Preparation of a High-quality Primary Cell Culture from Fish Pituitaries

Summary

Here we describe a protocol to prepare and maintain primary pituitary cell cultures from medaka (Oryzias latipes). The optimized conditions in this protocol take important parameters such as temperature, osmolality, and pH into consideration by mimicking the physiological conditions of the fish, thereby enabling physiologically more meaningful results.

Abstract

Primary cell culture is a powerful tool commonly used by scientists to study cellular properties and mechanisms of isolated cells in a controlled environment. Despite vast differences in the physiology between mammals and fish, primary cell culture protocols from fish are often based on mammalian culture conditions, often with only minor modifications. The environmental differences affect not only body temperature, but also blood serum parameters such as osmolality, pH, and pH buffer capacity. As cell culture media and similar working solutions are meant to mimic characteristics of the extracellular fluid and/or blood serum to which a cell is adapted, it is crucial that these parameters are adjusted specifically to the animal in question.

The current protocol describes optimized primary culture conditions for medaka (Oryzias latipes). The protocol provides detailed steps on how to isolate and maintain healthy dissociated pituitary cells for more than one week and includes the following steps: 1. the adjustment of the osmolality to the values found in medaka blood plasma, 2. the adjustment of the incubation temperature to normal medaka temperature (here in the aquarium facility), and 3. the adjustment of the pH and bicarbonate buffer to values comparable to other fish species living at similar temperatures. The results presented using the described protocol promote physiologically meaningful results for medaka and can be used as a reference guide by scientists making primary cell cultures from other non-mammalian species.

Introduction

Cell culture is one of the main tools used in molecular biological research, providing an excellent model system for answering different biological questions ranging from normal cellular physiology to drug screening and carcinogenesis¹. Primary cells, isolated directly from the animal tissue using enzymatic and/or mechanical methods,are often considered more biologically relevant than cell lines as the biological response may be closer to the in vivo situation. Protocols for preparing primary cell cultures should be optimized for each species and cell type of interest in order to mimic the characteristics to which a cell is adapted and....

Protocol

The animal experiments performed in this study were approved by the Norwegian University of Life Sciences, following guidelines for the care and welfare of research animals.

1. Preparation of Solutions

1. Calibrate the osmometer and pH meter instruments according to the manufacturer’s instructions to ensure correct measurements.
2. Prepare 500 mL of Ca²⁺- and Mg²⁺-free Dulbecco’s phosphate-buffered saline (dPBS), adjusting the pH to 7.75 (step 1.2.1) and the osmolality to 290 mOsm/kg (step 1.2.2) before a sterile filtration (step 1.2.3).
   1. Adjust the pH to 7.75 wit....

Results

This protocol describes the preparation of a primary cell culture from medaka pituitaries and provides healthy cells that can be maintained in a culture for at least one week. The protocol is based on physiological relevant values for medaka¹⁴ and is additionally optimized to the pituitary tissue in adult fish, using a pH of 7.75 and an osmolality of 290 mOsm/kg during the entire procedure from the tissue harvesting to the plated cells in culture (

Discussion

In vitro cell culture systems provide powerful tools for researchers to answer a plethora of different biological questions if used in the right way¹. It is important to remember that dissociated cells that have lost their connections to the neighboring cells may have obtained different functional properties than they originally had in vivo. To avoid being at the risk of misinterpreting the results obtained from in vitro experiments, it is important to consider adjusting.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Dulbecco’s Phosphate Buffered Saline (dPBS), without calcium chloride and magnesium chloride	Sigma (Merck, Damstadt, Germany)	D8537	Adjust solution to pH 7.75 with 1M NaOH and 290 mOsm with mannitol.
L-15 medium (Leibovitz), witout L-glutamine	Sigma (Merck, Damstadt, Germany)	L5520	Supplement 500 ml culture medium with 10 mM NaHCO3, 4.5 mM glucose, 2 mM Glutamax. Adjust solution to 290 mOsm with mannitol and filter solution through a 0.2 µm PES sterile filter, before adding 2.5 mL Penicillin-Streptomycin solution (see below for details).
NaOH	Sigma (Merck, Damstadt, Germany)	S5881	Add drops of 1 M solution to increase pH of dPBS and culture medium to 7.75.
NaHCO3	Sigma (Merck, Damstadt, Germany)	S5761	10 mM NaHCO3 equals 420 mg per 500 mL culture medium.
D-mannitol	Sigma (Merck, Damstadt, Germany)	63565	Use to increase osmolality of dPBS and culture medium. Calculate correct amount needed to reach an osmolality of 290 mOsm.
D-glucose	Sigma (Merck, Damstadt, Germany)	G5400	4.5 mM  D-glucose equals 405 mg per 500 mL culture medium.
GlutaMAX Supplement	Gibco (Life Technologies, Paisley, UK)	35050-061	Alternative to L-glutamine, with increased stability. 2 mM Glutamax equals 5 ml of 100x stock in 500 mL culture medium.
Penicillin-Streptomycin	Sigma (Merck, Damstadt, Germany)	P0781	Stock solution 10,000 units penicillin and 10 mg streptomycin per mL. Use 2.5 mL of stock solution in 500 mL L-15 medium (equivalent of 50 U/mL Penicillin and 50 µg/mL Streptomycin).
Trypsin type II-S	Sigma (Merck, Damstadt, Germany)	T7409	Prepare 1 mg/mL in dPBS solution.
Trypsin inhibitor type I-S	Sigma (Merck, Damstadt, Germany)	T6522	Prepare 1 mg/mL in dPBS solution, supplement with 2 µg/ml Dnase I (see details below).
Dnase I	Sigma (Merck, Damstadt, Germany)	D5025	Use in trypsin inhibitor solution (see above).
0.2 µm Polyethersulfone (PES) sterile filter system	Corning Inc. (Corning, NY)	431097	Use for sterile filtration of dPBS and L-15 medium after adjustments.
35 mm cell culture dish with glass bottom, poly d-lysine coated	MatTek Corporation (Ashland, MA)	P35GC-1.5-10-C	Can also be replaced by plastic dish, depending on downstream application.
Dumont #5 fine forceps	Fine Science Tools (CA)	11254-20	Straight tip
Dumont #5/45 fine forceps	Fine Science Tools (CA)	11253-25	Angled 45° tip
Stereo microscope SZ61	Olympus Corp. (Tokyo, Japan)		Use for dissection of pituitaries.
Alegra X-22R Centrufuge	Beckman Coulter Inc. (Brea, CA)		With cooling option (similar to current model XR-30).
Water bath	Techne (Staffordshire, UK)		Any water bath with the possibility of adjusting temperature will do.
Pasteur glass pipettes	VWR (NY)	612-1701	Outer diameter 1.6 mm, fire polish and autoclave before use.
Galaxy MiniStar table centrifuge	VWR (NY)	521-2844	Any small table centrigue will do.
Fine needles/insect pins	Fine Science Tools (CA)	26001-40	Diameter 0.03 mm. Other fine needles can be used instead.
Wax plate			Custom made by adding melted paraffin wax in large petri dish.