how are germ cells made

Full Answer

How are germ cells formed in animals?

In many animals, the germ cells originate in the primitive streak and migrate via the gut of an embryo to the developing gonads. There, they undergo meiosis, followed by cellular differentiation into mature gametes, either eggs or sperm.

What is the function of germ cells?

Germ cells are cells that create reproductive cells called gametes. Germ cells are located only in the gonads and are called oogonia in females and spermatogonia in males. ... In males, germ cells undergo spermatogenesis to produce spermatozoa, or sperm cells.

Where are germ cells found in the human body?

Germ cells are located only in the gonads and are called oogonia in females and spermatogonia in males. In females, they are found in the ovaries and in males, in the testes. During oogenesis, germ cells divide to produce ova, or eggs, in females.

Do germ cells come from somatic cells?

Instead, germ cells can arise from somatic cells in the adult, such as the floral meristem of flowering plants. Multicellular eukaryotes are made of two fundamental cell types. Germ cells produce gametes and are the only cells that can undergo meiosis as well as mitosis.

What are germ cells in humans?

Germ cells, or sex cells, in humans are cells used in sexual reproduction. Germ cells are produced in gonads and fuse upon sexual fertilization to...

What is a somatic cell? What is a germ cell?

A somatic cell is a diploid cell found throughout the body that is not involved in reproduction. A germ cell is a haploid cell that is produced by...

What are types of germ cells?

Germ cells can either be male or female. Male germ cells are called sperm, while female germ cells are called eggs.

What is a germ cell and how does it function?

A germ cell, also called a sex cell, is a cell that is involved in sexual reproduction. Germ cells contribute to the formation of a zygote upon fer...

Where do germ cells originate?

In many animals, the germ cells originate in the primitive streak and migrate via the gut of an embryo to the developing gonads. There, they undergo meiosis, followed by cellular differentiation into mature gametes, either eggs or sperm. Unlike animals, plants do not have germ cells designated in early development.

How do germ cells establish their lineage?

Specification. There are two mechanisms to establish the germ cell lineage in the embryo. The first way is called preformistic and involves that the cells destined to become germ cells inherit the specific germ cell determinants present in the germ plasm (specific area of the cytoplasm) of the egg (ovum).

What is the difference between induction and germ cell establishment?

One difference is that typically inheritance occurs almost immediately during development (around the blastoderm stage) while induction typically does not occur until gastrulation. As germ cells are quiescent and therefore not dividing, they are not susceptible to mutation.

Why is mutation rate higher in germ cells?

Since the germ cell lineage is not established right away by induction , there is a higher chance for mutation to occur before the cells are specified. Mutation rate data is available that indicates a higher rate of germ line mutations in mice and humans, species which undergo induction, than in C. elegans and Drosophila melanogaster, species which undergo inheritance. A lower mutation rate would be selected for, which is one possible reason for the convergent evolution of the germ plasm. However, more mutation rate data will need to be collected across several taxa, particularly data collected both before and after the specification of primordial germ cells before this hypothesis on the evolution of germ plasm can be backed by strong evidence.

What is the lineage of germ cells?

The lineage of germ cells is called germ line. Germ cell specification begins during cleavage in many animals or in the epiblast during gastrulation in birds and mammals. After transport, involving passive movements and active migration, germ cells arrive at the developing gonads.

Why are germ cells not susceptible to mutation?

As germ cells are quiescent and therefore not dividing, they are not susceptible to mutation. Since the germ cell lineage is not established right away by induction, there is a higher chance for mutation to occur before the cells are specified.

What is the name of the cell that gives rise to the gametes of an organism that reproduces sexually?

Germ cell . A germ cell is any biological cell that gives rise to the gametes of an organism that reproduces sexually. In many animals, the germ cells originate in the primitive streak and migrate via the gut of an embryo to the developing gonads.

How do germ cells develop?

Germ-cell development starts from spermatogonial stem cells (SSCs), the most undifferentiated type of spermatogonium, which usually occurs as single cells. When an SSC enters the differentiation pathway toward the spermatozoa, it shows a peculiar behavior upon dividing in all animals. At the end of mitosis, when the two new cells have formed, a cell division is incomplete in these differentiating cells since the daughter cells remain interconnected by a cytoplasmic bridge, instead of forming two separated cells. These bridges are also formed during all subsequent germ-cell divisions. In this way, the germ cells derived from a given SSC form a clone of interconnected cells. All members of the same clone are in the same stage of development, synchronized in their activities via the cytoplasmic bridges. These bridges are broken when spermatogenesis is completed and germ cells leave the germinal epithelium as spermatozoa. However, when dividing, an SCC can also form two independent cells. These daughter cells are two new SCCs and this mode of division is called stem-cell self-renewal.

What is the role of germ cells in spermatogenesis?

While germ cells appears dispensable for testis differentiation during fetal life, germ cell products, such as the above-mentioned RA or BMP4, are likely to influence somatic cells in order to induce and/or maintain somatic cell functions after birth. Due to their intimate location within the seminiferous epithelium, Sertoli cells which surround and support germ cells all along their differentiation process represent a preferential target for such signals.

What is the degeneration of germ cells?

Germ cell degeneration is common during testicular development and in adults and is a major factor in determining the efficiency of spermatogenesis in terms of the theoretic versus the observed yield of mature spermatozoa.51,193 Excessive germ cell degeneration may arise either in response to external or extratesticular influences (e.g., seasonality, nutrition, therapeutic drugs, environmental agents, infection) or as a result of intrinsic dysfunction of spermatogenesis, the details of which are largely unknown. Depending on the species, as much as 75% of the expected sperm yield may be lost in normal spermatogenesis. Degeneration with death of germ cells is attributable to apoptosis, in which activation or suppression of particular genes dictates a cell death or survival pathway. Apoptotic cells occur in most tissues in which a balance between cell proliferation and elimination is required for normal growth and/or maintenance of the cellular population. In contrast to necrosis, apoptotic cells fragment and form several or numerous condensed bodies that include the pyknotic nucleus, but these bodies do not lyse, and are instead phagocytosed by neighboring cells, and in the testis, the Sertoli cells rapidly dispose of these elements. This is an important outcome, because apoptosis does not normally initiate an inflammatory response that could otherwise disrupt function of testicular elements. In mice, a growing number of genes have been identified that, if deleted or disrupted, lead to inappropriate germ cell apoptosis at various phases of spermatogenesis, and most of these genetically altered mice are infertile. 193

What is germ cell transplantation?

Germ cell transplantation has revolutionized the study of the male germline of not only research species, but of all mammals, including companion animals, farm animals, endangered species and primates. Although the germ cell transplantation technique was originally developed in the mouse and allowed extensive characterization of murine SSCs, future studies will focus on a large range of species, including humans. Development of an efficient in vitro culture system supporting self-renewal and expansion of human SSCs and feasible germ cell transplantation protocols are critical to accelerate the advance of new medical applications and germ cell-based therapies.

What is the life cycle of the germline?

This cycle of the germline, from generation to generation, is a central feature of the continuum of multicellular life. Because the germline is essentially continuous from generation to generation, the germ-line lineage can be thought of as being ‘immortal,’ although individual germ cells are not.

What are the changes that occur in germ cell imprinting?

Germ cell imprinting to date has been shown to occur via different epigenetic changes, including DNA methylation, changes in noncoding RNA, histone modifications as well as changes in chromatin structure .

Do germ cells divide continuously?

Therefore, germ cells are syncytial. Germ cells divide continuously during larval and adult stages and do not follow a stereotypical division pattern (Kimble and Hirsh, 1979 ). This contrasts with both embryonic and larval somatic cells, whose divisions are tightly regulated. In L4-stage larvae and adults, germ cells in the proximal regions of the gonad enter meiosis; and mitotic proliferation is restricted to the distal end of the gonad arms ( Kimble and Crittenden, 2005 ). Germ cell proliferation is dependent on the germ cell receiving a cell surface-expressed signal from the distal tip cell (DTC). This DTC signal, the Delta homolog LAG-2, activates the Notch homolog GLP-1 on germ cells ( Kimble and Crittenden, 2005 ). Germ cells can be considered adult stem cells that proliferate in a stem cell niche created by the DTC. Germ cells that leave the niche enter meiosis. The extent of the stem cell niche appears to be defined at least in part by the cellular protrusions of the DTC, which extend ∼10 germ-cell diameters from the distal end of the gonad arm ( Hall et al., 1999 ).

How do germ cells develop?

Germ-cell development starts from spermatogonial stem cells (SSCs), the most undifferentiated type of spermatogonium, which usually occurs as single cells. When an SSC enters the differentiation pathway toward the spermatozoa, it shows a peculiar behavior upon dividing in all animals. At the end of mitosis, when the two new cells have formed, a cell division is incomplete in these differentiating cells since the daughter cells remain interconnected by a cytoplasmic bridge, instead of forming two separated cells. These bridges are also formed during all subsequent germ-cell divisions. In this way, the germ cells derived from a given SSC form a clone of interconnected cells. All members of the same clone are in the same stage of development, synchronized in their activities via the cytoplasmic bridges. These bridges are broken when spermatogenesis is completed and germ cells leave the germinal epithelium as spermatozoa. However, when dividing, an SCC can also form two independent cells. These daughter cells are two new SCCs and this mode of division is called stem-cell self-renewal.

What is the role of germ cells in spermatogenesis?

While germ cells appears dispensable for testis differentiation during fetal life, germ cell products, such as the above-mentioned RA or BMP4, are likely to influence somatic cells in order to induce and/or maintain somatic cell functions after birth. Due to their intimate location within the seminiferous epithelium, Sertoli cells which surround and support germ cells all along their differentiation process represent a preferential target for such signals.

What is the process of spermiation?

When spermatogenesis is completed, the close contact between germ and Sertoli cells is broken and the cysts open such that the lumen of spermatogenic cysts becomes continuous with the lumen of the spermatogenic tubules. This process is called spermiation. The term spermiation is used in two ways in fish: in a strict sense to describe the termination of close Sertoli–germ cell contact and in a broader sense to indicate that strippable sperm (milt) is present in the spermatic duct system. Here, the term spermiation is used in the strict sense.

What is germ cell transplantation?

Germ cell transplantation has revolutionized the study of the male germline of not only research species, but of all mammals, including companion animals, farm animals, endangered species and primates. Although the germ cell transplantation technique was originally developed in the mouse and allowed extensive characterization of murine SSCs, future studies will focus on a large range of species, including humans. Development of an efficient in vitro culture system supporting self-renewal and expansion of human SSCs and feasible germ cell transplantation protocols are critical to accelerate the advance of new medical applications and germ cell-based therapies.

What is the life cycle of the germline?

This cycle of the germline, from generation to generation, is a central feature of the continuum of multicellular life. Because the germline is essentially continuous from generation to generation, the germ-line lineage can be thought of as being ‘immortal,’ although individual germ cells are not.

What are mixed germ cell tumors?

Individual tumor components have the same antigenic profiles as already discussed. The heterogeneous appearance of mixed germ cell tumors includes distinctive regions that look different from one another, encompassing neuroectodermal tissue, squamous epithelium, and even cartilage and skeletal muscle. The neuroectodermal tissue may consist of neuroepithelial elements with anaplastic or mature giant cells. Mixed germ cell tumors are usually solid, encapsulated, and cystic, and often white in color . The tumor mass often has many low-density areas that represent necrosis and hemorrhage. The microscopic features are based on the component tumors. There are documented cases of pituitary mixed germ cell tumors, with parasellar and suprasellar extension.

Which cells give rise to germ cells in the gonads from which gametes are ultimately derived?

The primordial germ cells are the cells that give rise to the germ cells in the gonads from which the gametes are ultimately derived.

What is Germ Cell?

Gametes are formed by the germ cells in all sexually reproducing organisms. Invertebrates are the precursors of male sperm cells and female egg cells. The germline is collectively called to all the germ cells in an organism.

Function of Germ Cell

Germ cells can give rise to gametes. Thus, a person can pass the genetic information to their offspring by germ cells and they are the original cells of all sexually reproducing organisms.

What are germ cell tumors?

Germ cell tumors are benign (noncancerous) or malignant (cancerous) growths that arise from specialized cells called germ cells, which develop in a baby before birth (a fetus). Germ cells form within the yolk sac, a structure that helps to nourish a fetus before the placenta forms. The germ cells travel from the yolk sac to the fetal midsection, where the reproductive organs form. In males, germ cells transform into sperm within the testes; in females, they transform into eggs within the ovaries.

What is the outlook for people with germ cell tumors?

The good news is that most children and teens with malignant germ cell tumors can be treated successfully.

How are germ cell tumors diagnosed?

If a child or teen has a suspected germ cell tumor, the doctor will gather information about their medical history, examine them during an office visit, and send them for tests that can confirm the presence of a tumor.

Overview

Introduction

Specification

Migration

Gametogenesis

Oogenesis

Spermatogenesis

Diseases