A critique is provided of the physical and chemical control of primary and secondary xylem development in terms of mechanics, genetics, phylogenetics, and the larger field of plant physiology. Strengths and weaknesses of the phytohormone theory of vascular development are analyzed. Homeobox genes, sub-cellular phytohormone localization, anatomical responses to varied phytohormone ratios and dosages, polar auxin transport, second messengers, radial fluxes in water potential, intercellular signalling, lignin biochemistry, and the phylogenetic position of bryophytes in relation to xylogenesis are identified as some areas for future research. Homeodomain proteins are addressed in terms of cambial initials and cell-fate determination, and other genetic and environmental factors controlling differentiation of diverse cellular phenotypes are reviewed. As a 'continuum hypothesis', it is proposed that the extent of secondary wall sculpturing during tracheary element differentiation is a function of the duration of homeotic gene expression.
divergent taxa, since duplication of genes promotes functional divergence. Surveys of homeoboxgene diversity in vertebrates and amphioxus reveal that many classes of homeoboxgenes duplicated close to vertebrate origins. This raises the question of how widespread gene duplication was during early
Common sole (Solea solea) aquaculture production is based mostly on wild-caught breeders. Recently, the successful reproduction of first-generation fish that were reared in captivity was accomplished. A consistent good quality and quantity of produced eggs throughout the year, and of next-generation broodstock, is important for reducing the overall cost of production. Hox genes play a pivotal role in normal embryonic development and alterations of their temporal expression level may be important for egg viability. Expression profile analysis of five hox genes (hoxa1a, hoxa2a, hoxa2b, hoxb1a and hoxb1b) involved in early embryonic development and of hoxa13a, which is involved in late stages, was carried out. Results revealed a premature and/or maternal expression of hoxa13a in sole embryos, and the detection of hoxa2a and hoxa2b genes as members of paralog group 2. Principal Component Analysis of hox gene expression in 54 ± 6 hours post fertilization embryos coming from wild-caught broodstock and a first-generation one reared in the hatchery, unveiled that these broodstocks are clearly distinct. In addition, their pairwise comparison revealed significant differences in the expression levels of hoxb1a and hoxb1b genes. Hox gene regulation during embryonic development could give valuable insight into rearing sole broodstocks with different origin in concert, and also into gaining a steady mass production of eggs, either in quality or quantity, all year round.
. Aquaculture-Bamidgeh 1993 45 59 72
Cho K.W.Y. Blumberg B. Steinbeisser H. DeRobertis E.M. Molecular nature of Spemann's organizer: the role of Xenopus homeoboxgene goosecoid Cell 1991 67 1111 1120
Chourrout D. Genetic manipulation in fish: review of methods. Selection hybridization and genetic
cliniques de Montreal, Michael Crawford moved to the University of Windsor where he is presently Associate Professor in the Department of Biological Sciences. His work focuses upon the role of homeoboxgenes in directing the early body plan “mapping” of amphibian embryos. Melissa Barden Dowling completed
expression patterns described below. In zebrafish, a number of genes is preferentially cxprcssed in the area of early embryonic shicld formation. Among them are some homeoboxgenes: goosecoid will be expressed in very early internalizing cells anterior to the presumptivc notochord (STACHEL et al., 1993
more apparent at late stages" (cf. VON BAER, 1828), though vertebrates are not virtually identical at earlier stages. Hox genes (homeoboxgenes that are organised in four vertebrate clusters of hox genes) play an important role in the proper organisation of the vertebrate body plan, which takes place
all-trans-retinoic acid in hamster trachea and liver. Biochemistry 18: 2092. GAUNT, S.J., 1987. Homoeoboxgene Hox-1.5 expression in mouse embryos: earliest detection by in situ hybridization is during gastrulation. Development 101: 21. GAUNT, S.J., 1988. Mouse homeoboxgene transcripts occupy
-A response regulators OsRR2 and OsRR3. Overexpression of OsCKX4 in rice promotes crown root formation ( Gao et al. 2014 ). Finally, CRL5 is a positive regulator of crown root formation that acts by repressing cytokinin signaling ( Kitomi et al. 2011 ).
The WUSCHEL -related homeoboxgene WOX11 is