Dirk Hockemeyer

Dirk Hockemeyer

Title
Assistant Professor
Department
Dept of Molecular & Cell Biology
Research Expertise and Interest
developmental biology, cell biology
Research Description

The goal of Dirk Hockemeyer's research is to shed light on the key functions of telomeres and telomerase in tissue homeostasis, tumorigenesis and aging. Telomeres are the repetitive DNA sequences at the end of linear eukaryotic chromosomes that allow a cell to distinguish the natural chromosome end from aberrant DNA breaks. Telomeric DNA repeats can be generated de novo by the enzyme telomerase thereby providing a compensatory mechanism that counteracts terminal sequence loss caused by the end replication problem. As a result, telomeres and telomerase are essential to genomic integrity and their disruption is associated with cancer and aging. The use of genetic mouse models has been a powerful way to gain insight into the fundamental mechanisms of how the telomere evades recognition by the DNA-damage machinery, the consequences of telomerase loss, and how the single stranded telomeric overhang is established. However, telomere shortening naturally occurs only in human somatic cells, but not in mouse cells. This telomere shortening, which functions as a tumor suppressor mechanism by limiting the replicative potential of human cells, is the result of selective silencing of telomerase expression in human cells upon their differentiation. Notably, this process is reversed and telomerase reactivated in about 90% of all human tumors after which telomerase expression becomes essential for their proliferation.

Human pluripotent stem cells (hPSC) are an ideal model system to study telomerase regulation, as they are telomerase-positive, but can be rapidly differentiated into telomerase-negative cells.  Moreover, the reverse process of telomerase reactivation can be studied during the process of reprogramming somatic cells into induced pluripotent stem cells (iPSCs).  Owing to their constitutive telomerase expression, PSCs are immortal and can be expanded indefinitely in culture.  However, in contrast to other model systems such as tumor cells, they have functional DNA surveillance and cell cycle checkpoints and therefore are ideal for studying the effects of telomere shortening and dysfunction on these pathways. Over the last few years his team has developed robust protocols to derive and genetically modify human PSCs.Prior to this, primary human cells were resilient to conventional homologous recombination making gene targeting extremely inefficient and time consuming.

Due to these technical advancements it is possible now to overexpress or silence genes, correct disease-causing mutations, and engineer reporter genes in human PSCs. In his laboratory, the team will use these gene targeting strategies to study the biology of human telomeres to address:

  1. What is the mechanism of telomerase regulation in human stem cells, upon their differentiation and during tumor formation?
  2. What are the molecular mechanisms underlying the recruitment of telomerase to the telomere in human cells?
  3. What are the consequences of telomere shortening in stem cells and how does this impact tumor formation?

In the News

October 6, 2021

Neuroscientists roll out first comprehensive atlas of brain cells

When you clicked to read this story, a band of cells across the top of your brain sent signals down your spine and out to your hand to tell the muscles in your index finger to press down with just the right amount of pressure to activate your mouse or track pad. A slew of new studies now shows that the area of the brain responsible for initiating this action — the primary motor cortex, which controls movement — has as many as 116 different types of cells that work together to make this happen.
September 16, 2020

$14 million boost for Parkinson’s disease research

Two new grants totaling nearly $14 million over three years will jump-start research at UC Berkeley into the molecular and genetic causes of Parkinson’s disease, a neurodegenerative disorder that afflicts more than 1 million Americans, yet whose cause remains a mystery.
May 13, 2020

Campus lab takes COVID-19 testing to utility workers, underserved

A month after opening, a COVID-19 testing lab at the University of California, Berkeley, has branched out from evaluating symptomatic students to assessing a broader range of people potentially exposed to the new coronavirus, including residents of local nursing homes, the East Bay’s homeless population, front-line firefighters and police officers and, now, utility workers around the state.

In the News

October 6, 2021

Neuroscientists roll out first comprehensive atlas of brain cells

When you clicked to read this story, a band of cells across the top of your brain sent signals down your spine and out to your hand to tell the muscles in your index finger to press down with just the right amount of pressure to activate your mouse or track pad. A slew of new studies now shows that the area of the brain responsible for initiating this action — the primary motor cortex, which controls movement — has as many as 116 different types of cells that work together to make this happen.
September 16, 2020

$14 million boost for Parkinson’s disease research

Two new grants totaling nearly $14 million over three years will jump-start research at UC Berkeley into the molecular and genetic causes of Parkinson’s disease, a neurodegenerative disorder that afflicts more than 1 million Americans, yet whose cause remains a mystery.
May 13, 2020

Campus lab takes COVID-19 testing to utility workers, underserved

A month after opening, a COVID-19 testing lab at the University of California, Berkeley, has branched out from evaluating symptomatic students to assessing a broader range of people potentially exposed to the new coronavirus, including residents of local nursing homes, the East Bay’s homeless population, front-line firefighters and police officers and, now, utility workers around the state.
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