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Subjects Anatomy Embriology I: General Embriology

Evolution from the Fish Fin; Anomalies in Limb Development: Causes, Effects, and Management

Limb Development II - Evolution & Anomalies

The text discusses the evolution and development of limbs in tetrapods, as well as anomalies and malformations that can occur during limb development.

In the evolution of the tetrapod limb from the fish fin, significant changes in the underlying developmental processes occurred. These changes allowed for the development of complex limb structures, including bones, joints, muscles, and vessels. Variations in skeletal element number and proportion contribute to the diversity of limb forms in tetrapods. Different species have evolved different numbers of bones and joints in their limbs, allowing for a wide range of movements and adaptations. Limb morphology is closely associated with locomotion, feeding, and other behaviors, and is highly adapted to the specific ecological niche and lifestyle of each species.

The study of limb evolution in non-model tetrapods has provided valuable insights into the developmental basis of limb evolution. By comparing the expression patterns of genes and their regulatory elements in different species, researchers have identified key genetic changes that have led to the evolution of specific limb features. Linking evolutionary changes to regulatory elements, such as enhancers, has allowed researchers to uncover the genetic and molecular mechanisms that drive limb development.

Anomalies in limb development can be caused by various genetic factors. Mutations in specific genes can lead to malformations, such as synpolydactyly, polysyndactyly, and Holt-Oram syndrome. Certain malformations can result in the absence or insufficient development of limbs, while others involve incomplete development or developmental arrest. Exaggerated development or excessive growth can also occur, leading to conditions like macromelia and macrodactyly. Other limb anomalies include rotation of the knee, fusion of the lower limbs (sirenomelia), and extra digits (polydactyly).

Understanding the genetic causes and effects of limb malformations is crucial for diagnosis and management. By studying the underlying mechanisms of these conditions, medical professionals can develop effective treatment strategies for individuals with limb defects.

Last update: 05 Jan 2024 19:40

Evolution of the Tetrapod Limb

Transformation from fish fin to tetrapod limb

The evolution of the tetrapod limb from the fish fin is a remarkable example of evolutionary transformation. Through variations in skeletal element number and proportion, tetrapods have achieved diverse limb forms closely associated with locomotion, feeding, and other behaviors. The transition from fish fin to tetrapod limb involved significant changes in the underlying developmental processes. Key modifications included the development of limb buds and the establishment of distinct axes, such as the proximal-distal, anterior-posterior, and dorsal-ventral axes. These changes allowed for the development of complex limb structures, including bones, joints, muscles, and vessels.

Variations in skeletal element number and proportion

One of the major factors contributing to the diversity of limb forms in tetrapods is the variation in skeletal element number and proportion. Different species have evolved different numbers of bones and joints in their limbs, allowing for a wide range of movements and adaptations. For example, some species have elongated limbs with numerous bones, while others have reduced or fused bones. These variations in skeletal elements are controlled by the expression patterns of genes, such as the architectural homeobox (Hox) family of genes, which play a crucial role in determining limb identity along the rostrocaudal axis.

Diversity in limb forms and associated behaviors

The remarkable diversity in limb forms observed in tetrapods is closely associated with their diverse locomotion, feeding, and other behaviors. Limb morphology is highly adapted to the specific ecological niche and lifestyle of each species. For example, limbs of arboreal animals are often long and flexible, allowing for climbing and grasping, while limbs of aquatic animals are streamlined and adapted for swimming. The diversity in limb forms is a result of evolutionary changes in the developmental processes that control limb patterning and growth. Understanding the relationship between limb form and function is crucial for studying the evolution and adaptation of different species.

Developmental Basis of Limb Evolution

The developmental basis of limb evolution has been studied to varying degrees in a limited but growing number of non-model tetrapods. Researchers have aimed to understand how changes in the genetic regulatory mechanisms underlying limb development have contributed to the evolution of limb forms. By comparing the expression patterns of genes and their regulatory elements in different species, scientists have identified key genetic changes that have led to the evolution of specific limb features. These studies have provided valuable insights into the genetic and molecular mechanisms that drive limb evolution and have shed light on the evolutionary history of tetrapods. Further research in this field will contribute to our understanding of the complex relationship between development and evolution.

Study of limb evolution in non-model tetrapods

The study of limb evolution in non-model tetrapods has provided valuable insights into the developmental basis of limb evolution. While the majority of research has focused on model organisms such as mice and chickens, scientists have increasingly turned their attention to studying limb development in non-model tetrapods. By examining the limb development in a diverse range of species, researchers have been able to uncover the evolutionary variations in skeletal element number and proportion that have led to the remarkable diversity in limb forms observed in tetrapods.

Through comparative studies, researchers have identified key similarities and differences in limb development among non-model tetrapods. By analyzing the timing and morphological changes during limb development, scientists have been able to gain a better understanding of the mechanisms underlying limb evolution. This research has revealed that changes in gene expression patterns and the activity of regulatory elements play a crucial role in driving the evolutionary changes in limb form.

Linking evolutionary changes to regulatory elements

One of the major advancements in the study of limb development has been the ability to link evolutionary changes in limb form to specific regulatory elements. Regulatory elements, such as enhancers, play a critical role in instructing gene promoters when, where, and at what levels to activate gene transcription. By mapping thousands of enhancers associated with limb development in humans, monkeys, bats, and mice, researchers have been able to identify the regulatory components that control limb development.

Techniques such as chromatin immunoprecipitation followed by massively parallel sequencing (ChIP-seq) and RNA sequencing (RNA-seq) have been instrumental in identifying the specific transcription factors, cofactors, and histone marks associated with limb development on a genome-wide scale. These sequencing techniques have allowed researchers to identify numerous genes and genetic pathways that drive limb development at various time points.

By studying the disruption of these regulatory elements and their interactions, researchers have been able to gain insights into the causes of limb malformations. Understanding the role of regulatory elements in limb development not only provides important insights into normal limb development but also has implications for understanding and potentially treating limb abnormalities in clinical settings.

Overall, the study of limb evolution in non-model tetrapods and the linking of evolutionary changes to regulatory elements have greatly advanced our understanding of limb development. By uncovering the genetic and molecular mechanisms that underlie limb development, researchers are gaining valuable insights into the complex processes that shape the formation and diversity of limbs in humans and other species.

Anomalies in Limb Development

Genetic causes and effects of malformations

Limb development in humans is a complex process that can be influenced by various genetic factors. Many different genes have been identified to play a role in limb development and mutations in these genes can lead to malformations. For example, mutations in the HOXD13 gene can cause synpolydactyly, a condition characterized by the presence of extra digits on both the hands and feet. Similarly, mutations in the Gli3 gene can result in polysyndactyly, where extra digits are present only on the hands or feet.

Other genes implicated in limb defects include TBX5, which when mutated can cause Holt-Oram syndrome, a disorder affecting the development of the heart and upper limbs. Mutations in TBX3 can lead to ulnar mammary syndrome, which affects the development of the upper limbs. LMX1B gene mutations can cause nail-patella syndrome, a condition that affects the development of the fingers, toes, and knees. Additionally, mutations in FGFR genes can result in various limb dysplasias, including craniosynostosis and skeletal abnormalities.

Understanding the genetic causes of limb defects is crucial for diagnosing and managing these conditions. Genetic testing can help identify specific mutations and guide treatment options for affected individuals. Furthermore, studying the effects of these mutations on limb development provides insights into the underlying mechanisms of normal limb development.

Absence or insufficient development of limbs

Certain malformations in limb development can result in the absence or insufficient development of limbs. Amelia is a condition characterized by the complete absence of one or more limbs. This malformation occurs during a critical phase of limb development, typically between days 34-36 of gestation. On the other hand, phocomelia refers to the absence or insufficient development of the proximal segments of limbs and is typically observed during days 30-33 of gestation.

Adactyly, another malformation, involves the absence of fingers. This condition can occur as a result of developmental abnormalities during limb formation. Incomplete development or developmental arrest can lead to microphalangia and microdactyly, where the fingers or phalanges are smaller than normal. Micromelia refers to limbs that are smaller than expected due to incomplete development. These malformations can occur during critical phases of limb development and can have significant impacts on an individual's functional abilities.

Incomplete development or developmental arrest

In addition to absence or insufficient development of limbs, incomplete development or developmental arrest can also lead to limb malformations. Microphalangia and microdactyly are conditions characterized by the underdevelopment of the fingers or phalanges. These malformations can occur due to deficiencies in cell proliferation during limb development.

Another example of incomplete development is seen in hemimelia, where there is stunting of the development of long bones in the limb. This condition can result in significant limb length discrepancies and functional limitations. Brachydactyly, characterized by the shortened fingers or toes, is another malformation that can occur due to incomplete development or developmental arrest.

Dysplasia defects, such as syndactyly and synostosis, are also considered incomplete development abnormalities. Syndactyly refers to the fusion of digits by soft tissue, while synostosis involves the fusion of bones themselves. These malformations can occur due to disruptions in the cellular differentiation program during limb development.

Exaggerated development or excessive growth

While some malformations involve the absence or insufficient development of limbs, others are characterized by exaggerated development or excessive growth. Macromelia refers to limbs that are larger than normal. This condition can result from abnormalities in the growth and differentiation processes during limb development.

Macrodactyly and hyperphalangy are examples of malformations involving excessive growth of the fingers or phalanges. These conditions can lead to functional impairments and may require surgical interventions to manage.

Other limb anomalies and malformations

In addition to the previously mentioned malformations, there are several other anomalies and malformations that can affect limb development. Elenteromelia refers to the rotation of the knee, which can result in abnormal alignment and function of the lower limb.

Sirenomelia is a rare condition characterized by the partial or total fusion of the lower limbs, giving the appearance of a mermaid's tail. This malformation is typically associated with severe internal organ abnormalities and is often incompatible with life.

Polydactyly is a condition where there are extra digits present on the hands or feet. This malformation can be classified as preaxial or postaxial, depending on the location of the extra digits.

Congenital amputations and congenital hip dislocation are also considered limb anomalies. These conditions can occur due to disruptions in the developmental processes during limb formation.

Understanding these various limb anomalies and malformations is crucial for healthcare professionals involved in the diagnosis and management of patients with limb defects. By studying the underlying causes and mechanisms of these conditions, medical professionals can develop effective treatment strategies and provide appropriate care to individuals with limb malformations.

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Lesson authors: Dr. Mironescu Olivier
Published on: 05 Jan 2024 19:40
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The text discusses the evolution and development of limbs in tetrapods, as well as anomalies and malformations that can occur during limb development.

In the evolution of the tetrapod limb from the fish fin, significant changes in the underlying developmental processes occurred. These changes allowed for the development of complex limb structures, including bones, joints, muscles, and vessels. Variations in skeletal element number and proportion contribute to the diversity of limb forms in tetrapods. Different species have evolved different numbers of bones and joints in their limbs, allowing for a wide range of movements and adaptations. Limb morphology is closely associated with locomotion, feeding, and other behaviors, and is highly adapted to the specific ecological niche and lifestyle of each species.

The study of limb evolution in non-model tetrapods has provided valuable insights into the developmental basis of limb evolution. By comparing the expression patterns of genes and their regulatory elements in different species, researchers have identified key genetic changes that have led to the evolution of specific limb features. Linking evolutionary changes to regulatory elements, such as enhancers, has allowed researchers to uncover the genetic and molecular mechanisms that drive limb development.

Anomalies in limb development can be caused by various genetic factors. Mutations in specific genes can lead to malformations, such as synpolydactyly, polysyndactyly, and Holt-Oram syndrome. Certain malformations can result in the absence or insufficient development of limbs, while others involve incomplete development or developmental arrest. Exaggerated development or excessive growth can also occur, leading to conditions like macromelia and macrodactyly. Other limb anomalies include rotation of the knee, fusion of the lower limbs (sirenomelia), and extra digits (polydactyly).

Understanding the genetic causes and effects of limb malformations is crucial for diagnosis and management. By studying the underlying mechanisms of these conditions, medical professionals can develop effective treatment strategies for individuals with limb defects.

Limb development, evolution of the tetrapod limb, fish fin, tetrapod limb, skeletal element number, proportion, limb forms, locomotion, feeding, behaviors, limb buds, axes, bones, joints, muscles, vessels, genetic regulatory mechanisms, non-model tetrapods, gene expression patterns, Hox family of genes, limb identity, rostrocaudal axis, diversity in limb forms, ecological niche, lifestyle, limb patterning, growth, regulatory elements, enhancers, gene promoters, gene transcription, chromatin immunoprecipitation, ChIP-seq, RNA sequencing, RNA-seq, transcription factors, cofactors, histone marks, limb malformations, limb abnormalities, clinical settings, genetic factors, mutations, HOXD13 gene, synpolydactyly, Gli3 gene, polysyndactyly, TBX5, Holt-Oram syndrome, TBX3, ulnar mammary syndrome, LMX1B gene, nail-patella syndrome, FGFR genes, limb dysplasias, craniosynostosis, skeletal abnormalities, absence of limbs, insufficient development of limbs, Amelia, phocomelia, adactyly, microphalangia, microdactyly, micromelia, incomplete development, developmental arrest, hemimelia, brachydactyly, dysplasia defects, syndactyly, synostosis, exaggerated development, excessive growth, macromelia, macrodactyly, hyperphalangy, other limb anomalies, malformations, elenteromelia, sirenomelia, polydactyly, congenital amputations, congenital hip dislocation.Evolution from the Fish Fin; Anomalies in Limb Development: Causes, Effects, and ManagementLimb Development II - Evolution & Anomalies0000
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