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.
Castelli-Gair Hombría, J., Sánchez-Higueras, C., & Sánchez-Herrero, E. (2016). Control of organogenesis by Hox genes. In Organogenetic Gene Networks: Genetic Control of Organ Formation (pp. 319–373). Springer International Publishing. https://doi.org/10.1007/978-3-319-42767-6_12