Methods for rearing Mesostoma ehrenbergii in the laboratory for cell biology experiments, including identification of factors that influence production of different egg types

Mesostoma ehrenbergii spermatocytes are uniquely useful to study various aspects of cell division. Their chromosomes are large in size and few in number, with only 3 bivalent and 4 univalent chromosomes. During prometaphase, bipolar bivalents oscillate regularly to and from the poles for 1-2 hours. The univalents remain at the poles but occasionally move from one pole to the other. In addition, a precocious cleavage furrow forms during prometaphase and remains partially constricted until anaphase. Attempts to rear these animals indefinitely in laboratory conditions, however, have been mostly unsuccessful because of their reproductive strategy. M. ehrenbergiiare hermaphroditic flatworms that can produce viviparous offspring (termed S eggs) and/or diapausing eggs (termed D eggs) and they follow either one of two reproductive patterns: (1) they first form S eggs and following the delivery of these eggs produce D eggs, or (2) they only produce D eggs. When only D eggs are formed, which is common under laboratory conditions, the stocks die out until the diapausing eggs hatch, which is irregular and creates unpredictable wait times. As a result, to maintain M. ehrenbergii stocks in order to study their spermatocytes, we studied various factors that might influence egg type production. We have found that feeding them daily and keeping them at 25°C favours S egg production. Currently, our cultures have reached the 45th generation. In this article we describe our rearing and dissection methods and describe experiments which led to our present rearing methods.