HEDGEHOG SIGNALLING IN DROSOPHILA AND VERTEBRATEDEVELOPMENT by PETER D. CURRIE, ANTONIO JACINTO and PHILLIP W. INGHAM* (Mnleccular Embryology Laboratory Imperial Callar Research Fund 44 Linclon's Inns Field, London WC2A 3PX. UK) ABSTRACT The hedfielwg (hh) gene family encode secreted proteins
developmental control between vertebrates and invertebrates will be found in the general properties of each gene family, not in detailed comparisons between individual genes. KEY WORDS: gene duplication, homeobox genes, amphioxus, vertebratedevelopment, evolu- tion. INTRODUCTION Research over the past ten
The analysis of consecutive ontogenetic stages, or events, introduces a new class of data to phylogenetic systematics that are distinctly different from traditional morphological characters and molecular sequence data. Ontogenetic event sequences are distinguished by varying degrees of both a collective and linear type of dependence and, therefore, violate the criterion of character independence. We applied different methods of phylogenetic reconstruction to ontogenetic data including maximum parsimony and distance (cluster) analyses. Two different data sets were investigated: (1) four simulated ontogenies with defined phylogenies of six hypothetical taxa, and (2) a set of “real” data comprising sequences of 29 ontogenetic events from 11 vertebrate taxa. We confirm that heterochronic event sequences do contain a phylogenetic signal. However, based on our results we argue that maximum parsimony is a biased method to analyze such developmental sequence data. Ontogenetic events require a special analytical algorithm that would not neglect instances of chronological (horizontal) dependence of this type of data. One coding method, “event-pairing”, appeared to fulfill this requirement in the vertebrate analyses. However, to accurately analyze ontogenetic sequence data, a more sophisticated coding method and algorithm are needed, for example, measuring distances of dependent events.
Fish are the oldest vertebrates and the most divergent group, and therefore studies on developmental and molecular genetics in fish can provide a framework and reference for other vertebrates. The zebrafish embryo combines the advantages of experimental embryology and cell fate commitment as in amphibians with the genetic analysis of development as in mammalian systems. The zebrafish has very rapidly become a center of attention because of the thousands of induced developmental mutants that are currently in the process of isolation, characterization, mapping, and cloning. Together with more traditional approaches, like chromosomal and sex manipulation, the use of transgenic fish, and the attempts to produce targeted mutants in pluripotential fish embryonic stem cells, the field of molecular genetics of the fish embryo is now becoming the focus of studies on vertebrate development.
implementation and activation of the genetic instructions found within the zygote; genetics proposes, epigenitics disposes. Epigenetic control of vertebratedevelopment is discussed in the context of hierarchy and increasing complexity. The initial decision in vertebratedevelopment, that between soma or germ
unpolymerized monomers that can be mobilized for fast action.
220 In vertebratedevelopment the best known factors controlling growth are growth hormone (somatotropin), somatostatin and growth factors such as insulin-like growth factor and epidermal growth factor. The borderline between growth factors and
divergence finds its origin in ontogenetic divergence. Early ontogenetic divergence is usually coupled to early com- mon ancestors, while late ontogenetic divergence points to the close phy- logenetic relationship of the species compared. The phylotypic stage of vertebratedevelopment is not the earliest
profiles of hox genes may be related to egg quality and larval viability. Hox genes are known to play a key role in embryonic vertebratedevelopment by diversifying their morphology along the anterior-posterior axis (Deschamps et al., 1999; Lemons & McGinnis, 2006; Casaca et al., 2014). In teleosts
segmentation and tagmosis in arthropods, and it thus affects as yet open questions about their phylogeny. However, though inevitably evoking new questions, many of the 25 contributions in this book do provide significant answers to old ones as, e.g., in filling in some links in vertebratedevelopment that may
Sex steroids, such as oestrogen (e.g., 17β-estradiol, E 2 ), play a critical role in vertebratedevelopment, reproduction, and behaviour by producing a multitude of organisational and activational effects (reviewed in Goy & McEwen, 1980 ; MacLusky & Naftolin, 1981 ). The