Cross-kingdom comparison of the developmental hourglass

Hajk-Georg Drost,Philipp Janitza,Ivo Grosse,Marcel Quint

doi:10.1016/j.gde.2017.03.003

Abstract

The developmental hourglass model has its foundations in classic anatomical studies by von Baer and Haeckel. In this context, even the conservation of animal body plans has been explained by evolutionary constraints acting on mid-embryogenic development. Recent studies have shown that developmental hourglass patterns also exist on the transcriptomic level, mirroring the corresponding morphological patterns. The identification of similar patterns in embryonic, post-embryonic, and life cycle spanning transcriptomes in plant and fungus development, however, contradict the notion of a direct coupling between morphological and molecular patterns. To explain the existence of hourglass patterns across kingdoms and developmental processes, we propose the organizational checkpoint model that integrates the developmental hourglass model into a framework of transcriptome switches.

Highlights

Understanding genesis, evolution, and variability of complex organismal forms is among the most fundamental objectives of biological research
We review recent molecular findings in animals and plants, discuss theircompatibility with the developmental hourglass model originally conceived to explain morphological hourglass patterns in animals, and propose the organizational checkpoint model that is compatible with those findings in both animals and plants
We propose the organizational checkpoint model to integrate the developmental hourglass model into a framework of transcriptome switches

Summary

Introduction

Understanding genesis, evolution, and variability of complex organismal forms is among the most fundamental objectives of biological research. The developmental hourglass model is restricted to embryogenesis and (ii) constraints on organogenesis or body plan formation in mid embryogenesis are believed to be the main cause for the morphological resemblance of animal embryos in that stage or period. Only in depth morphological study that rigorously tested morphological transitions throughout embryogenesis and across species, (ii) includes only a fraction of the species for which transcriptomic hourglass patterns have recently been found, and (iii) was not especially supportive of a simplified hourglass model This notion is reflected by the introductory statement given by Richardson et al [8]: “One puzzling feature of the debate in this field is that while many authors have written of a conserved embryonic stage, no one has cited any comparative data in support of the idea. They thereby prohibit a larger period of overlapping of different developmental programs, ensuring ordered transition between programs

Conclusions

Richardson MK

10. Schleip W

27. Wardlaw C