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October, 2006
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Parental Care

JoVE 10921

Many animals exhibit parental care behavior, including feeding, grooming, and protecting young offspring. Parental care is universal in mammals and birds, which often have young that are born relatively helpless. Several species of insects and fish, as well as some amphibians, also care for their young.

Parental care can occur even before hatching in birds, when parents sit on their eggs to incubate them. After hatching, the parents provide food for their offspring, and may continue to brood their young to keep them warm. Both male and female birds provide parental care, depending on the species. In marsupial mammals, such as kangaroos, the embryos are often born at a very early stage and then crawl into their mother’s pouch. Here, the mother nurses and protects her offspring—sometimes for many months—until it can function more independently. Placental mammals are born more developed than marsupials, but they still require a lot of care. Mammalian parental care is mostly provided by the mother, triggered by the hormones of pregnancy and birth and the necessity of lactation for providing nutrients. Nursing is an essential kind of mammalian parental care since the mother’s milk is the primary source of food for the young. Mammals also often lick their newborns and carry them around—grooming, protecting, and bonding wi

 Core: Biology

An Introduction to Transfection

JoVE 5068

Transfection is the process of inserting genetic material, such as DNA and double stranded RNA, into mammalian cells. The insertion of DNA into a cell enables the expression, or production, of proteins using the cells own machinery, whereas insertion of RNA into a cell is used to down-regulate the production of a specific protein by stopping translation. While the site of action for…

 Basic Methods in Cellular and Molecular Biology

MALDI-TOF Mass Spectrometry

JoVE 5691

Matrix-assisted laser desorption ionization (MALDI) is a mass spectrometry ion source ideal for the analysis of biomolecules. Instead of ionizing compounds in the gaseous state, samples are embedded in a matrix, which is struck by a laser. The matrix absorbs the majority of the energy; some of this energy is then transferred to the sample, which ionizes as a result. Sample ions can then be…


Genome Editing

JoVE 5554

A well-established technique for modifying specific sequences in the genome is gene targeting by homologous recombination, but this method can be laborious and only works in certain organisms. Recent advances have led to the development of “genome editing”, which works by inducing double-strand breaks in DNA using engineered nuclease enzymes guided to target…


Action Potentials

JoVE 10844

Neurons communicate by firing action potentials—the electrochemical signal that is propagated along the axon. The signal results in the release of neurotransmitters at axon terminals, thereby transmitting information in the nervous system. An action potential is a specific “all-or-none” change in membrane potential that results in a rapid spike in voltage.

Neurons typically have a resting membrane potential of about -70 millivolts (mV). When they receive signals—for instance, from neurotransmitters or sensory stimuli—their membrane potential can hyperpolarize (become more negative) or depolarize (become more positive), depending on the nature of the stimulus. If the membrane becomes depolarized to a specific threshold potential, voltage-gated sodium (Na+) channels open in response. Na+ has a higher concentration outside of the cell as compared to the inside, so it rushes in when the channels open, moving down its electrochemical gradient. As positive charge flows in, the membrane potential becomes even more depolarized, in turn opening more channels. As a result, the membrane potential quickly rises to a peak of around +40 mV. At the peak of the action potential, several factors drive the potential back down. The influx of Na+ slows because the Na+ channels start to inactiv

 Core: Biology

Explant Culture for Developmental Studies

JoVE 5329

Explant culture is a technique in which living cells or tissues are removed from an embryo for continued development outside of the organism. This ex vivo approach allows researchers to manipulate and observe developing tissues in ways that are not possible in vivo. Once established, explant culture is frequently used to understand the role of genes and signaling molecules in …

 Developmental Biology

An Introduction to the Laboratory Mouse: Mus musculus

JoVE 5129

Mice (Mus musculus) are an important research tool for modeling human disease progression and development in the lab. Despite differences in their size and appearance, mice share a distinct genetic similarity to humans, and their ability to reproduce and mature quickly make them efficient and economical candidate mammals for scientific study.

This video provides a brief…

 Biology II

Convergent Evolution

JoVE 11133

Evolution shapes the features of organisms over time, ensuring that they are suited for the environments in which they live. Sometimes, selection pressure leads to the rise of similar but unrelated adaptations in organisms with no recent common ancestors, a process known as convergent evolution.

The structures that arise from convergent evolution are called analogous structures. They are similar in function even if they are dissimilar in structure. Further, structures can be analogous while also containing homologous features - those inherited from a common ancestor. Birds and bats have analogous wings, but the forelimb bones within their wings are homologous, adapted from a distant four-limbed ancestor. The wings of butterflies, on the other hand, are analogous to those of birds and bats, but they are not homologous. Sometimes it is clear when two organisms share traits as a result of convergent evolution, as in the case of bird, bat, and butterfly wings, but at other times it is less obvious. To determine whether traits are analogous and thus the result of convergent evolution or homologous and the result of shared ancestry, scientists can examine the DNA sequences of the organisms in question. Dolphins and many bats use echolocation to navigate and hunt. DNA sequence data has indicated that the gene Prestin, which encodes a protein in t

 Core: Biology

Internal Receptors

JoVE 11011

Many cellular signals are hydrophilic and therefore cannot pass through the plasma membrane. However, small or hydrophobic signaling molecules can cross the hydrophobic core of the plasma membrane and bind to internal, or intracellular, receptors that reside within the cell. Many mammalian steroid hormones use this mechanism of cell signaling, as does nitric oxide (NO) gas.

Similar to membrane-bound receptors, binding of a ligand to a receptor located in the cytoplasm or nucleus of a cell causes a conformational change in the receptor. Like transcription factors, the active receptor can bind to receptor-specific DNA binding sites to increase or decrease the transcription of target genes. In the case of an intracellular receptor located in the cytoplasm, the receptor-ligand complex must first cross the nuclear membrane. Many steroid hormones, including estrogen and testosterone, use intracellular receptors to induce specific effects. As an example, estrogen can diffuse across the membrane; binding of estrogen to its receptor results in dimerization of the receptors and transport of the ligand-receptor complex to the nucleus. Once in the nucleus, the complex can bind to DNA sequences called Estrogen-Response Elements (EREs). Depending on the other transcription factors and co-activators, binding of activated estrogen receptors (ERs) to EREs may cause an incre

 Core: Biology
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