Isolation and In vitro Activation of Caenorhabditis elegans Sperm

Podsumowanie

A protocol for isolating and activating spermatids from male C. elegans is described here. Cutting the posterior end of male releases spermatids. The spermatids can be activated by addition of protease.

Streszczenie

Males and hermaphrodites are the two naturally found sexual forms in the nematode C. elegans. The amoeboid sperm are produced by both males and hermaphrodites. In the earlier phase of gametogenesis, the germ cells of hermaphrodites differentiate into limited number of sperm - around 300 - and are stored in a small 'bag' called the spermatheca. Later on, hermaphrodites continually produce oocytes¹. In contrast, males produce exclusively sperm throughout their adulthood. The males produce so much sperm that it accounts for >50% of the total cells in a typical adult worm². Therefore, isolating sperm from males is easier than from that of hermaphrodites.

Only a small proportion of males are naturally generated due to spontaneous non-disjunction of X chromosome³. Crossing hermaphrodites with males or more conveniently, the introduction of mutations to give rise to Him (High Incidence of Males) phenotype are some of strategies through which one can enrich the male population³.

Males can be easily distinguished from hermaphrodites by observing the tail morphology⁴. Hermaphrodite's tail is pointed, whereas male tail is rounded with mating structures.

Cutting the tail releases vast number of spermatids stored inside the male reproductive tract. Dissection is performed under a stereo microscope using 27 gauge needles. Since spermatids are not physically connected with any other cells, hydraulic pressure expels internal contents of male body, including spermatids².

Males are directly dissected on a small drop of 'Sperm Medium'. Spermatids are sensitive to alteration in the pH. Hence, HEPES, a compound with good buffering capacity is used in sperm media. Glucose and other salts present in sperm media help maintain osmotic pressure to maintain the integrity of sperm.

Post-meiotic differentiation of spermatids into spermatozoa is termed spermiogenesis or sperm activation. Shakes⁵, and Nelson⁶ previously showed that round spermatids can be induced to differentiate into spermatozoa by adding various activating compounds including Pronase E. Here we demonstrate in vitro spermiogenesis of C. elegans spermatids using Pronase E.

Successful spermiogenesis is pre-requisite for fertility and hence the mutants defective in spermiogenesis are sterile. Hitherto several mutants have been shown to be defective specifically in spermiogenesis process⁷. Abnormality found during in vitro activation of novel Spe (Spermatogenesis defective) mutants would help us discover additional players participating in this event.

Protokół

1) Enrichment of male population

1. Depending on the experimental need, large numbers of males can be obtained by employing one of the following strategies:
   1. large population of wild type males can be obtained by crossing 5 wild type males and 1 hermaphrodite on a small lawn of OP50 seeded at the center of NGM plate. Roughly 50% of the succeeding generation will be wild type males.
   2. him-5(e1490) or him-8(e1489) hermaphrodites throw large number of males. him-5 and him-8 males are fertile and there is no obvious defect in sperm morphology and function. So, him-5 or him-8

Dyskusje

In addition to analyzing Spe mutants, this protocol has other important applications, such as analyzing sperm morphology with aging. Spermatids and spermatozoa isolated using this protocol can be used in other downstream experiments such as, immunostaining of wild type and mutant sperm^{8, 9}, motility of sperm on slides¹⁰, physiological measurements^{9, 11}, or even artificial insemination¹².

Materiały

Material Name	Type	Company	Catalogue Number	Comment
Name	Company	Catalog Number	Comments
Tuberculin syringe		Becton Dickinson	309623	Syringe: 1 ml, needle: 27G X ½ in
Pap pen		Zymed	00-8888
VWR VistaVision HistoBond Microscope Slides		VWR International	16004-406	Dimension: 75X25X1mm
Cover glass		VWR International	48366045
Protease		Sigma	P-6911