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Betsy
02-03-05, 02:27 AM
http://www.sciencedaily.com/images/2005/02/050201112034.jpg
Wild-type C. elegans hermaphrodite stained to highlight the nuclei of all cells. (Image courtesy of Public Library Of Science)

Source: Public Library Of Science
Date: 2005-02-03
URL: http://www.sciencedaily.com/releases/2005/02/050201112034.htm
The Evolution Of Self-Fertile Hermaphroditism: The Fog Is Clearing

The nematode Caenorhabditis elegans is a little less lonely than the rest of us—it is a self-fertile hermaphrodite, which as a larva makes and stores sperm before switching to egg production for the remainder of its lifespan. (C. elegans also maintains some males at a low frequency, about 1 in 500, and the hermaphrodite's eggs can be fertilized by sperm either from males or themselves.) A sister species, C. briggsae, is also hermaphroditic, but phylogenetic evidence suggests the last common ancestor of the two species had a female/male mode of reproduction. This raises the question of how the sex determination mechanisms, which must have evolved independently, differ between the two species. In this issue, Sudhir Nayak, Johnathan Goree, and Tim Schedl show that a crucial difference lies in the activities of two genes.

In C. elegans, the early period of sperm production is controlled by multiple proteins, two of which are the focus of this study, the RNA-binding protein GLD-1 (encoded by the gene gld-1) and the F-box-containing protein FOG-2 (encoded by the gene fog-2). Together, they repress translation of a gene, tra-2, by binding to its messenger RNA. This allows another gene, fem-3, to transiently masculinize the larval germline to produce sperm.

Comparing the genomes of C. elegans and C. briggsae, Schedl and colleagues found they share 30 out of 31 sex determination genes, but not fog-2. More surprisingly, they found that the role of gld-1 in sex determination is opposite in the two species. When C. elegans is deprived of gld-1, would-be hermaphrodites produce only oocytes. But when C. briggsae is deprived of gld-1, would-be hermaphrodites produce only sperm. Thus, the authors conclude, the control of hermaphrodite spermatogenesis is fundamentally different in the two species.

By further examining the C. elegans genome, the authors showed that fog-2 arose from a gene duplication event after the C. elegans–C. briggsae split, which occurred approximately 100 million years ago. Since then, its final exon, which codes for the C-terminal end of the protein, has undergone rapid evolution. The authors also show that this is the “business end” of the protein for its interaction with GLD-1, suggesting that the divergence of C. elegans and C. briggsae sex determination pathways resulted, in part, from FOG-2's new interaction with GLD-1.

Exactly what the role of fog-2 is in C. elegans is still unclear. The authors speculate that it may recruit additional factors onto the gld-1/tra-2 mRNA complex, increasing efficiency of translation repression. Much remains to be discovered about C. briggsae sex determination as well. The authors suggest that additional genetic differences promoting self-fertility are likely to have accumulated since the two species diverged, which may act to strengthen the male–female germline switching signal. Investigation of this possibility may shed more light on how hermaphroditism operates in these two species, and how a developmental pathway controlling sex determination can evolve.

Editor's Note: The original news release can be found here.

This story has been adapted from a news release issued by Public Library Of Science.

RGMCjim
02-05-05, 07:58 PM
Betsy,
I couldn't get the picture to copy but like all sea slugs and hares they are very pretty, graceful and peaceful creatures like a life of ballet complete with colorful costumes. AND they have very exciting sex lives - this was a photo of a "daisy chain" slug orgy. Beats the socks off some nasty old nematode. Google sea slugs to see pretty hermaphrodites. Clown fish, Damsel fish and Gobies are very pretty too, they are sequential hermaphrodites.


Mating chains
PHOTO
Aplysia dactylomela mating chain. PHOTO: Alison Miller.
Sea Hares, like all sea slugs, are hermaphrodite animals with fully functional male and female reproductive organs. Sometimes, usually in dense populations or in crowded aquariums, they form mating chains of three or more animals, the one at the front acting solely as a female and the one at the rear solely as a male. The animal(s) in between are acting as both males and females.
See messages below.
See also Michael Mrutzek's photo of a mating chain of the cephalaspidean Chelidonura livida.
Authorship details
Rudman, W.B., 2000 (May 8) Mating chains. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet.cfm?base=seahmat