Prelude to molecularization: The double gradient model of Sulo Toivonen and Lauri Saxén

Area of Science:

• Developmental biology
• Molecular embryology
• Genetics

Background:

• Classical embryology utilized transplantation to model embryonic induction.
• The dual gradient model proposed mechanisms for anterior-posterior and dorsal-ventral polarity.
• Early research focused on identifying `Induktionsstoffen` (inducing substances).

Purpose of the Study:

• To trace the historical connection between transplantation experiments and molecular investigations of Organizer phenomena.
• To discuss the development of the dual gradient model and the search for `Induktionsstoffen`.
• To highlight the transition from classical embryology to developmental genetics.

Main Methods:

• Historical review of transplantation experiments in embryology.
• Analysis of the conceptual development of the dual gradient model.
• Documentation of research leading to the identification of embryonic induction molecules.

Main Results:

• Transplantation studies provided foundational data for mechanistic models of induction.
• The search for `Induktionsstoffen` led to the formulation of the double gradient model.
• This research paved the way for developmental genetics and the discovery of key developmental molecules.

Conclusions:

• Molecular investigations confirm and extend insights from classical embryological transplantation studies.
• The historical pursuit of `Induktionsstoffen` was crucial for understanding embryonic polarity and induction.
• The evolution of research from transplantation to molecular genetics has elucidated primary embryonic induction mechanisms.