Desarrollo y patrones arquitectónicos Presentación 2 Dr. Robert J. Mayer UPR en Aguadilla http://math.uprag.edu/rmayer/zoopres2.ppt

Tareas Objetivos Leer hasta la página del libro de Carl Safina Escribir una biografía corta del autor y entregarla el 1.24.11 Leer los capítulos 8 y 9 del libro de texto “Zoology” Objetivos Conocer los conceptos básicos de la biología del desarrollo Conocer los conceptos básicos de la embriología

Phases of the Cell Cycle The cell cycle consists of The mitotic phase Interphase INTERPHASE G1 S (DNA synthesis) G2 Cytokinesis Mitosis MITOTIC (M) PHASE Figure 12.5

Mitosis consists of five distinct phases Prophase Prometaphase G2 OF INTERPHASE PROPHASE PROMETAPHASE Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Aster Centromere Fragments of nuclear envelope Kinetochore Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore microtubule Figure 12.6 Nonkinetochore microtubules

G2 of Interphase A nuclear envelope bounds the nucleus. The nucleus contains one or more nucleoli (singular, nucleolus). Two centrosomes have formed by replication of a single centrosome. In animal cells, each centrosome features two centrioles. Chromosomes, duplicated during S phase, cannot be seen individually because they have not yet condensed. The light micrographs show dividing lung cells from a newt, which has 22 chromosomes in its somatic cells (chromosomes appear blue, microtubules green, intermediate filaments red). For simplicity, the drawings show only four chromosomes.

G2 OF INTERPHASE PROPHASE PROMETAPHASE Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Aster Centromere Fragments of nuclear envelope Kinetochore Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore microtubule Figure 12.6 Nonkinetochore microtubules Prophase The chromatin fibers become more tightly coiled, condensing into discrete chromosomes observable with a light microscope. The nucleoli disappear. Each duplicated chromosome appears as two identical sister chromatids joined together. The mitotic spindle begins to form. It is composed of the centrosomes and the microtubules that extend from them. The radial arrays of shorter microtubules that extend from the centrosomes are called asters (“stars”). The centrosomes move away from each other, apparently propelled by the lengthening microtubules between them.

Figure 12.6 Prometaphase The nuclear envelope fragments. The microtubules of the spindle can now invade the nuclear area and interact with the chromosomes, which have become even more condensed. Microtubules extend from each centrosome toward the middle of the cell. Each of the two chromatids of a chromosome now has a kinetochore, a specialized protein structure located at the centromere. Some of the microtubules attach to the kinetochores, becoming “kinetochore microtubules.” These kinetochore microtubules jerk the chromosomes back and forth. Nonkinetochore microtubules interact with those from the opposite pole of the spindle. G2 OF INTERPHASE PROPHASE PROMETAPHASE Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Aster Centromere Fragments of nuclear envelope Kinetochore Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore microtubule Figure 12.6 Nonkinetochore microtubules

TELOPHASE AND CYTOKINESIS METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Spindle Metaphase plate Nucleolus forming Cleavage furrow Nuclear envelope forming Centrosome at one spindle pole Daughter chromosomes Metaphase Metaphase is the longest stage of mitosis, lasting about 20 minutes. The centrosomes are now at opposite ends of the cell. The chromosomes convene on the metaphase plate, an imaginary plane that is equidistant between the spindle’s two poles. The chromosomes’ centromeres lie on the metaphase plate. For each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles. The entire apparatus of microtubules is called the spindle because of its shape.

TELOPHASE AND CYTOKINESIS METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Spindle Metaphase plate Nucleolus forming Cleavage furrow Nuclear envelope forming Centrosome at one spindle pole Daughter chromosomes Anaphase Anaphase is the shortest stage of mitosis, lasting only a few minutes. Anaphase begins when the two sister chromatids of each pair suddenly part. Each chromatid thus becomes a full- fledged chromosome. The two liberated chromosomes begin moving toward opposite ends of the cell, as their kinetochore microtubules shorten. Because these microtubules are attached at the centromere region, the chromosomes move centromere first (at about 1 µm/min). The cell elongates as the nonkinetochore microtubules lengthen. By the end of anaphase, the two ends of the cell have equivalent—and complete—collections of chromosomes.

TELOPHASE AND CYTOKINESIS METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Spindle Metaphase plate Nucleolus forming Cleavage furrow Nuclear envelope forming Centrosome at one spindle pole Daughter chromosomes Telophase Two daughter nuclei begin to form in the cell. Nuclear envelopes arise from the fragments of the parent cell’s nuclear envelope and other portions of the endomembrane system. The chromosomes become less condensed. Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete. Cytokinesis The division of the cytoplasm is usually well underway by late telophase, so the two daughter cells appear shortly after the end of mitosis. In animal cells, cytokinesis involves the formation of a cleavage furrow, which pinches the cell in two.

Metaphase Anaphase Telophase Figure 12.6 Centrosome at one spindle pole Daughter chromosomes METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Spindle Metaphase plate Nucleolus forming Cleavage furrow Nuclear envelope forming Figure 12.6

Interphase and meiosis I Centrosomes (with centriole pairs) Sister chromatids Chiasmata Spindle Tetrad Nuclear envelope Chromatin Centromere (with kinetochore) Microtubule attached to kinetochore Tertads line up Metaphase plate Homologous chromosomes separate Sister chromatids remain attached Pairs of homologous chromosomes split up Chromosomes duplicate Homologous chromosomes (red and blue) pair and exchange segments; 2n = 6 in this example INTERPHASE MEIOSIS I: Separates homologous chromosomes PROPHASE I METAPHASE I ANAPHASE I Figure 13.8

MEIOSIS II: Separates sister chromatids Telophase I, cytokinesis, and meiosis II TELOPHASE I AND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II AND MEIOSIS II: Separates sister chromatids Cleavage furrow Sister chromatids separate Haploid daughter cells forming During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing single chromosomes Two haploid cells form; chromosomes are still double Figure 13.8

Preformación (siglos 17 y 18) Coherencia conceptual 1759 Kaspar Friedrich Wolff – epigénesis

Desarrollo – describe cambios progresivos en un individuo desde su concepción hasta la madurez.. Organismos multicelulares sexuales - Rearreglos extensos e interacciones = plan corporal (body plan) y celulas especializadas. Las células especializadas surgen gracias a una serie de condicines creadas en etapas anteriores. En cada paso del desarrollo surgen nuevas estructuras como resultado de interacciones. Cada interacción es incrementalmente restrictiva.

Determinación – localización citoplásmica - inducción

Durante la ovogénesis el óvulo (huevo) se prepara para la fertilización y para el comienzo del desarrollo. El espermatozoide es una célula vacía llena de material genético a diferencia del huevo El huevo se prepara durante la profase de meiosis I – producción de cuerpos polares (exceso de citoplasma)

Fertilización Fertilización externa Fertilización interna Especificidad (quimiotaxis) Se evita la polispermia “fast block” cambio en el potencial de la membrana b. “cortical reaction”

Fertilización Restauración del número diploide Activación del óvulo (a veces es lo único) Partenogénesis

Eventos que ocurren durante la fecundación y el desarrollo temprano.

Segmentación (cleavage) en distintos organismos “Cleavage furrow” Isolecitos < Mesolecitos < Telolecitos < Centrolecitos Holoblástico - (tunicados, equinodermos, tunicados, cefalocordados, nemerteos, y la mayor parte de los moluscos, marsupiales y mamíferos placentales) Meroblástico – aves, reptiles, peces, anfibios, moluscos cefalópodos, y mamíferos Monotremos Insectos = Centrolecitos

La cantidad de vitelo determina el tipo de desarrollo temprano del organismo Directo Indirecto

Formación de capas embrionarias (Gastrulación) archenteron Blastulación Blastocelo Blástula (Celoblástula – hueca y Stereoblástula – sólida) = 200 – varios miles de células Se forma en todos los organismos multicelulares El desarrollo continua mas allá de la blástula y se forman capas embrionarias (excepto en las esponjas) Invaginación = gastrulación

Tres capas embrionarias Endodermo Mesodermo Ectodermo Diploblástico Triploblástico Dos cavidades (celoma y sistema digestivo) Celoma – cavidad corporal completamente revestida por mesodermo

Dos tipos de organismos tripoblásticos Los mamíferos son deuterostomados pero su celoma se forma mediante un proceso esquizocélico modificado

Figure 08.14

Protostomes Deuterostomes