Male animals' evolutionary imperative to ensure the propagation of their own children resulted in the testicle's fast development.
Bioinformatic analyses done by an international team of researchers led by Prof. Dr. Henrik Kaessmann of Heidelberg University's Center for Molecular Biology demonstrated that this pressure accelerated the development of later stages of sperm production in particular.
The goal of these contrastive investigations was to decode the genetic control of sperm production in many species of animals and humans for the first time, tracking the evolution of this spermatogenesis.
At the same time, the researchers were able to identify genes whose activity had remained constant throughout evolution.
Rapid evolution of spermatogenesis
Spermatogenesis in the testis is governed by a carefully coordinated, complicated interplay of gene activity, often known as gene expression, as per ScienceDaily.
Previously, awareness of these genetic programs has been primarily limited to the mouse.
"As a result, little was known about the genetic foundations that constitute the big differences in spermatogenesis across different mammals, both in terms of the number of sperm cells formed and also their properties," explained Noe Mbengue, a doctoral researcher in Prof. Kaessmann's group "Evolution of the mammalian genome."
They investigated creatures from all major groupings of mammals, including humans and their closest relatives, great apes.
The researchers employed cutting-edge single-cell genomics tools to do this.
Based on this information, they were able to track the evolution of spermatogenesis using bioinformatic comparisons between animals.
This comparison research, according to Prof. Kaessmann, discovered a time-related pattern.
"While the genetic programs in the early stages of spermatogenesis are very similar among mammals, they differ greatly in later stages," said Dr. Florent Murat, a former postdoc in Henrik Kaessmann's research group and now a group leader at the National Research Institute for Agriculture, Food, and Environment (INRAE) in Rennes (France).
Further research by the scientists found genes whose activity had remained constant throughout evolution.
They govern essential sperm cell production mechanisms that are shared by all animals.
"As a result, our data provides essential aspects for understanding male fertility issues," Prof. Kaessmann continued.
Finally, the scientists' data enabled them to differentiate sperm cells that carry either an X or a Y chromosome and therefore determine the sex of the kid for the first time.
The researchers were able to analyze gene expression on these sex chromosomes in a systematic manner because of this division.
According to these findings, gene expression on all male animals' sex chromosomes is downregulated during the maturation stage known as meiosis.
This process is thought to be essential for preventing a harmful genetic exchange between the X and Y chromosomes during meiosis.
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Spermatogenesis
Even in widely diverse animals, the basic mechanisms of spermatogenesis are startlingly similar, and the genes involved are substantially conserved, as per NCBI.
Sperm production is normally maintained by a stem cell population throughout adulthood, and we will address the evolutionary parallels in molecular pathways defining spermatogenic stem cells and assuring their preservation and protection.
Spermatogonia derived from these male germline stem cells operate as transit-amplifying populations, proliferating in a semi-committed condition before maturing into spermatocytes.
Sister spermatocytes are connected by persistent cytoplasmic bridges formed by imperfect cytokinesis in each mitotic amplification stage.
As a result, sister cells create 'cysts,' the individuals of which go through spermatogenesis in unison.
The shift from spermatogonial cell to spermatocyte entails exiting the mitotic cell cycle and committing to the spermatogenic differentiation pathway, which includes meiotic activation.
Early in the main spermatocyte stage, DNA replication commences, and the cells enter a prolonged meiotic prophase.
The chromosomes in male germline cells drive transcription of a varied collection of spermatogenesis-specific genes in addition to carrying out the meiosis-specific chromosomal activities of pairing and recombination.
These genes are responsible for endowing spermatozoa with distinct characteristics such as free-living and motility.
Following meiotic divisions, spermatids undergo significant morphological processes that culminate in mature sperm.
This review focuses on the conserved characteristics of spermatogenesis, and there will be exceptions to many of the assertions made here.
They attempted to focus on the cohesive underlying parallels across systems rather than the outliers, which are intriguing in their own right.
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