Transcription and translation in bovine spermatozoa and their control by factors present in seminal plasma

P M BHARGAVA & E SP REDDY

Published in: In Recent Developments in Contraceptive Technology (Proceedings of an International Symposium, New Delhi, October 1974; Ed. K Laumas), Ankur Publishing House, New Delhi, 1976, 115-124.

Abstract:

In the late 1950s and the early 1960s we showed that washed, freshly ejaculated, mature bovine spermatozoa are capable of incorporating amino acids and precursors of nucleic acids into their protein and RNA respectively (1-6). Synthesis of RNA and protein by mature spermatozoa has since then been demonstrated and studied by other workers as well (7-10). Recently (11, 12) we showed that both transcription and translation in bovine spermatozoa was confined to their mitochondrial DNA. The conclusion that the transcription was exclusively mitochondrial in these cells was based on the following observations:

(1) Amongst the RNA species synthesised by these cells were 4S, 16S and 23S RNAs which behaved like the transfer and ribosomal RNAs of E. coli in four different fractionation systems (chromatography on Sephadex G-200 and MAK columns, centrifugation on sucrose density gradient, and electrophoresis on polyacrylamide gels). (In addition to the above RNAs, the spermatozoa synthesised a 16S non-ribosomal RNA which accounted for about three-quarters of the total label obtained in RNA in vitro).

(2) The total RNA synthesised by the sperm cells (excepting the 4S RNA which was not tested) hybridised well with bovine liver mitochondrial DNA but not at all with bovine liver nuclear DNA.

(3) The synthesis of RNA in these cells was inhibited by inhibitors which are known to inhibit RNA synthesis in prokaryotes.

The conclusion that the protein synthesised in mature bovine spermatozoa was coded for by their mitochondrial DNA was based on the following observations:

(1) Out of a large number of methods tried for the extraction of the in vitro-labelled sperm protein, the only method which was successful was based on the method which had been earlier found to be most suitable for extraction of proteins labelled in vitro in isolated mitochondria.

(2) The entire newly synthesised protein in these cells could be extracted by methods which extracted less than 1% of the total sperm protein. This showed that a relatively small number of proteins was synthesised in these cells in vitro. Fractionation of the newly synthesised proteins on a Sephadex column and on polyacrylamide gels suggested that only 5 proteins were labelled.

(3) Protein synthesis in the sperm cells was inhibited by inhibitors which are known to inhibit protein synthesis in mitochondria and in procaryotes but do not inhibit the synthesis of proteins on cytoribosomes, further, protein synthesis in these cells was not inhibited by inhibitors which inhibit only the synthesis of those proteins which are coded for by nuclear DNA and synthesised on cytoribosomes.

(4) The continuance of protein synthesis in these cells was dependent on the continuance of RNA synthesis which appeared to be exclusively mitochondrial.

The above observations have established that mitochondrial transcription and translation do not require concurrent nuclear transcription and/or translation and are, therefore, autonomous in this respect. These observations are also of significance from the point of view of the origin of mitochondria, specially as we were able to demonstrate the synthesis in spermatozoa of mitochondrial RNA species which seem to closely resemble bacterial ribosomal and transfer RNAs.

HOW TO CITE

Transcription and translation in bovine spermatozoa and their control by factors present in seminal plasma. P M BHARGAVA & E SP REDDY. In Recent Developments in Contraceptive Technology (Proceedings of an International Symposium, New Delhi, October 1974; Ed. K Laumas), Ankur Publishing House, New Delhi, 1976, 115-124.

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