Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 1: Background to spermatogenesis, spermatogonia, and spermatocytes

Abstract

As germ cells divide and differentiate from spermatogonia to spermatozoa, they share a number of structural and functional features that are common to all generations of germ cells and these features are discussed herein. Germ cells are linked to one another by large intercellular bridges which serve to move molecules and even large organelles from the cytoplasm of one cell to another. Mitochondria take on different shapes and features and topographical arrangements to accommodate their specific needs during spermatogenesis. The nuclear envelope and pore complex also undergo extensive modifications concomitant with the development of germ cell generations. Apoptosis is an event that is normally triggered by germ cells and involves many proteins. It occurs to limit the germ cell pool and acts as a quality control mechanism. The ubiquitin pathway comprises enzymes that ubiquitinate as well as deubiquitinate target proteins and this pathway is present and functional in germ cells. Germ cells express many proteins involved in water balance and pH control as well as voltage-gated ion channel movement. In the nucleus, proteins undergo epigenetic modifications which include methylation, acetylation, and phosphorylation, with each of these modifications signaling changes in chromatin structure. Germ cells contain specialized transcription complexes that coordinate the differentiation program of spermatogenesis, and there are many male germ cell-specific differences in the components of this machinery. All of the above features of germ cells will be discussed along with the specific proteins/genes and abnormalities to fertility related to each topic.

Mammalian gonocyte and spermatogonia differentiation: recent advances and remaining challenges

“…It consists of successive phases of primordial germ cells (PGCs) and gonocytes (also known as pre-or pro-spermatogonia) that can be distinguished by unique features, leading to the formation of the first spermatogonia, including spermatogonial stem cells (SSCs) (Culty 2009). The second phase, starting at prepuberty and extending throughout male adult life, comprises spermatogenic cycles that are initiated by the commitment of spermatogonia to differentiate, progressing through meiosis and spermiogenesis to end with the formation of immature spermatozoa (Hermo et al 2010). Spermatogenesis occurs within the seminiferous tubules, a group of well organized, long convoluted tubules connecting at both ends to the rete testis, which assure sperm transport to the efferent duct, the initial part of the epididymis (Hermo et al 2010).…”

“…The second phase, starting at prepuberty and extending throughout male adult life, comprises spermatogenic cycles that are initiated by the commitment of spermatogonia to differentiate, progressing through meiosis and spermiogenesis to end with the formation of immature spermatozoa (Hermo et al 2010). Spermatogenesis occurs within the seminiferous tubules, a group of well organized, long convoluted tubules connecting at both ends to the rete testis, which assure sperm transport to the efferent duct, the initial part of the epididymis (Hermo et al 2010). The seminiferous tubules are made up of supporting Sertoli cells and germ cells (Bellve et al 1977), and are surrounded by peritubular myoid cells.…”

“…The rodent spermatogenic cycle includes three main phases: a mitotic phase that takes place in SSCs, undifferentiated (A single , A pair , and A aligned ), differentiating (A 1 to A 4 , intermediate), and differentiated (type B) spermatogonia at various phases of maturation, followed by a lengthy meiotic phase including successive types of primary spermatocytes, secondary spermatocytes and the formation of haploid spermatids (round, elongated), which undergo spermiogenesis to become spermatozoa that will further achieve maturation in the epididymis (Hermo et al 2010). The human cycle is very similar, despite presenting stages spread over much longer periods (days instead of hours) and with the exception of having only three types of spermatogonia, A dark , A pale , and B.…”

Spata6is required for normal assembly of the sperm connecting piece and tight head–tail conjunction

“…flagellum | centriole | infertility | sperm anomaly | microtubule M ale gametes-spermatozoa-are produced in the testis through a process termed spermatogenesis, which can be divided into three phases: mitotic, meiotic, and haploid (1). In the mitotic phase, spermatogonial stem cells proliferate and differentiate into spermatogonia, which subsequently enter the meiotic phase and become spermatocytes.…”

Pluripotency of Male Germline Stem Cells

“…Spermatogenesis consists of three major phases: proliferative mitotic divisions, meiosis, and spermiogenesis (Hermo et al, 2010). Spermatogonia are the most primitive populations in the testes, which include type A, inter mediate, and type B spermatogonia.…”