Control of Organogenesis by Hox Genes
Hox genes encode a class of animal transcription factors well known for the segment transformations they generate when mutated or expressed ectopically. Hox genes are stably expressed during development in partially overlapping antero-posterior domains of
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Control of Organogenesis by Hox Genes J. Castelli-Gair Hombría, C. Sánchez-Higueras and E. Sánchez-Herrero
Abstract Hox genes encode a class of animal transcription factors well known for the segment transformations they generate when mutated or expressed ectopically. Hox genes are stably expressed during development in partially overlapping antero-posterior domains of the body where they impose their morphological characteristics. This is achieved in two main ways: first, Hox proteins are capable of activating (or repressing) the expression of gene networks responsible for cell specification and organ formation, and second, they compete out the activity of other Hox proteins, either by transcriptional repression or by posterior prevalence. Studies in Drosophila indicate that Hox proteins regulate genes required for organ development, indicating that Hox genes play a role in organogenesis that goes beyond providing antero-posterior regionalization. In a few cases Hox expression is transient, and the input is just required for organ specification. However, in other cases the Hox proteins remain active after organ specification and their function is required for fundamental aspects of organogenesis and cell differentiation. Keywords Organogenesis
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Hox Gene networks Drosophila Development
Introduction
Hox genes encode homeodomain transcription factors that confer specific morphological characteristics to the regions of the body where they are expressed. Mutations in Hox genes can cause spectacular homeotic transformations, where one segment transforms its morphology into that of a neighboring segment. The first J. Castelli-Gair Hombría (&) C. Sánchez-Higueras Centro Andaluz de Biología del Desarrollo (CSIC/JA/Universidad Pablo de Olavide), Seville, Spain e-mail: [email protected] E. Sánchez-Herrero Centro de Biología Molecular-Severo Ochoa (CSIC/Universidad Autónoma de Madrid), Madrid, Spain © Springer International Publishing Switzerland 2016 J. Castelli-Gair Hombría and P. Bovolenta (eds.), Organogenetic Gene Networks, DOI 10.1007/978-3-319-42767-6_12
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Hox mutation described, bx1, was isolated in Drosophila by Calvin Bridges around 1915 and was later studied in depth by Edward B. Lewis, who found it mapped to a region of the chromosome where other homeotic mutations clustered. Lewis published a comprehensive genetic analysis of this region, named the Bithorax complex (BX-C), and suggested it contained several genes controlling the morphological divergence of each thoracic and abdominal segment (Lewis 1978). Later work revealed that the BX-C is composed of only three genes: Ultrabithorax (Ubx), abdominal-A (abd-A) and Abdominal-B (Abd-B) (Sánchez-Herrero et al. 1985; Tiong et al. 1985) and that many of the mutations originally isolated where affecting cis-regulatory elements regulating the temporal and spatial expression of these three genes. A second homeotic complex was found, the Antennapedia complex (ANT-C) that included five Hox genes specifying the morphology
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