Nicole King (UC Berkeley, HHMI) 1: The origin of animal multicellularity

Summary

In this engaging presentation, Nicole King explores the origins of multicellularity and the evolution of animals. Focusing on choanoflagellates, the closest living relatives of animals, King discusses how these organisms offer unique insights into the transition from single-celled to multicellular life. By studying the genes and cell biology of choanoflagellates, researchers are uncovering how key traits of animals, like specialized cell types and gene regulation, evolved. The talk emphasizes the importance of genomic comparisons and the discovery of ancient genes that predate the emergence of multicellular animals, shedding light on evolutionary processes that shaped life on Earth.

Takeaways

• 😀 Choanoflagellates are single-celled organisms closely related to animals, providing insights into the evolution of multicellularity.
• 😀 The study of choanoflagellates helps reconstruct the genetic landscape of animal origins, revealing the common ancestry of animals and these unicellular organisms.
• 😀 Genes involved in animal multicellularity, such as those for cell signaling, adhesion, and gene regulation, existed before the emergence of animals.
• 😀 Key genes involved in cell signaling in animals, including GPCRs, receptor tyrosine kinases, and proto-oncogenes like Src, are also present in choanoflagellates.
• 😀 Choanoflagellates exhibit cell adhesion mechanisms similar to animals, including cadherins and lectins, which are essential for cell-cell interactions.
• 😀 Choanoflagellates express important transcription factors, such as Myc, p53, and Forkhead, which are involved in gene regulation and are found in animals.
• 😀 Despite sharing many genes with animals, choanoflagellates lack certain genes essential to animals, such as the classical cadherins and Hox genes, which are crucial for developmental patterning.
• 😀 The discovery of these genes in choanoflagellates suggests that the genetic tools for multicellularity predated the evolution of complex animals.
• 😀 Studying choanoflagellates helps identify genomic innovations that might have contributed to the origin of multicellularity in animals.
• 😀 Future research will focus on understanding how genes that evolved before multicellularity functioned in early unicellular organisms and what roles they played in the emergence of multicellularity.

Q & A

What are choanoflagellates, and why are they important for understanding animal evolution?

Choanoflagellates are single-celled eukaryotes and are considered the closest living relatives to animals. They play a key role in understanding animal evolution because they share critical cellular features, such as collar cells, which are also found in sponges, the simplest animals. Studying choanoflagellates helps researchers understand the genome and cell biology of the first animals.

How does the study of choanoflagellates help scientists understand the origin of multicellularity?

The study of choanoflagellates reveals that many genes required for multicellularity in animals existed before the origin of animals. These include genes involved in cell signaling, adhesion, and extracellular matrix interactions. By examining how these genes evolved, scientists can better understand the genetic and cellular foundations of multicellularity.

What key features of choanoflagellates are shared with animals?

Choanoflagellates share several key features with animals, including collar cells that are similar to those found in sponges. These cells play a role in filtering food particles, and their structure is believed to be an ancestral trait shared with early animals.

What types of genes were found in choanoflagellates that are typically associated with animal multicellularity?

Choanoflagellates express genes associated with animal multicellularity, including those involved in cell signaling (e.g., GPCRs, receptor tyrosine kinases), cell adhesion (e.g., cadherins, lectins), and gene regulation (e.g., Myc, p53). These genes are involved in processes like cell-cell interactions and coordination with the extracellular matrix.

How do choanoflagellates contribute to understanding the evolutionary origin of animals?

By studying choanoflagellates, scientists can identify genes that were likely present in the last common ancestor of animals. These genes provide insights into the early genetic makeup of multicellular organisms and help trace the evolutionary steps that led to the emergence of complex animal life.

What is the significance of finding certain genes exclusively in animals and not in non-animal organisms?

The discovery of genes like Hox genes and classical cadherins, which are exclusively found in animals, highlights key genomic innovations that were likely crucial for the transition to multicellularity. These genes are involved in developmental processes like body patterning and cellular differentiation, marking important steps in the evolution of complex animal structures.

How did choanoflagellates contribute to understanding the role of bacterial consumption in early animal evolution?

The study of choanoflagellates suggests that early animals, like choanoflagellates, might have relied on consuming bacteria for nutrition. This discovery supports the idea that bacteria played a crucial role in the diet and ecological interactions of early animal ancestors, potentially influencing the evolution of multicellularity.

What are some challenges in studying choanoflagellates and their relevance to animal evolution?

One challenge in studying choanoflagellates is understanding how genes, which are present in both choanoflagellates and animals, functioned in their common ancestors. It is also difficult to reconstruct the exact cellular behaviors and ecological conditions that led to the evolution of multicellularity, as these events happened nearly a billion years ago.

What is the potential future research direction mentioned in the script regarding choanoflagellates and animal origins?

Future research will focus on understanding the role of genes that are shared between choanoflagellates and animals, particularly how these genes functioned in unicellular ancestors. Additionally, researchers are interested in exploring how the transition to multicellularity occurred in choanoflagellates and what this can tell us about the evolution of animal life.

Why are developmental patterning genes like Hox genes important in the context of animal evolution?

Hox genes are crucial because they regulate the body plan of an organism during development, determining the arrangement of structures and organs. The fact that these genes are found exclusively in animals suggests they played a significant role in the evolution of animal complexity, enabling the precise control of development that is characteristic of multicellular animals.