Jean S. Deutsch

Phylogenetic Analysis of Invertebrate Lysozymes and the Evolution of Lysozyme Function

Abstract. We isolated and sequenced the cDNAs coding for lysozymes of six bivalve species. Alignment and phylogenetic analysis showed that, together with recently described bivalve lysozymes, the leech destabilase, and a number of putative proteins from extensive genomic and cDNA analyses, they belong to the invertebrate type of lysozymes (i type), first described by Jollès and Jollès (1975). We determined the genomic structure of the gene encoding the lysozyme of Mytilus edulis, the common mussel. We provide evidence that the central exon of this gene is homologous to the second exon of the chicken lysozyme gene, belonging to the c type. We propose that the origin of this domain can be traced back in evolution to the origin of bilaterian animals. Phylogenetic analysis suggests that i-type proteins form a monophyletic family.

Developmental stability: a major role for cyclin G in Drosophila melanogaster

Morphological consistency in metazoans is remarkable given the pervasive occurrence of genetic variation, environmental effects, and developmental noise. Developmental stability, the ability to reduce developmental noise, is a fundamental property of multicellular organisms, yet its genetic bases remains elusive. Imperfect bilateral symmetry, or fluctuating asymmetry, is commonly used to estimate developmental stability. We observed that Drosophila melanogaster overexpressing Cyclin G (CycG) exhibit wing asymmetry clearly detectable by sight. Quantification of wing size and shape using geometric morphometrics reveals that this asymmetry is a genuine—but extreme—fluctuating asymmetry. Overexpression of CycG indeed leads to a 40-fold increase of wing fluctuating asymmetry, which is an unprecedented effect, for any organ and in any animal model, either in wild populations or mutants. This asymmetry effect is not restricted to wings, since femur length is affected as well. Inactivating CycG by RNAi also induces fluctuating asymmetry but to a lesser extent. Investigating the cellular bases of the phenotypic effects of CycG deregulation, we found that misregulation of cell size is predominant in asymmetric flies. In particular, the tight negative correlation between cell size and cell number observed in wild-type flies is impaired when CycG is upregulated. Our results highlight the role of CycG in the control of developmental stability in D. melanogaster. Furthermore, they show that wing developmental stability is normally ensured via compensatory processes between cell growth and cell proliferation. We discuss the possible role of CycG as a hub in a genetic network that controls developmental stability.

Expression of a homologue of the fushi tarazu (ftz) gene in a cirripede crustacean

SUMMARY In Metazoa, Hox genes control the identity of the body parts along the anteroposterior axis. In addition to this homeotic function, these genes are characterized by two conserved features: They are clustered in the genome, and they contain a particular sequence, the homeobox, encoding a DNA‐binding domain. Analysis of Hox homeobox sequences suggests that the Hox cluster emerged early in Metazoa and then underwent gene duplication events. In arthropods, the Hox cluster contains eight genes with a homeotic function and two other Hox‐like genes, zerknullt (zen)/Hox3 and fushi tarazu (ftz). In insects, these two genes have lost their homeotic function but have acquired new functions in embryogenesis. In contrast, in chelicerates, these genes are expressed in a Hox‐like pattern, which suggests that they have conserved their ancestral homeotic function.

Do acoels climb up the “Scale of Beings”?

During the eighteenth century, Swiss naturalist Charles Bonnet promoted the idea of the ‘‘Scala Naturae’’: from minerals to animals and beyond, all beings on earth should be arranged on a smooth ladder, progressively increasing by degrees of perfection up to the most perfect creatures of God, not the human beings, as misbelievers such as you might expect, but the angels (Bonnet 1782). Lamarck first followed the same scheme for the evolution of living beings, but later, in an addendum to his ‘‘Philosophie Zoologique’’ (1809, pp. 641– 651), he abandoned this linear vision for a more complex picture. Darwin, as illustrated by the bushy representation of evolution given in ‘‘The Origin of Species’’ (1859), was far from the ‘‘Scala Naturae’’ (but see the discussion in Gould 2002, Chapter 6). Nevertheless, the view of evolution as continuous progress is pervasive, not only for the public at large, but even for the community of biologists (see for instance de Duve 2002). Now, Divine Providence is replaced by ‘‘complexity.’’ Most biologists of the twentieth century divided the animal kingdom according to the number of germ layers, that is, two, endoderm and ectoderm, for the diploblasts, namely the Porifera (sponges), the Cnidaria (sea anemones, corals, medusas, hydras) and the Ctenophora (comb jellies), and three for the remaining triploblasts, which added the mesoderm as a third layer. In the mid-century, the great zoologist Libbie Hyman (1940) dispatched the metazoan phyla into ‘‘grades’’ of complexity: the cellular grade (Porifera) versus the tissue grade of construction, the radiate phyla (Cnidaria and Ctenophora) versus the Bilateria, and among the bilaterian phyla, the acoelomates, with no coelom, the pseudocoelomates, also called ‘‘Aschelminthes,’’ where the internal body cavity is not or partially lined with mesoderm, and the ‘‘true’’ coelomates. These grades were thought to have appeared sequentially: the Porifera, then the Radiata, and among the Bilateria, the acoelomates first, then the Aschelminthes, followed by the coelomates. Accordingly, the Platyhelminthes (flat worms) as acoelomates were thought to be early branching (‘‘basal’’) in the metazoan phylogenetic tree, and the Acoela, a basal class belonging to this phylum. This view has been widely accepted until the end of the twentieth century.

Are Cirripedia hopeful monsters? Cytogenetic approach and evidence for a Hox gene cluster in the cirripede crustacean Sacculina carcini

The “hopeful monster” has haunted evolutionary thinking since Richard Goldschmidt coined the phrase in 1933. The phrase is directly related to genetic mechanisms in development and evolution. Cirripedes are peculiar crustaceans in that they all lack abdomens as adults. In a previous study aimed at describing the repertoire of Hox genes of the Cirripedia, we failed to isolate the abdominal-A gene in three species representative of all three cirripede orders. To address the question of whether the cirripede ancestor could have been a “hopeful monster” arising from a rearrangement of the Hox complex, we have performed a cytogenetic analysis of the Hox complex of the cirripede Sacculina carcini. We present here molecular and cytogenetic evidence for the grouping of the Hox genes on a single chromosome. This is the first direct evidence reported for the grouping of Hox genes on the same chromosome in a non-insect arthropod species.

Introduction—development and phylogeny of the arthropods: Darwin’s legacy

In the present essay, I first recall the genealogical concept of classification settled by Charles Darwin in the Origin of Species. Darwin tightly linked what we now call phylogeny and development. He often insisted to take into account embryonic and larval characters, most often using as examples his favourite animals, the cirripedes. Then I discuss remaining problems, and also perspectives, to address the link between phylogeny and development in the modern terms of molecular and cladistic phylogenetics and of molecular and genetic developmental biology.