Sunday, June 30, 2013

Zac Swider - My first week of embryology in the Maslakova Lab

Greetings from the Oregon Institute of Marine Biology!


This marks the end of my first week as a COSEE intern and I can't express enough how thankful I am for being given this opportunity. I will be spending the next seven weeks working in the Maslakova lab under Dr. Svetlana Maslakova and her husband Dr. George von Dassow, as well as Ph.D. students Laurel and Terra.  Everybody in the Maslakova lab has been unbelievably generous with their time in assisting both Leeah (a fellow COSEE intern) and myself with training and becoming familiar with the lab.

This lab is intently focused of the unraveling the mysteries of the Phylum Nemertea - commonly known as the "ribbon worms" - and they use a number of molecular biology and embryological techniques to accomplish this. The project that I am working on involves the studying the larval development of a very specific nemertean, Micrura alaskensis, that has been studied extensively by the Maslakova lab due to its ease of availability and the fact that it displays a "classic" developmental pattern for a nemertean. The larva of this species (and that of its closely related kin) are referred to as pilidium larvae and undergo an extreme type of metamorphosis (to the adult form) that is not seen anywhere else in the animal kingdom.  A time lapse video of this metamorphosis can be seen below.  This video was taken by Svetlana Maslakova and is included in her recent paper, published in Frontiers in Zoology, describing the development of Micrura alaskensis 

video

What you are seeing in this video is the juvenile worm literally eating its way out of the larval body and swallowing it as it does so.  When a pilidium larva begins to develop from an egg, the larval body appears first and, after a week or so, the juvenile worms begins to grow and develop around the larval stomach.  During this time, the larva continues to swim around water column, feeding on microscopic plankton and nourishing the larval body.  Once development of the juvenile body is complete the juvenile must break free, but it remains attached the larval body at the mouth.  A neat solution to this problem is for the juvenile to simply consume the larval body as it exits, kind of like a living sock turning itself inside out and crawling away.

 
Micrura alaskensis
 My first couple of mornings in the Maslakova lab were spent enjoying the especially low tides to go into the field and collect nemertean worms from various mudflats around the OIMB.  Nemertean collection is accomplished by walking around on the mudflats with a shovel and very carefully sifting through the mud to separate the tiny nemerteans away from all of the other minuscule worms that look extraordinarily like them... given the wind, rain, mud, and biting Nereis worms (also found in the mud) - this was by far the grungiest (but most enjoyable) field work that I have ever done!


The rest of my first week has been largely spent training - learning how to accurately pipette extremely small eggs, start cultures of larvae, take care of these cultures, and how to mount specimens for DIC (Differential Interference Contrast) imaging without damaging the larvae so badly that they cannot continue to grow.  On Monday I will begin learning how to inject eggs with various fluorescent markers and DNA analogues designed to inactivate certain genes - more information on this to come next week!



As a small side experiment I have started several cultures of dissected blastomeres - to accomplish this I fertilized a few hundred Micrura alaskensis eggs and as soon as the fertilized eggs divided, I separated the resulting two cells (very carefully, with a very thin glass needle) and set them aside to continue growing.  The significance of this is as follows:  Some animals develop in a regulative manner, meaning that these separated cells ought to be able to sense that they had been separated and compensate for the missing cells to make a complete (albeit smaller) embryo.  Other embryos are incapable of sensing this separation and will continue to divide as if nothing had ever happened, resulting in an embryo missing about half of its cells.  Micrura alaskensis is thought to be somewhere in between these two scenarios, meaning that it can regulate... but not very well - hopefully we will find out soon!

This week has not been all lab work, however.  We had the opportunity on Monday morning to get up at 530AM with the Marine Ecology class to see the Lighthouse tide-pools on the lowest tide of the summer.  It was by far the best tide-pooling that I have ever done and I took hundreds of pictures of intertidal invertebrates.  Unfortunately, until I can find a memory card adapter for my camera, all I have to share is this cell phone picture of a hermit crab :)  Other activities around the OIMB include hiking, swimming, mushroom hunting, birding, photography, insect collection and much more.  I hope to share about a number of these activities soon, stay tuned!

2 comments:

  1. Wow! That's a striking change through that pilidium metamorphosis. How long did it take to happen?

    ReplyDelete
    Replies
    1. This video is slightly sped up - two and half times - which would put the timing at about five minutes. I am sure that this is variable between events (and surely between species) but I believe the metamorphosis of most pilidia is likely to be on the order of ten minutes or less.

      Delete