human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

s and other mammals, the caudal cell mass (also tail bud or caudal eminence in humans) is the aggregate of undifferentiated cells at the caudal end on the spine. The caudal end of the spinal cord first begins to form after primary

neurulation Neurulation refers to the folding process in vertebrate embryos, which includes the transformation of the neural plate into the neural tube. The embryo at this stage is termed the neurula. The process begins when the notochord induces the forma ...

has taken place, indicating that it develops after the cranial portion of the spinal cord has developed. Following neurulation, the caudal tail begins to form a neurocele as it develops a hollow core. After this, secondary neurulation occurs in which the medullary cord begins to form and is filled with many cavities that ultimately form the lumen. The cavities formed from the initial and secondary neurulation combine to form one uninterrupted cavity. There is still speculation on the formation of the caudal cell mass in humans with arguments being made for it arising from many cavities or the continuing growth of the neurocele from the initial neurulation. The caudal cell mass will ultimately differentiate and form into many sacral structures such various nerve endings and the

conus medullaris ''Conus'' is a genus of predatory sea snails, or cone snails, marine gastropod mollusks in the family Conidae.Bouchet, P.; Gofas, S. (2015). Conus Linnaeus, 1758. In: MolluscaBase (2015). Accessed through: World Register of Marine Species ...

Role in disease

The caudal cell mass plays a role in many diseases and abnormalities related to the spinal cord. One group of abnormalities it plays a role in are occult spinal dysraphisms. These types of abnormalities arise from specific structures formed in the caudal mass, for example if proper differentiation of the caudal mass does not occur, it could result in a type of spinal dysraphism. One example of spinal dysraphism is

caudal regression syndrome Caudal regression syndrome, or sacral agenesis (or hypoplasia of the sacrum), is a rare birth defect. It is a congenital disorder in which the fetal development of the lower spine—the caudal partition of the spine—is abnormal. It occurs at ...

. Patients with caudal regression syndrome can experience a varying degree of the abnormality ranging from partial lack of the tail bone and pelvis to more significant cases where there may be paralysis and, as a result, inhibited function in the bowel and bladder. This abnormality can be caused by the caudal cell mass not developing properly due to improper differentiation, and it can lead to sacral

agenesis In medicine, agenesis () refers to the failure of an organ to develop during embryonic growth and development due to the absence of primordial tissue. Many forms of agenesis are referred to by individual names, depending on the organ affected: *A ...

, which is one of the hallmarks of caudal regression syndrome. Another class of abnormalities from caudal cell mass development includes caudal dysgenesis, which refers to abnormalities where the sacrum may be deformed or absent, or abnormalities in which the spinal cord and the complementary organ systems may be malformed. Some of the abnormalities that fall under this class includes currarino syndrome and

sirenomelia Sirenomelia, also called mermaid syndrome, is a rare congenital deformity in which the legs are fused together, giving the appearance of a mermaid's tail, hence the nickname. Classification Sirenomelia is classified by the skeletal structure ...

. These genetic defects were found to have a much higher rate of incidence in births to mothers with

gestational diabetes Gestational diabetes is a condition in which a woman without diabetes develops high blood sugar levels during pregnancy. Gestational diabetes generally results in few symptoms; however, it increases the risk of pre-eclampsia, depression, and o ...

. This trend may be due to the inhibition of critical elements of

morphogenesis Morphogenesis (from the Greek ''morphê'' shape and ''genesis'' creation, literally "the generation of form") is the biological process that causes a cell, tissue or organism to develop its shape. It is one of three fundamental aspects of deve ...

, that are found in the extracellular matrix, or due to the presence of an abnormal

hox gene Hox genes, a subset of homeobox genes, are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals. Hox proteins encode and specify the characteristics of 'position', ensuring that the co ...

. These abnormalities can be predicted ahead of time using ultrasound.

References

Embryology {{Developmental-biology-stub