Zebrafish Fam83f Regulates Hatching and the DNA Damage-Induced Autophagic Response

Core Concepts

Loss of the Fam83f protein in zebrafish leads to premature hatching and increased sensitivity to DNA damage, likely due to impairment of cellular degradation pathways, particularly autophagy.

Abstract

The study investigates the in vivo functions of the poorly understood Fam83f protein in zebrafish development and stress response. The key findings are:

Fam83f is strongly expressed in the embryonic hatching gland of developing zebrafish. Knockout of the fam83fa gene leads to premature hatching of the embryos, despite normal developmental rate.

Fam83fa knockout embryos show increased sensitivity to DNA-damaging agents like ionizing radiation and methyl methanesulfonate, but this is not due to altered p53 stability or activity.

Transcriptomic analysis reveals that loss of fam83fa leads to downregulation of genes encoding phosphatidylinositol-3-phosphate (PI(3)P) binding proteins, which are important for autophagy and lysosomal processes. This suggests Fam83f modulates autophagic/lysosomal pathways.

The Fam83fa protein itself is targeted to the lysosome when overexpressed, and this localization is dependent on a C-terminal signal sequence.

In summary, the zebrafish Fam83fa protein appears to play a key role in regulating autophagic/lysosomal processes, which in turn impacts embryonic hatching and the cellular response to DNA damage.

Stats

Fam83fa knockout embryos hatch on average 10 hours earlier than wild-type.
Fam83fa knockout embryos show increased sensitivity to ionizing radiation and methyl methanesulfonate treatment compared to wild-type.
Genes encoding predicted PI(3)P binding proteins are significantly downregulated in Fam83fa knockout embryos.

Quotes

"Insights into gene function can often be gained by studying the roles they play during development, and here we report the generation of fam83f knock-out (KO) zebrafish, which we have used to study the role of Fam83f in vivo."
"Transcriptomic analysis shows that loss of fam83f leads to downregulation of phosphatidylinositol-3-phosphate (PI(3)P) binding proteins and impairment of cellular degradation pathways, particularly autophagy, a crucial component of the DNA damage response."
"We show that Fam83f protein is itself targeted to the lysosome when over-expressed in HEK293T cells, and that this localization is dependent upon a C' terminal signal sequence."

Key Insights Distilled From

Zebrafish reveal new roles for Fam83f in hatching and the DNA damage-mediated autophagic response

by Jones,R. A.,... at www.biorxiv.org 02-12-2024

https://www.biorxiv.org/content/10.1101/2024.02.10.579757v1

Deeper Inquiries

How might the dysregulation of autophagy and lysosomal processes in Fam83fa knockout embryos contribute to their increased sensitivity to DNA damage?

The dysregulation of autophagy and lysosomal processes in Fam83fa knockout embryos can contribute to their increased sensitivity to DNA damage through several mechanisms. Autophagy is a crucial cellular process involved in the degradation and recycling of damaged organelles and proteins, as well as in response to stress conditions such as DNA damage. Lysosomes play a key role in the autophagic process by fusing with autophagosomes to degrade their contents.
In Fam83fa knockout embryos, the downregulation of phosphatidylinositol-3-phosphate (PI(3)P) binding proteins, which are involved in autophagy and lysosomal function, can lead to impaired autophagic flux and lysosomal degradation. This impairment can result in the accumulation of damaged cellular components, including DNA lesions, leading to increased sensitivity to DNA damage. Without proper autophagy and lysosomal function, the cells in Fam83fa knockout embryos may struggle to efficiently repair DNA damage and maintain genomic stability.
Furthermore, the dysregulation of autophagy and lysosomal processes can impact the cellular response to genotoxic stress. DNA damage triggers a cascade of signaling pathways, including p53 activation, to initiate DNA repair or induce apoptosis. If autophagy and lysosomal processes are compromised in Fam83fa knockout embryos, the cells may have difficulty in clearing damaged DNA and activating appropriate DNA damage response pathways. This can result in increased cell death and sensitivity to genotoxic stress, as observed in the increased susceptibility of Fam83fa knockout embryos to ionizing radiation and MMS treatment.

What are the specific mechanisms by which Fam83f regulates autophagy and lysosomal function, and how do these processes impact embryonic development and stress responses?

Fam83f regulates autophagy and lysosomal function through its interaction with PI(3)P binding proteins and other autophagy-related genes. The downregulation of PI(3)P binding proteins in Fam83fa knockout embryos suggests that Fam83f may play a role in the recruitment of these proteins to the autophagosome/lysosome membrane, facilitating the degradation of cellular components. By modulating the expression of these proteins, Fam83f can influence the efficiency of autophagic flux and lysosomal degradation.
In embryonic development, proper autophagy and lysosomal function are essential for cellular homeostasis, differentiation, and tissue morphogenesis. Dysregulation of these processes, as seen in Fam83fa knockout embryos, can disrupt normal development by impairing the clearance of cellular debris, damaged organelles, and misfolded proteins. This can lead to developmental defects, as observed in the premature hatching phenotype of Fam83fa knockout embryos.
In response to stress, such as DNA damage, autophagy and lysosomal function are critical for cell survival and the maintenance of genomic integrity. Fam83f's role in regulating these processes can impact the cell's ability to repair DNA damage, remove damaged cellular components, and activate stress response pathways. The dysregulation of autophagy and lysosomal function in Fam83fa knockout embryos can compromise the cell's ability to cope with genotoxic stress, leading to increased sensitivity to DNA damage and impaired stress responses.

Given the links between Fam83f, p53, and Wnt signaling, how might these pathways be interconnected in the context of cellular homeostasis and response to genotoxic stress?

The interconnected pathways of Fam83f, p53, and Wnt signaling play crucial roles in maintaining cellular homeostasis and responding to genotoxic stress. Fam83f interacts with p53 to stabilize and enhance its activity, leading to the activation of p53-dependent pathways involved in DNA damage response and cell cycle regulation. This interaction between Fam83f and p53 can influence the cell's ability to sense and repair DNA damage, promoting genomic stability and cell survival in response to genotoxic stress.
Additionally, Fam83f is involved in the regulation of Wnt signaling, a pathway that plays diverse roles in development, cell proliferation, and differentiation. Dysregulation of Wnt signaling can impact cellular processes such as cell fate determination and tissue morphogenesis. The interaction between Fam83f and Wnt signaling pathways may influence embryonic development and tissue homeostasis by modulating Wnt target genes and downstream signaling cascades.
In the context of genotoxic stress, the interconnected pathways of Fam83f, p53, and Wnt signaling can coordinate the cellular response to DNA damage. Activation of p53 by Fam83f in response to DNA damage can lead to the induction of genes involved in cell cycle arrest, DNA repair, and apoptosis. The modulation of Wnt signaling by Fam83f may further influence the cell's response to genotoxic stress by regulating cell survival, proliferation, and differentiation pathways.
Overall, the crosstalk between Fam83f, p53, and Wnt signaling pathways provides a complex network of interactions that contribute to cellular homeostasis, embryonic development, and the response to genotoxic stress. Understanding the interplay between these pathways is essential for elucidating their roles in maintaining cellular integrity and coping with environmental challenges.