-Delta signalling [3,4], a pathway which in vertebrates has been implicated in defining somite boundaries [5-9]. These observations place the segmentation clock upstream of the Notch-Delta pathway during vertebrate somitogenesis.     

Lune/eye gone, a Pax-like protein, uses a partial paired domain and a homeodomain for DNA recognition

Pax proteins, characterized by the presence of a paired domain, play key regulatory roles during development. The paired domain is a bipartite DNA-binding domain that contains two helix-turn-helix domains joined by a linker region. Each of the subdomains, the PAI and RED domains, has been shown to be a distinct DNA-binding domain. The PAI domain is the most critical, but in specific circumstances, the RED domain is involved in DNA recognition. We describe a Pax protein, originally called Lune, that is the product of the Drosophila eye gone gene (eyg). It is unique among Pax proteins, because it contains only the RED domain. eyg seems to play a role both in the organogenesis of the salivary gland during embryogenesis and in the development of the eye. A high-affinity binding site for the Eyg RED domain was identified by using systematic evolution of ligands by exponential enrichment techniques. This binding site is related to a binding site previously identified for the RED domain of the Pax-6 5a isoform. Eyg also contains another DNA-binding domain, a Prd-class homeodomain (HD), whose palindromic binding site is similar to other Prd-class HDs. The ability of Pax proteins to use the PAI, RED, and HD, or combinations thereof, may be one mechanism that allows them to be used at different stages of development to regulate various developmental processes through the activation of specific target genes.