Doesn´t one sperm suffice?

Reproduction is, for its comparative strength and dynamic character, a major sentinel of the health of animals and humans. 

Environmental and societal changes, including an increased stressful lifestyle, constrain reproduction. Reproduction is also indicative of the health of our ecosystems, including the undesirable presence of environmental pollutants, which have been linked - including those acting as endocrine disruptors - to reports of decreased semen quality in human and other species. Symptomatic alleviation through assisted reproduction techniques is today priority, including use of single spermatozoa and of cryopreserved gametes.

Spermatozoa are able, despite being highly differentiated terminal cells with a definite functional programming (to fertilize the oocyte and to initiate embryonic development), to actively interact with the various compartments of the female genital tract. This interaction commands fertility by the selection the female exerts during sperm transport, of those most suitable spermatozoa. Simultaneously, the entry of spermatozoa alongside proteins of the seminal plasma, both foreign to the female immune system, initiates a series of modifications of the latter, reaching - under normal circumstances - a state of female immune tolerance, which also ultimately commands fertility. Intriguing is thus how spermatozoa can survive and maintain fertilizing capacity in some segments of the Fallopian tube, which act as functional pre-ovulatory sperm reservoirs. Despite their enormous relevance, details of the mechanisms behind these processes still remain veiled. Interestingly, many of these processes seem well conserved over species, and even classes, thus denoting evolutionary relevance.

Basic discoveries, using comparative studies over several species, in relation to sperm selection and preservation of cell integrity through sperm transport and capacitation have been central in our research, particularly in relation to the capacity of spermatozoa to respond to stimuli mediated via specific membrane receptors and to elicit signaling to the neighboring epithelia. Findings regarding modulation of the process of sperm capacitation and the manner spermatozoa loose fertilizing capacity before and during interaction with the oocyte had been pivotal when these concepts are applied to both diagnostics and technological processes, such as sperm freezing.

Diagnosis of the fertilizing capacity of spermatozoa is highly searched for prognosis of treatments through assisted reproductive techniques (artificial insemination, in vitro fertilization), but it is yet elusive. This reinforces our basic interest for the location of biomarkers for male fertility, including the capacity of spermatozoa to elicit genomic shift in the female genitals in relation to maternal tolerance. Of particular interest is the role of the complicated proteome of the seminal plasma and its role as signaling source during the preparatory events of fertilization, an area of major interest for diagnostic purposes.

Spermatozoa possess a large number of general and specific surface receptors which enable them to react to hormonal, ionic, voltage and other membrane receptors, opening a major field for basic research but also for screening of drug candidates, for example. Such a concept; using spermatozoa as monitor cell type for toxicological testing, waives the need for experimental animals following the 3-R concept, and widens our capabilities for biomedical interaction between University and the industry.

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