Metabolic complementation between cells drives the evolution of tissues and organs

Area of Science:

• Evolutionary biology
• Cellular metabolism
• Developmental biology

Background:

• Evolutionary transitions of individuality are well-theorized, but the origin of internal organismal organization is less understood.
• The formation of specialized tissues and organs from individual cells raises questions about the drivers of these transitions, especially when cell types already perform functions.
• Existing theories lack a clear explanation for how and why cells aggregate into higher organizational levels within multicellular organisms.

Purpose of the Study:

• To propose a novel hypothesis for the evolutionary transition of cellular organization into tissues and organs.
• To explain the origin of organizational levels within organisms, focusing on the integration of specialized cell types.
• To identify the key factors that trigger a transition in organizational level when constituent cell types already possess the necessary functions.

Main Methods:

• The study proposes a hypothesis based on two key features of cellular metabolism: metabolic constraints and metabolic complementation.
• It outlines a scenario where environmental changes favor offloading metabolic burdens between cell types.
• The hypothesis is illustrated using examples from the nervous system and pancreas.

Main Results:

• The hypothesis suggests that metabolic constraints on cell function and the ability of different cell types to complement each other metabolically are crucial.
• Environmental changes can drive the integration of specialized cells into tissues by promoting the offloading of metabolic demands.
• This process, termed 'supra-functionalization,' explains how pre-existing cell types can form more complex structures.

Conclusions:

• Metabolic factors, specifically constraints and complementation, provide a framework for understanding the evolution of multicellular organization.
• Environmental pressures can lead to the development of tissues and organs through the metabolic integration of specialized cells.
• The concept of 'supra-functionalization' offers a new perspective on how higher levels of organization arise within organisms.