My PhD project studies how the temporally sequential Hox gene expression is regulated during head-tail patterning of the frog embryo. This question has not been solved and remains one of the... Show moreMy PhD project studies how the temporally sequential Hox gene expression is regulated during head-tail patterning of the frog embryo. This question has not been solved and remains one of the greatest unsolved mysteries in developmental biology. Currently, a very attractive explanation attributes sequential Hox gene activation to progressive opening of the chromosome, because it parallels the linear arrangement of Hox genes on the chromosome. While promising, this explanation is surrounded by extra complexities that ensure Hox expression is synchronized between different cells. By using gain-of-function and loss-of-function approaches, I discovered that Hox-Hox interactions play a crucial role in the regulation of Hox expression, and for the first time, I dissected different roles for these interactions in axis formation. The findings are likely to resolve the above complexities, and reveal a new facet of the mechanisms underlying Hox gene regulation. Furthermore, by timed modulation of the actions of BMP signaling, I showed that there is a BMP-dependent timing mechanism in the head that could be continued by the Hox temporal sequence in the trunk. The two constitute an integrative timer which can be translated into spatial patterns of gene expression along the whole head-tail axis via a BMP/anti-BMP dependent mechanism. Show less
The origin and diversification of novel morphological traits is a major research theme in evolutionary developmental biology, or evo-devo. Wing patterns of butterflies, in particular eyespots, are... Show moreThe origin and diversification of novel morphological traits is a major research theme in evolutionary developmental biology, or evo-devo. Wing patterns of butterflies, in particular eyespots, are lineage-specific novelties crucial for visual communication. This thesis explores different aspects of eyespot evo-devo, ranging from redeployment of conserved developmental genes in their formation, to the genetic basis of variation in laboratory populations of the model Bicyclus anynana, to evolutionary diversification of eyespot gene networks in a range of butterfly species. We demonstrated that the conserved Hox protein Antennapedia is involved in eyespot formation, in a particular subfamily of Nymphalidae. This highlights the diversification of the regulatory interactions underlying the very first step in eyespot development. We also characterized the segregation and developmental effects of alleles at a single locus that controls eyespot morphology and embryonic segment polarity via the regulation of Wingless signalling. Linkage mapping of this locus revealed that it is a novel, possibly lineage-specific, negative regulator of this signalling pathway. This suggests that not only conserved, but also putative lineage-specific genes can play a role in the formation of novel traits. Show less
Hox genes are a very important family of transcription factors during development of vertebrate and invertebrates. This family of genes contains up to 39 Hox gene members organized in 4 clusters in... Show moreHox genes are a very important family of transcription factors during development of vertebrate and invertebrates. This family of genes contains up to 39 Hox gene members organized in 4 clusters in the genome. The main function of Hox genes is the establishment of the anteroposterior axis of the embryo. During gastrulation of the frog Xenopus laevis, Hox genes start to be expressed in the mesoderm excluding the Spemann organizer mesoderm. However, a necessary interaction between the involuting mesodermal cells and the signals from the Spemann organizer center freeze the pattern of Hox expression at that time point. Thus a temporal Hox expression is converted into a spatial Hox expression during development. Moreover, Hox gene expression within the mesoderm seems to be important for Hox expression within the neural tissue. We missexpressed several Hox genes and analyzed their phenotype within the hindbrain and more posterior neural tissue. Paralogous 1 group Hox genes are important for globally pattern the hindbrain, while Hoxc6 gene seems to very important during neurogenesis in Xenopus. Axis elongation and segmentation are liked processes during development. We showed that Hoxc6 is an important gene for proper segmentation of Xenopus embryo. Show less
