Microscopy of Fission Yeast Sexual Lifecycle

Summary

We provide a reproducible basic method for the long-term microscopy of the fission yeast sexual lifecycle. With minor adjustments described, the presented protocol allows research focus on different steps of the reproductive process.

Abstract

The fission yeast Schizosaccharomyces pombe has been an invaluable model system in studying the regulation of the mitotic cell cycle progression, the mechanics of cell division and cell polarity. Furthermore, classical experiments on its sexual reproduction have yielded results pivotal to current understanding of DNA recombination and meiosis. More recent analysis of fission yeast mating has raised interesting questions on extrinsic stimuli response mechanisms, polarized cell growth and cell-cell fusion. To study these topics in detail we have developed a simple protocol for microscopy of the entire sexual lifecycle. The method described here is easily adjusted to study specific mating stages. Briefly, after being grown to exponential phase in a nitrogen-rich medium, cell cultures are shifted to a nitrogen-deprived medium for periods of time suited to the stage of the sexual lifecycle that will be explored. Cells are then mounted on custom, easily built agarose pad chambers for imaging. This approach allows cells to be monitored from the onset of mating to the final formation of spores.

Introduction

Though genetic exchange between two cells is the central event in sexual reproduction, it relies on a chain of events that promote cell differentiation, allow for partner choice, carry out cell-cell fusion and maintain genomic stability. Thus the sexual lifecycle presents itself as a model system to study a number of biological questions regarding developmental switches, response to extrinsic stimuli, plasma membrane fusion, chromosome segregation, etc. Exploring the fission yeast sexual cycle to study these phenomena brings the benefits of the model system's powerful genetics, well-established high-throughput approaches and sophisticated microscopy. Sex ....

Protocol

Microscopy analysis of fission yeast sexual reproduction

1. Media Preparation

1. Prepare Minimum Sporulation medium (MSL-N)¹⁵ by mixing the following components: Glucose: 10 g/L, KH₂PO₄: 1 g/L, NaCl: 0.1 g/L, MgSO₄·7H₂O: 0.2 g/L. Add Trace elements (10,000x): 100 µl/L, Vitamins (1,000x): 1 ml/L, and 0.1 M CaCl₂ ml/L. Filter-sterilize using a 0.22 μm pore size filter and store at room temperature (RT).
   1. Use the following Vitamins (1,000x) stock: Pantothenate: 1 g/L, Nicotinic Acid: 10 g/L, Inositol: 10 g/L, Biotin: 10 mg/L. Filter-sterilize using a 0.22 μm pore size ....

Results

Fission Yeast Growth and Mating Dynamics Upon Removal of a Nitrogen Source
As nitrogen starvation is a prerequisite for initiation of sexual reproduction in fission yeast, wild-type homothallic h90 strain was monitored upon shift from nitrogen-rich to nitrogen-deprived medium (Figure 2), following the protocol outlined in Figure 1. Briefly, cells were grown O/N to exponential phase (O.D.₆₀₀ = 0.5) in MSL+N medium, collected, washed.......

Discussion

Environmental conditions, and nutrient availability in particular, strongly affect the fission yeast physiology. Nitrogen starvation is necessary for commitment to the sexual reproduction and initially leads to striking changes in the mitotic cell cycle progression (Ref.²¹ and Figure 2). Upon nitrogen removal from exponentially growing population, cell size at division rapidly decreases (Figure 2C) and the majority of cells arrest mitotic progression shorter than the length of.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Glucose	Sigma-Aldrich	G8270-10KG
KH2PO4	Sigma-Aldrich	1.05108.0050
NaCl	Sigma-Aldrich	71381
MgSO4•7H2O	Sigma-Aldrich	63140
CaCl2	Sigma-Aldrich	12095
Pantothenate	AppliChem	A2088,0025
Nicotinic Acid	AppliChem	A0963,0100
Inositol	AppliChem	A1716,0100
Biotin	AppliChem	A0967,0250
Boric Acid	Sigma-Aldrich	B6768-1KG
MnSO4	AppliChem	A1038,0250
ZnSO4•7H2O	Sigma-Aldrich	Z4750
FeCl2•6H2O	AppliChem	A3514,0250
Molybdenum oxide (VI) (MoO3)	Sigma-Aldrich	69850
KI	AppliChem	A3872,0100
CuSO4•5H2O	AppliChem	A1034,0500
Citric Acid	AppliChem	A2344,0500
Agarose	Promega	V3125
(NH4)2SO4	Merck	1.01217.1000
L-Leucine	Sigma-Aldrich	L8000-100G
Adenine Hemisulfat Salt, mini 99%	Sigma-Aldrich	A9126-100G
Uracil	Sigma-Aldrich	U0750
Lanolin	Sigma-Aldrich	L7387
Vaseline	Reactolab	92045-74-4
Paraffin	Reactolab	7005600