If your next meal could be as much as a year off, the pressure is on whenever a tasty snack shambles past. Medicinal leeches (Hirudo verbana) only have one shot to pump their victims full of anticoagulant and anti-inflammatory saliva to ensure that their host is none the wiser as the blood is drained from them. Having satisfied their hunger, leeches then have to prepare for whenever the next meal may pass their way by recharging their salivary glands with the proteins that are essential for when they feed. However, it was not clear whether leeches refilled their salivary gland cells straight after finishing sucking on their victim or waited until they had finished digesting the meal. Jan-Peter Hildebrandt, from the Ernst Moritz Arndt University, Germany, explains that the first alternative would leave the leeches better prepared to grasp any opportunities that brushed past, at the expense of maintaining the fully charged salivary glands, whereas recharging the salivary glands after completely digesting the meal would be less costly but prevent the leeches from feeding opportunistically when another meal presented itself.
Intrigued, Hildebrandt and his colleagues Sarah Lemke and Christian Müller began investigating the salivary tissue of recently fed leeches over a 3-week period. The trio observed the salivary cells immediately after the leeches had fed, and saw that the salivary glands collapsed as they emptied. However, within a week the cells had returned to their pre-feeding size. And when the team analysed the proteins in the salivary tissue before and after feeding, they saw a dramatic reduction in one group of proteins – which recovered over the following week – while other proteins remained unaffected over the weeks following feeding. ‘This indicates that one portion of the extracted proteins represented secretary proteins, while the other portion represented housekeeping proteins from salivary gland cells and surrounding tissues’, says the team. They also investigated the mRNA level of the anticoagulant protein hirudin in the salivary tissue, and found that it peaked 5 days after the leeches’ meal.
‘The results of our study indicate that synthesis of salivary gland proteins starts within days of feeding and results in virtually compete refilling of the gland cell reservoirs within 1 week of feeding’, says Hildebrandt and colleagues, adding that this ensures that the leeches are well prepared for any new dining opportunities that pass their way.