The Ubiquitin Diary

The Krebs Cycle Cycle

Some facts about human brain:

• Your brain keeps developing until your late 40s

• New brain connections are created every time you form memory.

• Your brain uses 20% of the total oxygen in your body.

• 60% of your brain is fat.

• The human brain has the same consistency as tofu.

Building Asteroids

For a blockbuster movie, you need more than an A-list cast, you need a supporting crew to help them shine. In the human brain, neurons are the stars of the show but they wouldn’t work properly without support too. Cells called astrocytes do just this but studying their effects on neurons is often limited to human brain explants, which are in short supply. Researchers now present lab-grown 3D models – organoids – made by growing astrocytes and neurons, created from human pluripotent stem cells, in a dish together. They named these organoids asteroids (pictured). Growing astrocytes (green) with a high density of neurons (red) produced astrocytes with complex structures similar to those seen in the human brain, visualised here using fluorescent microscopy. The team were able to control the exact number of cells grown together, resulting in a tightly controlled system suitable for modelling disease and drug screening.

Written by Lux Fatimathas

Image from work by Robert Krencik and colleagues

Center for Neuroregeneration, Department of Neurosurgery, Houston Methodist Research Institute, Houston, TX 77030, USA

Image copyright held by the original authors

Published in Stem Cell Reports, November 2017

Quiescent/ senescent 

Gap 0/G0 

A resting phase where the cell has left the cycle and has stopped dividing. 

Interphase

 Gap 1 / G1 

Cells increase in size. The G1 checkpoint control mechanism ensures that everything is ready for DNA synthesis. 

DNA Synthesis / S 

DNA replication occurs during this phase. 

Gap 2 / G2 

During the gap between DNA synthesis and mitosis, the cell will continue to grow. The G2 checkpoint control mechanism ensures that everything is ready to enter the M (mitosis) phase and divide. 

Cell division 

Mitosis / M 

Cell growth stops at this stage and cellular energy is focused on the orderly division into two daughter cells. 

A checkpoint in the middle of mitosis (Metaphase Checkpoint) ensures that the cell is ready to complete cell division. 

Cyclins 

family of proteins control cells through the cell cycle by activating cyclin-dependent kinases (CDKs). 

G1 /S cyclins – essential for the control of the cell cycle at the G1/S transition, Cyclin D/ CDK4, Cyclin D /CDK6, and Cyclin E / CDK2 – regulates transition from G1 to S phase. 

G2 /M cyclins – essential for the control of the cell cycle at the G2/M transition (mitosis). G2 /M cyclins accumulate steadily during G2 and are abruptly destroyed as cells exit from mitosis. Cyclin B / CDK1 – regulates progression from G2 to M phase 

Image of the Week – April 16, 2018

CIL:40965 - http://www.cellimagelibrary.org/images/40965

Description: Brightfield micrograph of a living diatom (Mediopyxis helysia) showing the cell nuclei and golden chloroplasts. There is a bacteria colony in mucilage located on the top of the diatom. The image won the Ninth Prize, 2011 Olympus BioScapes Digital Imaging Competition®.

Authors: Wolfgang Bettighofer and 2011 Olympus BioScapes Digital Imaging Competition®